Background of the Invention

The invention pertains to medical systems and. more particularly, to methods and apparatus for delivery of compounds through the blood-brain barrier to the brain.

The blood-brain barrier prevents many compounds in the blood stream from entering the tissues and fluids of the brain. Nature provides this mechanism to insure a toxin-free environment for neurologic function. However, it also prevents delivery to the brain of compounds, such as neuropharmaceuticals, potential neuropharmaceuticals. and other neurologically active agents, that might otherwise remedy or modify neurologically-related activities and disorders.

Today, non-surgical treatments of neurologic disorders are limited to systemic introduction of compounds through the blood stream. A drawback of this form of treatment, as suggested above, is the relatively small number of known compounds that pass through the blood-brain barrier. Even those that do cross the barrier often produce adverse reactions in other parts of the body or in non-targeted regions of the brain.

Prior art surgical treatments of neurologic disorders are limited to removal or ablation of brain tissue. While these treatments have proven effective for certain localized disorders, such as tumors, they involve delicate, time-consuming procedures that may result in destruction of otherwise healthy tissues. The surgical treatments are generally not appropriate for disorders in which diseased tissue is integrated into healthy tissues, except in instances where destruction of the latter will not unduly effect neurologic function.

Patrick, et al, "Ultrasound and the Blood-Brain Barrier," Consensus on Hvperthermia for the 1990's (Plenum, 1990), pp. 369, et seq., suggest that focused ultrasound might be used to introduce chemotherapeutic agents through the barrier.

The article is specifically directed to the use of ultrasound to modify the blood- - brain barrier at targets within feline and canine brains and, thereby, to increase the barrier ^' s permeability to a circulating dye/albumin complex. Ultrasound targeting, according to the article, is accomplished by surgically exposing the dura matter and positioning thereon a transducer/lens complex Targets are located via stereotactic coordinates, as determined from directly-visualized or roentgenographically- visuahzed cranial structures Delivery of ultrasound in the manner disclosed in the article resulted in histologically irreversible damage Though the authors suggest that chemotherapeutic agents, such as monoclonal antibodies and immunotoxins. might also be introduced into the brain by ultrasonic modification of the blood- brain barrier, they state that further research would be necessary to determine whether permeability can be increased sufficiently for these high molecular weight compounds

An object of this invention is to provide improved methods and apparatus for delivery of compounds to the brain, particularly, through the blood-brain barrier

A further object of the invention is to provide such methods and apparatus as can be employed to deliver such compounds to precise locations within the brain.

A still further objects of the invention is to provide such methods and apparatus as can deliver compounds through the blood-brain barrier without surgery.

Yet another object of the invention is to provide such methods and apparatus as can deliver a full range of compounds through the blood-brain barrier.

Yet still another object of the invention is to provide cost-effective methods and apparatus for delivery of compounds through the blood-brain barrier

Still further obiects of the invention are to provide improved methods and- apparatus for remedying or modifying neurological and neurological ly-related activities and disorders via delivery of compounds through the blood-bram barrier

Summary of the Invention

These and other objects are attained by the invention which provides methods and apparatus for image-guided ultrasound delivery of compounds through the blood-brain barrier to selected locations in the brain

A method according to one aspect of the invention includes targeting a selected location in the brain and applying ultrasound to induce, in the central nervous system (CNS) tissues and/or fluids at that location, a change detectable by imaging At least a portion of the brain in the vicinity of the selected location is imaged, e g , via magnetic resonance imaging, to confirm the location of the change A compound, e g , a neuropharmaceutical, in the patient ^' s bloodstream is delivered to the confirmed location by applying ultrasound to effect opening of the blood-brain barrier at that location (or a location based thereon) and. thereby, to induce uptake of the compound there.

In one aspect of the invention, the change induced in the CNS tissues and/or fluids by ultrasound is heating or cavitation The location of that change is confirmed by characteristic patterns in the image. In another aspect, the change is the uptake of contrast agents (or other compounds detectable by imaging) induced at the selected location via ultrasonic "opening" of the blood-brain barrier there Again, the location of such change can be confirmed by characteristic patterns generated during imaging. In the text that follows, the change induced in the CNS tissues and/or fluids by ultrasound is referred to as "ultrasomcally-induced change," "imaging-detectable change," and similar such terms).

In a further aspect, the invention provides methods that combine the above- described targeting and delivery steps in order to introduce a compound through the

blood-brain barrier. The invention of this aspect calls for delivering a compound - from the patient ^' s bloodstream to a selected location in the brain by applying ultrasound to that location. Delivery to the selected location is confirmed by imaging the brain to confirm ultrasonically-induced change there. Particularly, where the compound is itself can be detected via imaging, confirmation is made by imaging the brain during or after delivery, and by identifying the compund's characteristic pattern at the selected location. Where the compound itself cannot be detected by imaging, confirmation is made by imaging the brain during delivery, and by identifying in the image patterns representative of ultrasonically-induced heating or ultrasonically-induced cavitation at the desired location.

In a further aspect, the invention provides methods as described above in which ultrasound is applied to the selected location in the patient's brain by surgically exposing the dura matter and by applying ultrasound through the exposed dura matter.

In a preferred aspect, the ultrasound is applied through the skull itself, e.g., via a phased array of transducers, a focused ultrasound transducer, or the combination of an ultrasound source (e.g., transducer) and an acoustic lens, placed outside the skull. According to this aspect of the invention, there is no need to perform a craniectomy or other surgical procedure on the patient.

The invention provides, in still further aspects, methods as described above in which the brain is imaged via magnetic resonance imaging, positron emission tomography, or computed tomography in order to confirm ultrasonically-induced change at the selected location in the brain.

According to further aspects of the invention, such change is ultrasonically induced in the brain at the selected location by cavitation and, particularly, by applying ultrasound to the selected location of the brain at frequencies ranging from 20 kHz to 5 MHz, and with sonication duration ranging from 100 nanoseconds to 1 minute.

In a related aspect of the invention, delivery of compounds through the blood-brain barrier is induced at the selected location by cavitation and, particularly, by applying ultrasound to the selected location of the brain at frequencies ranging from 20 kHz to 10 MHz. sonication duration ranging from 100 nanoseconds to 30 minutes, with continuous wave or burst mode operation, where the burst mode repetition varies from 0.01 Hz to 1 MHz.

Likewise, according to further aspects of the invention, imaging-detectable change is uitrasonically induced in the brain at the selected location by heating and, particularly, by applying ultrasound to the selected location of the brain at frequencies ranging from 200 kHz to 10 MHz. and with sonication duration ranging from 100 milliseconds to 30 minutes.

In a related aspect of the invention, delivery of compounds through the blood-brain barrier is induced at the selected location by heating and, particularly, by applying ultrasound to the selected location of the brain at frequencies ranging from 250 kHz to 10 MHz. and with sonication duration ranging from 0.10 microseconds to 30 minutes.

Other aspects of the invention provide methods as described above in which ultrasound is applied to the selected location in the brain at a focal region sized in accord with the volume of CNS tissue and/or fluids to which the compound is to be delivered. That region can range from 1 mm ³ - 1 cm ³ .

Still further aspects of the invention provide methods as described above for image-guided ultrasonic delivery of compounds through the blood-brain barrier, where the compounds administered into the patient's bloodstream include, by way of non-limiting example, any of neuropharmacologic agents, neuroactive peptides (e.g., hormones, gastrointestinal peptides, angiotensin, sleep peptides. etc.), proteins (e.g, calcium binding proteins), enzymes (e.g., cholineacetyltransferase, glutamic acid decarboxylase, etc.), gene therapy agents, neuroprotective or growth factors, biogenic amines (e.g., dopamine, GABA), trophic factors to brain or spinal

transplants, immunoreactive proteins (e.g. antibodies to neurons, myelin. antireceptor antibodies), receptor binding proteins (e.g.. opiate receptors), radioactive agents (e.g.. radioactive isotopes), antibodies, and cytotoxins, among others.

Related aspects of the invention provide methods for treating neurological disorders by image-guided ultrasonic delivery of compounds through the blood- brain barrier in accord with the methods described above. Such disorders include tumors, cancer, degenerative disorders, sensory and motor abnormalities, seizure, infection, immunologic disorder, mental disorder, behavioral disorder, and localized CNS disease, among others.

In still further related aspects, the invention provides methods for modification of neurologic and neurologically-related activity (e.g., behavioral activity, memory-related activity, and sexual activity, among others) by such methods.

The invention provides, in still further aspects, an apparatus for image- guided ultrasonic delivery of compounds through the blood-brain barrier.

Such an apparatus, according to one aspect of the invention, includes an ultrasound source and a targeting mechanism for applying ultrasound generated thereby to a selected location of the brain to effect change a change there that is detectable by imaging. An imaging element generates a radiologic image of at least a portion of the brain in the vicinity of the selected location and. thereby, permits confirmation of that location. The apparatus further includes a delivery mechanism for applying ultrasound to the confirmed location (or a location based thereon) to effect opening of the blood-brain barrier at that location and, thus, to induce delivery there of a compound from the bloodstream.

By way of further example, an apparatus according to further aspects of the invention utilizes as an ultrasound source, a phased array, a focused ultrasound

transducer, or the combination of an ultrasound source and an acoustic lens. capable of applying ultrasound to the targeted location through the skull itself, without need for surgery to expose the brain.

Still other aspects of the invention provide an apparatus as described above incorporating functionality for effecting the methods described above.

These and other aspects of the invention are evident in the drawings and in the description that follows.

Brief Description of the Drawings

A more complete understanding of the invention may be attained by reference to the drawings in which:

Figure 1 depicts an apparatus according to the invention for image-guided ultrasonic delivery of compounds through the blood-brain barrier;

Figure 2 depicts an alternative configuration for an ultrasound source used in practice of the invention;

Figure 3 depicts a method according to the invention for image-guided ultrasonic delivery of compounds through the blood-brain barrier;

Figure 4 depicts an alternative method according to the invention for image- guided ultrasonic delivery of compounds through the blood-brain barrier;

Figure 5 depicts another alternative method according to the invention for image-guided ultrasonic delivery of compounds through the blood-brain barrier; and

Figure 6 depicts configurations of ultrasound sources and lenses used in practice of the invention.

Detailed Description of the Illustrated Embodiment

Figure 1 depicts an apparatus 10 according to the invention for image- guided ultrasonic delivery of compounds through the blood-brain barrier. The apparatus 10 includes an ultrasound source, shown here as a phased array of transducers 12 disposed about the head 14 of a human patient. The phased array 12 is powered and controlled by ultrasound controller 16, which includes targeting control element 18 that tunes and drives array 12 to apply ultrasound to a selected location in the patient's brain so as to effect there a change (e.g., heating, cavitation or uptake of contrast agent) that is detectable by imaging. The controller 16 also includes delivery control element 20 that tunes and drives array 12 to apply ultrasound to open the blood-brain barrier at that same location and. thereby, to induce delivery a compound from the patient's bloodstream to the brain at that location.

The apparatus 10 further includes a magnetic resonance imaging (MR1) device, comprising magnetic gradient coil and radiofrequency coil 22 and MRI controller 24, together capable of generating an image of at least a portion the patient's head (and, more particularly, of the patient's brain) to permit confirmation of ultrasonically induced change at the selected location. Controller 24 comprises scanning control functionality 26 for generating an magnetic resonance image 28 of the patient's head 14. A headholder (not shown) holds the patient's head 14 in place within the MRI tube 22, as shown.

The phased array 12 applies focused ultrasound to selected locations within the patient's brain. The array 12 can be constructed in the manner of the aperiodic ultrasound phased array disclosed in United States Provisional Patent Application No. 60/006,413, filed November 9, 1995, for APERIODIC ULTRASOUND PHASED ARRAY, assigned to the assignee hereof, the teachings of which are incorporated herein by reference.

Phased array 12 is operated in accord with the teachings herein to deliver - ultrasound, through the patient ^' s skull, in doses suitable for inducing non¬ destructive imaging-detectable change (e.g.. heating, cavitation or uptake of contrast agent) and/or non-destructive opening of the blood-brain barrier at selected locations within the brain.

In alternate embodiments, a focused ultrasound transducer, or the combination of an ultrasound source and an acoustic lens, is substituted for the phased array 12 as a means of generating ultrasound and applying it to the brain. In such alternate embodiments, the focused ultrasound transducer, or source/lens combination, is mechanically moved in order to target differing locations within the brain (as opposed to the phased array which is aimed "electronically"). The design of such transducers and acoustic lens, is well known in the art.

More particularly, under control of targeting control 18, phased array 12 delivers ultrasound to a selected location in the brain to heat or to cause cavitation in the tissues, fluids and other structures there sufficient to induce imaging- detectable change at that location, i.e., change in the CNS tissues and/or fluids that can be detected in images generated by the illustrated imaging device. That change may constitute direct heating or cavitation of the tissues and/or fluids or, alternatively, it may constitute the uptake of contrast agent induced by opening the blood-brain barrier at the selected location. The direct inducement of imaging- detectable change is discussed immediately below. Inducement via the uptake of contrast agent is discussed later, in connection with Figure 4.

In a preferred embodiment of the invention for use with human patients, direct non-destructive heat-based imaging-detectable change is induced at the selected location in the brain applying ultrasound to the selected location of the brain at frequencies ranging from 200 kHz to 10 MHz. and with sonication duration ranging from 100 milliseconds to 30 minutes.

Likewise, direct non-destructive cavitation-based imaging-detectable change- is induced at the selected location in the brain applying ultrasound to the selected location of the brain at frequencies ranging from 20 kHz to 5 MHz, and with sonication duration ranging from 100 nanoseconds to 1 minute. In contrast to imaging-detectable changes induced by heating, those induced by cavitation occur at higher peak intensity levels within this range.

Likewise, under control of delivery control 18. phased array 12 delivers ultrasound to the selected location in the brain (or a location based thereon) to heat or to cause cavitation sufficient to open the blood-brain barrier, thereby, effecting uptake of neuropharmaceuticals, potential neuropharmaceuticals or other compounds in the blood into that location of the brain.

In a preferred embodiment of the invention for use with human patients, non-destructive heat-based opening of the blood-brain barrier is induced at the selected location in the brain applying ultrasound to the selected location of the brain at frequencies ranging from 250 kHz to 10 MHz, and with sonication duration ranging from 0.10 microseconds to 30 minutes.

Likewise, non-destructive cavitation-based opening of the blood-brain barrier is induced at the selected location in the brain applying ultrasound to the selected location of the brain at frequencies ranging from 20 kHz to 10 MHz, sonication duration ranging from 100 nanoseconds to 30 minutes, with continuous wave or burst mode operation, where the burst mode repetition varies from 0.01 Hz to 1 MHz.

A further appreciation of the ultrasound dosing levels for opening the blood- brain barrier may be attained by reference to the article supplied in the Appendix I hereof and, particularly, to teachings therein with respect to the effect of differing ultrasound pulse intensities on blood-brain barrier permeability. That article, and those teachings in particular, are incorporated herein by reference.

The magnetic resonance imaging device, including MRI device 22 and MRI controller 24, comprises a conventional, commercially available MRI device. The device is operated in the conventional manner known in the art in order to generate images 28 of the patient ^' s head (and, particularly, of the brain) in accord with the teachings herein.

It will be appreciated that any device permitting determination of the location of change in the CNS tissues and/or fluids effected by the phased array 12 (e.g., under control of targeting control 18) in the patient's brain may be substituted for the magnetic resonance imaging device. Preferably, however, the substituted device is itself a radiologic imaging device, such as, by way of non- limiting example, a computed tomography (CT) imaging device, positron emission tomography (PET) imaging device. In further embodiments of the invention, other medical imaging devices capable of detecting, distinguishing and/or locating tissues, fluids, masses, structures, substances, conditions, and other features (naturally occurring or otherwise) within the human body and, particularly, within the head and brain, are used in place of MRI, CT or PET imaging devices. These other medical imaging devices include, by way of non-limiting example, ultrasound imaging devices, X-ray imaging devices, and gamma camera imaging devices, among others.

To this end. as used herein the terms "image," "radiologic image," and the like, refer to results (whether or not human readable) generated by MRI, CT or PET imaging devices, or by such other imaging devices for use in detecting, distinguishing and/or locating tissues, fluids, masses, structures, substances, conditions, and other features (naturally occurring or otherwise) within the human body and, particularly, within the head and brain. Likewise, the terms "radiologically imaging," "imaging" and the like refer to the act of obtaining such results.

Figure 2 depicts an alternative configuration for an ultrasound source used in practice of the invention. The source comprises an ultrasound transducer 30 in

combination with a lens 30. As above, this arrangement permits focused doses of- ultrasound to be applied to target ^' s within the patient ^' s 14 brain for inducing non¬ destructive imaging-detectable changes and/or non-destructive opening of the blood- brain barrier at selected locations within the brain. The illustrated source is applied directly to the dura matter, following surgical removal of corresponding portions of the scalp and skull (as illustrated by hole 34). As above, the source is powered and controlled by an ultrasound controller 16. not illustrated.

In a preferred embodiment, an ultrasound source is used to deliver ultrasound doses through the skull, obviating the need for surgery. The source is fabricated from piezoelectric material that converts an electrical signal applied on the electrode surfaces of the material to mechanical motion of the applicator. The piezoelectric material has a backing of low (for example air) or high acoustic impedance to maximize energy output through the front surface of the applicator. The electrical signal for each transducer element is provided by a signal generator and amplified by a radio frequency (RF) amplifier. The ultrasound energy can be focused by making the piezoelectric element curved or inserting a lens in front of the applicator. In these cases a minimum of one transducer is required. By using multiple transducers enhanced focusing effect may be produced.

In the case of a phased array a number of piezoelectric elements are operating together with each of them having their own RF amplifier. The electrical signals for each element are provided by a phase shifter that introduces a proper phase shift between the driving signals so that the ultrasound waves launched by each element form a common focus at a desired locations. This phase shift is modified such that the effect of skull bone and other intervening tissues between the element and the target point is compensated for so that all of the waves come to a common focus regardless of their propagation medium. The effect of the skull and other tissues are calculated based on image information (for example CT or MRI) on its properties. Thus, the phased arrays allow elimination of phase shifts introduced by skull bone that destroys an ultrasound beam focus of a focused beam at frequencies above about 1 MHz. In addition, the phased arrays can eliminate a

movement in the focal location caused by the skull during a lower frequency sonication.

A further appreciation of the construction and operation of a system according to the invention may be attained by reference to Appendix II, filed herewith.

Figure 3 depicts a method of operating the apparatus 10 of Figure 1 in order to effect image-guided ultrasonic delivery of compounds through the blood-brain barrier. In step 40. the ultrasound source is aimed to target the selected location within the patient ^' s brain. Particularly, in sub-step 40a, the ultrasound source is aimed at the selected location. In sub-step 40b. the ultrasound source is activated to apply a dose sufficient to directly effect imaging-detectable change in the CNS tissues and/or fluids at the selected location as described above.

In sub-step 40c. at least a portion of the brain in the vicinity of the selected location is imaged, e.g.. via the imaging device shown in Figure 1. to confirm the location of the imaging-detectable change. Confirmation is made, via a human or an automated image reader, via identification of patterns characteristic of ultrasonically-induced heating or cavitation at expected locations in the image. In instances where the patterns do not appear at the expected location, sub-steps 40a - 40c are repeated with revised aiming of the ultrasound source.

In instances where the ultrasound applied in step 40b effects temporary changes in CNS function (e.g., a taste sensation, a tingling sensation, an involuntary muscle motion or cessation thereof, etc.), detection of those functional changes can also be used to confirm the selected location targeted in sub-step 40a.

Once aiming of the ultrasound source has been confirmed in step 40, the compound intended for delivery through the blood-brain barrier is administered into the patient's bloodstream, e.g., via injection, ingestion, inhalation, or other such

method In the case of injection, the compound can be administered in the vicinity- of the brain, e g , via injection into the carotid artery

These compounds can include, by way of non-limiting example. neuropharmacologic agents, neuroactive peptides (e g . hormones, gastrointestinal peptides. angiotensin sleep peptides. etc ), proteins (e g, calcium binding proteins), enzymes (e g , cholineacetyltransferase, glutamic acid decarboxvlase. etc ), gene therapy, neuroprotectivc or growth factors, biogenic amines (e g , dopamine, GABA). trophic factors to brain or spinal transplants, immunoreactive proteins (e g, antibodies to neurons, mvelin. antireceptor antibodies), receptor binding proteins (e g . opiate receptors), radioactive agents (e g , radioactive isotopes), antibodies, and cytotoxins, among others

In addition, compounds to be administered into the bloodstream in step 40 can include high molecular weight complexes formed by combining relatively inert substances, such as LDTA with neuropharmaceuticals or other substances currently known to pass through the blood-brain barrier Due to their sizes and/or molecular configurations, such complexes are prevented from crossing the barrier, except at selected locations in the brain opened via ultrasound as described herein Use of such complexes in connection with the invention, therefore, permits localized application of compounds that might otherwise produce unwanted effects in other parts of the brain or body

In step 42, the compound(s) are delivered from the blood stream to the selected (and confirmed) location in the patient's brain by application of an ultrasound that effects opening of the blood-brain barrier at that location and, thereby, to induces uptake of the compound there Ultrasound doses necessary to achieve this are discussed above

It will be appreciated that administration of the compound in step 42 need not necessarily precede application of the ultrasound in step 44 Because the ultrasomcally-opened blood-bram barrier typically permits uptake of administered

compounds for at least a short period of time, the compound 42 can be introduced into the blood stream after the barrier-opening ultrasound dose is applied.

As an alternative to applying ultrasound and delivering compounds to the confirmed location, an embodiment of the invention calls for taking at least one of these actions with respect to a location based on the confirmed location. Thus, for example, neurophysiological properties or constraints may necessitate delivering the compound (and. therefore, applying the barrier-opening ultrasound) to a location different from ~ but based on — that location targeted in step 40.

Figure 4 depicts an alternative method of operating the apparatus 10 of Figure 1 to effect image-guided ultrasonic delivery of compounds through the blood-brain barrier. In step 50. the ultrasound source is aimed to target the selected location within the patient ^' s brain. Particularly, in sub-step 50a, a contrast agent is introduced into the patient ^' s bloodstream, e.g., via injection, ingestion, inhalation, or other such method. In sub-step 50b. the ultrasound source is aimed to dose a selected location in the brain. In sub-step 50c. the ultrasound source is activated to apply a dose sufficient to open the blood-brain barrier at the selected location and, thereby, induce uptake of the contrast agent there.

As above, it will be appreciated that administration of the compound in sub- step 50a need not necessarily precede application of the ultrasound in sub-step 50c due to the period during which the blood-brain barrier typically remains open.

In sub-step 50d. at least a portion of the brain in the vicinity of the selected location is imaged, e.g.. via the imaging device shown in Figure 1, to confirm the location of the imaging-detectable change — to wit, the uptake of a contrast agent at the selected location. Confirmation is made, via a human or an automated image reader, via identification of patterns characteristic of the contrast agent at expected locations in the image. In instances where the patterns do not appear at the expected location, sub-steps 50a - 50d with revised aiming of the ultrasound source.

As above, in instances where the compound induced for uptake in sub-step- 50c effects temporary changes in CNS function (e.g., a taste sensation, a tingling sensation, an involuntary muscle motion or cessation thereof, etc.). this can also be used to confirm the selected location targeted in sub-step 40a. To this end. the compound introduced in step 50a can be selected so as to induce such temporary changes in CNS function.

Once aiming of the ultrasound source has been confirmed, step 52 of the method calls for administration into the patient's bloodstream of the compound intended for delivery. This proceeds in the manner of step 42, described above. Further, in step 54, those compound(s) are delivered from the blood stream to the selected (and confirmed) location in the patient's brain. This proceeds in the manner of step 44. described above.

As above, an alternative to applying ultrasound and delivering compounds to the confirmed location, an embodiment of the invention calls for taking at least one of ^" these actions with respect to a location based on the confirmed location. Thus, for example, neurophysiological properties or constraints may necessitate delivering the compound (and, therefore, applying the barrier-opening ultrasound) to a location different from — but based on — that location targeted in step 50.

Figure 5 depicts another alternative method of operating the apparatus 10 of Figure 1 to effect image-guided ultrasonic delivery of compounds through the blood-brain barrier. In step 60, the compound intended for delivery through the blood-brain barrier is administered into the patient's bloodstream. Optionally, a contrast agent is also be administered to the bloodstream at this time. As above, these compounds can be administered via injection, ingestion, inhalation, or other such methods.

In step 62, the ultrasound source is aimed to dose a selected location in the brain. In step 64, the ultrasound source is activated to apply a dose sufficient to open the blood-brain barrier at the selected location and, thereby, induce uptake of

the compound and optional contrast agent there As above, it will be appreciated , that administration of the compound in step 60 need not necessarily precede application of the ultrasound in step 64 due to the period during which the blood- brain barrier typically remains open.

In step 66. at least a portion of the brain in the vicinity of the selected location is imaged, e g., via the imaging device shown in Figure 1 , to confirm the location of the ultrasound dosing. If no contrast agent was administered in step 60, confirmation is made by identifying patterns characteristic of ultrasonically-induced cavitation or heating in the image. In these instances, step 66 is preferably performed concurrently with step 64 If a contrast agent was administered in step 60. confirmation is made identification of patterns characteristic of the contrast agent at expected locations in the image In these instances, step 66 is preferably performed subsequent to step 64

In instances where the compound induced for uptake in sub-step 64 effects temporary changes in CNS function (e g.. a taste sensation, a tingling sensation, an involuntary muscle motion or cessation thereof, etc.), this can also be used to confirm the selected location targeted in step 62.

The methods and apparatus described in the embodiments above can be employed for treating neurological disorders by image-guided ultrasonic deliver of compounds through the blood-brain barrier. Such disorders include tumors, cancer, degenerative disorders, sensory and motor abnormalities, seizure, infection, immunologic disorder, mental disorder, behavioral disorder, and localized CNS disease, among others. For example, as an alternative to conventional functional neurosurgery, the foregoing apparatus and methods can be used to introduce selective cytotoxins into selected locations of the brain to destroy all or selected cell types there. Likewise, these apparatus and methods can be employed to introduce immunologic agents at those selected locations. Still further, they can be employed in neural pathway tracing studies using retrograde or anteretrograde

axonal transport, or in neurophysiological testing using localized delivery of activation or inhibition.

In still further related aspects, the invention provides methods for modification of neurologic and neurologically-related activity (e.g., behavioral activity, memory-related activity, and sexual activity, among others) by such methods.

Described above are methods and apparatus for image-guided ultrasound delivery of compounds through the blood-brain barrier meeting the above-cited goals. It will be appreciated that the embodiments described herein are illustrative and that other embodiment, incorporating modifications, fall within the scope of the invention.

For example, a vaπety of ultrasound sources may be used to practice the invention. Such sources are shown, by way of non-limiting example, in Figures 6A - 6F. Thus, Figures 6A - 6B illustrate the use of a single linear and curvilinear phased array as ultrasound sources. Likewise, Figures 6C - 6D illustrate the use of a multiple linear and curvilinear phased arrays as ultrasound sources. Figure 6E illustrates the use of a large lens to focus an ultrasound beam generated by a source (not shown). Figure 6F illustrates the use of a smaller lens to focus such a beam. Finally, figure 6G illustrates the use of a partially spherical phased array as an ultrasound source. As above, the beams generated by these sources may pass through the skull or through the exposed dura matter.

IN THE UNITED STATES PATENT AND TRADEMARK OFFICE

Patent Application for

METHODS AND APPARATUS FOR IMAGE-GUIDED ULTRASOUND DELIVERY OF COMPOUNDS THROUGH THE BLOOD-BRAIN BARRIER

APPENDIX I

Contribution

HISTOLOGIC EFFECTS OF HIGH INTENSITY PULSED

ULTRASOUND EXPOSURE WITH SUBHARMONIC EMISSION EN

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Image-guided focused ultrasound surgery has shown

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W en ultrasound mieraeα wπh tusse. tbe effects through a bqtαd. it can came teucrobubbies to grow and ovilrair witmn the varying pressure held. Wben can be classified as (base related to the absorpooα of acousαc energy resulting m temperature ipcrraiie aad these gas boobk. pulsate m response to the ultrasound thoae related *o the tnrr amπ of ive propagation, they act on the suuuuuiing media by unique forms of pπmanry cavwanoo. The tbcπnal effects have been radiance prenπe. forces and torque. ^-—Tg sbeansg exttaxavefy studied tod are fairly well αadentαod stresses, vibration of e cell ^m^y^ an aggjega- (C-iweruen et al. 1974: Lek and Pierce 1971: Pond tκ» o pΛTt es. Tbe cDUaBje c^ a bobble caβ ι^aκraιe 1970: Robiasoβ and Leie 1972). However. cavuaoon hifh local prea αre aad mψeiamπa (Apfel 1981b. 1982. 1986: Hynn. 1982).

Several mventaiors have utilized various ap¬ proaches m dnr.ιnd»(n vtrro oo cs{h aα crE nιιms in suspextuoα. and m oα plants, flies and small

9β»

rodents to Ηrτ"»r" "me o. ΛoW ^* for bubble-asso¬ instances at a foo. .u ciated pheαxncaa a* they occur at ultrasonic frequen¬ ail irmancπ at latcasmes ofc 184m0 and 26^09 W 9th/.t-*- cies in the lower megahertz range They observed a These sotunπoni also resulted in a stroAg Tufflat- ¹ πuπώcr ol bmlopal c ftra. tor instinct. Jαϋujje 0 moojc and ideband ooa emmion am correlated hemof lobtn from red cells caused by shearing stresses ith histologK observauons of mccruuucal αssuc dam- exerted bv the streaming and concentrated in a thin boundary layer near the bubble ( ooney 1 ". i human Using a defocused ultrasound beam at an intensity platelet aggregation I Barnert 1979 Miller et U 1979 ) ol -1000 VV cm ^: . i pulse width of 0 3 s and a pulse and release of ATP and ether substances from platelets. pcnod of 1.0 s. Balianune et al. ( I960) found that die erythnxytes and leukocytes (Williams and Miller blood -brain barrier could be modified without damag¬ 1980). Alterations to membrane pcrmeabtbry and rup¬ ing die surrounding parenchyma. The effects on the ture of vacuoiar nxmoranes resulted in exposure of biood- brain barrier were shown by heavily stained cytooiasπuc maienal β the vaoaak. and deleterious parenchyma with vital dye without evidence of discrete effecti to cells were abo reported (Gershoy and Ny- ksaons. Barnard et al. ( 1956) and Fry et aL ( 1957) bαrg 1973. Taylor and Pood 1972). Migraoon of cells reported that it was pαssibie to produce cnraplctr de- and other nancies toward the bobble nbnang in an sαucooo of the nervous ctssoc elements widsout dam¬ uhxaaoojc bead has been predicted by Nyborg and Ger- age to the circulatory system m dtst area. la small shoy ( 1974) and then- aaalym seemed coosisietu with lesions (noncaviuDoo). even though all parcachymal reports of cell agxregaooo blood vessels of chick ektneats were destroyed, capillary vessels might re- embryo* (Dyson et aL 1974. 19X2). So far it has not mam intact. been possible to determine whether similar effects are Previous bram studies have shown duu different produced wrdun living mammalian tissue irradiated by types of tisaaαe damage can occur during high power ultrasound. ultrasound exposure. f~ ^,r * ^w» tt cavnaaon in me brain.

One study ( _l er riaaret aL I9β) has demonstrated These mctude mrrrtatnral frapaeaiaooB of the nssue. the foπnaaoα of gaseous cavmes in guinea p g legs hestastrhasje as a result of biood vessel damage as well during 0.73-MHz ultrasound irradsaDon at 680 mW as local disturbance of the blood-brain bamcr. We eta' ² όt VTVCL However, das study did not include any hypothesize dial these effects on brain tissue can be hsstoiofic resuhs- separated from ooc mo if i by conQoumg the exposure scene cases, the ~-aι«ι—« of bubbles may be¬ rnodrooca. aad nun, different biological effects can come unstabk aad tbe bubb s may couaose vjoieatty. be setectrveiy used for πxiapeuoc purposes. This is of resulting ragoiy fcxaaxed reβαc* of datt-age. hmann ajor imcn wT mc tor d-crapy. ****-.m** tse r"fimtiTii and Herrick ( 1953) were the first to report the transient of cells, for e-uunpk. could be used during trackless αvάaoσu effects on mammalian πvaan in vivo. They tzasound surgery of tbe bram. Similarly, controlled j r e biood vessel damage m once caused by ultra¬ local damage and increased permeability of die blood - sound cn-jwiie. at a he ucacy of I MHz. bram barrier without anatomical evidence of vascular

One of the sites mat could most benefit from fo¬ damage could have significant prtrnnal in aiding che¬ cused ultrasound surgery is die brain. There have been motherapeutic agents to reach cancer cells. a number of «»-■<■»« mvecαgaaag me "~-*"""~ ^>1 ef¬ fects of uhraaoo _D d m bram tecsue, Warwick and Pond MATERIALS AND METHODS ( 1968). producing local saons m rat brants with fo¬ cused ultrasound at a reqoeucy of 3.0 MHz. found Equipment that mai _l ttrttatsnα (2S00 W eo ^": or more ) aad short For geueiauon of die ultrasound helds. spherically _" ipmiπ caoβed smaD ksaons that wen cocapliπarrl curved pvezcccramic transducers with resonant fre¬ by cavitaoon effects tn me form of disrupuve vends m quencies of 0.936 aad 1.72 MHz. diameters of 80 mm (be tissue, almost always murmrrt with uuuutihage. and curvature radii of 70 mm were used. High fre¬ Fry et aL ( 1970) described " ΛIUΛUUU ksaons" to cat quency generators were cαDsructcd to drive the trans¬ brams produced at a frequency of 1.0 MHz and at a ducers wim mjTi nft, power output of 1500 aad 230 peak uueastty of 5000 W cm" ¹ at αme duraαons of W ai 0.936 aad 1.72 MHz. respecave y (Λadreev exposure between 25 and 200 ins. eie ( 1977. 1987) Acoustic Ixβtmne. Moscow). Pulse duration and pulse used focused ttluasuuud at a fiequeacy of 2.7 MHz rcpetmoo frequency could be varied from 0.0001 to aad peak fecal iiiirnsitirt of 1050-2600 W cm ^~J to 1.0 s and from 0.1 to 5.0 Hz. respecavery. Tbe acousoc produce lesions m cat brain. He observed gross ossue output of the transducer was comroUed by altering the fragsneatatwα. iacbjdus; thai of capillaries, expressed voltage output of tbe generator. The n-aasducer tested as hemorrhage, within the kendo volume m 50* of was mounted on fee X-Y-2 poήacecr of a uereo-

I N 1 uuiisatA a at m uxic apparatus, aad coαld be positioned accurate to controlled blanket to body tcasDrnsar . A within 0.01 cm in each of die tttree mutually perpend ⁱ c ^¬ detachable pouiβsr was fixed to dx nasbacsr bolder. The length 0/ the pouter was equal to dx fssnvs of ular rccπlιnc*r plxoes. curvature of die ptezøcerxπuc spόencal crmoadscer. By means of (be pouiter die focal region of 0* acoustic

Ultrasound calibration beam wis located with respect to die dura, which had

Trie _t oul acoustic ower a 1 runction 01 Uie ap ^¬ been previously exposed by removing a 4 cm' piece plied electπcal power was measured using a rad ⁱ a ^ti on of the skull After removing the pouiter. tbe nasdwccr force technique with a laboratory balance. Tbe acouαuc *u reposiuooed so (be center of die focal ιegκα of power ouqwt was measured ihrougaoui die whole die beam was 11 mm below tae surface of Be dura. range of powers used is ύx cipcπmeats Tbe relat ⁱ ve acoustic pressure outnbOTons at low power level were obta _i ned by scanning a bydrσpoooe and a focused re ^¬ ce _i ver along tbe axis cod across tbe focal plane of tbe focusug πasdaosr (Dαstnev 19*7: Gavruσv α al. 1988). Tbe tnteosrty at tbe focus was cotsαned by in- _{K i} atiB us total acousoc power over tae theoretical field distribution across αse focus. Tbe tbet ^j reucAl and espenmcn _t al beam profiles gave peak intensity values accurate _t o wnfain 10%. Tbe peak spaαai intensity at tbe focas to tae rabbit's bram was ralαilam. from d e equation: /(assue) «= f(watcr) e ^' "" where a ^t s die "— »«— coefficient ( •=■ 0024 / ' " cm ^' ' ) (Gon et aL 1979). / _t s tbe ultrasound frequency ( MHz ⁾ aad A a ibe fecal depth (cm) m tbe tissue. Tbe effects of _nn γ r — propagation were not taken mto account tbe intensity esαmaooα. The rmnlmrar propagation of t e u rasouad beam may reduce die actual intensity at ibe focus usaag these high power levels.

Momtor tg of cavaaaon

Λcousoc emission from tbe treated area was mon¬ itored with an in-boαse— manufactured wi ebaad ul ^t ra¬ sound receiver (cylindrical picεoceraαuc hydiuuuone ^, 2 mm m ieagd _l . wtd esteraal and uueraal diame ^t ers of 1.2 sad QΛ mm. respectively ) ( Cavrύov and Tsirul- tavesDgaied. αikov I980-. Ro _t aaneako 1969) Tbe outaut of die re¬ Experiment 2. To sajdy aae effects of csvnaooo ceiver was displayed on an oscilloscope after aasaag _t hrough a narrowband filter centered at tbe balf-har- tnonic rm- _H mo frequency A bandwidth of 10 kHz was used in tae aine-domain studies. Tbe oscilloscope display was rccoided 00 aim.

Tbe half-baπnoruc sound emission was used as uidicatrve of tbe ocεiαrencc of cavitaαoα ⁽ Coakley 1971:EUerand FryBn 1969 Hynyβen I991 : Lele 1987. Neppiras 1969).

Aiumal cφeτvnaia

Ezpaimaaal set-up. All experiments reported ta das arac were pc fanned to adult rabbit brains ⁰ 1 vrvo. la μtcuHauoa for msdiaήoB with ivhrsaoaad. die anαaals were anarnuruml with nrmhntal (40 mg kg body wβgbt). shaved and prmtioorrl tbe stereotaxic apparatus. Tbe animal was lying on a tcaφeraαire-

- ?cι,vs lesions were determined dmcdy in serial *bAρ^£' ^• inierviis of 0.1 turn by measurement of the exβot of screte, mtaae πγpan blue aiming 24 h after eutha¬ nasia, not allowing for rrf βvai of βγpaa blue and snnnkage due to ftsauon. There was evidence of an additional zone of edema surrounding the large lesions and to ing faint blue coloration Biiay et al. ι [956 i found dial die effect was reversible and subsided with Lbe regression of die edema. Thus, die dimensions of die lesions were measured without rhe extent of (he edema. on Bistolog _K changes brain nssue. 63 adult rabbits For histotogK eiamiaaaoo the brains of ox 14 were irradiated wnh short pulse durations of 0.01. 0.05 rabbis ( 12 at 24 h after eutaanasa nd 2 after 7 days) aad 0.1 s at a frequency of 1.72 MHz and peak focal were stained with cresyl violet, or -«•■ ■■*»■■£ _u ^ mieasaty m tissue of 7000 W cm ^'1 This is higher methods of Masson for giia and collagen fibrils, Spiel- than ibe cavnauon threshold but lower dian BX lesion meyer for myelia sheaths and Bielscbøwsky for axons. thrataoid dosage level for these single pu c diuaoons- In each ananal. rwo (26 rabbits ) or four ( 37 rabbits) RESULTS stogie and multspulse exposures were placed m ata- mus oeucus ( nuclear gray laarte ) and cansula tnicπu Sabitarmonic emission thrtshoU ( white matter). A screeujuc atlas of dse rabbit's brain Tbe dxresnolds for dse onset of subc^πnoeuc emis- (Fifkova aad Marsala 1969) aad a rectilinear nereo- sioo from dx rabbit's bram wmrairrl m vrvo at fre¬ taxic apparatus were used for seiecooα and location of quencies of 0.936 and 1.72 MHz are presented in fig. rrradiaόoo targets. Tbe pulse reneooon πmueucy was 2. No acousoc ππmion at half-harmonic frequency UUWC LB 0.1 aad S.O Hz and 1 to 33 pubcs were given. was observed below a certain diresboid intensity Pulse duraαoo exposures ( supradxresboid lesion do ¬ (which was dependent on dx pulse duration as well age level ) of 0_5 s were made in brains of 12 animals as on dx frequency of ultrasound). It uu-uued only ( ee Table 1 for number of exposures for each pulse sporadically at near-threshold intensity levels and ap¬ durance). peared to be essentially dependent oo dx utmju e of cavnaooo nuclei or "weak spots'' in tbe sonxaoon

Annas/ preparation after the totucβaons. The Ba- area. The threshold for suhharmuc r r««-n« t dx kay el aL ( 1956) technique was followed ucog trypan frequency o 0.936 MHz was found to be approxi- bbx. A dose of 0.1 g kg of body weight was prepared tmtnediatery befcre HIJΠIMW m 0.454 Nad. atnouaβng to about 10 mi. of aoluααo. boiled and hsereeL Intrave¬ nous tajecaon of the solunoo was made naneduae-y afasr soaicanoα Tbe blue coieraoon resuned from utaasoni- caDy produced breakdown of the blood— πm bamer- Thus, π faαlttaxd (he asentincaoon of the -aiima at "-""T ¹ frozen secnons and yielded lufutuauuu con- ccrβmsj me sι_se of the bloo raui baπier wsatn die uiauiBSed area.

Wbeo ibe latmals were killed under nembutal an¬ esthesia 4 h to 7 days after x vrwtcaooc. the arterial system of die rabbn was perfused with 90 to 200 mL of ύotoo c saline through die aorta. After saime perfo- SIODL me brain was also perfused with aαaml 10% fcrtaalin. uzαnosiatefy removed and stored m ftxaave solution ( 10% buffered formalin ) « ^• '

All * ^«» — ^■» ' cjψtiuueats were earned out m accor¬ Λdaa Ouraflon (<) dance wim uMtiiwional guidriinrs

Histolog ie preparation

Brains were frozen aad serially wtmunj at 0.02- πan intervals m a frontal plane. Tbe dimenjions of die

Mar icαnoαα fπmiian ιHιι

ma _t ely 2000 W em "' aad 3600 W cm ^" ' for pulse dara- dvesaold vaiues varied more as a function of I oons of 1 s aad 0.001 a. respeeavely. Tbe threshold ■ad from ammal so anπaal. Tbe d-resbotd was approxj- ι»> >ri"-* with decreasing pulse duraoon. bowe-. er. tbe mately U nines as hieh at the neqoeacy of 1.72 MHi.

The dstsboid for haif-αsrmoe

- 24 -

SUBST1TUTE SHEET (RULE 26)

i f — «d a > I ■>! ^■ !■> ■. B-alαg? Voaa 21. N^ rrK v „ , !

^J 4 A ^■ lanes looked normal wiusa the irradiated IrcL fct

/ lamina were empty due ιo perfusion and dx capillary waj)j showed no aαatcciiesj chxogcj.

Hacmorrhagia vere clearly visible oo gross exaπv- inauon of unstained frozen secuoαs as red areas occa¬ sionally with additional light blueing tn sues sonicated with 15 or more pulses repeated ai i low frequency ( 0 1 Hz ) or wns 3 to 10 pulses repeated at higher frequencies (0-5 and 1.0 Hz). Such lesions were up to 1.5 mm in diimnrr and were round in shape, but in some cases die size sad shape of dx lesions varied, figure 3 shows a 1-2-mm-ioπg lesion m dx thalamtn. The lesion consists of some separated areas with large etyttmxytr conceuutuuu fhrongboat each of mem and exhibits a curved shape, rnrbrirtng a μ feienoal onen- taaon. perhaps doe » large blood vessel plsoemeu. Between dx sxeas occupasd by crvtbrocytes dxre were areas m which αythrocyna were not present and dx blood vessels appeared to be intact. All irlrnαaabte OCUΓOQS showed varying degrees of abnormality. One predominant feamre was shrinkage and nease staia-

ce - or er-stained sccoons were observed. e capil- ^' X27.

a few iliπmaiiaiuj cetb. Crtayi vwk. sum. X275 emg missing, perhaps occurring dunng Ox preoara-

: Jl. l

TTS ooa of the aec oαs. The ι . « the matrix was com¬ pletely disorganized. There were a large number of T997 notes and clefts, and many of x small Mood vessels appeared broken and were surroynde ; ty kTW Wlύl erythrocyte dispersement into tbe surrounding αssuc ₍ Fig 9). Some blood vessels were unbroken but ap¬ peared to be dilated and contested by eηrThrocv ^t es which probably were coagulated. No intact neurons appeared in any part of the lcsioo. Much indisuoguisb- abie cell debris. ' 'ghost ' ' cells, small dark and pyfcnouc nuclei wi _t h steeds of cytoplasm and invisible nuclcou as well as pykaooc gha cell nuclei could be observed m dx lesion (fig. 10). Single nerve cells close us the border, but outside x lesion, were also aflected. Tbe nuclei were pale and cytoplasms were vacuoiaxd some cells, whereas m others dx cytoplasms were dark aad dx cell cabas shrunken The gha cells in the vicini _t y of _f ix lesion were less affected than dx neu¬ rons.

Large lesions of about 1.7 mm m diameter, pro-

fil. V. laάaaBgaata c biaBpέύic bmotBtOi i se o y flam vie. irwihiTig hum BX aw* JQOCL Cresyl Mas: x* 0 (the same ezpeβare as α> fit. t).

duccd with 20 to 35 pulses of 0.1-s duration, showed a characteπsac Hlaad moax' ^* paβern. On gross caam- iaaboo dx center of dx lesson showed little or no vital staining, whereas the peripheral region siirroβnding the center was intensely stained wim trypao blue. Micro¬ scopic exaaanaaon showed dx ceacral zone to be co- agulaoøn narmns aad tfx surtDOBdmg tone to be nq- uefacoon nrrrorg Tissue fngaxaαooo. including chat of capillaries (expressed as local hαnorrhage). was fouad m most of ox a* mais

Pulse duraaon of OJ s. Soa ariom wim rwo to usree pulses caused lcsioas wim tbe ^■ island-most-' paαera. Gross Isf iiaaiunge asstcndmg βx lesioQ aad spreading iiiU- uebrally, and often rupuuiug into me lateral vtaBs lct, was ofasu »ul Soaicaaon with three passes resalied m postoperative death of aaimals due to gross hemoπbage in all cases.

He. 8. A I i ce' a iabMt ' Oraimnally "echo lessons'' could be detected at I to be lost daπαg pnaxnoαs of s ^β e- _JIU In u luiai fmiiiixaniπi - 1.72 MHz. / ^» dx base of the bram. which could have been caused

7α» em-\ PD » 0.1 PllF - 5.01iz. FN « IS. Ciesyl by dx divugmi beam absorption aad renecnon at tbe Kttu X27. concave regions m the base of dx skull.

of as ataasouad du ajjuu. «"_»*»? of

exsax rmaBy. S axsrvaj OX hπhhsu less βme m

ι αsαtBty of did

,

r >N I "•» πai. 1Ψ

IN THE UNITED STATES PATENT AND TRADEMARK OFFICE

Patent Application for

METHODS AND APPARATUS FOR IMAGE-GUIDED ULTRASOUND DELIVERY OF COMPOUNDS THROUGH THE BLOOD-BRAIN BARRIER

APPENDIX H

Materials and Methods

Somcations

The ultrasound was generated by using m-house manufactured focused ultrasound transducers Three different transducers were used for this study They were all manufactured by mounting a spherically curved 10 cm diameter piezoelectric ceramic (PZT4) bowl in a plastic holder using silicon rubber The ceramic had silver or gold electrodes both in the front and back surface The single element transducer had a radius of curvature of 8 cm and was connected to one coaxial The transducer had a fundamental resonance frequency of 0 556 MHz and the third harmonic frequency of 1 67 MHZ One coaxial cable connected the electrodes to a LC matching network (separate for each frequency) that matched the electrical impedance of the transducer and the cable to the RF amplifier output impedance of 50 ohm and zero phase The matching circuit was connected to an ENI amplifier (both ENI A240L and A500 were used in the tests) The RF signal was generated by a signal generator (Stanford Research Systems, Model DS345)

The two phased arrays had similar structure and the same driving hardware, the resonant frequency being their only main difference The two arrays operated at 0 6 MHz and 1 58 MHz The radius of curvature of both of the transducers was 10 cm and both of them were cut into about 1 cm2 square elements as shown in figure 1 The total number of elements in both arrays was 64 although only 60 were dπven m the experiments due to hardware limitations The ceramic bowl was cut using a diamond wire saw so that the elements were completely separated by a 0 3-0 5 mm space The space left by the cutting was filled by sihcone rubber that kept the array elements together and isolated them acoustically from each other The sihcone rubber allowed the transducer elements to move with minimum amount of clamping Each transducer element was connected to a coaxial cable and a matching circuit that was individually tuned The array was dπven by a m-house manufactured 64 channel driving system that included a RF amplifier and phase shifter for each channel The phase and amplitude of the driving signal of each channel was under computer control (see Buchanan and Hynynen for detail)

Ultrasound measurements

The ultrasound pressure wave distributions were measured using needle hydrophones (spot diameter 0 5 and 1 mm) and an amplifier (Precision Acoustics Ltd). The amplified signal was measured and stored by a oscilloscope (Tektronix, model 2431L ) The hydrophone was moved by stepper motors in three dimensions under computer control. The pressure amplitudes measured by the oscilloscope were stored by the computer for each location

The absolute pressure amplitudes at the maximum power levels at the focus were measured by a shock wave hydrophone (Sonic Industries) and the oscilloscope

Experiments'

A piece of human skull ( top part of the head: front to back 18 cm and maximum width 12 cm) was obtained and fixed with formaldehyde It has been shown that the acoustic properties of formaldehyde fixed skull and a fresh skull are almost identical. The experimental setup is shown in figure 2. The ultrasound applicator under test was positioned in a water tank the walls and bottom of which were covered by rubber mat to reduce ultrasound reflections The tank was filled with degassed deionized water. The hydrophone that was connected to the scanning frame, was positioned to the focus of the ultrasound field The pressure amplitude distributions were measured in the water by scanning the needle hydrophone After the water experiments the piece of skull was positioned in front of the transducer and the ultrasound field measurements repeated. In the phased array experiments the phase shifts introduced by the skull were also mapped and corrected. This was done by positioning the hydrophone in the focal position of the ultrasound field without the skull and then driving each transducer element separately while measuring the phase of the wave with the hydrophone. From these measurements a phase correction for each transducer element was calculated and programmed in the phase shifters. Then the ultrasound field measurements were repeated while driving the array with the

corrected signals In all of the above measurements the ultrasound field was continuously on at a low power level

In a second set of experiments the total peak pressure amplitudes achievable in the focus through the skull were measured In this experiment the transducer was placed on the bottom of the tank and the beam aimed up towards the water surface The skull was placed on the transducer so that it was supported by the edges of the applicator but not by the piexoelectπc elements The shock hydrophone was lowered at the focal depth and positioned to the acoustic focus The tranducer was used in the burst length of 10 or 20 cycles This was done to avoid electrical interference that was picked up by the hydrophone during sonication

Results

It was possible to produce a well focused beam with the 0.559 MHZ single element transducer through the bone The beam had secondary peaks introduced by the skull but the main peak was the highest The location of the peak was also shifted by the skull by 1-2 mm from its geometric position (figure 3). However, focus was completely destroyed when 1 67 MHZ was used. (Figure 3 b) Similar results were obtained with the phased array. Figure 4 demonstrates the effect of skull on the pressure amplitude distribution across the focus. The effect of the skull in the focal shape can be reduced by correcting the phase. The main impact of the phase is in the location of the focus that can be corrected back to the geometric focus The magnitude is reduced to 26 % and 31 % of its water value without and with the phase correction, respectively. The importance of the phase correction is demonstrated more clearly with the higher frequency array. With this array the focus is completely destroyed by the skull. However, when the phase correction is introduced the focal spot is returned into its original shape.

To demonstrate the power transmission capability of the skull the peak pressure amplitude in the focus with the 0.559 MHZ single transducer was measured. The maximum pressure amplitude was 8 0+/- 0 6 MPa. The variation resulted from reposioning the peace of skull on the transducer Similar measurements with the 0.6 MHZ phased array revealed that the RF-amplifiers could not deliver adequate power and pressure amplitudes of 1 5 MPa were measured. Higher powers could have been delivered with a higher power amplifier system

Discussion

The results demonstrated that an ultrasound beam can be focused through the skull at frequencies around 0 6 MHz or lower with a few millimeter shift in the focal position away from its geometric focus The secondary pressure peaks are also enhanced by the skull These effects on the focal shape can be reduced by using phased array and correcting for the phase shifts caused by the bone. At higher frequencies the wavelengths are shorter and the propagation delay variations caused by the variable thickness of the skull become significant when compared with the wavelength. This results in destruction of the focal spot when the focused beam propagates through the skull The results demonstrated that the effects of the skull to the beam shape can be eliminated using a phased array with proper phase corrections and sharp focusing can be achieved. In this study the phase correction was calculated from hydrophone measurements. We predict that the same corrections could be made by obtained the skull thickness from a CT scan and then calculating the phase correction required for each array element.

Our driving hardware did not permit us to deliver adequate energy through the skull to reach cavitation threshold with the phased array. However, the single element transducer at the 0.554 MHz allowed us to deliver up to 8 MPa pressure amplitudes through the skull. With a phased array the phase correction could increase the pressure amplitude to about 9 5 MPa at the same driving conditions. This value was reached through an area of 10 cm in diameter. If the whole available skull surface

around the brain is utilized then at least three times larger window could be used. Thus it is estimated that pressure amplitudes around 30 MPa can be induced in the brain through the skull. These values are significantly above the 4 MPa that was measured to be the threshold value in vivo muscle at 0.6 MHz (Hynynen 1991) and the value of 8.5 MPa at 0.936 MHz measured in vivo rabbit brain (Vykhtodseva et al., 1995). The cavitation threshold is frequency dependent decreasing with the frequency. Thus the results demonstrate that adequate ultrasound transmission through skull can be generated to induce cavitation. The pressure values at the skull or skin are well below the thermal and cavitation damage thresholds. Although good results were achieved with only 60 transducer elements in the phased array it is likely that more and smaller elements are needed in order to be able to move the focal spot inside of the brain. Much more work needs to be done before the array geometry is optimized

References:

Buchanan, M.T., Hynynen. K , The design and evaluation of an intracavitary ultrasound phased array for hyperthermia. IEEE Trans. Biomedical Engineering 41, 1 178 - 1 187, 1994.

Hynynen, K., The threshold for thermally significant cavitation in dog's thigh muscle in vivo. Ultrasound in Med. Biol., 17, 157 - 169, 1991.

Vykhodtseva, N.I., Hynynen, K., Damianou, C, The mechanical effects of high intensity pulsed ultrasound exposure with half-harmonic emission in rabbit brain in vivo. Ultrasound Med. Biol. 21, 969-979, 1995.

Figures :

Figure 1. A diagram of one of the phased arrays.

Figure 2. A diagram of the experimental set up.

Figure 3. A The ultrasound intensity distribution across the focus of the 0 559 MHZ - single transducer measured in water B The same distribution when the skull was in front of the transducer, C The intensity distribution at 1 67MHz measured in water and D through the skull

Figure 4 A Pressure amplitude profiles across the focus of the 0 6 MHz phased array in water, through the bone and through the bone when phase correction was used.

Figure 4 B The same but along the axis

Figure 5 The ultrasound intensity distribution measured across the focus of the 1.58 MHz phased array A In water B through skull without phase correction and C Through skull with phase correction

0 6 8 10 12 14 16 18 20

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