FOR

RESOLUTION ENHANCEMENT FOR LIGHT SHEET MICROSCOPY

SYSTEMS AND METHODS

Inventors:

Hari Shroff

Yicong Wu

Sara Abrahamsson

Entity:

Large Entity

International Searching Authority:

Korean Intellectual Property Office (South Korea)

Priority Claim:

U.S. Provisional Application Serial No. 62/054,484

Filed September 24, 2014

Prepared by:

Polsinelli PC

One East Washington Street, Suite 1200

Phoenix, Arizona, 85004

(602) 650-2061 RESOLUTION ENHANCEMENT FOR LIGHT SHEET MICROSCOPY

SYSTEMS AND METHODS

GOVERNMENT INTEREST STATEMENT

[0001] The present subject matter was made with U.S. government support. The U.S. government has certain rights in this subject matter.

FIELD

[0002] This document relates to methods and systems related to light sheet microscopy, and in particular, to resolution enhancement techniques for light sheet microscopy systems and methods.

BACKGROUND

[0003] Light sheet fluorescence microscopy uses parallelized excitation and a perpendicular geometry between excitation and detection to enable optically sectioned, high speed, volumetric imaging with massively reduced photo-damage and photo-bleaching compared to conventional imaging methods. Although this combination of benefits is enabling for biology, the spatial resolution of the light sheet microscopy has lagged behind other convention microscopy systems.

[0004] The main reason for the relatively poor resolution of light sheet microscopy is that the perpendicular geometry required necessitates the use of relatively low numerical aperture objectives. Acquiring images from multiple directions/views or using structured illumination to illuminate the sample in combination with image processing software does improve resolution, but these approaches fail to improve spatial resolution in light sheet microscopy applications to the extent possible in conventional microscopy, such as confocal microscopy.

Furthermore, multi-view acquisition or structured illumination approaches have thus far required the sample to be exposed to more illumination than conventional, single- view light sheet fluorescence microscopy, thereby sacrificing some of the available signal/photon budget and mitigating the original advantages of light sheet

fluorescence microscopy. In addition, such approaches require more images to be captured than a single-view light sheet fluorescence microscopy, thereby sacrificing the inherent speed. [0005] As shown in FIG. 1 , a conventional light sheet microscopy system, designated 10, is illustrated, in which a light sheet 18 generated from an illumination source (not shown), such as a laser source, is introduced into the sample (not shown) through a first objective lens 12. The illuminated sample emits fluorescence emissions 20 scattered at substantially a ninety degree angle relative to the light sheet 18 illuminating the sample and detected by a second objective lens 14. In particular, scanning the light sheet 18 through the first objective 12 while maintaining the focus in the second objective lens 14 generates an imaging volume of the sample. Although ninety degree detection ensures that the illumination plane defined through the sample is in focus, and that minimal out-of-focus light corrupts detection of the fluorescence emissions 20, it requires the use of relatively low NA optics. In addition, the majority of the fluorescence emissions excited by the light sheet 18 is scattered outside the aperture of the second objective 14 and wasted.

[0006] To collect a portion of the wasted fluorescence emissions 22, a third objective lens 16 may be positioned to capture some of the wasted fluorescence emissions 22 emitted by the sample. If the fluorescence emissions are imaged conventionally using only a tube lens and camera arrangement (e.g., conventional epifluorescence microscopy), relatively little of the fluorescence emissions 22 are used efficiently (i.e., "in focus"). This is because the depth of field of a high numerical objective is inversely proportional to the square of the numerical aperture.

[0007] Other techniques seek to capture more imaging planes at once and fusing them together to improve resolution relative to conventional light sheet fluorescence microscopy; however, such techniques suffer from out-of-focus light. As such, further improvements in the collection of fluorescence emissions in a light sheet microscopy system are desired.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a simplified illustration showing a conventional light sheet microscopy system that uses a dual objective lens arrangement;

[0011] FIG. 2 is a simplified illustration showing one embodiment of a light sheet microscopy system that uses a dual objective lens arrangement having an extended depth-of-focus optical system;

[0012] FIG. 3A is an image of microtubules taken from the embodiment of the light sheet fluorescence microscopy system of FIG. 2;

[0013] FIG. 3B is an image of beads taken from the embodiment of the light sheet fluorescence microscopy system of FIG. 2;

[0014] FIG. 4A is an image of microtubules taken from a conventional light sheet microscopy system;

[0015] FIG. 4B is an image of beads taken from a conventional light sheet microscopy system;

[0016] FIG. 5 is a simplified block diagram showing another embodiment of a light sheet microscopy system in which one of the objective lenses is oscillated to extend the depth of field;

[0017] FIG. 6A is an image taken with the light sheet microscopy system of FIG. 5, while FIG. 6B is a similar image taken with a convention light sheet microscopy system;

[0018] FIG. 7 is a graph showing the intensity in relation to lateral distance for illustrating the difference in resolution between the image of FIG. 6A and the image of FIG. 6B; and

[0019] FIG. 8 is a simplified block diagram showing another embodiment of a light sheet microscopy system in which a multi-focus grating device is positioned at the fourier (back focal) plane of the third objective lens to extend the effective depth of field of the third objective lens.

[0020] Corresponding reference characters indicate corresponding elements among the view of the drawings. The headings used in the figures should not be interpreted to limit the scope of the claims. DETAILED DESCRIPTION

[0021] Various embodiments for applying a resolution enhancement technique for light sheet microscopy systems using a depth-of-focus optical arrangement to improve lateral resolution are disclosed. The resolution

enhancement technique utilizes an arrangement of three objective lenses and a processor to combine images captured from one objective lens with images captured from another objective lens to enhance lateral resolution. Referring to the drawings, various embodiments of a light sheet microscopy system utilizing a resolution enhancement technique are illustrated and generally indicated as 100, 300 and 500 in FIGS. 2-8.

[0022] As shown in FIG. 2, a simplified block diagram illustrates one embodiment of a light sheet microscopy system 100 that utilizes the resolution enhancement technique. In one embodiment, the light sheet microscopy system 100 may include an illumination source 101 , for example a laser, that generates a single light beam 103 transmitted through an optics arrangement 130 for producing an excitation light sheet 122 that is focused through a first objective lens 102 for illuminating a sample 128. The first objective lens 102 defines a longitudinal axis 200 that forms at an angle B relative to the plane 204 of the sample 128. When the sample 128 is illuminated by the excitation light sheet 122 focused on the sample 128 through the first objective lens 102, fluorescence emissions 124 are generated by the sample 128 which are detected by a second objective lens 124 defining a longitudinal axis 202 that forms a perpendicular angle A relative to longitudinal axis 200 defined by the first objective lens 102. The second objective lens 104 focuses the fluorescence emissions 124 through an optics arrangement 126 for detection through a first camera 116. The detected images of the fluorescence emissions 124 are then sent to a processor 120 having one or more applications for processing the detected images of the fluorescence emissions 124.

[0023] As further shown in FIG. 2, fluorescence emissions 124 are also detected by a third objective lens 106 aligned along a longitudinal axis 206 that is in perpendicular relation to plane 204 of the sample 128. In one embodiment, the third objective lens 106 is a high numerical aperture objective lens. A first lens 110 and a second lens 112 may be arranged in 4f configuration so as to image the back focal plane of the third objective lens 106 at the back focal plane of the second lens 112. [0024] In addition, an extended depth-of-focus optical system 108 for converting the fluorescence emissions 124 may be positioned between the second lens 112 and a third lens 114 to collapse the fluorescence emissions 124 focused by the third objective 106 to a single plane. This single plane formed by the

fluorescence emissions 124 by the extended depth-of-focus optical system 108 may be imaged onto a second camera 118, for example a widefield detector, by the third lens 114, which is positioned one focal length away from the extended depth-of- focus optical system 108. In one embodiment, the second lens 112 and the third lens 114 are arranged in a 4f telescopic configuration.

[0025] In some embodiments, the extended depth-of-focus optical system 108 may be an incoherent "layer cake" optical arrangement or a cubic phase mask component. In some embodiments, the cubic phase mask component is a conventional diffractive optic that introduces strong aberration that dominates other aberrations, such as defocus, provides a much extended depth of field. Importantly, the cubic phase mask component preserves lateral resolution while degrading axial resolution, i.e. extending the depth of field, and therefore the cubic phase mask component has application in collecting fluorescence emissions 124 along a tilted imaging plane generated in the light sheet microscopy system 100.

[0026] In some embodiments, the incoherent "layer cake" optical arrangement may be a 'phase mask with circularly symmetric stair steps', such as a conventional refractive optic that enables incoherent addition of a series of annular sub-apertures which collectively fill the pupil of a high aperture third objective lens 106. The refractive optic produces an effect that creates a rotationally symmetric point-spread function with dramatically extended axial extent. When the incoherent "layer cake" optical arrangement is positioned in the (primary or secondary) back focal plane (e.g., Fourier plane) of the light sheet microscopy system 100, the incoherent "layer cake" optical arrangement can extend the axial depth of the field of the third objective lens 106.

[0027] In either embodiment of the extended depth-of-focus optical system 108 the depth of field is increased while largely preserving the lateral resolving power of the third objective lens 106. Any loss in lateral resolution may be compensated for by deconvolution. In some embodiments, other optics can provide extended depth of field could be used, such as an axicon or annular aperture. [0028] In some embodiments, the third objective lens 106 may be arranged to both introduce the light sheet 122 into the sample 128 and collect the resulting fluorescence emissions 124. This arrangement allows for a more compact light sheet microscopy system 100 with fewer optic components. Moreover, additional depth-of-field optics may be added or retrofitted to a conventional light sheet microscopy system 10, which would provide enhanced resolution and higher signal-to-noise ratio than images acquired by light sheet microscopy system 10.

[0029] In some embodiments, the processor 120 receives images from the fluorescence emissions 124 collected by the second objective lens 104 and the images from the fluorescence emissions 124 collected by the third objective lens 106. In the light sheet microscopy system 100, the lateral resolution of the fluorescence emissions 124 collected by the third objective lens 106 is preserved with a sacrifice in axial resolution, while images from the fluorescence emissions 124 that are collected by the second objective lens 104 have the axial resolution preserved with a sacrifice in lateral resolution. In one embodiment, the processor 120 combines the corresponding images of the fluorescent emissions 124 having the lateral resolution preserved with the images of the fluorescent emissions 124 having the axial resolution preserved to produce a combined image with enhanced axial and lateral resolution in comparison to the images from only the second objective lens 104 with the axial resolution preserved and the lateral resolution degraded.

[0030] Referring to FIGS. 4A and 4B, images of beads and microtubules are shown that were produced by a conventional light sheet microscopy system 10, while FIGS. 3A and 3B show images of the same beads and microtubules that were produced by the light sheet microscopy system 100. The boxes shown in FIGS. 3B and 4B and the arrows shown in FIGS. 3A and 4A highlight features that undergo resolution enhancement between the conventional light sheet microscopy system 10 and the light sheet microscopy system 100.

[0031] Referring to FIG. 5, another embodiment of the light sheet microscopy system, designated 300, may include an illumination source 301 , for example a laser, that generates a single light beam 305 transmitted through an optics arrangement 302 for producing an excitation light sheet 307 that is focused through a first objective lens 306 for illuminating a sample 313. The first objective lens 306 defines a longitudinal axis 400 that forms at an angle B relative to the plane 402 of the sample 313. When the sample 313 is illuminated by the excitation light sheet 307 focused on the sample 313 through the first objective lens 306,

fluorescence emissions 309 and 311 are generated by the sample 313 which are detected by a second objective lens 308 defining a longitudinal axis 404 that forms a perpendicular angle A relative to longitudinal axis 400 defined by the first objective lens 306. The second objective lens 308 focuses the fluorescence emissions 309 through an optics arrangement 318 for detection through a first camera 320. The detected images of the fluorescence emissions 309 are then sent to a processor 322 having one or more applications for processing the detected images of the fluorescence emissions 309.

[0032] As further shown, fluorescence emissions 311 emitted in another direction by the sample 313 are detected by a third objective lens 312 aligned along a longitudinal axis 406 that is in perpendicular relation to plane 402 of the sample 313. In some embodiments, the third objective lens 312 is operatively connected to a piezoelectric device 315 that rapidly scans the third objective lens 312 during a time period when the light sheet 307 illuminating the sample 313 is stationary as is commonly used in acquiring "z stacks" or imaging volumes on a conventional microscope. As such, the scanning operation has been found to extend the depth of field of the third objective lens 312, thereby allowing detection or capture of the fluorescence emissions 311 from an entire light sheet for each light sheet position when the sample 313 is illuminated. In one embodiment, the third objective lens 312 is a high numerical aperture objective lens.

[0033] In some embodiments, a tube lens 314 may be arranged in 4f telescopic relation so as to image the fluorescence emissions 31 1 captured by the third objective lens 312 onto a second camera 316 for capturing raw images of the sample 313. In this arrangement, the raw images captured by the second camera 316 have degraded lateral resolution; however, the extended depth of field of the raw images and the fact that lateral resolution of these images may be recovered to substantially normal levels using conventional deconvolution techniques offsets any degradation of lateral resolution that occurs prior to deconvolution techniques being applied.

[0034] In some embodiments, the images from the first camera 320 and the second camera 316 are transmitted to the processor 322 and the images combined to produce a composite image with extended depth of field. [0035] FIG. 6A is an image of beads taken by the light sheet microscopy system 300 with the axial movement of the third objective lens 316, while FIG. 6B is another image taken of the same beads by the conventional light sheet system 10 without the axial movement of the third objective 316. FIG. 7 is a graph that illustrates the improved resolution of a three (x-y-z axes) view arrangement as shown in FIG. 6A in comparison to the two view (x-y axes) arrangement without axial movement of the third objective 316 of FIG. 6B.

[0036] Referring to FIG. 8, another embodiment of the light sheet microscopy system, designated 500, may include a multi-focus grating component 503 that is positioned at the fourier (back focal) plane of the third objective lens 512 to extend the effective depth of field of the third objective lens 512. In other embodiments, the multi-focus grating component 503 can be positioned at any plane conjugate to the back focal plane of the third objective 512.

[0037] In some embodiments, the light sheet microscopy system 500 may include an illumination source 501 , for example, a laser, that generates a single light beam 505 transmitted through an optics arrangement 502 for producing an excitation light sheet 507 that is focused through a first objective lens 506 for illuminating a sample 513. The first objective lens 506 defines a longitudinal axis 600 that forms at an angle B relative to the plane 602 of the sample 513. When the sample 513 is illuminated by the excitation light sheet 507 focused on the sample 513 through the first objective lens 506, fluorescence emissions 509 and 511 are generated by the sample 513 which are detected by a second objective lens 508 defining a

longitudinal axis 604 that forms a perpendicular angle A relative to longitudinal axis 600 defined by the first objective lens 506. The second objective lens 508 focuses the fluorescence emissions 509 through an optics arrangement 518 for detection through a first camera 520. The detected images of the fluorescence emissions 509 are then sent to a processor 522 having one or more applications for processing the detected images of the fluorescence emissions 509.

[0038] As further shown, fluorescence emissions 511 emitted in another direction by the sample 513 are detected by a third objective lens 512 aligned along a longitudinal axis 606 that is in perpendicular relation to plane 602 of the sample 513. A first lens 524 and a second lens 526 may be arranged in 4f configuration so as to image the back focal plane of the third objective lens 512 at the back focal plane of the second lens 526. In addition, the multi-focus grating component 503 may be positioned between the second lens 526 and a third lens 528 to separate and collapse the fluorescence emissions 511 onto a single plane. The multi-focus grating component 503 processes the fluorescence emissions 511 from the back focal plane of the second lens 526 such that the fluorescence emissions 511 from each focal plane are separated on the second camera 516, and can thus be spatially resolved as distinct depths in the sample 513. As such, the scanning operation using the multi-focus grating device 501 has been found to extend the depth of field of the third objective lens 512, thereby allowing detection or capture of the fluorescence emissions 511 from an entire light sheet for each light sheet position when the sample 513 is illuminated. In one embodiment, the third objective lens 512 is a high numerical aperture objective lens.

[0039] In some embodiments, a tube lens 514 may be arranged in 4f telescopic relation so as to image the fluorescence emissions 511 captured by the third objective lens 512 onto a second camera 516 for capturing raw images of the sample 513. In this arrangement, the raw images captured by the second camera 516 have degraded lateral resolution; however, the extended depth of field of the raw images and the fact that lateral resolution of these images may be recovered to substantially normal levels using conventional deconvolution techniques offsets any degradation of lateral resolution that occurs prior to deconvolution techniques being applied.

[0040] In some embodiments, the images from the first camera 520 and the second camera 516 are transmitted to the processor 522 and the images combined to produce a composite image with extended depth of field.

[0041] It should be understood from the foregoing that, while particular embodiments have been illustrated and described, various modifications can be made thereto without departing from the spirit and scope of the invention as will be apparent to those skilled in the art. Such changes and modifications are within the scope and teachings of this invention as defined in the claims appended hereto.