Recently, we have presented a thin optical detector assembly consisting of a microlens array (MLA) coupled to
a large area CMOS sensor through a septum mask. The sensor is placed in the physical focal plane of the MLA.
Each lens of the MLA forms a small image on the sensor surface, with individual images being separated from
each other by the septum mask. The resulting sensor image thus shows a multitude of small sub-images. A
low-resolution image can be attained by extracting only those pixels that are located on the optical axis of a
microlens, as reported previously. Herein we describe an improved post-processing method to extract images of
higher resolution (which can be focused to an arbitrary plane) from a single raw sensor image: Each lens of the
MLA results in a mapping from points in object space to corresponding sensor pixels. By tracing back the light
paths from sensor pixels through the lenses onto an arbitrary focal plane in object space this mapping can be
inverted. Intensities captured on individual sensor pixels can be attributed to virtual pixels on that focal plane
using the computed inverse mapping.
As a result, from a single acquisition by the detector, images focused to any plane in object space can be
calculated. In contrary to the approach of extracting focal point intensities, the spatial resolution is not limited
by microlens pitch. We present experimental examples of extracted images at various object plane distances and
studies determining the spatial resolution.
An optical detector suitable for inclusion in tomographic arrangements for non-contact in vivo bioluminescence
and fluorescence imaging applications is proposed. It consists of a microlens array (MLA) intended for field-of-view definition, a large-field complementary metal-oxide-semiconductor (CMOS) chip for light detection, a septum mask for cross-talk suppression, and an exchangeable filter to block excitation light. Prototype detector
units with sensitive areas of 2.5 cm x 5 cm each were assembled. The CMOS sensor constitutes a 512 x 1024 photodiode matrix at 48 μm pixel pitch. Refractive MLAs with plano-convex lenses of 480 μm in diameter and pitch were selected resulting in a 55 x 105 lens matrix. The CMOS sensor is aligned on the focal plane of
the MLA at 2.15mm distance. To separate individual microlens images an opaque multi-bore septum mask
of 2.1mm in thickness and bore diameters of 400 μm at 480 μm pitch, aligned with the lens pattern, is placed
between MLA and CMOS. Intrinsic spatial detector resolution and sensitivity was evaluated experimentally as a
function of detector-object distance. Due to its small overall dimensions such detectors can be favorably packed
for tomographic imaging (optical diffusion tomography, ODT) yielding complete 2 π field-of-view coverage. We
also present a design study of a device intended to simultaneously image positron labeled substrates (positron
emission tomography, PET) and optical molecular probes in small animals such as mice and rats. It consists of
a cylindrical allocation of optical detector units which form an inner detector ring while PET detector blocks
are mounted in radial extension, those gaining complementary information in a single, intrinsically coregistered
experimental data acquisition study. Finally, in a second design study we propose a method for integrated optical
and magnetic resonance imaging (MRI) which yields in vivo functional/molecular information that is intrinsically
registered with the anatomy of the image object.
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