Targeted multi-pinhole SPECT

Abstract

PurposeSmall-animal single photon emission computed tomography (SPECT) with focused multi-pinhole collimation geometries allows scanning modes in which large amounts of photons can be collected from specific volumes of interest. Here we present new tools that improve targeted imaging of specific organs and tumours, and validate the effects of improved targeting of the pinhole focus.MethodsA SPECT system with 75 pinholes and stationary detectors was used (U-SPECT-II). An XYZ stage automatically translates the animal bed with a specific sequence in order to scan a selected volume of interest. Prior to stepping the animal through the collimator, integrated webcams acquire images of the animal. Using sliders, the user designates the desired volume to be scanned (e.g. a xenograft or specific organ) on these optical images. Optionally projections of an atlas are overlaid semiautomatically to locate specific organs. In order to assess the effects of more targeted imaging, scans of a resolution phantom and a mouse myocardial phantom, as well as in vivo mouse cardiac and tumour scans, were acquired with increased levels of targeting. Differences were evaluated in terms of count yield, hot rod visibility and contrast-to-noise ratio.ResultsBy restricting focused SPECT scans to a 1.13-ml resolution phantom, count yield was increased by a factor 3.6, and visibility of small structures was significantly enhanced. At equal noise levels, the small-lesion contrast measured in the myocardial phantom was increased by 42%. Noise in in vivo images of a tumour and the mouse heart was significantly reduced.ConclusionTargeted pinhole SPECT improves images and can be used to shorten scan times. Scan planning with optical cameras provides an effective tool to exploit this principle without the necessity for additional X-ray CT imaging.

VECTor: A Preclinical Imaging System for Simultaneous Submillimeter SPECT and PET

“…Because all clusters in the VECTor collimator focus on a central scan volume that is smaller than a mouse, focusing on a restricted volume of interest can increase the number of detected counts from that region, resulting in improved noise-resolution trade-offs (21). The benefits of focusing are well illustrated by the mouse bone scans in Figures 5 and 6; the visibility of small details is enhanced in the focused scan, compared with the whole-body scan.…”

“…All the pinhole clusters together observe a field of view that extends over the entire collimator tube diameter (48 mm) and has the shape of an hourglass (21). The average longitudinal length of the collimator field of view is 36 mm.…”

Fast Spiral SPECT with Stationary γ-Cameras and Focusing Pinholes

“…Combining stationary setups and focusing multiple pinholes with high pinhole magnification has resulted in dedicated small-animal SPECT systems that have overcome the limitation of poor spatial resolution and sensitivity. Sub-half-millimeter resolutions over the entire mouse and very detailed images of tracer uptake in tiny subcompartments of organs and tumors have been achieved (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). In such focusing multipinhole (FMP) SPECT systems, all pinholes focus on a central field of view (CFOV) in order to maximize the scan speed and the count yield for imaging tumors or organs.…”

Onboard functional and molecular imaging: A design investigation for robotic multipinhole SPECT

“…10 Notably several ROI SPECT methods have been developed for cardiac imaging, [11][12][13] including multipinhole methods. Multipinhole SPECT methods have been highly effective in small animal imaging, [14][15][16] in part because the pinholes can be positioned close to any ROI, given the small size of the animal, and in part because magnification can overcome the limitations of gamma detector spatial resolution. For human ROI imaging, a major issue can be that other portions of the body force the multipinhole system away from the ROI.…”