Inclusion of quasi-vertex views in a brain-dedicated multi-pinhole SPECT system for improved imaging performance

Abstract

With brain-dedicated multi-detector systems employing pinhole apertures the usage of detectors facing the top of the patient’s head (i.e. quasi-vertex (QV) views) can provide the advantage of additional viewing from close to the brain for improved detector coverage. In this paper, we report the results of simulation and reconstruction studies to investigate the impact of the QV views on the imaging performance of AdaptiSPECT-C, a brain-dedicated stationary SPECT system under development. In this design, both primary and scatter photons from regions located inferior to the brain can contribute to SPECT projections acquired by the QV views, and thus degrade AdaptiSPECT-C imaging performance. In this work, we determined the proportion, origin, and nature (i.e. primary, scatter, and multiple-scatter) of counts emitted from structures within the head and throughout the body contributing to projections from the different AdaptiSPECT-C detector rings, as well as from a true vertex view detector. We simulated phantoms used to assess different aspects of image quality (i.e. uniform activity concentration sphere, and Derenzo), as well as anthropomorphic phantoms with different count levels emulating clinical 123I activity distributions (i.e. DaTscan and perfusion). We determined that attenuation and scatter in the patient’s body greatly diminish the probability of the photons emitted outside the volume of interest reaching to detectors and being recorded within the 15% photopeak energy window. In addition, we demonstrated that the inclusion of the residual of such counts in the system acquisition does not degrade visual interpretation or quantitative analysis. The addition of the QV detectors improves volumetric sensitivity, angular sampling, and spatial resolution leading to significant enhancement in image quality, especially in the striato-thalamic and superior regions of the brain. Besides, the use of QV detectors improves the recovery of clinically relevant metrics such as the striatal binding ratio and mean activity in selected cerebral structures. Our findings proving the usefulness of the QV ring for brain imaging with 123I agents can be generalized to other commonly used SPECT imaging agents labelled with isotopes, such as 99mTc and likely 111In.

Multiple-pinhole collimators improve intra- and between-rater agreement and the certainty of the visual interpretation in dopamine transporter SPECT

“…As a consequence, the interpretation of DAT-SPECT can be affected by the limited spatial resolution of conventional SPECT imaging, particularly at early disease stages. Multiple-pinhole (MPH) collimator technology has the potential for concurrent improvement of both spatial resolution and count sensitivity compared to conventional imaging with parallel-hole and fan-beam collimators in clinical SPECT of small organs [7], including DAT-SPECT with 123 I-FP-CIT [8][9][10][11][12][13][14][15][16].…”

Design Study of an Ultrahigh Resolution Brain SPECT System Using a Synthetic Compound-Eye Camera Design With Micro-Slit and Micro-Ring Apertures

“…As the demand for brain SPECT instrumentation with higher spatial resolution, energy resolution and sensitivity continue to rise for studies of neurodegenerative diseases and brain functions, the latest research and commercial systems are based on stationary multi-detector geometries coupled with stationary high-resolution collimators. The G-SPECT-I system [ 2 ], [ 3 ] uses nine large FOV NaI crystals coupled with 54 focusing pinholes, providing an excellent 2.5 mm spatial resolution with a sensitivity of 415 cps/MBq (0.0415%) when 3 mm-diameter pinhole collimators are used, but in a limited FOV of 10 cm D × 6 cm L. A collaboration between the University of Massachusetts and University of Arizona is developing the AdaptiSPECT-C system [ 4 ], [ 5 ], a stationary helmet-shaped brain-dedicated SPECT system. The system presents 23 hexagonal detector heads based on NaI(Tl) scintillators and a multi-aperture collimator with temporal shuttering mechanism [ 6 ], according to the concept of “Adaptive SPECT” introduced by Barrett et al .…”

“…in [ 7 ]. From preliminary performance evaluation, the AdaptiSPECT-C system offers 8 mm spatial resolution with 0.0305% volumetric sensitivity when 2.72 mm-diameter pinhole collimators are used, in a clinically relevant spherical FOV of 21 cm in diameter [ 4 ]. Finally, the INSERT project from several groups in Europe developed the first MR-compatible clinical SPECT insert [ 8 ].…”

“…Similarly, the under-development AdaptiSPECT-C system shows a truncated spherical geometry [ 5 ], suited for three-dimensional brain imaging. Extensive work has been done to quantify the improved performance of such geometry [ 4 ], [ 5 ], [ 16 ].…”

Cerebral SPECT imaging with different acquisition schemes using varying levels of multiplexing versus sensitivity in an adaptive multi-pinhole brain-dedicated scanner

“…We at the University of Massachusetts Medical School in collaboration with the University of Arizona are developing a next-generation adaptive SPECT scanner, AdaptiSPECT-C, for brain imaging. It has a stationary gantry of MPH collimators coupled with multiple detectors providing an adaptable high sensitivity-resolution trade-off and therefore enabling dynamic imaging in addition to static imaging [6,23,24]. Following our investigations of the application of hexagonal detectors and square detectors [25,26], we are designing the final prototype of the AdaptiSPECT-C with square detectors [27] and based on multiple pinhole apertures per detectors with adaptable MUX level.…”