Evaluation of a variable-aperture full-ring SPECT system using large-area pixelated CZT modules: A simulation study for brain SPECT applications

Innovations in imaging modalities: a comparative review of MRI, long-axial field-of-view PET, and full-ring CZT-SPECT in detecting bone metastases

The accurate diagnosis of bone metastasis, a condition in which cancer cells have spread to the bone, is essential for optimal patient care and outcome. This review provides a detailed overview of the current medical imaging techniques used to detect and diagnose this critical condition focusing on three cardinal imaging modalities: positron emission tomography (PET), single photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI). Each of these techniques has unique advantages: PET/CT combines functional imaging with anatomical imaging, allowing precise localization of metabolic abnormalities; the SPECT/CT offers a wider range of radiopharmaceuticals for visualizing specific receptors and metabolic pathways; MRI stands out for its unparalleled ability to produce high-resolution images of bone marrow structures. However, as this paper shows, each modality has its own limitations. The comprehensive analysis does not stop at the technical aspects, but ventures into the wider implications of these techniques in a clinical setting. By understanding the synergies and shortcomings of these modalities, healthcare professionals can make diagnostic and therapeutic decisions. Furthermore, at a time when medical technology is evolving at a breakneck pace, this review casts a speculative eye towards future advances in the field of bone metastasis imaging, bridging the current state with future possibilities. Such insights are essential for both clinicians and researchers navigating the complex landscape of bone metastasis diagnosis.

Simulation studies of a full-ring, CZT SPECT system for whole-body imaging of 99m Tc and 177 Lu

BACKGROUND

Single photon emission computed tomography (SPECT) is an imaging modality that has demonstrated its utility in a number of clinical indications. Despite this progress, a high sensitivity, high spatial resolution, multi-tracer SPECT with a large field of view suitable for whole-body imaging of a broad range of radiotracers for theranostics is not available.

PURPOSE

With the goal of filling this technological gap, we have designed a cadmium zinc telluride (CZT) full-ring SPECT scanner instrumented with a broad-energy tungsten collimator. The final purpose is to provide a multi-tracer solution for brain and whole-body imaging. Our static SPECT does not rely on the dual- and the triple-head rotational SPECT standard paradigm, enabling a larger effective area in each scan to increase the sensitivity. We provide a demonstration of the performance of our design using a realistic model of our detector with simulated body-sized phantoms filled with 99m Tc and 177 Lu.

METHODS

We create a realistic model of our detector by using a combination of a Geant4 Application for Tomographic Emission (GATE) Monte Carlo simulation and a finite element model for the CZT response, accounting for low-energy tail effects in CZT that affects the sensitivity and the scatter correction. We implement a modified dual-energy-window scatter correction adapted for CZT. Other corrections for attenuation, detector and collimator response, and detector gaps and edges are also included. The images are reconstructed using the maximum-likelihood expectation-maximization. Detector and reconstruction performance are characterized with point sources, Derenzo phantoms, and a body-sized National Electrical Manufacturers Association (NEMA) Image Quality (IQ) phantom for both 99m Tc and 177 Lu.

RESULTS

Our SPECT design can resolve 7.9 mm rods for 99m Tc (140 keV) and 9.5 mm for 177 Lu (208 keV) in a hot-rod Derenzo phantom with a 3-min exposure and reach an image contrast of 78% for 99m Tc and 57% for 177 Lu using the NEMA IQ phantom with a 6-min exposure. Our modified scatter correction shows an improved contrast-recovery ratio compared to a standard correction.

CONCLUSIONS

In this paper, we demonstrate the good performance of our design for whole-body imaging purposes. This adds to our previous demonstration of improved qualitative and quantitative 99m Tc imaging of brain perfusion and 123 I imaging of dopamine transport with respect to state-of-the-art NaI dual-head cameras. We show that our design provides similar IQ and contrast to the commercial full-ring SPECT VERITON for 99m Tc. Regarding 177 Lu imaging of the 208 keV emissions, our design provides similar contrast to that of other state-of-the-art SPECTs with a significant reduction in exposure. The high sensitivity and extended energy range up to 250 keV makes our SPECT design a promising alternative for clinical imaging and theranostics of emerging radionuclides.