Simulation study of a high‐performance brain PET system with dodecahedral geometry

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145295/1/mp12996_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/145295/2/mp12996.pd

An energy-optimized collimator design for a CZT-based SPECT camera

In single photon emission computed tomography, it is a challenging task to maintain reasonable performance using only one specific collimator for radio-tracers over a broad spectrum of diagnostic photon energies, since photon scatter and penetration in a collimator differ with the photon energy. Frequent collimator exchanges are inevitable in daily clinical SPECT imaging, which hinders throughput while subjecting the camera to operational errors and damage. Our objective is to design a collimator, which independent of the photon energy performs reasonably well for commonly used radiotracers with low- to medium-energy levels of gamma emissions. Using the Geant4 simulation toolkit, we simulated and evaluated a parallel-hole collimator mounted to a CZT detector. With the pixel-geometry-matching collimation, the pitch of the collimator hole was fixed to match the pixel size of the CZT detector throughout this work. Four variables, hole shape, hole length, hole radius/width and the source-to-collimator distance were carefully studied. Scatter and penetration of the collimator, sensitivity and spatial resolution of the system were assessed for four radionuclides including 57Co, 99m Tc, 123I and 111In, with respect to the aforementioned four variables. An optimal collimator was then decided upon such that it maximized the total relative sensitivity (TRS) for the four considered radionuclides while other performance parameters, such as scatter, penetration and spatial resolution, were benchmarked to prevalent commercial scanners and collimators. Digital phantom studies were also performed to validate the system with the optimal square-hole collimator (23 mm hole length, 1.28 mm hole width, 0.32 mm septal thickness) in terms of contrast, contrast-to-noise ratio and recovery ratio. This study demonstrates promise of our proposed energy-optimized collimator to be used in a CZT-based gamma camera, with comparable or even better imaging performance versus commercial collimators such as low-energy high resolution (LEHR) and medium energy general purpose (MEGP) collimators

Longitudinal Evaluation of Sympathetic Nervous System and Perfusion in Normal and Spontaneously Hypertensive Rat Hearts with Dynamic Single-Photon Emission Computed Tomography

The objective of this work was to evaluate the sympathetic nervous system and structure remodeling during the progression of heart failure in a rodent model using dynamic cardiac single-photon emission computed tomography (SPECT). The spontaneously hypertensive rat (SHR) model was used to study changes in the nervous system innervation and perfusion in the left ventricular (LV) myocardium with the progression of left ventricular hypertrophy (LVH) to heart failure. Longitudinal dynamic SPECT studies were performed with seven SHR and seven Wistar-Kyoto (WKY) rats over 1.5 years using a dual-head SPECT scanner with pinhole collimators. Time-activity curves (TACs) of the 123 I-MIBG and 201 Tl distribution in the LV blood pool and myocardium were extracted from dynamic SPECT data and fitted to compartment models to determine the influx rate, washout rate, and distribution volume (DV) of 123 I-MIBG and 201 Tl in the LV myocardium. The standardized uptake values (SUVs) of 123 I-MIBG and 201 Tl in the LV myocardium were also calculated from the static reconstructed images. The influx and washout rates of 123 I-MIBG did not show a significant difference between SHRs and WKY rats. The DVs of 123 I-MIBG were greater in the SHRs than in the WKY rats ( p = .0028). Specifically, the DV of 123 I-MIBG became greater in the SHRs by 6 months of age ( p = .0017) and was still significant at the age of 22 months. The SUV of 123 I-MIBG in SHRs exhibited abnormal values compared to WKY rats from the age of 18 months. There was no difference in the influx rate and the washout rate of 201 Tl between the SHRs and WKY rats. The SHRs exhibited greater DV of 201 Tl than WKY rats after the age of 18 months ( p = .034). The SUV of 201 Tl in SHRs did not show any significant difference from WKY at all ages. The higher DV of 123 I-MIBG in the LV myocardium reveals abnormal nervous system activity of the SHRs at an age of 6 months, whereas a greater DV of 201 Tl in the LV myocardium can only be detected at an age of 18 months. The results show that the abnormal nervous system activity appears earlier than perfusion. Furthermore, the comparison between the DV and the SUV indicates that dynamic SPECT with 123 I-MIBG and 201 Tl with the kinetic parameter DV is capable of detecting abnormalities of the LV at an early age

Dynamic FDG-PET Imaging to Differentiate Malignancies from Inflammation in Subcutaneous and In Situ Mouse Model for Non-Small Cell Lung Carcinoma (NSCLC)

<div><p>Background</p><p>[¹⁸F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) has been widely used in oncologic procedures such as tumor diagnosis and staging. However, false-positive rates have been high, unacceptable and mainly caused by inflammatory lesions. Misinterpretations take place especially when non-subcutaneous inflammations appear at the tumor site, for instance in the lung. The aim of the current study is to evaluate the use of dynamic PET imaging procedure to differentiate in situ and subcutaneous non-small cell lung carcinoma (NSCLC) from inflammation, and estimate the kinetics of inflammations in various locations.</p><p>Methods</p><p>Dynamic FDG-PET was performed on 33 female mice inoculated with tumor and/or inflammation subcutaneously or inside the lung. Standardized Uptake Values (SUVs) from static imaging (SUVmax) as well as values of influx rate constant (<i>Ki</i>) of compartmental modeling from dynamic imaging were obtained. Static and kinetic data from different lesions (tumor and inflammations) or different locations (subcutaneous, in situ and spontaneous group) were compared.</p><p>Results</p><p>Values of SUVmax showed significant difference in subcutaneous tumor and inflammation (<i>p</i><0.01), and in inflammations from different locations (<i>p</i><0.005). However, SUVmax showed no statistical difference between in situ tumor and inflammation (<i>p</i> = 1.0) and among tumors from different locations (subcutaneous and in situ, <i>p</i> = 0.91). Values of <i>Ki</i> calculated from compartmental modeling showed significant difference between tumor and inflammation both subcutaneously (<i>p</i><0.005) and orthotopically (<i>p</i><0.01). <i>Ki</i> showed also location specific values for inflammations (subcutaneous, in situ and spontaneous, <i>p</i><0.015). However, <i>Ki</i> of tumors from different locations (subcutaneous and in situ) showed no significant difference (<i>p</i> = 0.46).</p><p>Conclusion</p><p>In contrast to static PET based SUVmax, both subcutaneous and in situ inflammations and malignancies can be differentiated via dynamic FDG-PET based <i>Ki</i>. Moreover, Values of influx rate constant <i>Ki</i> from compartmental modeling can offer an assessment for inflammations at different locations of the body, which also implies further validation is necessary before the replacement of in situ inflammation with its subcutaneous counterpart in animal experiments.</p></div

Examples of visual analysis.

<p>(A) In situ tumor. Red arrow: high FDG uptake caused by tumor inside the lung (value of SUV was around 1.7) (B) In situ inflammation. Yellow arrow: high FDG uptake caused by inflammation inside the lung (value of SUV was also around 1.7)</p

Three-compartment model of FDG.

<p>Three-compartment model of FDG.</p