PURPOSE:This study aims to evaluate statistical low-contrast detectability (SLCD) at multiple confidence levels (CLs) in computed tomography (CT) images and to determine the smallest detectable object sizes compared with human observers (HO). METHODS:SLCD was calculated on a homogeneous region of the CT images using grids of varying cell sizes. For each grid, mean CT numbers were calculated and the standard deviation was used to derive the minimum detectable contrast (MDC) as a function of CL via the separation distance between object and background distributions. CLs from 95% to 99.99% were evaluated. The target sizes (smallest object sizes detected) were compared with visual assessment performed by 30 experienced medical physicists. The evaluation was carried out on the low-contrast module (module #2) of the ACR CT phantom scanned by GE Revolution EVO 128 slice CT scanner in various tube currents (80-200 mA), tube voltage (80-140 kV), and field of view (170-230 cm). RESULTS:At 95% CL, SLCD estimated target sizes were approximately half of those identified by HO. Increasing CL produced larger SLCD target sizes, where 99.99% CL yielded target sizes comparable to HO results across all parameter variations. CONCLUSION:SLCD outcomes depend strongly on the selected CL. To align with human performance at 6 HU, using ∼99.99% CL is recommended. This has implications for quality control (QC) and protocol optimization where statistical methods substitute for human reads.

Purpose:Dual-tracer hybrid imaging is used for concurrent evaluation of two distinct molecular biomarkers, enhancing diagnostic capabilities. However, concerns about increased radiation exposure to patients arise with this technique. This study investigates the representative radiation doses and cancer risks associated with dual-tracer imaging and explores personalized dosimetry approaches. Materials and Methods:A literature-based protocol identification was performed to obtain the required dosimetric inputs. Dose coefficients were applied to convert tracer activities into effective dose estimates. Internal dose assessments using reference phantom models were compared with personalized dosimetry results obtained through GATE-based Monte Carlo simulations specific to dual-tracer positron emission tomography. In addition, complementary computed tomography (CT) imaging was performed, and cancer risks were quantified using the BEIR VII risk model. Results:Whole-body CT dose estimates closely matched those from the MIRDct tool, with a maximum discrepancy of 9.2%. Among the tracers evaluated, 201Tl resulted in the highest effective dose and cancer risk, while 81mKr and 13N-ammonia exhibited the lowest doses. Personalized dosimetry for dual-tracer imaging with ¹⁸F-fludeoxyglucose (FDG) and 68Ga-PSMA showed a maximum deviation of 5.6% from phantom-based models. The total effective dose reached up to 34 mSv. Conclusions:The study emphasizes the importance of addressing increased radiation doses and harmonizing dual-tracer hybrid imaging protocols. Personalized dosimetry enhances patient-specific risk assessments and safety by providing more accurate estimates of radiation exposure and associated cancer risks.

BACKGROUND:A contrast detail (C-D) curve is one important tool for computed tomography (CT) dose optimization and it can be developed using detectability index (d'). This approach involves constructing a d' map over a series of task objects with varying sizes and contrasts. However, generating a smoothed d' map can be computationally intensive. PURPOSE:This study aims to develop and implement a smooth d'-based C-D curve for optimizing CT liver imaging protocol at varying tube voltages. METHODS:The task transfer function (TTF) and noise power spectrum (NPS) were derived from CT images of the ACR 464 phantom acquired at 80, 100, 120, and 140 kVp. A matrix of task objects was defined, incorporating both Gaussian and Designer signal profiles, with object sizes ranging from 1 to 15 mm and contrast levels from -1 to -15 HU. To simulate clinical liver imaging, each task object was modelled on a 50 HU background. The d' values were calculated for each task using two model observers: non-prewhitening (NPW) and NPW with eye filter (NPWE). A d' map was generated by iterating these measurements across all tasks, and subsequently interpolated to produce a smooth d' map. Finally, a smooth C-D curve was obtained by applying a contour-finding algorithm on the interpolated d' map using a specific d' cut off. The results of C-D curves at d' = 3 were compared with those from human observers (HOs). RESULTS:Smooth C-D curves and their corresponding synthetic image matrices were successfully generated for the image data. Increasing the tube voltage leads to an improved object detectability limit for the simulated liver examination. This trend was consistently observed for both Gaussian and Designer signals as evaluated by the NPW and NPWE models. In comparison, the NPW model yielded higher detectability estimates than NPWE. Comparison with HO data suggests that NPWE produce more similar detection patterns with human observation. CONCLUSION:The smooth d'-based C-D curve was successfully developed and implemented as a robust tool for CT protocol optimization.

Objective. Dose-voxel kernel (DVK) convolution provides a physics-based approach for absorbed-dose calculation from nuclear medicine imaging. This study implemented DVK convolution within the particle and heavy ion transport code system (PHITS) and evaluated its performance against Monte Carlo (MC) simulations and clinical dosimetry methods.Approach. Five post-radioembolization90Y bremsstrahlung single photon emission computed tomography/computed tomography (SPECT/CT) and positron emission tomography/CT (PET/CT) datasets from the University of Michigan Deep Blue Data repository were converted into PHITS-readable formats using the radiotherapy package based on PHITS. Activity distributions were mapped onto CT voxel grids, and DVKs were generated for 24 human tissue materials. A new DVK mode was implemented in PHITS to calculate voxel-wise absorbed-dose rates by convolving tissue-specific DVKs with activity distributions. Performance was evaluated against MC simulations using gamma index analysis, mean absorbed-dose rates within volumes of interests (VOIs), and voxel-wise absorbed-dose differences in liver, lung, and liver-lung interface regions. VOI-based mean absorbed doses were further benchmarked against the local deposition model (LDM) and voxelS-value (VSV) convolution in MIM Software (v7.4.3).Main results. Following one-time DVK generation, DVK mode calculations required ∼40 s compared with >9 h for high-statistics MC simulations. Gamma pass fractions ranged from 92.1%-99.9%, while mean DVK-MC differences in VOI-based dose rates were -1.2 ± 2.9% (SPECT/CT) and -1.0 ± 4.3% (PET/CT). Voxel-wise dose differences showed good agreement between DVK and MC in homogeneous liver tissue, while lung regions exhibited lower absorbed-dose estimates and the liver-lung interface showed increased variability, (P95up to 39%). Compared with MIM, VOI-based dose differences were 9.7 ± 7.2% for SPECT/CT (LDM-based) and -0.1 ± 8.4% for PET/CT (VSV-based).Significance. The PHITS-integrated DVK implementation enables efficient voxel-based dosimetry while maintaining close agreement with high-statistics MC simulations. This framework provides a practical physics-based approach for patient-specific radiopharmaceutical therapy dosimetry.

Gastrointestinal motility and transit time assessment is clinically important for diagnosing motility disorders, but whole-gut gamma scintigraphy remains underutilised due to limited availability of suitable radiopharmaceuticals. This study developed a neutron-activatable, non-absorbable radiotracer for whole GI transit imaging. Polystyrene (PS) particles loaded with samarium-152 oxide (152Sm2O3) and size-fractioned (600–800 μm). Samples were neutron activated to 153Sm in a nuclear research reactor. Morphology, particle size and elemental composition were assessed using SEM/EDX and laser diffraction. Radionuclide impurity was evaluated by HPGe gamma spectrometry. Thermal profile was acquired by DSC and TGA. Radionuclide retention was quantified in simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) for 120 h. Neutron activation did not alter particle morphology or size distribution. The 153Sm2O3-PS particles achieved a mean specific activity of 57.2 ± 2.0 MBq/g at 48 h post-irradiation, corresponding to an overall prepared activity of approximately 5.7 MBq per 100 mg batch. Gamma spectrometry demonstrated only the expected 153Sm photopeaks without detectable long-lived impurities. In-vitro radionuclide retention exceeded 99% in both SGF and SIF over 120 h. The 153Sm2O3-PS particles are stable, non-absorbable markers with high radionuclide purity and retention, supporting their use as a low-cost radiotracer for whole gastrointestinal transit scintigraphy. Further in vivo validation and manufacturing controls, including endotoxin and residual-monomer testing, are required before clinical use.

The second in a three-volume set exploring Problems and Solutions in Medical Physics, this volume explores common questions and their solutions in Nuclear Medicine. This invaluable study guide should be used in conjunction with other key textbooks in the field to provide additional learning opportunities. Topics include radioactivity and nuclear transformation, radionuclide production and radiopharmaceuticals, non-imaging detectors and counters, instrumentation for gamma imaging, SPECT and PET/CT, imaging techniques, radionuclide therapy, internal radiation dosimetry, and quality control and radiation protection in nuclear medicine. Each chapter provides examples, notes, and references for further reading to enhance understanding. Features: Consolidates concepts and assists in the understanding and applications of theoretical concepts in medical physics Assists lecturers and instructors in setting assignments and tests Suitable as a revision tool for postgraduate students sitting medical physics, oncology, and radiology sciences examinations

This study aimed to 3D print a patient-specific chest phantom simulating multiple lung nodules to optimise low-dose Computed Tomography (CT) protocols for lung cancer screening. The chest phantom, which was developed from a single patient’s chest CT images, was fabricated using a variety of materials, including polylactic acid (PLA), Glow-PLA, acrylonitrile butadiene styrene (ABS), and polyurethane resin. The phantom was scanned under different low-dose (LDCT) and ultra-low-dose CT (ULDCT) protocols by varying the kilovoltage peak (kVp) and milliampere-seconds (mAs). Subjective image quality of each scan (656 images) was evaluated by three radiologists using a five-point Likert scale, while objective image quality was assessed using signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). Anatomical conformance was assessed by comparing tissue diameters of the phantom and patient scans using Bland–Altman analysis. The phantom’s lung tissue, lung nodules, and diaphragm demonstrated radiation attenuation comparable to patient tissue, as measured in Hounsfield Units (HU). However, significant variations in HU were observed for the skin, subcutaneous fat, muscle, bone, heart, lung vessels, and blood vessels compared to patient tissues, with values ranging from 93.9 HU to −196 HU (p < 0.05). Both SNR and CNR decreased as the effective dose was reduced, with a strong positive linear correlation (r = 0.927 and r = 0.931, respectively, p < 0.001, Jamovi, version 2.3.28). The median subjective image quality score from radiologists was 4, indicating good diagnostic confidence across all CT protocols (κ = −0.398, 95% CI [−0.644 to −0.152], p < 0.002, SPSS Statistics, version 30). An optimal protocol of 80 kVp and 30 mAs was identified for lung nodule detection, delivering a dose of only 0.23 mSv, which represents a 96% reduction compared to standard CT protocols. The measurement error between patient and phantom scans was −0.03 ± 0.14 cm. These findings highlight the potential for significant dose reductions in lung cancer screening programs. Further studies are recommended to improve the phantom by selecting more tissue-equivalent materials.

In voxel-based dosimetry, dose-voxel kernels (DVKs) represent the absorbed dose in a target voxel per decay in a source voxel. In this work, we aimed to validate DVKs generated using Particle and Heavy Ion Transport Code System (PHITS) as a first step in establishing a quantitative SPECT/CT-based dosimetry framework for selective internal radiation therapy (SIRT). A 1-MBq source of 90Y, 153Sm, 177Lu, 188Re, and 166Ho located in central cubic voxels of 1 mm, 3 mm, and 6 mm dimension within soft tissue (1.04 g⋅cm−³), was simulated using 2.5 × 10⁷ histories in PHITS. The DVK results were compared to published data (Lanconelli et al., 2012). In a pilot study, 17 MBq of 153Sm microspheres were injected into a liver tumor-bearing rat and imaged 24 h later using SPECT/CT. SPECT/CT images were then converted to cumulated activity and convolved with a 153Sm DVK using Fast Fourier Transform in MATLAB to create an absorbed dose map. As expected, DVKs for the radionuclides showed a steep decrease from the source voxel to the maximum continuous slowing down approximation (CSDA) of beta components. Beyond the CSDA, gamma and bremsstrahlung contributed minimally (10⁻⁶ to 10⁻⁴) to voxel doses. Observed DVK changes as voxel size increased were in good agreement with published data, with differences in source voxel ranging from 1 to 24

Liver cancer is the 6th most common cancer and the 4th leading cause of cancer death worldwide. The high mortality rate is primarily due to delayed diagnosis of the liver cancer. Chemoembolization and radioembolization are known effective treatments for intermediate to advance staged liver cancer. However, the treatments are currently performed separately. This study aimed to develop a theranostic microspheres loaded with both radioactive Samarium-153 oxide ([153Sm]Sm2O3) and chemotherapy drug, Doxorubicin (Dox) for chemo-radioembolization. The sulphonated polystyrene (SPS) microspheres loaded with [152Sm]Sm2O3 was synthesized using solvent evaporation synthesis. The Dox was then loaded on to the microspheres through electrostatic interactions. The synthesized [152Sm]Sm2O3- and Dox-loaded polystyrene ([152Sm]Sm2O3-Dox-SPS) microspheres were then neutron activated in a nuclear research reactor (TRIGA MARK II, General Atomics). Physicochemical properties, Dox loading capacity, radionuclide impurities, radionuclide retention efficiency of the microspheres were evaluated. The microspheres had an average diameter of 31.95 ± 0.26 μm and all microspheres were within 15 to 60 μm. The microspheres achieved a nominal specific radioactivity of 2.82 ± 0.6 GBq/g. No radionuclide impurities were observed in the microspheres after neutron activation. The encapsulation efficiency and loading capacity of Dox on the [152Sm]Sm2O3-Dox-SPS microspheres was determined as 55.6 ± 1.1