Biodistribution of the cationic host defense peptide LL-37 using SPECT/CT.

Human cathelicidin LL-37, a cationic host defense peptide (CHDP), has several important physiological roles, including antimicrobial activity, immune modulation, and wound healing, and is a being investigated as a therapeutic candidate for several indications. While the effects of endogenously produced LL-37 are well studied, the biodistribution of exogenously administered LL-37 are less known. Here we assess the biodistribution of a gallium-67 labeled variant of LL-37 using nuclear imaging techniques over a 48 h period in healthy mice. When administered as an intravenous bolus just over 20 µg, the LL-37-based radiotracer was rapidly cleared from the blood, largely by the liver, while an appreciable fraction of the dose temporarily distributed to the lungs. When administered subcutaneously at the same dose level, the radiotracer was absorbed systemically following a two-phase kinetic model and was predominately cleared renally. Uptake into sites rich in immune cells, such as the lymph nodes and the spleen, was observed for both routes of administration. Scans of free gallium-67 were also performed as controls. Important preclinical insights into the biodistribution of exogenously administered LL-37 were gained from this study, which can aid in the understanding of this and related cationic host-defense peptides.

Hyperostosis Frontalis Simulating Metastatic Deposits: Unmasked on SPECT-CT.

Skeletal scintigraphy has a pivotal role in detecting a number of bone pathologies, but it has its own limitations because of 2D image acquisition. Hybrid imaging acts as a savior in these cases where it is difficult to distinguish between benign and malignant lesions just on the basis of planar images. We present one such case of known breast carcinoma with abnormal increased radiotracer uptake in the skull which was difficult to characterize as benign lesion such as hyperostosis frontalis or metastatic osseous lesion. The importance of describing this case is to have a thorough understanding of hyperostosis patterns and to not confuse it with metastatic deposits in patients with known malignancies.

68Ga-Trivehexin PET/CT: a promising novel tracer for primary hyperparathyroidism.

INTRODUCTION: This study aims to assess 68Ga-Trivehexin PET/CT for detecting hyperfunctioning parathyroid tissue in comparison to [99mTc]Tc-MIBI scintigraphy-SPECT/CT (MIBI scan) in patients with primary hyperparathyroidism (PHPT). METHODS: The cohort comprised 13 patients diagnosed with PHPT based on biochemical analyses, including serum calcium, phosphorus, and parathyroid hormone (PTH) levels. Each participant underwent cervical ultrasonography, MIBI scan, and 68Ga-Trivehexin PET/CT imaging. Complementary 4D-CT and [18F]fluorocholine PET/CT were conducted in 7 patients. Ten lesions of 7 patients underwent PTH wash-out (WO) procedure. 68Ga-Trivehexin PET/CT findings were compared with other modalities and PTH-WO results. RESULTS: Ten patients had sporadic PHPT, while 3 were diagnosed with MEN-1 syndrome-associated PHPT. One patient did not have any identifiable parathyroid lesion across the imaging modalities. On a patient-based analysis, MIBI scan and 68Ga-Trivehexin PET/CT identified parathyroid lesions in 10 and 11 patients, respectively. However, 68Ga-Trivehexin PET/CT detected 7 additional parathyroid lesions that were negative on the MIBI scan. Consequently, 17 lesions were identified and confirmed as hyperfunctioning parathyroid tissue through imaging, PTH-WO, or a combination of both modalities. In lesion-based evaluation, 68Ga-Trivehexin identified 16 lesions compared to 10 by MIBI scan, resulting in a detection rate of 94.1% and 58.8%, respectively. Notably, in three patients who underwent [18F]fluorocholine PET/CT, no lesions were detected; yet 68Ga-Trivehexin PET/CT successfully identified parathyroid lesions in two of these patients. CONCLUSION: Our study provides the first evidence that 68Ga-Trivehexin PET/CT can effectively identify hyperfunctioning parathyroid tissue with a high detection rate warranting further investigations to comprehensively explore its potential in PHPT management.

Image-guided patient-specific optimization of catheter placement for convection-enhanced nanoparticle delivery in recurrent glioblastoma.

BACKGROUND: Proper catheter placement for convection-enhanced delivery (CED) is required to maximize tumor coverage and minimize exposure to healthy tissue. We developed an image-based model to patient-specifically optimize the catheter placement for rhenium-186 (186Re)-nanoliposomes (RNL) delivery to treat recurrent glioblastoma (rGBM). METHODS: The model consists of the 1) fluid fields generated via catheter infusion, 2) dynamic transport of RNL, and 3) transforming RNL concentration to the SPECT signal. Patient-specific tissue geometries were assigned from pre-delivery MRIs. Model parameters were personalized with either 1) individual-based calibration with longitudinal SPECT images, or 2) population-based assignment via leave-one-out cross-validation. The concordance correlation coefficient (CCC) was used to quantify the agreement between the predicted and measured SPECT signals. The model was then used to simulate RNL distributions from a range of catheter placements, resulting in a ratio of the cumulative RNL dose outside versus inside the tumor, the "off-target ratio" (OTR). Optimal catheter placement) was identified by minimizing OTR. RESULTS: Fifteen patients with rGBM from a Phase I/II clinical trial (NCT01906385) were recruited to the study. Our model, with either individual-calibrated or population-assigned parameters, achieved high accuracy (CCC > 0.80) for predicting RNL distributions up to 24 h after delivery. The optimal catheter placements identified using this model achieved a median (range) of 34.56 % (14.70 %-61.12 %) reduction on OTR at the 24 h post-delivery in comparison to the original placements. CONCLUSIONS: Our image-guided model achieved high accuracy for predicting patient-specific RNL distributions and indicates value for optimizing catheter placement for CED of radiolabeled liposomes.

Quantitative assessment of cardiac 123iodo-metaiodobenzylguanidine SPECT/CT in patients with arrhythmogenic right ventricular cardiomyopathy: novel insight in disease monitoring.

PURPOSE: The heart-to-mediastinum ratio (H/M-Ratio) of 123iodo-metaiodobenzylguanidine (123I-MIBG) represents state-of-the-art assessment for sympathetic dysfunction in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC). This study aims to evaluate quantitative reconstruction of 123I-MIBG uptake and to demonstrate its correlation with echocardiographic parameters. METHODS: Cardiac innervation was assessed in 23 patients diagnosed with definite ARVC or borderline ARVC and 12 patients with other cardiac disease presenting arrhythmia, using quantitative 123I-MIBG Single Photon Emission Computed Tomography / Computed Tomography (SPECT/CT) imaging. Tracer uptake was evaluated in the left (LV) and right ventricle (RV) based on a CT scan after quantitative image reconstruction. The relationship between tracer uptake and echocardiographic parameter data was examined. RESULTS: Absolute quantification of 123I-MIBG uptake in the LV and RV is feasible and correlates accurately with the gold standard H/M-Ratio. When comparing sensitivity and specificity, the area under the curve (AUC) favors standardized uptake value (SUV) of the RV over the right-ventricle-to-mediastinum-ratio (RV/M-Ratio) for diagnosing ARVC. A reduced RV-SUV in patients with definite ARVC is associated with reduced RV function. RV polar maps revealed globally reduced 123I-MIBG uptake without segment-specific reduction in the RV. CONCLUSION: Quantitative 123I-MIBG SPECT in ARCV patients offers robust potential for clinical reporting and demonstrates a significant correlation with RV function. Segmental RV analysis needs to be evaluated in larger samples. In summary, cardiac 123I-MIBG imaging using SUV could facilitate image-guided therapy in patients diagnosed with ARVC.

Volumetric differences in the temporomandibular joint in patients with condylar hyperplasia in active and passive state, SPECT/CT study.

AIM: Condylar hyperplasia (CH) is a progressive and deforming disease that modifies anatomy of the temporomandibular joint (TMJ) structures. This study aims to correlate the metabolic bone activity of the condyle measured by SPECT with the volumetry anatomic information from the condyle, fossa and joint space provided by CT images, in patients with CH in active and inactive forms. MATERIALS AND METHODS: A cross-sectional comparative study was performed with a set of 116 images from healthy and diagnosed CH patients to compare volumetric measures of the TMJ. Images were acquired through a bone tissue mask using a three-dimensional DICOM reconstruction for SPECT/CT and CBCT images and the Threshold option for segmentation with standardized values for each tissue on the HU scale. RESULTS: there are differences (p<0.01), with greater condylar volume on the affected side in patients with active CH compared to passive CH. The volume of the glenoid cavity shows no differences in either form of CH (p>0.05), however, there were differences for the volume of the joint space on the affected right side of hemimandibular elongation (HE) in the active form. The volume of the mandibular condyle on the affected side in CH cases were larger in HE cases in active and inactive form (p<0.01) compared to healthy patients. Similar results were presented for the glenoid cavity and joint space. CONCLUSIONS: Volumetric anatomical evaluation of TMJ structures, as well as information on condylar metabolic activity, can be obtained from SPECT/CT. The study shows a greater condylar volume on the affected side of the CH compared to the contralateral side, but there are more significant differences in the active than in the inactive form.

The Role of SPECT/CT and PET/CT Hybrid Imaging in the Management of Ectopic Thyroid Carcinoma-A Systematic Review.

BACKGROUND AND OBJECTIVES: Thyroid ectopy represents a rare disease with an incidence of 0.3-1/100,000. It occurs due to the defective embryological process of the thyroid gland development. The thyroid ectopic tissue may suffer malignant transformation. This review aims to shed light on the roles that I-131 SPECT/CT (radioiodine 131 single-photon emission tomography fused with computed tomography) and F-18 PET/CT (fluorodeoxyglucose F18 positron emission tomography fused with computer tomography) may play in managing patients with ectopic thyroid carcinoma. MATERIALS AND METHODS: A total number of 47 articles were identified on the PubMed and Google Scholar databases, and 3 other articles were selected from articles identified in the references cited in the retrieved articles. After refining the selection, the inclusion and exclusion criteria were applied, resulting in 10 articles that were included in the review. RESULTS: The cases of ectopy included in this review were localised as follows: four cases in the thyroglossal duct, two cases in the mediastinum, one case in the oesophagus, one case in the thorax, one case with a pre-tracheal location, and one case with a latero-cervical location. In all the cases, F-18 FDG PET/CT was used as a diagnostic tool. In one case, F-18 FDG PET/CT was combined with I-131 SPECT/CT and MRI (magnetic resonance imaging). In one case, it was combined with 68 Ga-FAPI PET/CT (Ga-68 radiolabelled FAP inhibitor positron emission tomography fused with computer tomography). The maximum SUVs (standardised uptake values) ranged from 5.5 to 25 g/mL. CONCLUSIONS: F-18 PET/CT and I-131 SPECT/CT hybrid nuclear imaging is of great value in assessing ectopic thyroid carcinoma. F-18 FDG PET/CT plays an important role in the primary tumour evaluation and distant disease detection. Ga-68 FAPIs are a promising alternative. I-131 SPECT/CT adds important information related to the anatomical characterization of primary and distant iodine-avid lesions.

Technological Advances in SPECT and SPECT/CT Imaging.

Single photon emission tomography/computed tomography (SPECT/CT) is a mature imaging technology with a dynamic role in the diagnosis and monitoring of a wide array of diseases. This paper reviews the technological advances, clinical impact, and future directions of SPECT and SPECT/CT imaging. The focus of this review is on signal amplifier devices, detector materials, camera head and collimator designs, image reconstruction techniques, and quantitative methods. Bulky photomultiplier tubes (PMTs) are being replaced by position-sensitive PMTs (PSPMTs), avalanche photodiodes (APDs), and silicon PMs to achieve higher detection efficiency and improved energy resolution and spatial resolution. Most recently, new SPECT cameras have been designed for cardiac imaging. The new design involves using specialised collimators in conjunction with conventional sodium iodide detectors (NaI(Tl)) or an L-shaped camera head, which utilises semiconductor detector materials such as CdZnTe (CZT: cadmium-zinc-telluride). The clinical benefits of the new design include shorter scanning times, improved image quality, enhanced patient comfort, reduced claustrophobic effects, and decreased overall size, particularly in specialised clinical centres. These noticeable improvements are also attributed to the implementation of resolution-recovery iterative reconstructions. Immense efforts have been made to establish SPECT and SPECT/CT imaging as quantitative tools by incorporating camera-specific modelling. Moreover, this review includes clinical examples in oncology, neurology, cardiology, musculoskeletal, and infection, demonstrating the impact of these advancements on clinical practice in radiology and molecular imaging departments.

Clinical Significance of Hepatobiliary Localization of Tc-99m EC in Diuretic Renography.

Objective Technetium-99m ethylene dicysteine (Tc-99m EC) is a well-established, tubular tracer for diuretic renography. Few occasional cases have been reported in literature regarding visualization of liver, gallbladder (GB), or bowel due to increased hepatobiliary route of excretion of Tc-99m EC on diuretic renography. This study aimed to retrospectively review the incidence of visualization of liver, GB, or bowel and its clinical significance in Tc-99m EC diuretic renography. Materials and Methods Data of all patients who underwent diuretic renography in the department from January 24, 2022 to March 31, 2023 was included in the study. The data was analyzed to assess the incidence of visualization of GB or bowel loops, correlation of the hepatobiliary localization with factors like age of the patient, concentration of 99m TcO4 solution, quality control parameters, presence of renal stone disease, serum creatinine, relative renal function, and effective renal plasma flow. Effect of hepatobiliary localization on scan interpretation and reporting was assessed. Results The retrospective analysis of 437 diuretic renograms revealed the hepatobiliary localization of tracer in 34 patients. Out of these 34 patients, 14 patients had only faint visualization of tracer at 4 hours delayed image. Twenty scans had visualization of both GB and bowel. Out of these 20 scans, GB and bowel were visualized during dynamic imaging in one scan, after initial 20 minutes in two scans and in 2 to 4 hours delayed images in rest of the 17 scans. Two out of 20 patients had increased serum creatinine, 16 patients had either single kidney or relative renal function less than 26%, and 12 patients had renal stone disease. Out of the four patients in whom relative renal function was more than 25%, one patient had raised serum creatinine and three patients had renal stone disease. Interpretation of images was affected only in three patients, in which reporting of the scans required single-photon emission computed tomography imaging and correlation with other imaging modalities. Conclusion Hepatobiliary excretion of Tc-99m EC usually does not usually affect the scan interpretation and quantitative renogram analysis, but reader should be cognizant of the potential pitfalls during scan interpretation. In this study, we reviewed the possible causes of this hepatobiliary clearance and importance of additional views and correlation with other imaging modalities to clarify the suspicion arises for accurate reporting.

Unusual Metastatic Sites and Radioiodine Uptake in Patients of Differentiated Thyroid Carcinoma with Atypical Clinical Presentations: Utilization of 131 I-Whole-Body Scintigraphy with Regional SPECT/CT.

Differentiated thyroid carcinoma (DTC) usually is slow growing and carries a good prognosis. It most commonly tends to spread locally to regional lymph nodes in 20 to 60% of patients. The presence of distant metastasis impacts overall survival and prognosis. The lungs, bones, and the brain are typically involved in distant sites with less common metastatic sites that include the liver, kidney, skeletal muscle, adrenal glands, bladder, and skin. These unusual sites are rare and pose a diagnostic challenge and impact clinical decision-making to a great extent. The radioiodine 131 I whole-body scintigraphy with single-photon emission computed tomography/computed tomography can provide a thorough investigation of unusual sites of uptake leading to diagnosis of these metastases. We present a case series of DTC showing unusual sites of metastasis and/or radioiodine uptake in urinary bladder, in the third metacarpal bone of left hand and lastly in the forearm at postoperative hypertrophic scar area.

A survey of gamma camera and SPECT/CT quality control programs across a sample of public hospitals in Australia.

Performance testing of gamma cameras and single photon computed tomography/computed tomography (SPECT/CT) systems is not subject to regulatory requirements across states and territories in Australia. Internationally recognised testing standards from organisations such as the National Electrical Manufacturers Association (NEMA) describe methodologies for recommended tests. However, variations exist in suggested quality control (QC) schedules from professional bodies such as the Australia and New Zealand Society of Nuclear Medicine (ANZSNM). In this study, a survey was conducted to benchmark current QC programs across a selected sample of eight standalone and networked Australian public hospitals. Vendor-specific flood-field uniformity (intrinsic or extrinsic/system) verification without photomultiplier (PMT) tuning and CT QC were performed at all sites. Weekly and monthly PMT tuning followed by intrinsic flood-field verifications were performed at most sites. At least half of the sites performed monthly centre of rotation (COR) offset verifications. SPECT/CT alignment calibrations and verifications were undertaken by service engineers at all sites, and periodic verifications were performed by local staff at varying frequencies. Variations were observed for other periodic QC tests such as spatial resolution and planar sensitivity. Similarly, variations were observed for tests specific to whole-body systems and SPECT systems. Most sites checked daily and periodic QC results against pass/fail criteria set by vendors. Additional analyses of the QC results, including trend analysis and periodic reviews, were not common practice. The lack of regulatory requirements is likely to have led to variations in QC tests that are generally either harder to perform or are more labour intensive.

Update in imaging tests used for the localization of parathyroid pathology.

Preoperative localization of parathyroid pathology, generally a parathyroid adenoma, can be difficult in some cases due to the anatomical variants that these glands present. The objective of this review is to analyse the different imaging techniques used for preoperative localization of parathyroid pathology (scintigraphy, ultrasound, CT, MRI and PET). There is great variability between the different tests for the preoperative localization of parathyroid pathology. The importance of knowing the different diagnostic options lies in the need to choose the most suitable test at each moment and for each patient for an adequate management of primary hyperparathyroidism (PHP) with surgical criteria.

Quantitative Bone SPECT/CT of Central Cartilaginous Bone Tumors: Relationship between SUVmax and Radiodensity in Hounsfield Unit.

(1) Background: it is challenging to determine the accurate grades of cartilaginous bone tumors. Using bone single photon emission computed tomography (SPECT)/computed tomography (CT), maximum standardized uptake value (SUVmax) was found to be significantly associated with different grades of cartilaginous bone tumor. The inquiry focused on the effect of the tumor matrix on SUVmax. (2) Methods: a total of 65 patients from 2017 to 2022 with central cartilaginous bone tumors, including enchondromas and low-to-intermediate grade chondrosarcomas, who had undergone bone SPECT/CT were retrospectively enrolled. The SUVmax was recorded and any aggressive CT findings of cartilaginous bone tumor and Hounsfield units (HU) of the chondroid matrix as mean, minimum, maximum, and standard deviation (SD) were reviewed on CT scans. Pearson's correlation analysis was performed to determine the relationship between CT features and SUVmax. Subgroup analysis was also performed between the benign group (enchondroma) and the malignant group (grade 1 and 2 chondrosarcoma) for comparison of HU values and SUVmax. (3) Results: a significant negative correlation between SUVmax and HU measurements, including HUmax, HUmean, and HUSD, was found. The subgroup analysis showed significantly higher SUVmax in the malignant group, with more frequent CT aggressive features, and significantly lower HUSD in the malignant group than in the benign group. (4) Conclusions: it was observed that higher SUVmax and lower HUSD were associated with a higher probability of having a low-to-intermediate chondrosarcoma with aggressive features and a less calcified tumor matrix.

Accuracy of patient-specific I-131 dosimetry using hybrid whole-body planar-SPECT/CT I-123 and I-131 imaging.

PURPOSE: This study aimed to assess the accuracy of patient-specific absorbed dose calculations for tumours and organs at risk in radiopharmaceutical therapy planning, utilizing hybrid planar-SPECT/CT imaging. METHODS: Three Monte Carlo (MC) simulated digital patient phantoms were created, with time-activity data for mIBG labelled to I-123 (LEHR and ME collimators) and I-131 (HE collimator). The study assessed the accuracy of the mean absorbed doses for I-131-mIBG therapy treatment planning. Multiple planar whole-body (WB) images were simulated (between 1 to 72 h post-injection (p.i)). The geometric-mean image of the anterior and posterior WB images was calculated, with scatter and attenuation corrections applied. Time-activity curves were created for regions of interest over the liver and two tumours (diameters: 3.0 cm and 5.0 cm) in the WB images. A corresponding SPECT study was simulated at 24 h p.i and reconstructed using the OS-EM algorithm, incorporating scatter, attenuation, collimator-detector response, septal scatter and penetration corrections. MC voxel-based absorbed dose rate calculations used two image sets, (i) the activity distribution represented by the SPECT images and (ii) the activity distribution from the SPECT images distributed uniformly within the volume of interest. Mean absorbed doses were calculated considering photon and charged particle emissions, and beta emissions only. True absorbed doses were calculated by MC voxel-based dosimetry of the known activity distributions for reference. RESULTS: Considering photon and charged particle emissions, mean absorbed dose accuracies across all three radionuclide-collimator combinations of 3.8 ± 5.5% and 0.1 ± 0.9% (liver), 5.2 ± 10.0% and 4.3 ± 1.7% (3.0 cm tumour) and 15.0 ± 5.8% and 2.6 ± 0.6% (5.0 cm tumour) were obtained for image set (i) and (ii) respectively. Considering charged particle emissions, accuracies of 2.7 ± 4.1% and 5.7 ± 0.7% (liver), 3.2 ± 10.2% and 9.1 ± 1.7% (3.0 cm tumour) and 13.6 ± 5.7% and 7.0 ± 0.6% (5.0 cm tumour) were obtained for image set (i) and (ii) respectively. CONCLUSION: The hybrid WB planar-SPECT/CT method proved accurate for I-131-mIBG dosimetry, suggesting its potential for personalized treatment planning.

When in Doubt, Add SPECT/CT: A Case of Mistaken Identity.

A 63-y-old woman with a history of breast cancer presented with concerns of osseous metastasis. Initial whole-body planar bone scintigraphy revealed a focus of concern overlying the sternum. SPECT/CT images revealed the anomaly-localized activity in the needleless hub attached to the chemotherapy port. If not for the precision of SPECT/CT, such a rare artifact could have led to a false-positive diagnosis, particularly impactful in breast cancer patients. This case emphasizes the critical role of SPECT/CT in accurate diagnoses.

Coexistence of Eutopic Thyroid Gland and Ectopic Thyroid Tissue: Rare but Not Uncommon.

Ectopic thyroid tissue is very rare, but the coexistence of ectopic and eutopic thyroid glands is even more rare. The recognition of this diagnosis is important in patients who are being treated for thyrotoxicosis, but it is also crucial to exclude other associated serious disease conditions. In this article, we report three different cases that showed ectopic thyroid tissue with the coexisting presence of an eutopic thyroid gland. All three cases showed different outcomes. The recognition of this condition is of great importance because it alerts the referring physicians to this rare, yet possible occurrence and the potential pathological conditions associated with it. The first case showed how imaging could help outline even small ectopic thyroid tissue outside of the neck region even in cases where histopathological confirmation is difficult. The second case was very rare as thyroid carcinoma originated in ectopic thyroid tissue. In the last case, the initial imaging was misleading as it mimicked greatly ectopic thyroid tissue, and only detailed history and careful inspection of the images could lead to the correct interpretation of the findings.

4D SPECT/CT: A Hybrid Approach to Primary Hyperparathyroidism.

Our rationale was to review the imaging options for patients with primary hyperparathyroidism and to advocate for judicious use of 4-dimensional (4D) SPECT/CT to visualize diseased parathyroid glands in patients with complex medical profiles or in whom other imaging modalities fail. We review the advantages and disadvantages of traditional imaging modalities used in preoperative assessment of patients with primary hyperparathyroidism: ultrasound, SPECT, and 4D CT. We describe a scheme for optimizing and individualizing preoperative imaging of patients with hyperfunctioning parathyroid glands using traditional modalities in tandem with 4D SPECT/CT. Using the input from radiologists, endocrinologists, and surgeons, we apply patient criteria such as large body habitus, concomitant multiglandular disease, multinodular thyroid disease, confusing previous imaging, and unsuccessful previous surgery to create an imaging paradigm that uses 4D SPECT/CT yet is cost-effective, accurate, and limits extraneous radiation exposure. 4D SPECT/CT capitalizes on the strengths of SPECT and 4D CT and addresses limitations that exist when these modalities are used in isolation. In select patients with complicated clinical parameters, preoperative imaging with 4D SPECT/CT can improve accuracy yet remain cost-effective.

A Review of Advances in Molecular Imaging of Rheumatoid Arthritis: From In Vitro to Clinic Applications Using Radiolabeled Targeting Vectors with Technetium-99m.

Rheumatoid arthritis (RA) is a systemic autoimmune disorder caused by inflammation of cartilaginous diarthrodial joints that destroys joints and cartilage, resulting in synovitis and pannus formation. Timely detection and effective management of RA are pivotal for mitigating inflammatory arthritis consequences, potentially influencing disease progression. Nuclear medicine using radiolabeled targeted vectors presents a promising avenue for RA diagnosis and response to treatment assessment. Radiopharmaceutical such as technetium-99m (99mTc), combined with single photon emission computed tomography (SPECT) combined with CT (SPECT/CT), introduces a more refined diagnostic approach, enhancing accuracy through precise anatomical localization, representing a notable advancement in hybrid molecular imaging for RA evaluation. This comprehensive review discusses existing research, encompassing in vitro, in vivo, and clinical studies to explore the application of 99mTc radiolabeled targeting vectors with SPECT imaging for RA diagnosis. The purpose of this review is to highlight the potential of this strategy to enhance patient outcomes by improving the early detection and management of RA.

Position dependence of recovery coefficients in 177Lu-SPECT/CT reconstructions - phantom simulations and measurements.

BACKGROUND: Although the importance of quantitative SPECT has increased tremendously due to newly developed therapeutic radiopharmaceuticals, there are still no accreditation programs to harmonize SPECT imaging. Work is currently underway to develop an accreditation for quantitative 177Lu SPECT/CT. The aim of this study is to verify whether the positioning of the spheres within the phantom has an influence on the recovery and thus needs to be considered in SPECT harmonization. In addition, the effects of these recovery coefficients on a potential partial volume correction as well as absorbed-dose estimates are investigated. METHODS: Using a low-dose CT of a SPECT/CT acquisition, a computerized version of the NEMA body phantom was created using a semi-automatic threshold-based method. Based on the mass-density map, the detector orbit, and the sphere centers, realistic SPECT acquisitions of all possible 720 sphere configurations of both the PET and the SPECT versions of the NEMA Body Phantom were generated using Monte Carlo simulations. SPECT reconstructions with different numbers of updates were performed without (CASToR) and with resolution modeling (STIR). Recovery coefficients were calculated for all permutations, reconstruction methods, and phantoms, and their dependence on the sphere positioning was investigated. Finally, the simulation-based findings were validated using SPECT/CT acquisitions of six different sphere configurations. RESULTS: Our analysis shows that sphere positioning has a significant impact on the recovery for both of the reconstruction methods and the phantom type. Although resolution modeling resulted in significantly higher recovery, the relative variation in recovery within the 720 permutations was even larger. When examining the extreme values of the recovery, reconstructions without resolution modeling were influenced primarily by the sphere position, while with resolution modeling the volume of the two adjacent spheres had a larger influence. The SPECT measurements confirmed these observations, and the recovery curves showed good overall agreement with the simulated data. CONCLUSION: Our study shows that sphere positioning has a significant impact on the recovery obtained in NEMA sphere phantom measurements and should therefore be considered in a future SPECT accreditation. Furthermore, the single-measurement method normally performed for PVC should be reconsidered to account for the position dependency.