Observer studies of image quality of denoising reduced-count cardiac single photon emission computed tomography myocardial perfusion imaging by three-dimensional Gaussian post-reconstruction filtering and deep learning.

BACKGROUND: The aim of this research was to asses perfusion-defect detection-accuracy by human observers as a function of reduced-counts for 3D Gaussian post-reconstruction filtering vs deep learning (DL) denoising to determine if there was improved performance with DL. METHODS: SPECT projection data of 156 normally interpreted patients were used for these studies. Half were altered to include hybrid perfusion defects with defect presence and location known. Ordered-subset expectation-maximization (OSEM) reconstruction was employed with the optional correction of attenuation (AC) and scatter (SC) in addition to distance-dependent resolution (RC). Count levels varied from full-counts (100%) to 6.25% of full-counts. The denoising strategies were previously optimized for defect detection using total perfusion deficit (TPD). Four medical physicist (PhD) and six physician (MD) observers rated the slices using a graphical user interface. Observer ratings were analyzed using the LABMRMC multi-reader, multi-case receiver-operating-characteristic (ROC) software to calculate and compare statistically the area-under-the-ROC-curves (AUCs). RESULTS: For the same count-level no statistically significant increase in AUCs for DL over Gaussian denoising was determined when counts were reduced to either the 25% or 12.5% of full-counts. The average AUC for full-count OSEM with solely RC and Gaussian filtering was lower than for the strategies with AC and SC, except for a reduction to 6.25% of full-counts, thus verifying the utility of employing AC and SC with RC. CONCLUSION: We did not find any indication that at the dose levels investigated and with the DL network employed, that DL denoising was superior in AUC to optimized 3D post-reconstruction Gaussian filtering.

COVID-19 Vaccination-Related Uptake on FDG PET/CT: An Emerging Dilemma and Suggestions for Management.

As mass COVID-19 vaccination is underway, radiologists are encountering transient FDG uptake in normal or enlarged axillary, supraclavicular, and cervical lymph nodes after ipsilateral deltoid vaccination. This phenomenon may confound interpretation in patients with cancer undergoing FDG PET/CT. In this article, we present our institutional approach for management of COVID-19 vaccine-related lymphadenopathy on FDG PET/CT according to early experience. We suggest performing PET/CT at least 2 weeks after vaccination in patients with a cancer for which interpretation is anticipated to be potentially impacted by the vaccination but optimally 4-6 weeks after vaccination given increased immunogenicity of mRNA vaccines and potentially longer time for resolution than lymphadenopathy after other vaccines. PET/CT should not be delayed when clinically indicated to be performed sooner. Details regarding vaccination should be collected at the time of PET/CT to facilitate interpretation. Follow-up recommendations for postvaccination lymphadenopathy are provided, considering the lymph node's morphology and likely clinical relevance. Consideration should be given to administering the vaccine in the arm contralateral to a unilateral cancer to avoid confounding FDG uptake on the side of cancer. Our preliminary experience and suggested institutional approach should guide radiologists in management of patients with cancer undergoing PET/CT after COVID-19 vaccination.

Advantages of day-before lymphoscintigraphy and undiluted methylene blue dye injections for sentinel lymph node biopsies for melanoma.

BACKGROUND AND OBJECTIVES: Lymphatic mapping (LM) and blue dye injections are essential to identification of sentinel lymph nodes (SLN) for melanoma. LM is performed the day before (DB) or the same day (SD) of surgery, but the optimal timing is unknown. Similarly, methylene blue (MB), used during SLN biopsy (SLNB), is administered diluted (dMB) or undiluted (uMB), but the relative efficacies are unknown. METHODS: Patients who underwent SLNB for melanoma from 2009 to 2013 at our institution were evaluated. Outcomes included operative correlation with LM, SLN identification, and postoperative complications. RESULTS: One hundred seventy-one patients underwent SLNB. Sixty-seven (39%) had DB LM. Sixty-seven (39%) received uMB. Operative findings correlated with both LM groups, though the DB patients had lower background count (P = 0.018) and lower highest SLN radioactive signal count (P = 0.046). More uMB patients had blue SLNs (90% vs. 68%, P = 0.001). There was no difference in the total number of SLNs or complication rates in the LM and MB groups. CONCLUSIONS: This is the first study to compare the use of DB LM with SD LM and the efficacy of uMB versus dMB. DB LM and uMB offer advantageous alternatives for patients and their surgeons without loss of accuracy or increased morbidity. J. Surg. Oncol. 2016;114:947-950. © 2016 Wiley Periodicals, Inc.

Design of a Multi-Pinhole Collimator for I-123 DaTscan Imaging on Dual-Headed SPECT Systems in Combination with a Fan-Beam Collimator.

For the 2011 FDA approved Parkinson's Disease (PD) SPECT imaging agent I-123 labeled DaTscan, the volume of interest (VOI) is the interior portion of the brain. However imaging of the occipital lobe is also required with PD for calculation of the striatal binding ratio (SBR), a parameter of significance in early diagnosis, differentiation of PD from other disorders with similar clinical presentations, and monitoring progression. Thus we propose the usage of a combination of a multi-pinhole (MPH) collimator on one head of the SPECT system and a fan-beam on the other. The MPH would be designed to provide high resolution and sensitivity for imaging of the interior portion of the brain. The fan-beam collimator would provide lower resolution but complete sampling of the brain addressing data sufficiency and allowing a volume-of-interest to be defined over the occipital lobe for calculation of SBR's. Herein we focus on the design of the MPH component of the combined system. Combined reconstruction will be addressed in a subsequent publication. An analysis of 46 clinical DaTscan studies was performed to provide information to define the VOI, and design of a MPH collimator to image this VOI. The system spatial resolution for the MPH was set to 4.7 mm, which is comparable to that of clinical PET systems, and significantly smaller than that of fan-beam collimators employed in SPECT. With this set, we compared system sensitivities for three aperture array designs, and selected the 3 × 3 array due to it being the highest of the three. The combined sensitivity of the apertures for it was similar to that of an ultra-high resolution fan-beam (LEUHRF) collimator, but smaller than that of a high-resolution fan-beam collimator (LEHRF). On the basis of these results we propose the further exploration of this design through simulations, and the development of combined MPH and fan-beam reconstruction.

An evaluation of iterative reconstruction strategies based on mediastinal lesion detection using hybrid Ga-67 SPECT images.

Using psychophysical studies, the authors have evaluated the effectiveness of various strategies for compensating for physical degradations in SPECT imaging. The particular application was Ga-67-citrate imaging of mediastinal tumors, which was chosen because Ga-67 is a particularly challenging radionuclide for imaging. The test strategies included compensations for nonuniform attenuation, distance-dependent spatial resolution, and scatter applied in various combinations as part of iterative reconstructions with the rescaled block iterative-expectation maximization (RBI-EM) algorithm. The authors also evaluated filtered backprojection reconstructions. Strategies were compared on the basis of human-observer studies of lesion localization and detection accuracy using the localization receiver operating characteristics (LROC) paradigm. These studies involved hybrid images which were obtained by adding the projections of Monte Carlo-simulated lesions to disease-free clinical projection data. The background variability in these images can provide a more realistic assessment of the relative utility of reconstruction strategies than images from anthropomorphic digital phantoms. The clinical datasets were obtained using a GE-VG dual-detector SPECT system with CT-estimated attenuation maps. After determining a target lesion contrast, they conducted pilot LROC studies to obtain a near-optimal set of reconstruction parameters for each strategy, and then conducted the strategy comparison study. The results indicate improved detection accuracy with RBI-EM as more compensations are applied within the reconstruction. The relative rankings of the test strategies agreed in most cases with those of previous studies that employed simulated projections of digital anthropomorphic phantoms, thus confirming the findings of those studies.

Validation of neutron activation as a novel method to determine glomerular filtration rate.

BACKGROUND/AIMS: Despite widespread interest in determining the glomerular filtration rate (GFR) of patients, current methods all have significant limitations. Therefore, a compelling need exists for new tests of GFR that are both accurate and easy to perform. We have previously reported that the technique of neutron activation (NA) accurately measures iohexol in vitro. In this study, we demonstrate that NA can be used to determine GFR by measuring the clearance of iohexol, and directly compare these results to a gold-standard method based on (99m)Tc-DTPA. METHODS: We studied 57 patients with mild to moderate chronic kidney disease and normal volunteers. Subjects were simultaneously injected with iohexol and (99m)Tc-DTPA. Blood and urine samples were collected over 4 h to calculate GFR by the UV/P method. RESULTS: The range of GFRs was 28-212 ml/min. GFRs obtained using iohexol and (99m)Tc-DTPA correlated closely (R = 0.95). The bias between the 2 techniques was 0.96 ml/min, and precision (defined as the standard deviation of the mean of the difference between the 2 values for each patient) was 10.6 ml/min. Accuracy was such that 98% of subjects had NA GFRs within 20% of the reference (99m)Tc-DTPA measurements. CONCLUSIONS: We conclude that NA is an excellent technique to measure GFR. NA has several advantages over current methods to directly measure GFR, including the ability to reassay samples, high throughput and the avoidance of patient and hospital radioactivity exposure. In the future, NA could be applied to GFR agents that do not contain iodine, such as Gd-DTPA, and to the simultaneous measurement of agents that reflect renal blood flow, such as iodohippurate. Therefore, NA holds great potential to improve the measurement of renal function in a safe, easily obtainable way.

Inaccuracy of Tl-201 brain SPECT in distinguishing cerebral infections from lymphoma in patients with AIDS.

PURPOSE: Studies have suggested using Tl-201 brain SPECT to differentiate lymphoma from infectious processes and to determine the timing for biopsy or empirical therapy for patients with AIDS-related brain lesions. This study prospectively investigated the utility of Tl-201 SPECT in distinguishing central nervous system lymphoma from non-neoplastic disease in patients with AIDS. MATERIALS AND METHODS: Fourteen patients with AIDS and focal abnormalities on computed tomography or magnetic resonance imaging underwent brain SPECT before diagnosis (12 by biopsy, 2 by clinical course and response to therapy). A an uptake ratio (UR) was obtained by drawing a region of interest around the lesion, measuring average counts per pixel, and dividing this value by the value of a non-lesion-containing contralateral region of interest. The UR cutoff producing the highest accuracy (TP+TN/TP+TN+FP+FN) in discriminating lymphoma from another condition was determined from URs generated from these 14 patients. RESULTS: Five patients had lymphoma, five had toxoplasmosis, one had Herpes simplex virus encephalitis, two had progressive multifocal leukoencephalopathy, and one had gliosis (UR, 0.8). Patients were separated into categories of lymphoma or nonlymphoma. The mean UR was 2.2 +/- 1.6 (range, 1.0 to 3.85) for lymphoma and 1.7 +/- 0.8 (range, 0.7 to 3.2) for nonlymphoma. Only a UR of 1.63 resulted in sensitivity and specificity better than 50% (60% and 55%, respectively), with an accuracy of 57%, positive predictive value of 43%, and negative predictive value of 71%. CONCLUSIONS: Tl-201 brain SPECT appears unreliable for differentiating primary lymphoma from nonmalignant brain lesions in patients with AIDS. Early brain biopsy is necessary to establish a definitive diagnosis when appropriate.

Impact on reader performance for lesion-detection/ localization tasks of anatomical priors in SPECT reconstruction.

With increasing availability of multimodality imaging systems, high-resolution anatomical images can be used to guide the reconstruction of emission tomography studies. By measuring reader performance on a lesion detection task, this study investigates the improvement in image-quality due to use of prior anatomical knowledge, for example organ or lesion boundaries, during SPECT reconstruction. Simulated (67)Ga -citrate source and attenuation distributions were created from the mathematical cardiac-torso (MCAT) anthropomorphic digital phantom. The SIMIND Monte Carlo software was then used to generate SPECT projection data. The data were reconstructed using the De Pierro maximum a posteriori (MAP) algorithm and the rescaled-block-iterative (RBI) algorithm for comparison. We compared several degrees of prior knowledge about the anatomy: no knowledge about the anatomy; knowledge of organ boundaries; knowledge of organ and lesion boundaries; and knowledge of organ, lesion, and pseudo-lesion (non-emission uptake altering) boundaries. The MAP reconstructions used quadratic smoothing within anatomical regions, but not across any provided region boundaries. The reconstructed images were read by human observers searching for lesions in a localization receiver operating characteristic (LROC) study of the relative detection/localization accuracies of the reconstruction algorithms. Area under the LROC curve was computed for each algorithm as the comparison metric. We also had humans read images reconstructed using different prior strengths to determine the optimal trade-off between data consistency and the anatomical prior. Finally by mixing together images reconstructed with and without the prior, we tested to see if having an anatomical prior only some of the time changes the observer's detection/localization accuracy on lesions where no boundary prior is available. We found that anatomical priors including organ and lesion boundaries improve observer performance on the lesion detection/localization task. Use of just organ boundaries did not provide a statistically significant improvement in performance however. We also found that optimal prior strength depends on the level of anatomical knowledge, with a broad plateau in which observer performance is near optimal. We found no evidence that having anatomical priors use lesion boundaries only when available changes the observer's performance when they are not available. We conclude that use of anatomical priors with organ and lesion boundaries improves reader performance on a lesion-detection/localization task, and that pseudo-lesion boundaries do not hurt reader performance. However, we did not find evidence that a prior using only organ boundaries helps observer performance. Therefore we suggest prior strength should be tuned to the organ-only case, since a prior will likely not be available for all lesions.

Human-observer LROC study of lesion detection in Ga-67 SPECT images reconstructed using MAP with anatomical priors.

We compare the image quality of SPECT reconstruction with and without an anatomical prior. Area under the localization-response operating characteristic (LROC) curve is our figure of merit. Simulated Ga-67 citrate images, a SPECT lymph-nodule imaging agent, were generated using the MCAT digital phantom. Reconstructed images were read by human observers.Several reconstruction strategies are compared, including rescaled block iterative (RBI) and maximum-a-posteriori (MAP) with various priors. We find that MAP reconstruction using prior knowledge of organ and lesion boundaries significantly improves lesion-detection performance (p < 0.05). Pseudo-lesion boundaries, regions without increased uptake which are incorrectly treated as prior knowledge of lesion boundaries, do not decrease performance.