UK audit of variation in nuclear medicine occupational exposure calculations in 2021.

It is a core requirement of UK ionising radiations regulations 2017 (IRR17) compliance for radiation risk assessments and the investigation of accidental exposure scenarios that the magnitude of doses likely to be encountered are evaluated. A novel national audit was undertaken to investigate the variation in dose estimations for a range of foreseeable accidental exposure scenarios in nuclear medicine (NM). Participants were asked to estimate the levels of exposure in 15 foreseeable scenarios; covering whole-body and extremity exposures from external sources, internal exposure and exposures from skin (surface contamination and needle-stick injury) and eye contamination. Questions were intentionally simplified to reduce variation from assumptions made by the participants and to focus more on the underlying gross systematic variation. Twenty-seven centres participated. There was generally a very wide variation in the estimated exposures across all the categories of exposures, apart from internal exposure estimates. Whilst there was no ground truth for each individual question, the variation in results itself often exceeded the relevant threshold for classification and annual dose limits. The majority of variation was due to differences in methods, models and assumptions used by each participant. This audit raises questions around how IRR17 compliance can be universally demonstrated with such wide national variation. It evidences the need for a more standardised practice in NM radionuclide exposure estimates through national consensus guidelines or standards etc.

Tailoring the sampling time of single-sample GFR measurement according to expected renal function: a multisite audit.

BACKGROUND: The 2018 BNMS Glomerular Filtration Rate (GFR) guidelines recommend a single-sample technique with the sampling time dictated by the expected renal function, but this is not known with any accuracy before the test. We aimed to assess whether the sampling regime suggested in the guidelines is optimal and determine the error in GFR result if the sample time is chosen incorrectly. We can then infer the degree of flexibility in the sampling regime. METHODS: Data from 6328 patients referred for GFR assessment at 6 different hospitals for a variety of indications were reviewed. The difference between the single-sample (Fleming) GFR result at each sample time and the slope-intercept GFR result at each hospital was calculated. A second dataset of 777 studies from one hospital with nine samples collected from 5 min to 8 h post-injection was analysed to provide a reference GFR to which the single-sample results were compared. RESULTS: Recommended single-sample times have been revised: for an expected GFR above 90 ml/min/1.73m2 a 2-h sample is recommended; between 50 and 90 ml/min/1.73m2 a 3-h sample is recommended; and between 30 and 50 ml/min/1.73m2 a 4-h sample is recommended. Root mean square error in single-sample GFR result compared with slope-intercept can be kept less than or equal to 3.30 ml/min/1.73m2 by following these recommendations. CONCLUSION: The results of this multisite study demonstrate a reassuringly wide range of sample times for an acceptably accurate single-sample GFR result. Modified recommended single-sample times have been proposed in line with the results, and a lookup table has been produced of rms errors across the full range of GFR results for the three sample times which can be used for error reporting of a mistimed sample.

Calculating the precision of slope-intercept glomerular filtration rate measurements.

Glomerular filtration rate (GFR) can be measured by observing the clearance of a suitable tracer from blood plasma after an intravenous injection. Slope-intercept GFR is an estimate of GFR calculated from an exponential fit to multiple blood sample measurements. The precision of the result depends on the uncertainties on all the measured quantities, but the most important factor is the error on the slope and intercept of the fit. However, these two errors are not independent as an increase in slope tends to produce an increase in intercept as well. This study derives the appropriate equations for calculating the precision of the result and shows that, if this dependence is not taken into account, the uncertainty in GFR can be significantly overestimated. The advantage of using Chi-square as a quality control measure is also introduced.

A preliminary evaluation of a high temporal resolution data-driven motion correction algorithm for rubidium-82 on a SiPM PET-CT system.

BACKGROUND: In myocardial perfusion PET, images are acquired during vasodilator stress, increasing the likelihood of intra-frame motion blurring of the heart in reconstructed static images to assess relative perfusion. This work evaluated a prototype data-driven motion correction (DDMC) algorithm designed specifically for cardiac PET. METHODS: A cardiac torso phantom, with a solid defect, was scanned stationary and being manually pulled to-and-fro in the axial direction with a random motion. Non-motion-corrected (NMC) and DDMC images were reconstructed. Total perfusion deficit was measured in the defect and profiles through the cardiac insert were defined. In addition, 46 static perfusion images from 36 rubidium-82 MPI patients were selected based upon a perception of motion blurring in the images. NMC and DDMC images were reconstructed, blinded, and scored on image quality and perceived motion. RESULTS: Phantom data demonstrated near-perfect recovery of myocardial wall visualization and defect quantification with DDMC compared with the stationary phantom. Quality of clinical images was NMC: 10 non-diagnostic, 31 adequate, and 5 good; DDMC images: 0 non-diagnostic, 6 adequate, and 40 good. CONCLUSION: The DDMC algorithm shows great promise in rubidium MPI PET with substantial improvements in image quality and the potential to salvage images considered non-diagnostic due to significant motion blurring.

The prevalence of image degradation due to motion in rest-stress rubidium-82 imaging on a SiPM PET-CT system.

BACKGROUND: Motion of the heart is known to affect image quality in cardiac PET. The prevalence of motion blurring in routine cardiac PET is not fully appreciated due to challenges identifying subtle motion artefacts. This study utilizes a recent prototype Data-Driven Motion Correction (DDMC) algorithm to generate corrected images that are compared with non-corrected images to identify visual differences in relative rubidium-82 perfusion images due to motion. METHODS: 300 stress and 300 rest static images were reconstructed with DDMC and without correction (NMC). The 600 DDMC/NMC image pairs were assigned Visual Difference Score (VDS). The number of non-diagnostic images were noted. A "Dwell Fraction" (DF) was derived from the data to quantify motion and predict image degradation. RESULTS: Motion degradation (VDS = 1 or 2) was evident in 58% of stress images and 33% of rest images. Seven NMC images were non-diagnostic-these originated from six studies giving a 2% rate of non-diagnostic studies due to motion. The DF metric was able to effectively predict image degradation. The DDMC heart identification and tracking was successful in all images. CONCLUSION: Motion degradation is present in almost half of all relative perfusion images. The DDMC algorithm is a robust tool for predicting, assessing and correcting image degradation.

Assessment of motion correction in dynamic rubidium-82 cardiac PET with and without frame-by-frame adjustment of attenuation maps for calculation of myocardial blood flow.

BACKGROUND: Patient motion during pharmacological stressing can have substantial impact on myocardial blood flow (MBF) estimated from dynamic PET. This work evaluated a motion correction algorithm with and without adjustment of the PET attenuation map. METHODS: Frame-by-frame motion correction was performed by three users on 30 rubidium-82 studies. Data were divided equally into three groups of motion severity [mild (M1), moderate (M2) and severe (M3)]. MBF data were compared for non-motion corrected (NC), motion-corrected-only (MC) and with adjustment of the attenuation map (MCAC). Percentage differences of MBF were calculated in the coronary territories and 17-segment polar plots. Polar plots of spill-over were also generated from the data. RESULTS: Median differences of 23% were seen in the RCA and 18% for the LAD in the M3 category for MC vs NC images. Differences for MCAC vs MC images were considerably smaller and typically < 10%. Spill-over plots for MC and MCAC were notably more uniform compared with NC images. CONCLUSION: Motion correction for dynamic rubidium data is desirable for future MBF software updates. Adjustment of the PET attenuation map results in only marginal differences and therefore is unlikely to be an essential requirement. Assessing the uniformity of spill-over plots is a useful visual aid for verifying motion correction techniques.

Assessing Reliability of Myocardial Blood Flow After Motion Correction With Dynamic PET Using a Bayesian Framework.

The estimation of myocardial blood flow (MBF) in dynamic PET can be biased by many different processes. A major source of error, particularly in clinical applications, is patient motion. Patient motion, or gross motion, creates displacements between different PET frames as well as between the PET frames and the CT-derived attenuation map, leading to errors in MBF calculation from voxel time series. Motion correction techniques are challenging to evaluate quantitatively and the impact on MBF reliability is not fully understood. Most metrics, such as signal-to-noise ratio (SNR), are characteristic of static images, and are not specific to motion correction in dynamic data. This study presents a new approach of estimating motion correction quality in dynamic cardiac PET imaging. It relies on calculating a MBF surrogate, K1 , along with the uncertainty on the parameter. This technique exploits a Bayesian framework, representing the kinetic parameters as a probability distribution, from which the uncertainty measures can be extracted. If the uncertainty extracted is high, the parameter studied is considered to have high variability - or low confidence - and vice versa. The robustness of the framework is evaluated on simulated time activity curves to ensure that the uncertainties are consistently estimated at the multiple levels of noise. Our framework is applied on 40 patient datasets, divided in 4 motion magnitude categories. Experienced observers manually realigned clinical datasets with 3D translations to correct for motion. K1 uncertainties were compared before and after correction. A reduction of uncertainty after motion correction of up to 60% demonstrates the benefit of motion correction in dynamic PET and as well as provides evidence of the usefulness of the new method presented.

The impact of prompt gamma compensation on myocardial blood flow measurements with rubidium-82 dynamic PET.

BACKGROUND: Rubidium-82 myocardial perfusion imaging is a well-established technique for assessing myocardial ischemia. With continuing interest on myocardial blood flow (MBF) and myocardial flow reserve (MFR) measurements, there is a requirement to fully appreciate the impact of technical aspects of the process. One such factor for rubidium-82 is prompt gamma compensation (PGC). This study aims to assess the impact of PGC on MBF and MFR calculated from dynamic Rb-82 data. METHODS: Dynamic rest and stress images were acquired on a Siemens Biograph mCT and reconstructed with and without PGC in 50 patients (29 male). MBF and MFR were measured in the three main coronary territories as well as globally. RESULTS: With PGC, statistically significant reductions in MBF were observed in LAD (-6.9%), LCx (-4.8%), and globally (-6.5%) but only in obese patients. Significant increases in MBF were observed in RCA (+6.4%) in only nonobese patients. In very obese patients, differences of up to 40% in MBF were observed between PGC and non-PGC images. In nearly all cases, similar PGC differences were observed at stress and rest so there were no significant differences in MFR; however, in a small number of very obese patients, differences in excess of 20% were observed. CONCLUSION: PGC results in statistically significant changes in MBF, with the greatest reductions observed in the LAD and LCx territories of obese patients. In most cases, the impact on stress and rest data is of similar relative magnitudes and changes to MFR are small.

Impact of pharmacological stress agent on patient motion during rubidium-82 myocardial perfusion PET/CT.

BACKGROUND: Patient motion has been demonstrated to have a significant impact on the quality and accuracy of rubidium-82 myocardial perfusion PET/CT. This study aimed to investigate the effect on patient motion of two pharmacological stressing agents, adenosine and regadenoson. METHODS AND RESULTS: Dynamic data were retrospectively analyzed in 90 patients undergoing adenosine (n = 30), incremental adenosine (n = 30), or regadenoson (n = 30) rubidium-82 myocardial perfusion PET/CT. Severity of motion was scored qualitatively using a four-point (0-3) scale and quantitatively using frame-to-frame pixel shifts. The type of motion, returning or non-returning, and the frame in which it occurred were also recorded. There were significant differences in both the qualitative and quantitative scores comparing regadenoson to adenosine (P = .025 and P < .001) and incremental adenosine (P = .014, P = .015), respectively. The difference in scores between adenosine and incremental adenosine was not significant. Where motion was present, significantly more adenosine patients were classed as non-returning (P = .018). The median frames for motion occurring were 12 for regadenoson and 14 for both adenosine cohorts. CONCLUSIONS: The choice of stressing protocol impacts significantly on patient motion. Patients stressed with regadenoson have significantly lower motion scores than those stressed with adenosine, using local protocols. This motion is more likely to be associated with a drift of the heart away from a baseline position, coinciding with the termination of infusion.

The performance of quantitation methods in the evaluation of cardiac implantable electronic device (CIED) infection: A technical review.

BACKGROUND: Quantitative assessment of [18F]-FDG PET/CT images has been shown to be useful in the diagnosis of cardiac implantable electronic device (CIED) infection. This study aimed to compare the accuracy of various quantitative methods, using the same patient cohort and to assess the utility of dual time point imaging. METHODS: The study comprised a retrospective review of 80 [18F]-FDG PET/CT studies. Of these, 41 were oncological patients with an asymptomatic CIED in situ (Group 1), and 39 were studies performed in patients with symptomatic devices. Of these, 14 were subsequently deemed on follow-up to be non-infected (Group 2), and 25 confirmed as infected post-device extraction (Group 3). Ratios of maximal uptake around the CIED in both the attenuation corrected and non-attenuation corrected images were calculated to regions of normal physiological uptake, along with the maximal standardized uptake value (SUVmax) alone. Receiver operating characteristic analysis was performed for all methods at both time points. Measurement reliability was assessed using the intraclass correlation coefficient (ICC). RESULTS: Using Group 1 as a reference, all methods gave an area under the curve (AUC) greater than 0.93. Using Group 2 as reference, the accuracy varied greatly, with AUC values ranging from 0.71 to 0.97. The hepatic blood pool (HBP) ratio gave the highest AUC values. The calculated ICC values for each method showed the SUVmax and HBP measurement to have the greatest reliability, with values of 1.0 and 0.97, respectively. CONCLUSIONS: Quantitation of [18F] FDG uptake was found to have a high degree of accuracy in confirming the diagnosis of CIED infection. Normalization to HBP uptake was found to give the greatest AUC and demonstrated excellent reliability. Inconsistencies from published data indicate that individual imaging centers should only use published data for guidance.

Radionuclide Imaging of Cardiovascular Infection.

Owing to expanding clinical indications, cardiac implantable electronic devices (CIEDs) are being increasingly used. Despite improved surgical techniques and the use of prophylactic antimicrobial therapy, the rate of CIED-related infection is also increasing. Infection is a potentially serious complication, with clinical manifestations ranging from surgical site infection and local symptoms in the region of the generator pocket to fulminant endocarditis. The utility of radionuclide imaging as a stand-alone noninvasive diagnostic imaging test in patients with suspected endocarditis has been less frequently examined. This article summarizes the recent advances in radionuclide imaging for evaluation of patients with suspected cardiovascular infections.