Nathan Better

Current worldwide nuclear cardiology practices and radiation exposure: results from the 65 country IAEA Nuclear Cardiology Protocols Cross-Sectional Study (INCAPS)

Aims To characterize patient radiation doses from nuclear myocardial perfusion imaging (MPI) and the use of radiation-optimizing ‘best practices’ worldwide, and to evaluate the relationship between laboratory use of best practices and patient radiation dose. Methods and results We conducted an observational cross-sectional study of protocols used for all 7911 MPI studies performed in 308 nuclear cardiology laboratories in 65 countries for a single week in March–April 2013. Eight ‘best practices’ relating to radiation exposure were identified a priori by an expert committee, and a radiation-related quality index (QI) devised indicating the number of best practices used by a laboratory. Patient radiation effective dose (ED) ranged between 0.8 and 35.6 mSv (median 10.0 mSv). Average laboratory ED ranged from 2.2 to 24.4 mSv (median 10.4 mSv); only 91 (30%) laboratories achieved the median ED ≤ 9 mSv recommended by guidelines. Laboratory QIs ranged from 2 to 8 (median 5). Both ED and QI differed significantly between laboratories, countries, and world regions. The lowest median ED (8.0 mSv), in Europe, coincided with high best-practice adherence (mean laboratory QI 6.2). The highest doses (median 12.1 mSv) and low QI (4.9) occurred in Latin America. In hierarchical regression modelling, patients undergoing MPI at laboratories following more ‘best practices’ had lower EDs. Conclusion Marked worldwide variation exists in radiation safety practices pertaining to MPI, with targeted EDs currently achieved in a minority of laboratories. The significant relationship between best-practice implementation and lower doses indicates numerous opportunities to reduce radiation exposure from MPI globally.

Results of strontium-89 therapy in patients with prostate cancer resistant to chemotherapy.

Purpose: Strontium-89 (Sr-89) chloride is an effective palliative treatment of the bone metastases of prostate cancer. Chemotherapy has also been shown to have a palliative benefit in this disease. We aimed to determine the benefits and complications of Sr-89 therapy in patients with prostate cancer who had become refractory to chemotherapy. We conducted a retrospective review of 14 treatments administered to 13 patients with chemotherapy-resistant and hormone-resistant prostate cancer. Results: Of the 14 administered treatments, 8 (57%) resulted in improved pain control, with 2 patients able to stop analgesia. The median duration of response was 56 days. No prostate-specific antigen response was seen in the 8 patients tested. There was significant and prolonged bone marrow toxicity, with 6 patients requiring red blood cell transfusion. Prolonged thrombocytopenia was seen, with platelet counts remaining below baseline levels after treatment in all but one patient. Leukopenia was generally mild and not associated with infection. Conclusions: Sr-89 is an effective treatment of patients with chemotherapy-refractory prostate cancer, but careful and prolonged monitoring of hematologic parameters after therapy is required.

Antiphospholipid syndrome in renal transplantation

Antiphospholipid syndrome (APS) may occur in isolation or in association with systemic lupus erythematosus (SLE), with the potential to cause renal failure via several distinct pathologies. Renal transplantation in the presence of APS carries a risk of early graft loss from arterial or venous thrombosis, or thrombotic microangiopathy (TMA). Whilst perioperative anticoagulation reduces the risk of large vessel thrombosis, it may result in significant haemorrhage, and its efficacy in preventing post‐transplant TMA is uncertain. Here, we report a patient with end‐stage kidney disease (ESKD) due to lupus nephritis and APS, in whom allograft TMA developed soon after transplantation despite partial anticoagulation. TMA resolved with plasma exchange‐based therapy albeit with some irreversible graft damage and renal impairment. We discuss the differential diagnosis of post‐transplant TMA, and current treatment options.

Quantitative assessment of thyroid-to-background ratio improves the interobserver reliability of technetium-99m sestamibi thyroid scintigraphy for investigation of amiodarone-induced thyrotoxicosis.

Background Amiodarone-induced thyrotoxicosis (AIT) is caused by excessive hormone synthesis and release (AIT I), a destructive thyroiditis (AIT II), or a combination of both (AIT Ind). Although no gold-standard diagnostic test is available, technetium-99m sestamibi thyroid scintigraphy (99mTc-STS) has been previously reported to be an accurate tool for differentiating subtypes with important therapeutic implications. However, the information to guide reporting of 99mTc-STS is qualitative and highly subjective. This study aims to compare the interobserver reliability of 99mTc-STS before and after the use of quantitative thyroid-to-background ratios (TBRs) displayed on a time–activity curve for differentiation of AIT subtypes. Methods A retrospective audit of Nuclear Medicine Departments at Royal Melbourne Hospital (Parkville, Victoria, Australia) and Cabrini Hospital (Malvern, Victoria, Australia) identified 15 consecutive 99mTc-STS studies performed for AIT. Four nuclear medicine physicians reported the studies according to previously established criteria (series 1). Quantitative TBR and estimated ‘normal’ range TBR were subsequently provided before the studies were reordered and reported again (series 2). Interobserver reliability was calculated using Fleiss’ &kgr; statistic for each assessment. Results The overall percentage of agreement (PoA) and &kgr; statistics for use of conventional 99mTc-STS for diagnosis of AIT improved from 47 to 80% and from 0.30 to 0.67 following the use of quantitative TBR displayed on a time–activity curve with reference to a normal population. Interobserver reliability improved substantially under all diagnostic comparisons, particularly for differentiation of either AIT I (PoA 80% to 94%, &kgr;: 0.48 to 0.84) or AIT Ind (PoA 47% to 82%, &kgr;: −0.05 to 0.51) from other types of AIT. Conclusion Use of quantitative TBR improves the interobserver reliability of reporting 99mTc-STS for investigation of different types of AIT. There is ‘almost perfect’ agreement upon differentiation of AIT I from AIT II and AIT Ind, with important implications for rationalizing the use of corticosteroid therapy. Prospective identification of AIT Ind is improved from ‘poor’ to a ‘moderate’ level of agreement to facilitate rational use of combination therapy at diagnosis.

Fixed defect on rest/stress Tc-99m sestamibi study underestimates myocardial ischemia: comparison with 24-hour thallium-201 study for short- and intermediate-term follow-up.

Purpose: We assessed whether a same day rest/stress gated Tc-99m sestamibi (MIBI) SPECT myocardial study underestimates reversible ischemia in patients with fixed perfusion defects compared with a 24-hour thallium-201 (Tl-201) study. The short- and intermediate-term outcome with or without Tl-201 reversibility was assessed. Methods: Forty-nine consecutive patients with fixed MIBI defects received an additional Tl-201 study and were evaluated. Tl-201 was given to patients with a high clinical suspicion of underestimation of reversibility. Images were interpreted semiquantitatively by 3 nuclear medicine physicians using a 17-segment, 5-point model. A summed stress score (SSS) from stress MIBI images, a summed rest score (SRS) from Tl images, and a summed difference (SDS = SSS − SRS) score were calculated. SDS >3 indicated significant Tl-201 redistribution. Composite end points included acute myocardial infarction, unstable angina needing admission, cardiac death, or revascularization within 3 and 6 months. Results: Fifteen of 49 patients showed no Tl-201 redistribution. Thirty-four of 49 (69%) patients had significant Tl-201 redistribution, and these patients had significantly higher cardiac events (CE) at 3 months (29% vs. 7%; P = 0.039), and higher at 6 months (32% vs. 7%; P = 0.027). These patients with CE had a larger amount of Tl-201 redistribution, mean SDS 8.6 vs. 5.3 (P = 0.047). Patients with significant Tl-201 redistribution had a lower left ventricular ejection fraction (mean 37%; P = 0.001). Conclusion: With short- and intermediate-term follow-up, our study shows a significant association towards fixed defects on the rest/stress MIBI study underestimating CE risk when compared with a delayed Tl-201 study, especially in patients with a large amount of Tl-201 redistribution. Hence, the addition of a Tl-201 study may be useful in the management of patients with large fixed MIBI defects, especially with a depressed left ventricular ejection fraction.

Nuclear cardiology practices and radiation exposure in Africa: Results from the IAEA Nuclear Cardiology Protocols Study (INCAPS)

Summary Objective: While nuclear myocardial perfusion imaging (MPI) offers many benefits to patients with known or suspected cardiovascular disease, concerns exist regarding radiationassociated health effects. Little is known regarding MPI practice in Africa. We sought to characterise radiation doses and the use of MPI best practices that could minimise radiation in African nuclear cardiology laboratories, and compare these to practice worldwide. Methods: Demographics and clinical characteristics were collected for a consecutive sample of 348 patients from 12 laboratories in six African countries over a one-week period from March to April 2013. Radiation effective dose (ED) was estimated for each patient. A quality index (QI) enumerating adherence to eight best practices, identified a priori by an IAEA expert panel, was calculated for each laboratory. We compared these metrics with those from 7 563 patients from 296 laboratories outside Africa. Results: to that of the rest of the world [9.1 (5.1–15.6) vs 10.3 mSv (6.8–12.6), p = 0.14], although a larger proportion of African patients received a low ED, ≤ 9 mSv targeted in societal recommendations (49.7 vs 38.2%, p < 0.001). Bestpractice adherence was higher among African laboratories (QI score: 6.3 ± 1.2 vs 5.4 ± 1.3, p = 0.013). However, median ED varied significantly among African laboratories (range: 2.0–16.3 mSv; p < 0.0001) and QI range was 4–8. Conclusion: Patient radiation dose from MPI in Africa was similar to that in the rest of the world, and adherence to best practices was relatively high in African laboratories. Nevertheless there remain opportunities to further reduce radiation exposure to African patients from MPI.

D-SPECT: New technology, old tricks

The dedicated cardiac cadmium-zinc-telluride (CZT) camera is the latest major technological advancement in Nuclear Cardiology after Tc-99 mbased myocardial perfusion tracers, gated single-photon emission computed tomography (SPECT) imaging, and iterative reconstruction. The high performance of dedicated cardiac CZT cameras is due to the integration of solid-state semiconductor detectors, cardiac-centric collimator choice, and geometrical setup and improvements in image reconstruction. Depending on the injected radiotracer activity, dedicated cardiac CZT cameras may achieve 5-10 times higher count sensitivity and 3-6 times faster scanning times than standard sodium iodide (NaI) SPECT cameras. The main dedicated cardiac CZT cameras commercially available are the Discovery NM series (GE Healthcare) and the Spectrum Dynamics (D-SPECT). The diagnostic performance of the Discovery NM 530c was found to be comparable to that of standard NaI SPECT with the advantage of superior image quality and shorter acquisition time. In terms of diagnostic accuracy referenced to coronary angiography, the DSPECT with upright-supine acquisition and quantitative perfusion analysis achieved a sensitivity of 94% and specificity of 86% for angiographically significant coronary artery stenosis. Furthermore, the Discovery NM 530c was found to correctly diagnose more patients with multi-vessel disease than standard NaI SPECT, referenced to coronary angiography. However, with new technology comes new technical traps that may adversely affect diagnostic accuracy for any new user. Therein lies the intangible asset of clinical experience in the usage of any new medical technology. Artifacts of dedicated cardiac CZT cameras are routinely encountered in daily clinical practice, but are scarcely described in the literature. Recognition of common technical artifacts and the different methods available to overcome them is vital to overall diagnostic accuracy. Over time, a new user of a dedicated cardiac CZT camera will slowly gain experience and familiarity with its technical traps, although an apprenticeship in an experienced center may ameliorate the learning curve. These traps will be different not only from the NaI SPECT cameras, but also between the different CZT technologies. In this issue of the Journal of Nuclear Cardiology, Allie et al describes the common pitfalls and artifacts of the D-SPECT dedicated cardiac CZT camera. Their paper is based on single-center experience and is largely qualitative, but is nevertheless a useful resource for those new to cardiac CZT technology on the recognition and troubleshooting of common technical artifacts in clinical practice. In general, technical artifacts in myocardial perfusion scintigraphy may be classified into radiotracer, camera hardware, software, and patient-related factors. Rigorous adherence to protocol is essential to ensure a diagnostic quality test. Each institution must optimize their protocol based on their experience, camera type, clinical workflow, and patient demographics. Soft tissue attenuation is one of the most common causes of artifacts. The soft tissue involved is usually due to obesity, breast tissue, or the diaphragm. An apparent perfusion defect in a typical location, demonstrating normal wall motion, changing appearance with patient repositioning, which does not conform to an expected coronary arterial territory would favor Reprint requests: Nathan Better, Department of Nuclear Medicine, The Royal Melbourne Hospital, Ground Floor, Clinical Sciences Building, Grattan Street, Parkville, Melbourne, VIC, 3050, Australia; nathan.better@mh.org.au J Nucl Cardiol 2016;23:311–2. 1071-3581/

Tailoring 99mTc Macroaggregated Albumin administration to optimize patient dose reduction

34.00 Copyright 2015 American Society of Nuclear Cardiology.

Mediastinal Tumor Presenting as a Cardiac Halo on Equilibrium Radionuclide Angiography A Differential Diagnosis to Pericardial Effusion

In the ever-changing field of nuclear medicine, best-practice considerations cannot simply go unchallenged for months and years, with the need to minimize radiation exposure to patients highlighted in “as low as reasonably achievable” principles. The Australian Radiation Protection and Nuclear Safety Agency reports that the dose for 99mTc-macroaggregated albumin (99mTc-MAA) administered should be 180–200 MBq. An objective of imaging in pulmonary embolism, or indeed any diagnostic procedure involving radiation, is to minimize radiation exposure without sacrificing image quality and diagnostic accuracy. The amount of radiation involved must be considered together with imaging protocols. Our aim was to reduce the amount of 99mTc-MAA administered without compromising the diagnostic quality of the scan. Methods: To achieve a ventilation-to-perfusion ratio of 1:4, we ventilated the patient as per standard protocol and then placed intravenous access into the patient. For the perfusion component, 180–200 MBq were prepared in a 2-mL injection. Aliquots of 0.5 mL of 99mTc-MAA were administered every 30 s followed by a 5-mL saline flush until the required ventilation-to-perfusion ratio was achieved. Results: With this protocol, the average administered dose was 105 ± 20.7 MBq (vs. 180 ± 5.3 MBq, P < 0.0001). Conclusion: By individually tailoring the administered dose, diagnostic quality is maintained while achieving a significant dose reduction.

Opening the door to noninvasive assessment of cardiac transplant rejection: It’s all in the preparation

A 52-year-old man with metastatic liposarcoma underwent equilibrium radionuclide angiography before commencing chemotherapy. Biventricular systolic function was normal, but an enlarged photon deficient area (cardiac halo) was seen surrounding the cardiac blood pool. Correlation with computed tomography was sought to exclude the possibility of a pericardial effusion, but a large medlastinal tumor was seen in the absence of a pericardlal effusion. Literature review suggests alternative causes of a cardiac halo as clotted blood, particularly seen after cardiac surgery, ventricular hypertrophy, or subepicardial fat. The authors conclude that the presence of a cardiac halo, particularly within an oncologic population, can represent mediastinal tumor as an alternative to pericardial effusion. This possibility should be strongly considered in the analytical process.