Erick Alexanderson

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.

Fusion of positron emission tomography and coronary computed tomographic angiography identifies fluorine 18 fluorodeoxyglucose uptake in the left main coronary artery soft plaque

Case report. A 71 year-old man underwent F-18 FDG-PET scanning with noncontrast computed tomography (CT) for attenuation and anatomic correction (PET/CT) 1 year after surgical resection with diverting colostomy and adjuvant chemotherapy and radiotherapy for colonic adenocarcinoma. A PET/CT scan was done after 10 hours of fasting, 90 minutes after FDG injection. His medical history included type 2 diabetes mellitus controlled with metformin and glibenclamide, cigarette smoking for 15 years (8-10 cigarettes per day), chronic gastritis, heavy alcohol use, and esophageal varices. The patient denied any allergies, chest pain, or previous heart disease. FDG-PET/CT showed focal hypermetabolic activity in the rectum and its neighboring fatty tissue, liver, and multiple lymph nodes in the mediastinum and neck. In addition, noticeable FDG uptake was present in the aorta, most consistent with aortic atherosclerotic plaque, and in a structure that appeared to be within or adjacent to the left main coronary artery (Figure 1). To further investigate the latter finding, retrospectively gated 64-slice CCTA was performed on the same day with the Siemens HI-REZ Biograph 64 hybrid PET/CT scanner (Siemens Medical Solutions, Malvern, Pa). Analysis of the reconstructed 3-dimensional CCTA images identified significant coronary atherosclerosis, i n cluding a large noncalcified plaque in the left main coronary artery and the proximal left anterior descending artery, the latter associated with a 50% stenosis, as well as multiple areas of calcified plaque in the right coronary artery (Figure 2). Subsequent software fusion of CCTA and FDG-PET/CT images by use of the Cedars-Sinai CT-Fusion option in the QPS program (Cedars-Sinai Medical Center, Los Angeles, Calif) showed anatomic correspondence between the abnormal extra-aortic FDG uptake and the noncalcified plaque within the left main coronary artery (Figure 3). In view of these findings, the patient was referred to the cardiology clinic, and we recommended aspirin and statin therapy and further examination by coronary angiography. However, because of his current serious oncologic condition, coronary angiography was not performed. Discussion. There is mounting evidence that FDG-PET uptake reflects inflammation in atherosclerotic plaques. Animal studies with atherosclerotic rabbits have confirmed that FDG uptake corresponds with plaque macrophage content. In patients with angiographic evidence of internal carotid stenosis, Rudd et al found significantly higher FDG uptake in 8 symptomatic carotid plaques than in 6 contralateral asymptomatic plaques; normal carotid arteries exhibited no identifiable uptake. Major limitations of plaque imaging with FDG-PET in the coronary vessels include cardiac motion during PET, FDG uptake in adjacent structures such as the myocardium, and limited PET resolution. Despite these limitations, our case shows the ability of FDG-PET/CT and CCTA image fusion to identify and localize areas of noticeable FDG uptake in the proximal segments of the coronary arteries, which could be related to inflamed atherosclerotic lesions.

Image quality and radiation dose of a prospectively electrocardiography-triggered high-pitch data acquisition strategy for coronary CT angiography: The multicenter, randomized PROTECTION IV study.

BACKGROUND Concerns have been raised about radiation dose of coronary CT angiography. Although high-pitch acquisition technique yields high potential for radiation dose savings, it is more vulnerable to artifacts, which impair diagnostic image quality. OBJECTIVE The purpose of this study was to compare 2 scan strategies for coronary CT angiography: a high-pitch helical scan first or a conventional scan first strategy. METHODS In this prospective, multicenter trial, we randomized 303 consecutive patients with a low and stable heart rate to either of the aforementioned mentioned strategies. Intravenous β-blockers were administered to achieve target heart rates. All scans were performed on a second-generation dual-source CT scanner. In case of nondiagnostic image quality, coronary CT angiography was allowed to be repeated. The primary end point was to demonstrate noninferior image quality in the high-pitch group. Image quality was assessed on a 4-point scale (1: nondiagnostic, 4: excellent). Secondary end point was total radiation dose. RESULTS In the high-pitch helical first group, repeat scanning was necessary in 21 patients compared with 14 patients in the conventional first scan group (P = .25). Image quality in the high-pitch group was noninferior compared to the conventional scan group (3.81 ± 0.35 vs. 3.83 ± 0.37; P for noninferiority <.0001). The total effective radiation dose estimate was 58% lower in the high-pitch group (2.0 ± 2.4 vs. 4.7 ± 4.8 mSv; P < .0001). CONCLUSIONS In patients with a low and stable heart rate diagnostic image quality can be maintained with a high-pitch helical scan first strategy while 58% of radiation dose can be saved.

Endothelial Dysfunction in Recently Diagnosed Type 2 Diabetic Patients Evaluated by PET

PurposeTo demonstrate the presence of endothelial dysfunction (ED) in asymptomatic patients with type 2 diabetes mellitus (DM) by using 13N-ammonia–positron emission tomography (PET). PET can identify ED by quantifying myocardial blood flow (MBF) during rest, cold pressor test (CPT), and pharmacologic stress. The endothelial-dependent vasodilation index (EDVI), myocardial flow reserve (MFR), and the percentage of the change between rest and CPT (%ΔMBF) are markers of endothelial function.ProceduresThirty-nine subjects were studied (19 women and 20 men); 22 recently diagnosed type 2 diabetic patients and 17 healthy controls (HC). A three-phase 13N-ammonia–PET was performed.ResultsMean EDVI was 1.208 ± 0.34 vs. 1.55 ± 0.37 (diabetic vs. HC group, respectively) (p = 0.002), MFR was 2.803 ± 1.39 vs. 3.27 ± 0.72 (p = NS), and the %ΔMBF was 20 ± 34% vs. 55 ± 37% (p = 0.002). Rest MBF and CPT MBF were normalized to the rate pressure product (RPP). EDVI′ and %ΔMBF′ were calculated using the corrected values for the RPP. Mean EDVI′ was (0.864 ± 0.250 vs. 1.110 ± 0.238, p = 0.004) and mean %ΔMBF′ was (−8.2 ± 14.7% vs. 4.5 ± 12.1%, p = 0.005).ConclusionsAsymptomatic, recently diagnosed type 2 diabetes patients present ED that can be quantified by 13N-ammonia–PET.

Endothelial Dysfunction in Systemic Lupus Erythematosus: Evaluation with 13N-Ammonia PET

Systemic lupus erythematosus (SLE) affects multiple organs and systems, severely involving the cardiovascular system. The aim of this study was to evaluate the presence of endothelial dysfunction with 13N-ammonia PET in asymptomatic SLE patients. Methods: We enrolled 16 women with SLE and 16 healthy women. Myocardial blood flow (MBF) was quantified in a 64-slice PET/CT scanner at rest, during a cold pressor test (CPT), and during stress. Endothelium-dependent vasodilation index, %ΔMBF, and myocardial flow reserve (MFR) were calculated. Results: There were 16 women in the SLE group (mean age ± SD, 31.4 ± 8.3 y) and 16 women in the healthy control group (31.5 ± 11.1 y). Mean endothelium-dependent vasodilatation index and %ΔMBF were significantly lower in SLE patients (1.18 ± 0.55 vs. 1.63 ± 0.65, P = 0.04, and 18 ± 55 vs. 63 ± 65, P = 0.04, respectively). MFR was also lower in the SLE group (2.41 ± 0.59 vs. 2.73 ± 0.77, P = 0.20). Conclusion: SLE patients who are free of active disease present abnormal coronary flow and endothelial dysfunction. It is necessary to develop and intensify treatment strategies directed to CAD in SLE patients.

The role of PET quantification in cardiovascular imaging

Positron emission tomography (PET) has several clinical applications in cardiovascular imaging. Myocardial perfusion imaging with PET allows accurate global and regional measurements of myocardial perfusion, myocardial blood flow and function at stress and rest in a single examination. Simultaneous assessment of function and perfusion by PET with quantitative software is currently routine practice. Combination of ejection fraction reserve with perfusion information may improve the identification of severe coronary artery disease. Myocardial viability can be estimated by quantitative comparison of fluorine-18 fluorodeoxyglucose (18F-FDG) and rest perfusion imaging. Quantitative myocardial blood flow and myocardial flow reserve measurements are becoming routinely included in clinical assessments due to the enhanced dynamic imaging capabilities of the latest PET/CT scanners. Absolute flow measurements allow evaluation of coronary microvascular dysfunction and provide additional prognostic and diagnostic information in coronary disease. Quantitative clinical software tools for computing myocardial blood flow from kinetic PET data in an automated and rapid fashion have been developed for use with several radiotracers: 13N-ammonia, 15O-water and 82Rb. The level of agreement between various software methods available for such analyses is excellent. Relative quantification of 82Rb PET myocardial perfusion tracer uptake, based on comparisons with normal perfusion databases, demonstrates high performance for the detection of obstructive coronary disease. Computerized analysis of myocardial perfusion at stress and rest reduces the variability of the assessment compared with visual analysis. New tracers, such as 18F-flurpiridaz may allow further improvements in myocardial blood flow quantification and disease detection. PET quantification can be enhanced by precise coregistration with CT angiography. In emerging clinical applications, the potential to identify vulnerable plaques by quantification of atherosclerotic plaque uptake of 18FDG and 18F-sodium fluoride tracers in carotids, aorta and coronary arteries has been demonstrated.

Prognostic value of cardiovascular CT: Is coronary artery calcium screening enough? The added value of CCTA

Coronary artery disease (CAD) is the primary cause of death in adults in the United States. Only 50% of patients who present with a myocardial infarction have a prior history of CAD. Non-invasive cardiac imaging tests have been developed to diagnose CAD. Current guidelines and systematic reviews have tried to determine the prognostic value of the coronary artery calcium (CAC) scoring and the coronary computed tomography angiography (CCTA) for major adverse cardiovascular events. Several studies support the roles of CCTA and CAC scoring for the diagnosis of CAD in asymptomatic patients. Further studies are needed to confirm the superior role of CCTA over CAC scoring in symptomatic patients.

Relationship Between Quantitative Adverse Plaque Features From Coronary Computed Tomography Angiography and Downstream Impaired Myocardial Flow Reserve by 13N-Ammonia Positron Emission Tomography A Pilot Study

Background—We investigated the relationship of quantitative plaque features from coronary computed tomography (CT) angiography and coronary vascular dysfunction by impaired myocardial flow reserve (MFR) by 13N-Ammonia positron emission tomography (PET). Methods and Results—Fifty-one patients (32 men, 62.4±9.5 years) underwent combined rest–stress 13N-ammonia PET and CT angiography scans by hybrid PET/CT. Regional MFR was measured from PET. From CT angiography, 153 arteries were evaluated by semiautomated software, computing arterial noncalcified plaque (NCP), low-density NCP (NCP<30 HU), calcified and total plaque volumes, and corresponding plaque burden (plaque volumex100%/vessel volume), stenosis, remodeling index, contrast density difference (maximum difference in luminal attenuation per unit area in the lesion), and plaque length. Quantitative stenosis, plaque burden, and myocardial mass were combined by boosted ensemble machine-learning algorithm into a composite risk score to predict impaired MFR (MFR⩽2.0) by PET in each artery. Nineteen patients had impaired regional MFR in at least 1 territory (41/153 vessels). Patients with impaired regional MFR had higher arterial NCP (32.4% versus 17.2%), low-density NCP (7% versus 4%), and total plaque burden (37% versus 19.3%, P<0.02). In multivariable analysis with 10-fold cross-validation, NCP burden was the most significant predictor of impaired MFR (odds ratio, 1.35; P=0.021 for all). For prediction of impaired MFR with 10-fold cross-validation, receiver operating characteristics area under the curve for the composite score was 0.83 (95% confidence interval, 0.79–0.91) greater than for quantitative stenosis (0.66, 95% confidence interval, 0.57–0.76, P=0.005). Conclusions—Compared with stenosis, arterial NCP burden and a composite score combining quantitative stenosis and plaque burden from CT angiography significantly improves identification of downstream regional vascular dysfunction.

Multiplane Transesophageal Echocardiography with Dobutamine in Patients with Biventricular Inferior Myocardial Infarction

The purpose of this study was to evaluate the alterations of ventricular wall movement in patients with acute posteroinferior myocardial infarction with extension to right cavities with multiplane transesophageal echocardiography (TEE), as well as the utility of dobutamine with this technique to analyze myocardial viability. Nine men with a mean age of 51 years fulfilled the inclusion criteria. Myocardial TEE was performed in all the men 72 hours after the acute event with long‐ and short‐axis transgastric images of both ventricles under basal conditions and with dobutamine infusions of 5 and 10 μg/kg per minute. Results were compared with myocardial perfusion findings obtained with Tc‐99m Sestamibi SPECT. Left ventricular myocardial viability was demonstrated in 28 of 45 altered segments with dobutamine stress myocardial TEE and Tc‐99m Sestamibi SPECT. Right ventricular myocardial viability was identified in 27 of 30 altered segments with dobutamine stress myocardial TEE in transgastric short and long axes, and with Tc‐99m Sestamibi SPECT in 23 of 25 segments only in short‐axis images. Multiplane TEE provided excellent image resolution and better definition of endocardial and epicardial borders, which facilitated detailed evaluation of ventricular segmental wall movement. Infusion of low doses of dobutamine made it possible to identify viable tissue in both ventricles, and results were comparable to those of nuclear medicine.

Multicenter Evaluation of Coronary Dual-Source CT Angiography in Patients with Intermediate Risk of Coronary Artery Stenoses (MEDIC): Study design and rationale

BACKGROUND The diagnostic performance of multidetector row CT to detect coronary artery stenosis has been evaluated in numerous single-center studies, with only limited data from large cohorts with low-to-intermediate likelihood of coronary disease and in multicenter trials. The Multicenter Evaluation of Coronary Dual-Source CT Angiography in Patients with Intermediate Risk of Coronary Artery Stenoses (MEDIC) trial determines the accuracy of dual-source CT (DSCT) to identify persons with at least 1 coronary artery stenosis among patients with low-to-intermediate pretest likelihood of disease. METHODS The MEDIC trial was designed as a prospective, multicenter, international trial to evaluate the diagnostic performance of DSCT for the detection of coronary artery stenosis compared with invasive coronary angiography. The study includes 8 sites in Germany, India, Mexico, the United States, and Denmark. The study population comprises patients referred for a diagnostic coronary angiogram because of suspected coronary artery disease with an intermediate pretest likelihood as determined by sex, age, and symptoms. All evaluations are performed by blinded core laboratory readers. RESULTS The primary outcome of the MEDIC trial is the accuracy of DSCT to identify the presence of coronary artery stenoses with a luminal diameter narrowing of 50% or more on a per-vessel basis. Secondary outcome parameters include per-patient and per-segment diagnostic accuracy for 50% stenoses and accuracy to identify stenoses of 70% or more. Furthermore, secondary outcome parameters include the influence of heart rate, Agatston score, body weight, body mass index, image quality, and diagnostic confidence on the accuracy to detect coronary artery stenoses >50% on a per-vessel basis. CONCLUSION The results of the MEDIC trial will assess the clinical utility of coronary CT angiography in the evaluation of patients with intermediate pretest likelihood of coronary artery disease.