Cumulative exposure to ionizing radiation from diagnostic and therapeutic cardiac imaging procedures: a population-based analysis.

OBJECTIVES: The purpose of this study was to describe radiation exposure from cardiac imaging procedures over time in a general population. BACKGROUND: Cardiac imaging procedures frequently expose patients to ionizing radiation, but their contribution to effective doses of radiation in the general population is unknown. METHODS: We used administrative claims to identify cardiac imaging procedures performed from 2005 to 2007 in 952,420 nonelderly insured adults in 5 U.S. health care markets. We estimated 3-year cumulative effective doses of radiation in millisieverts from these procedures We then calculated population-based annual rates of radiation exposure to effective doses < or =3 mSv/year (background level of radiation from natural sources), >3 to 20 mSv/year, or >20 mSv/year (upper annual limit for occupational exposure averaged over 5 years). RESULTS: A total of 90,121 (9.5%) individuals underwent at least 1 cardiac imaging procedure using radiation. Among patients who underwent > or =1 cardiac imaging procedures, the mean cumulative effective dose over 3 years was 23.1 mSv (range 1.5 to 543.7 mSv). Myocardial perfusion imaging accounted for 74% of the cumulative effective dose. Overall, 47.8% of cardiac imaging procedures were performed in physician offices; this proportion was higher for myocardial perfusion imaging (74.8%) and cardiac computed tomography studies (76.5%). The annual population-based rate of receiving an effective dose of >3 to 20 mSv/year was 89.0 per 1,000; and 3.3 per 1,000 for cumulative doses >20 mSv/year. Annual effective doses increased with age and were generally higher among men. CONCLUSIONS: Cardiac imaging procedures lead to substantial radiation exposure and effective doses for many patients in the U.S.

Ejection fraction assessment and survival: an analysis of the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT).

BACKGROUND: Ejection fraction (EF) is an important method of mortality prediction among cardiac patients, and has been used to identify the highest risk patients for enrollment in the defibrillator primary prevention trials. Evidence suggests that measures of EF by different imaging modalities may not be equivalent. In the SCD-HeFT (Sudden Cardiac Death in Heart Failure Trial), the type of imaging modality for EF assessment was not mandated. METHODS: Baseline assessment of EF was performed using either echocardiography, radionuclide angiography (RNA), or contrast angiography. Multivariable analysis using a Cox proportional hazards model was used to examine whether the modality of assessing EF affected the likelihood of survival. RESULTS: Among the 2,521 patients enrolled in SCD-HeFT, EF was measured by RNA in 616 (24%), echocardiography in 1,469 (58%), and contrast angiography in 436 (17%). Mean EF as measured by RNA was 25.1% +/- 6.9%; by echocardiography, 23.8 +/- 6.9%; and by angiography, 21.9 +/- 6.9%. These measures were significantly different (P < .001), and each pairwise comparison differed significantly (P < .001 for each). Multivariable analysis showed no significant difference in survival between patients enrolled based on RNA versus echocardiography (HR 1.06, 95% CI 0.88-1.28), RNA versus angiography (HR 1.25, 95% CI 0.97-1.62), or echocardiography versus angiography (HR 1.18, 95% CI 0.94-1.48). CONCLUSIONS: Among patients enrolled in SCD-HeFT, the distribution of ejection fractions measured by radionuclide angiography differed from those measured by echocardiography or contrast angiograms. Survival did not differ according to modality of EF assessment.

Prediction of death and nonfatal myocardial infarction in high-risk patients: a comparison between the Duke treadmill score, peak exercise radionuclide angiography, and SPECT perfusion imaging.

UNLABELLED: Radionuclide exercise testing provides prognostic information in patients with known or suspected coronary artery disease (CAD). The relative contribution of 3 noninvasive tests--the Duke treadmill score (DTS), first-pass radionuclide angiography with calculation of the ejection fraction (RNA-EF), and perfusion SPECT--has not been comparatively assessed in a high-risk population undergoing all 3 tests. METHODS: We identified 997 patients (75% male; median age, 60 y) who underwent exercise treadmill testing with RNA-EF and SPECT perfusion imaging as a single test. The relative prognostic power of each test was evaluated in both an unadjusted manner and after adjustment for differences in baseline characteristics using Cox proportional hazards models. RESULTS: During a median follow-up of 4.1 y, 175 patients experienced outcome events. Without adjustment for baseline patient characteristics, each of the modalities proved highly predictive of the composite endpoint of cardiovascular death or nonfatal myocardial infarction (MI) (DTS chi(2) = 18.9, P = 0.0001; RNA-EF chi(2) = 34, P = 0.0001; SPECT chi(2) = 11.5, P = 0.0007). In clinically risk-adjusted models, RNA-EF was the most powerful predictor of cardiovascular death compared with the DTS and SPECT (chi(2) = 40.5, 27.6, and 19.8, respectively). Conversely, exercise SPECT perfusion was a stronger predictor of nonfatal MI than the DTS or RNA-EF (chi(2) = 26.7, 15.7, and 16.7, respectively). CONCLUSION: The DTS, perfusion SPECT, and RNA-EF are each significant predictors of cardiovascular events in high-risk patients. The optimal risk stratification of patients for CAD may include all 3 modalities.

Do myocardial perfusion SPECT and radionuclide angiography studies in adult patients with hypertrophic cardiomyopathy have prognostic implications?

BACKGROUND: Some myocardial perfusion single photon emission computed tomography (SPECT) and radionuclide ventriculography studies have suggested that the presence of regional perfusion defects and diastolic abnormalities could have prognostic implications in patients with hypertrophic cardiomyopathy (HC). The aim of this prospective study was to analyze the prognostic value of these techniques in adult patients with HC. METHODS AND RESULTS: One hundred one patients with HC (44 women; mean age, 54 +/- 16 years; 55% obstructive) were prospectively studied by means of myocardial perfusion SPECT and radionuclide angiography. Of these patients, 55 (54.4%) had an abnormal myocardial perfusion SPECT study: 28 (27.7%) had fixed defects and 41 (40.6%) had reversible defects; 15 (14.8%) of these patients had both types of defect. Of the patients, 16% had left ventricular ejection fraction lower than 60%, 25.7% had an abnormal peak filling rate, and 51% had an abnormal time to peak filling rate. During 5.6 +/- 2.7 years of follow-up, 13 patients (12.8%) died (heart failure 8 and sudden death in 5) and 14 had one or more severe complications develop (syncope in 6, angina III-IV in 4, dyspnea III-IV in 10, and acute myocardial infarction in 3). The summed difference score was higher in patients with cardiac death (2.2 +/- 2.3 vs 1.1 +/- 1.3, P = .008), and fixed defects were more prevalent in patients with severe complications (57% vs 21%, P = .01). In the Kaplan-Meier survival plot analysis, severe complications were more likely in patients with fixed defects (P = .01) or ejection fraction lower than 60% ( P = .01). CONCLUSIONS: Prognostic information from myocardial perfusion SPECT and radionuclide angiography has limited clinical significance with regard to cardiac death in adult patients with HC. However, the presence of fixed defects and lower ejection fraction in these patients has an adverse prognostic meaning for severe complications.

Reproducibility of the ventricular synchronization parameters assessed by multiharmonic phase analysis of radionuclide angiography in the normal heart.

Radionuclide angiography (RNA) permits analysis of contractility and conduction abnormalities. We determined the parameters of normal ventricular synchronization, assessed the reproducibility of the technique, and compared first harmonic (1H) and third harmonic (3H) analysis. Forty-four normal subjects (28 men and 16 women) were studied. RNA was performed in left anterior oblique (LAO) and left lateral (LL) projections. The onset (To), mean time (Tm), total contraction time (Tt) for right ventricle (RV) and left ventricle (LV), interventricular time (T(RV-LV) = Tm(LV - Tm(RV)) in LAO, and the apex-to-base time (T(a-b)) in LL were measured on the histograms of the time-activity curve. Reproducibility (R) was tested by studying 26 consecutive patients with two successive RNAs. RV starts contracting 25 ms before LV (To(RV) = 29 +/- 37 ms; To(LV) = 54 +/- 39 ms; mean +/- SD) with a 37 ms longer total contraction time. T(RV-LV) is 3 +/- 16 ms. In LL projection, apex and base contract synchronously: T(a-b) = 2 +/- 16 ms. 3H analysis enlarges all duration parameters (To, Tm and Tt), but does not alter synchronization (deltaT(a-b) and deltaT(RV-LV) between 1H and 3H <1%, p = NS). Reproducibility of the duration (T(tLV) and T(tRv)) and synchronization parameters (T(a-b) and T(RV-LV)) is high (R < or = 2.2%). In conclusion, the simultaneous contraction of right and left ventricles and of apex and base can be quantified by RNA phase analysis with high reproducibility. These results, consistent with published electrophysiological data, provide the basis for further non-invasive investigations of ventricular resynchronization in patients with basal electrical or mechanical asynchrony.

Coded aperture nuclear scintigraphy: a novel small animal imaging technique.

We introduce and demonstrate the utility of coded aperture (CA) nuclear scintigraphy for imaging small animals. CA imaging uses multiple pinholes in a carefully designed mask pattern, mounted on a conventional gamma camera. System performance was assessed using point sources and phantoms, while several animal experiments were performed to test the usefulness of the imaging system in vivo, with commonly used radiopharmaceuticals. The sensitivity of the CA system for 99mTc was 4.2 x 10(3) cps/Bq (9400 cpm/microCi), compared to 4.4 x 10(4) cps/Bq (990 cpm/microCi) for a conventional collimator system. The system resolution was 1.7 mm, as compared to 4-6 mm for the conventional imaging system (using a high-sensitivity low-energy collimator). Animal imaging demonstrated artifact-free imaging with superior resolution and image quality compared to conventional collimator images in several mouse and rat models. We conclude that: (a) CA imaging is a useful nuclear imaging technique for small animal imaging. The advantage in signal-to-noise can be traded to achieve higher resolution, decreased dose or reduced imaging time. (b) CA imaging works best for images where activity is concentrated in small volumes; a low count outline may be better demonstrated using conventional collimator imaging. Thus, CA imaging should be viewed as a technique to complement rather than replace traditional nuclear imaging methods. (c) CA hardware and software can be readily adapted to existing gamma cameras, making their implementation a relatively inexpensive retrofit to most systems.

Gender-related imaging issues in assessment of coronary artery disease by nuclear techniques.

Heart disease is a major threat to women's health. However, noninvasive evaluation of women for the presence of significant heart disease is often problematic. Cardiovascular nuclear tests interrogate different consequences of physiologically significant coronary artery disease (CAD). Myocardial perfusion imaging supplies information about regional myocardial blood flow. Radionuclide angiocardiography provides information about ejection fraction and regional wall motion. Infarct and metabolic imaging yield information about myocardial viability. This article briefly discusses the concepts and radionuclides involved in cardiovascular nuclear testing and reviews published studies as they relate to assessment of coronary artery disease in women. Myocardial perfusion imaging is a reasonable test for detection of coronary artery disease in women, especially when attenuation artifacts from breast tissue are taken into account. Intravenous dipyridamole stress provides comparable overall accuracy in women and men although women reportedly have a higher incidence of side effects; gender-specific data have not been reported for adenosine. Sufficient gender-specific data are also not currently available for either 99mTc or positron-emitting perfusion tracers. Exercise radionuclide angiography can help determine the probability of significant left main or severe three vessel disease but provides only limited prognostic information in women with CAD. Thus in women, although choice of testing using nuclear techniques depends in part on local experience and expertise, myocardial perfusion imaging appears preferable to radionuclide angiocardiography for detection of significant CAD. To determine the most accurate methods to evaluate women for the presence of significant CAD, all current and future studies of diagnostic testing for CAD should analyze data separately for women and men.

Fourier phase analysis of first-pass data: noninvasive detection of pulmonary sequestration.

Nuclear medicine Fourier phase analysis of first-pass data was used to evaluate blood flow to cystic lung masses in two children suspected of having pulmonary sequestrations. In both cases, the Fourier images provided a rapid, noninvasive, inexpensive analysis of the blood supply to the masses and permitted identification of the masses as pulmonary sequestrations. The analysis does not depend on the location of the mass and demonstrates the location of systemic rather than pulmonic arterial blood supply to the mass. In one case, Fourier analysis identified a second source of systemic blood supply not visible with other imaging modalities. Preoperative assessment of a cystic lung mass using Fourier analysis enables noninvasive classification of the mass as a pulmonary sequestration with systemic blood supply and aids the surgeon in resection.

Rest-redistribution thallium-201 scintigraphy to determine myocardial viability early after myocardial infarction.

OBJECTIVES: This study attempted to determine the utility of early rest-redistribution thallium-201 imaging in detecting residual myocardial viability after myocardial infarction. BACKGROUND: The early detection of myocardial viability after myocardial infarction would have clinical relevance. METHODS: Thirty-one patients with acute myocardial infarction had early (mean [+/- SD] 2 +/- 1 day) rest-redistribution thallium-201 imaging followed by radionuclide and coronary angiography. Late studies included stress-redistribution-reinjection thallium-201 imaging or radionuclide angiography, or both. Viability was defined by the rest thallium-201 scan as an initial mild rest defect or any defect that demonstrated redistribution. RESULTS: Group 1 (n = 15) was predicted to have viable and Group 2 (n = 16) nonviable myocardium in the infarct zone. Group 1 patients were more likely to have a patent infarct-related artery (15 of 15 vs. 10 of 16, p < 0.03), higher initial ejection fraction (61 +/- 12% vs. 53 +/- 9%, p < 0.05), higher infarct wall motion score (p < 0.0001) and fewer abnormal thallium-201 segments (p < 0.0001). On follow-up studies, ejection fraction improved in Group 1 (from 57 +/- 13% to 66 +/- 10%, p < 0.05, n = 9) and deteriorated in Group 2 (from 53 +/- 10% to 46 +/- 8%, p < 0.05, n = 13). On late stress testing with thallium-201 reinjection, Group 1 patients had fewer abnormal segments (p < 0.03) and higher infarct zone counts during exercise (p < 0.05) and after reinjection (p < 0.05) than Group 2 patients. CONCLUSIONS: If confirmed by larger studies, early rest-redistribution thallium-201 imaging may be a useful technique for identifying residual viability after myocardial infarction.

Gender differences in the noninvasive evaluation and management of patients with suspected coronary artery disease.

OBJECTIVE: To determine if gender-based differences exist in the post-test management and clinical outcome of patients with clinically suspected coronary artery disease who have stress electrocardiographic or myocardial perfusion imaging evaluation. DESIGN: Retrospective cohort study. SETTING: University medical center. PATIENTS: From a cohort of 3975 middle-aged patients referred for outpatient stress testing, 840 (47% women) were evaluated noninvasively for clinically suspected coronary artery disease. MEASUREMENTS: The rates of subsequent diagnostic procedures and the incidence of subsequent coronary revascularization, myocardial infarction, or cardiac death were determined for women and men. RESULTS: Pretest cardiac risk profiles were similar, except hypertension and hypercholesterolemia were more frequent in women. Atypical angina was more common in women than in men (57.5% compared with 44.5%, respectively; P < 0.001). Rates of initial test positivity (defined as exercise-induced horizontal or downsloping ST-segment depression > or = 1.0 mm or > or = 1 reversible thallium-201 defect) were similar in women and men. Compared with men, most women with an initial positive test result had no additional coronary artery disease evaluation (62.3% compared with 38.0%; P = 0.002). Coronary revascularization procedures were done more frequently in men (4.9% [22 of 449] compared with 2.0% [8 of 391]; P = 0.03). Cardiac death or myocardial infarction occurred more often in women during 2 years of follow-up (6.9% [27 of 391] compared with 2.4% [11 of 449]; P = 0.002). CONCLUSIONS: Women with suspected coronary artery disease have fewer additional diagnostic tests than men after an initial abnormal noninvasive stress test result, even though the incidence of typical angina, cardiac risk factors, and initial diagnostic test positivity rates are similar.

Testicular circulatory isolation in man: comparison of radionuclide angiography with Doppler evaluation.

Testicular circulatory isolation (TCI) holds promise as a method to avoid drug-induced infertility in male patients about to receive cancer chemotherapy. Complete exclusion of blood flow to the testicle is essential to the success of this technique. We have compared the hand-held Doppler probe and radionuclide angiography (technetium-99m pertechnetate) as monitors of testicular blood flow in 10 patients subjected to unilateral TCI. When Doppler evaluation indicated that testicular circulation had been interrupted, the radionuclide angiogram uniformly confirmed and quantified this conclusion. These results validate the hand-held Doppler as an appropriate tool for assessing testicular blood flow in patients undergoing TCI.