Kevin W. Moser

Radiation Dose to Patients From Cardiac Diagnostic Imaging

The volume of cardiac diagnostic procedures involving the use of ionizing radiation has increased rapidly in recent years. Whereas in 1990, fewer than 3 million nuclear cardiology studies were performed in the United States, by 2002 this figure more than tripled to 9.9 million.1 Cardiac computed tomographic (CT) volume doubled between 2002 and 2003, to 485 000 cases,2 and has continued to grow since then. The volume of procedures performed in cardiac catheterization labs increased from 2.45 million in 1993 to 3.85 million in 2002.3 The powerful diagnostic and risk-stratification data provided by these procedures play a central role in clinical cardiology and have contributed to the decrease in morbidity and mortality from coronary heart disease. Nevertheless, performance of any diagnostic test requires a careful assessment of the risks and benefits of the test and optimization of protocols to minimize risks to patients, staff members, and the public. Procedures that utilize ionizing radiation should be performed in accordance with the As Low As Reasonably Achievable (ALARA) philosophy. Thus, physicians ordering and performing cardiac imaging should be very familiar with the dosage of radiation from cardiac diagnostic tests and ways in which dose can be minimized. In this report we discuss the measurement of radiation and the dosimetry of commonly performed cardiac diagnostic imaging tests, including nuclear scintigraphy, CT for calcium scoring and coronary angiography (CTCA), and conventional coronary angiography (CCA). For each modality, we address the terminology and methodology used to quantify radiation received by patients, doses to patients with typical protocols, and dose-reduction techniques. Biological effects of ionizing radiation can be classified as deterministic or stochastic. Deterministic effects such as skin injuries and cataract formation occur predictably when dose exceeds a certain threshold, whereas stochastic effects such as cancer incidence and germ cell mutations occur with …

Coronary calcium screening in asymptomatic patients as a guide to risk factor modification and stress myocardial perfusion imaging

Background. Previous studies have demonstrated a correlation between the extent of coronary artery calcification (CAC) and atherosclerotic plaque. As a result, CAC screening could be useful in predicting cardiovascular risk in individuals in whom atherosclerosis is developing. One possible method of detecting and quantifying CAC is by x-ray computed tomography, which potentially allows one to stratify patients into groups requiring risk factor modification or follow-up testing such as myocardial perfusion single photon emission computed tomography (SPECT).Methods and Results. This study was designed to evaluate the clinical utility of multidetector computed tomography (MDCT) in a cardiology practice setting. A retrospective analysis was performed on data from 794 asymptomatic patients who underwent CAC screening over an 8-month period. On the basis of the CAC score and physician consultation, 102 patients underwent subsequent myocardial perfusion SPECT imaging. A substudy was also conducted in 306 patients to measure the interscan variability of MDCT across different CAC score ranges. CAC was detected in 422 of 794 patients. Of these, the CAC was moderate (Agatston score = 101–400) in 14% and severe (>400) in 9%. Patients with 3 or more cardiac risk factors were most likely to exhibit moderate to severe CAC. In myocardial perfusion SPECT testing, no patient with an Agatston score lower than 100 had an abnormal study. In contrast, 41% of patients with severe CAC had an abnormal SPECT study. In the reproducibility substudy the minimal CAC group had the largest variability (86.0%) whereas the severe CAC group had the lowest variability (9.5%).Conclusion. CAC screening with MDCT is justified for asymptomatic patients with 3 or more cardiac risk factors. However, risk factor assessment is poor at predicting which individuals will have CAC if fewer risk factors are present. In terms of the interscan variability, MDCT is capable of following changes in CAC for patients with Agatston scores greater than 100. Finally, this study demonstrated that an Agatston score of 400 is a logical threshold to initiate follow-up myocardial perfusion SPECT testing. (J Nucl Cardiol 2003;10:590-8.)

Drinking games, tailgating, and pregaming: precollege predictors of risky college drinking

Abstract Background: The transition from high school to college is a critical period for developing college drinking habits. Hazardous alcohol consumption increases during this period, as well as participation in drinking games, pregaming, and tailgating. All of these risky drinking practices are associated with higher levels of intoxication as well as an increased risk of alcohol-related problems. Objective: The current study aimed to evaluate pre-college predictors (personality, social norms, and beliefs reflecting the internalization of the college drinking culture [ICDC]) of estimated peak BAC (pBAC) reached during drinking games, pregaming, and tailgating, as well as pBAC and alcohol-related problems during the first 30 days of college. Methods: Participants (n = 936) were incoming freshmen at a large university who completed a baseline assessment prior to college matriculation and a follow-up assessment after they had been on campus for 30 days. Results: Using path analysis, ICDC was significantly associated with pBAC reached during the three risky drinking practices. ICDC had an indirect effect on both pBAC and alcohol-related problems via pBAC from drinking games, pregaming, and tailgating. Hopelessness and sensation seeking were significantly related to alcohol use outcomes. Conclusion: Precollege perceptions of the college drinking culture are a stronger predictor of subsequent alcohol use than social norms. Interventions that target these beliefs may reduce peak intoxication and associated harms experienced during the first 30 days of college.

Optimization of patient dose and image quality with z-axis dose modulation for computed tomography (CT) head in acute head trauma and stroke

The purpose of this study is to retrospectively analyze the effect of z-axis modulation for CT head protocols on patient dose and image quality in patients with acute head trauma and stroke. The study was approved by the Institutional Review Board. We retrospectively evaluated the effect of dose modulation on unenhanced CT head examinations in patients with acute head trauma and stroke. Two series of 100 consecutive studies were reviewed: 100 studies performed without dose modulation, 100 studies performed with z-axis dose modulation. Multidetector 16-section CT was performed sequentially and axial 5-mm-thick slices were obtained from base of skull to vertex. With z-axis dose modulation, the same tube current range was maintained, but a computer algorithm altered the tube current applied to each CT section. For each examination, the weighted volume CT dose index (CTDI (vol)) and dose-length product (DLP) were recorded and noise was measured. Each study was also reviewed for image quality by two independent, blinded readers. The variables (CTDI (vol) and DLP, image quality, and noise) in the two groups were compared by using student t test and Wilcoxon rank-sum test. For unenhanced CT head examinations, the CTDI (vol) and DLP, respectively, were reduced by 35.8% and 35.2%, respectively, by using z-axis dose modulation. Image quality and noise were unaffected by the use of this dose modulation technique (P < 0.004). Utilization of z-axis modulation technique for CT head examination in patients with acute head trauma and stroke offers significant radiation dose reduction while image quality is optimally maintained.

Single injection, inspiratory/expiratory high-pitch dual-source CT angiography for median arcuate ligament syndrome: Novel technique for a classic diagnosis

This article discusses a novel technique for dynamic imaging of median arcuate ligament syndrome utilizing low dose CT technology and a single contrast injection.

Vestibular pneumolabyrinth: why assessment with temporal bone computed tomography utilizing dynamic focal spot mode is important for the diagnosis

We present an interesting and relatively uncommon case of vestibular pneumolabyrinth in a young child post-trauma. His initial clinical exam and imaging studies of the head and cervical spine were negative. He subsequently developed nystagmus and a dedicated temporal bone study demonstrated a subtle fracture and vestibular pneumolabyrinth. Temporal bone fractures can be difficult to appreciate, and therefore, associated findings of fluid in the middle ear, stapes dislocation, or vestibular pneumolabyrinth must be carefully evaluated. Temporal bone computed tomography is a high resolution study, utilizing dynamic focal spot mode which leads to increased sampling and resolution, thereby reducing aliasing artifacts but a longer scan time and increased radiation dose. CT head and cervical spine normally obtained without using this technique leads to aliasing artifacts where even the normal endolymph in the inner ear structures appear hypodense mimicking pneumolabyrinth, thereby obscuring true pneumolabyrinth. It is important to be aware of this finding and technique-related artifact, if a temporal bone injury is suspected, to ensure an earlier diagnosis and optimum management.

A new Bayesian reconstruction method to improve the accuracy and reduce the acquisition time of GE-68 attenuation maps for cardiac PET

Abstract Background: Ge-68 rod sources are utilized in PET scanners for measuring non-uniform patient attenuation. To compensate for insufficient signal in larger patients or shortened acquisition time, attenuation maps (AM) are segmented prior to attenuation correction. Although segmented FBP (SFBP) is widely utilized, it can be of limited value when the projection data has significant noise. We investigate a previously validated Bayesian reconstruction method (BITGA) from cardiac SPECT to improve the accuracy of AM estimates in low count PET studies acquired with significantly reduced scan time. Methods: BITGA uses a prior function that preferentially weights the current attenuation coefficient estimate at each pixel toward the value for soft-tissue region. Lung, air and bone regions are minimally weighted allowing a data-driven solution. The prior function was optimized for the soft-tissue (water) narrow-beam linear attenuation coefficient at 511 keV (0.097 cm-1). The data was created from smoothing and normalizing projection data to a high-count reference scan. Ge-68 transmission scans of 1 and 4-minute of a female anthropomorphic phantom were acquired on a CTI ACCEL™ LSO PET scanner and reconstructed by FBP, SFBP and BITGA. We examined profiles across the phantom chest and calculated the mean difference of attenuation coefficients (MDAC) between both scans. A 2-minute scan of patient data was studied to evaluate the noise-reduction capability of BITGA in a large patient (BMI=49). Results: In the phantom study, the 1-minute scan increased approximately by 2 times the projection noise components of the 4-minute scan. The MDACs of 1-minute scan were 0.020/cm (FBP), 0.0038/cm (SFBP), 0.0018/cm (BITGA) (p Conclusions: BITGA is a promising new method for accurately reconstructing the Ge-68 AM acquired with significantly reduced time for cardiac PET compared with the current methods of FBP and SFBP. Download : Download full-size image