Trends in magnetic resonance and computed tomography angiography utilization among Medicare beneficiaries between 2013 and 2020.

PURPOSE: To evaluate relative and absolute utilization trends and practice patterns in the United States for MRA and CTA. METHODS: Using Medicare Part B physician payment databases (2013-2020), MRA and CTA interpreting physicians and exams were identified using the unique MRA and CTA Healthcare Common Procedure Coding System codes. The number of exams, physicians, demographics, use of contrast, and payments were summarized annually and analyzed to evaluate trends before and during the first year of the COVID-19 pandemic. RESULTS: From 2013 to 2019, the annual number of MRA exams performed decreased by 17.9 %, while the number of CTA exams increased by 90.3 %. The number of physicians interpreting MRA decreased in both hospital (-17.2 %) and outpatient (-7.5 %) environments. The number of physicians interpreting CTA increased in both hospital (+29.4 %) and outpatient (+54.3 %) environments. During the first year of the COVID-19 pandemic, MRA utilization decreased across all imaging environments by 25.0 % whereas CTA only decreased by 5.5 %. Intracranial MRA studies were most often performed without contrast, while contrast use for neck MRA was performed at similar rates as non-contrast exams. CONCLUSION: The overall utilization of MRA and the number of interpreting physicians are decreasing. On the other hand, CTA use and its number of interpreting physicians are increasing. During the first year of the COVID-19 pandemic, use of both MRA and CTA decreased, but the utilization of MRA decreased at five times the rate of CTA.

Effects of transcytolemmal water exchange on the assessment of myocardial extracellular volume with cardiovascular MRI.

Quantitative analysis of the myocardial interstitial space is gaining increased interest as a biomarker in the MRI and clinical cardiovascular communities. To investigate the effect of water exchange on the calculation of myocardial extracellular volume (ECV), we employed two tissue models: the standard ECV two-point model (SM) and the shutter speed model (SSM). Twenty individuals (18 men and two women; age 61.9 ± 10.3 years) underwent MRI at 1.5 T with pre-contrast and post-contrast dynamic T1 quantification. Means, standard deviations and ranges for SM and SSM model parameters were calculated. Infarct and viable myocardial model parameters as well as apparent ECV values calculated with the SM and SSM were statistically compared. Viable ECV(SM) remained temporally constant (27.3-28.0%: P = 0.5) and infarcted myocardial ECV(SM) changed significantly (49.3-58.8%; P < 0.001), reaching a steady-state value after 15 min. The intracellular lifetime of water was three times greater in infarcted myocardium when compared with viable myocardium (τi: 66.6 ± 115 versus 208.7 ± 72.7 ms) and accompanied a twofold increase in ECV (ECV(SSM) : 30.3 ± 11.1 versus 71.0 ± 13.1%; P < 0.001). There was a consistent significant difference in ECV values of infarcted myocardium at different timepoints between the SM and SSM, but not viable myocardium, presumably due to slower water exchange. In summary, we found a significant change in apparent ECV and water exchange in infarcted myocardium when compared with viable myocardium. This was visualized by changes in dynamic contrast enhanced curve shapes and quantified using the SSM as not only an increase in apparent ECV but also a decrease in water exchange.

Magnetic resonance susceptibility weighted phase imaging for the assessment of reperfusion intramyocardial hemorrhage.

PURPOSE: To quantitatively investigate myocardial phase in multiple-gradient-echo images to determine normal phase angle ranges as a function of echo time and anatomical position and then compare phase values from patients with myocardial infarction with those normal ranges to determine the feasibility of intramyocardial hemorrhage detection. METHODS: Fifteen normal control and 11 patients with reperfused myocardial infarction participated in this prospective study. A 1.5 T magnetic resonance system was used to perform volumetric CINE, high-pass filtered (HPF) phase, T2-weighted, T2*-weighted and late gadolinium-enhanced infarct imaging at four times points after myocardial infarction. HPF-phase analyzed using a 16-segment model was compared with late gadolinium-enhanced infarct imaging and T2* measurements. RESULTS: Myocardial HPF-phase angle in the normal control group was small (-0.008 ± 0.027 radians). There was a difference between anatomical segments, with less variation in septal segments compared with cyclic variations in non-septal segments. Abnormal phase was only shown in myocardial segments with transmural late gadolinium-enhanced and microvascular obstruction consistent with intramyocardial hemorrhage. There were six studies from three patients (seven segments at 3 days, five segments at follow-up) with HPF-phase outside of normal range indicative of intramyocardial hemorrhage. CONCLUSION: Myocardial HPF-phase angle is normally small and varies by anatomical myocardial segment. intramyocardial hemorrhage causes a phase decrease beyond normal variations.

Myocardial fat deposition after left ventricular myocardial infarction: assessment by using MR water-fat separation imaging.

PURPOSE: To prospectively investigate the prevalence of fat deposition in chronic myocardial infarction (MI) by using magnetic resonance (MR) fat-water separation imaging with sampling of the entire left ventricular (LV) myocardium. A subsidiary aim was to determine the relationship between LV fat deposition and scar characteristics, as well as regional and global cardiac functional parameters. MATERIALS AND METHODS: Twenty-five patients with LV MI were evaluated in this prospective institutional review board-approved, Health Insurance Portability and Accountability Act-compliant study after they provided written informed consent. A 1.5-T MR system was used to perform volumetric cine, fat-sensitive, and late gadolinium-enhanced (LGE) infarct imaging. Water-fat separation was performed by using a three-point Dixon reconstruction from in- and opposed-phase black-blood gradient-echo images. Fat deposition location was compared with LGE infarct imaging by using a 17-segment model. Global and regional functional variables, LGE volumes, and fat deposition were compared by using the Pearson correlation, Student t test, and multiple regression. RESULTS: A fat deposition prevalence of 68% was found in areas of chronic MI. The patients with fat deposition had larger infarctions (30.0 mL +/- 15.1 [standard deviation] vs 14.8 mL +/- 6.1; P = .002), decreased wall thickening (2.3% +/- 20.0 vs 37.8% +/- 34.4; P = .003), and impaired endocardial wall motion (2.9 mm +/- 2.0 vs 5.8 mm +/- 2.6; P = .007). The volume of fat deposition was correlated with infarct volume, LV ejection fraction, LV end-diastolic volume index, and LV end-systolic volume index. CONCLUSION: There is a high prevalence of fat deposition in healed MI. It is associated with post-infarction characteristics including infarct volume, LV mass, wall thickness, wall thickening, and wall motion.

Recent myocardial infarction: assessment with unenhanced T1-weighted MR imaging.

The purpose of the study was to prospectively evaluate a T1-weighted technique for detection of myocardial edema resulting from recent myocardial infarction (MI) or intervention. This study was HIPAA compliant and institutional review board approved. Fifteen men and one woman (mean age, 57.8 years+/-11.5 [standard deviation]) were examined with T1-weighted magnetic resonance (MR) imaging and inversion-recovery cine pulse sequence in two groups, recent MI and chronic MI, and gave informed consent. T1 relaxation times of MI and adjacent myocardium were compared (Student t test and correlation analysis). In patients with recent MI, areas of myocardial edema were well depicted with T1-weighted MR imaging. T1 relaxation times of recent infarcts were longer than those of older MIs (925 msec+/-169 vs 551 msec+/-107, P<.001). From local edema, T1 relaxation time of infarcted myocardium is increased, may remain elevated for 2 months, and enables imaging with T1-weighted techniques.