Multidetector CT urography: experimental analysis of radiation dose reduction in an animal model

The purpose of this study was to evaluate the possibility of reducing X-ray exposure during multidetector CT urography (MDCTU) considering image quality using a porcine model. MDCTU was performed in eight healthy pigs. Scanning was conducted using a gradual reduction of the tube current-time product at 120 kV [200–20 mAs (eff.) in ten steps]. Three blinded observers independently evaluated the image data for anatomic detail, subjective image quality, and subjective image noise. Overall image quality was compared to milliampere-second settings and radiation dose. Objective noise measurements were assessed. Noise measurements in patients were also performed to verify the comparabilty of the animal model. Adequate image quality allowing for detailed visualization of the upper urinary tract was obtained when the tube current-time product was decreased to 70 eff. mAs at 120 kV. Image noise did not impair image quality to a relevant degree using these parameters. There was high agreement among the observers (ICC = 0.95). In the animal experiments, reduced-dose MDCTU produced good image quality. A maximum current-time product reduction to 70 eff. mAs at 120 kV (CTDI_vol = 5.3 mGy) proved to be feasible, thereby offering an advantageous dosage reduction. The study provides a basis for the development of reduced-dose MDCTU protocols in humans.     

Characterization of the peri-infarction zone using T2-weighted MRI and delayed-enhancement MRI in patients with acute myocardial infarction

To characterize the peri-infarction zone using T2-weighted (T2w) magnetic resonance imaging (MRI) and infarct size on delayed enhancement (DE) MRI in patients with acute myocardial infarction (AMI). In 65 patients, short-axis T2w and DE MRI images were acquired 5 ± 3 d after AMI. The MRI was analyzed using a threshold method defining infarct size on DE MRI and edema on T2w MRI as areas with signal intensity larger than +2 SD above remote normal myocardium. The peri-infarction zone was calculated as the difference between the size of edema and the infarct size. The size of edema on T2w MRI (31.3 ± 13.4% of LV area) was larger than the infarct size on DE MRI (20.3 ± 10.4% of LV area, p< 0.0001). The size of the peri-infarction zone was 11.0 ± 10.0% of the LV area. Good correlation was found between infarct size on DE MRI and peak creatine kinase (CK) isoenzyme MB (r = 0.65, p< 0.0001), but there was no correlation between the size of the peri-infarction zone and CK MB (r = 0.05, p = 0.67). The peri-infarction zone was larger in patients with an infarct size <28% of the LV area (12.6 ± 10.0% LV area) compared with patients with an infarct size ≥28% of the LV area (6.7 ± 9.0% of the LV area, p< 0.05). The peri-infarction zone does not correlate with enzymatic parameters of infarct size and is substantially larger in small infarcts, indicating viable myocardium.This study was funded in part by Pinguin-Stiftung, Duesseldorf, Germany and by Schering Company, Berlin, Germany.     

Predictive value of B-type natriuretic peptide levels in patients with paroxysmal and persistent atrial fibrillation undergoing pulmonary vein isolation

Background  

Atrial fibrillation (AF) is the most common cardiac arrhythmia reducing the health-related quality of life. Radiofrequency catheter ablation (CA) became the therapy of choice in patients with drug-resistant AF with success rates between 30% and 86%. However, CA remains a challenging intervention with major complications in about 5% of cases. Therefore, stratification into high and low success patient groups would be helpful. The aim of this study was to investigate the predictive value of B-type natriuretic peptide (BNP) on the outcome of pulmonary vein isolation (PVI) in patients with paroxysmal (PAF) and persistent (Pers-AF) atrial fibrillation.     

Acute myocardial infarction: evaluation with first-pass enhancement and delayed enhancement MR imaging compared with 201Tl SPECT imaging

PURPOSE: To evaluate acute myocardial infarction by using first-pass enhancement (FPE) and delayed enhancement (DE) magnetic resonance (MR) imaging compared with thallium 201 ((201)Tl) single photon emission computed tomography (SPECT). MATERIALS AND METHODS: Contrast material-enhanced FPE MR, inversion-recovery DE MR, and rest-redistribution (201)Tl SPECT images were obtained in 60 consecutive patients (53 men, seven women; mean age [+/- SD], 56 years +/- 13; range, 30-78 years) at 6 days +/- 3 after reperfused first myocardial infarction. Presence of microvascular obstruction was determined on FPE MR images. Infarct size was defined on DE MR images as percentage of left ventricular (LV) area and compared with uptake defect on redistribution (201)Tl SPECT images. Differences in continuous data were analyzed with Student t test. Linear regression and Bland-Altman analysis were used to compare measurements of infarct size. RESULTS: Mean infarct size was not significantly different between DE MR imaging (20.7% +/- 11.5% of LV area) and (201)Tl SPECT (19.4% +/- 14.3% of LV area; P =.26); good correlation (r = 0.73; P <.001) and agreement were found, with a mean difference of +1.3% +/- 9.8% of LV area. (201)Tl SPECT failed to depict infarct in six (20%) of 30 patients with inferior myocardial infarction (mean size, 6.4% +/- 5.7% of LV area on DE MR images), whereas DE MR images showed the infarct in all patients (P <.01). FPE MR images depicted microvascular obstruction in 23 (38%) of 60 patients; these patients had larger infarctions at DE MR imaging than did patients without microvascular obstruction (30.4% +/- 9.0% vs 15.1% +/- 8.4% of LV area, P <.001). (201)Tl SPECT showed larger infarcts in patients with microvascular obstruction (26.7% +/- 16.2% vs 15.0% +/- 11.2% of LV area, P <.01). CONCLUSION: Good correlation and agreement with (201)Tl SPECT indicate DE MR imaging may be used to estimate infarct size 6 days after reperfused acute myocardial infarction. DE MR imaging is more sensitive for detection of inferior infarction than is (201)Tl SPECT. Patients with microvascular obstruction on FPE MR images have larger infarcts.     

MRI of the coronary vessel wall at 3 T: comparison of radial and cartesian k-space sampling

OBJECTIVE: The purpose of our study was to compare the quality of 3D gradient-echo images obtained using radial versus cartesian k-space sampling at 3 T. CONCLUSION: This study shows that the quality of coronary vessel wall imaging of the right coronary artery with radial k-space sampling in 3D turbo field-echo sequences is superior to cartesian k-space sampling at 3 T. Radial k-space sampling at 3 T makes it possible to combine low motion artifact susceptibility with high signal-to-noise ratio.     

Prediction of left ventricular remodeling and analysis of infarct resorption in patients with reperfused myocardial infarcts by using contrast-enhanced MR imaging

PURPOSE: To prospectively evaluate the accuracy of clinical and cardiac magnetic resonance (MR) imaging parameters for predicting left ventricular (LV) remodeling by using follow-up imaging as reference standard, and to prospectively evaluate infarct resorption in patients with reperfused first myocardial infarcts. MATERIALS AND METHODS: The study was approved by the institutional ethics committee and all patients gave written informed consent. In 55 patients (48 men, seven women; mean age+/-standard deviation, 56 years+/-13), contrast material-enhanced and cine MR imaging were performed 5 days+/-3 and 8 months+/-3 after myocardial infarction (MI). Microvascular obstruction (MO) and infarct size were estimated at first-pass enhancement (FPE) and delayed enhancement (DE) MR, respectively. Remodeling was defined as an increase in LV end-diastolic volume index of 20% or higher at follow-up. Differences in continuous and categorical data were analyzed by using Student t test and Fischer exact test as appropriate. RESULTS: Patients with remodeling (n=13, 24%) had higher creatine kinase MB (P<.05), more anterior infarcts (P<.05), more often a reduced Thrombolysis in Myocardial Infarction flow (P<.05), larger infarct size at DE MR (P<.001), a greater extent of MO at FPE MR (P<.01), lower ejection fraction (P<.001) and higher LV end-systolic volume index (P<.01). Infarct size at DE MR was a powerful predictor for remodeling (odds ratio: 1.18, P<.001), demonstrating that the risk for remodeling increased 2.8-fold with each 10% increase in infarct size. Infarct size of 24% or more of LV area predicted remodeling with high sensitivity (92%), specificity (93%), and accuracy (93%). Infarct resorption was larger in patients with remodeling (P<.01). CONCLUSION: Infarct size 24% or more of the LV area constitutes an important threshold to predict remodeling. Patients with remodeling develop disproportionate infarct resorption.