Comparison of two single-breath-held 3-D acquisitions with multi-breath-held 2-D cine steady-state free precession MRI acquisition in children with single ventricles.

BACKGROUND: Breath-held two-dimensional balanced steady--state free precession cine acquisition (2-D breath-held SSFP), accelerated with parallel imaging, is the method of choice for evaluating ventricular function due to its superior blood-to-myocardial contrast, edge definition and high intrinsic signal-to-noise ratio throughout the cardiac cycle. OBJECTIVE: The purpose of this study is to qualitatively and quantitatively compare the two different single-breath-hold 3-D cine SSFP acquisitions using 1) multidirectional sensitivity encoding (SENSE) acceleration factors (3-D multiple SENSE SSFP), and 2) k-t broad-use linear acceleration speed-up technique (3-D k-t SSFP) with the conventional 2-D breath-held SSFP in non-sedated asymptomatic volunteers and children with single ventricle congenital heart disease. MATERIALS AND METHODS: Our prospective study was performed on 30 non-sedated subjects (9 healthy volunteers and 21 functional single ventricle patients), ages 12.5 +/- 2.8 years. Two-dimensional breath-held SSFP with SENSE acceleration factor of 2, eight-fold accelerated 3-D k-t SSFP, and 3-D multiple SENSE SSFP with total parallel imaging factor of 4 were performed to evaluate ventricular volumes and mass in the short-axis orientation. Image quality scores (blood myocardial contrast, edge definition and interslice alignment) and volumetric analysis (end systolic volume, end diastolic volume and ejection fraction) were performed on the data sets by experienced users. Paired t-test was performed to compare each of the 3-D k-t SSFP and 3-D multiple SENSE SSFP clinical scores against 2-D breath-held SSFP. Bland-Altman analysis was performed on left ventricle (LV) and single ventricle volumetry. Interobserver and intraobserver variability in volumetric measurements were determined using intraclass coefficients. RESULTS: The clinical scores were highest for the 2-D breath-held SSFP images. Between the two 3-D sequences, 3-D multiple SENSE SSFP performed better than 3-D k-t SSFP. Bland-Altman analysis for volumes indicated that variability was more between 3-D k-t SSFP and 2-D breath-held SSFP acquisitions than between 3-D multiple SENSE SSFP and 2-D breath-held SSFP acquisitions. In the non-sedated population, interslice alignment scores were better for 3-D k-t SSFP and 3-D multiple SENSE SSFP than 2-D breath-held SSFP. The blood-myocardial contrast and edge definition scores were better for 2-D breath-held SSFP than 3-D k-t SSFP and 3-D multiple SENSE SSFP. Scan duration was shorter for 3-D acquisition sequences compared to the 2-D breath-held stack. CONCLUSION: Three-dimensional k-t SSFP and 3-D multiple SENSE for ventricular volumetry release the constraints of multiple breath-holds in children and overcome problems related to interslice misalignment caused by inconsistent amplitude of breathing. Three-dimensional multiple SENSE SSFP performed better in our pediatric population than 3-D k-t SSFP. However, these 3-D sequences produce lower-quality diagnostic images than the gold standard 2-D breath-held SSFP sequence.

Effect of variation of portal venous blood flow on radiofrequency and microwave ablations in a blood-perfused bovine liver model.

PURPOSE: To assess whether there is a significant difference in the effect of incremental changes of portal venous blood flow rates on the size of radiofrequency (RF) versus microwave (MW) ablation lesions in an ex vivo blood-perfused bovine liver model. MATERIALS AND METHODS: This study was exempt from approval by the Institutional Animal Care and Use Committee. Sixty ablations (30 MW and 30 RF ablations) were performed ex vivo in 15 bovine livers perfused with autologous blood via the portal vein at 60, 70, 80, 90, and 100 mL/min per 100 g of liver tissue (three livers were used for each flow rate). Long-axis diameter (LAD), short-axis diameter (SAD), and volume were measured for each ablation lesion. A general linear mixed model was used to examine the effect of location, ablation device, and flow rate on LAD, SAD, and volume. Results were considered to indicate a significant difference at P less than .05. RESULTS: Location was not a significant predictor of LAD, SAD, or volume (P ≥ .4). The slope of the relationship between flow rate and LAD, SAD, and volume was significantly different according to ablation device (P < .0001). For RF ablation lesions, the mean LAD, SAD, and volume demonstrated a significant inverse relationship with flow rate, while the measurements for MW ablation did not change with variation in flow rates. CONCLUSION: The size of RF ablation lesions is highly variable, with a significant inverse relationship to the rate of portal venous blood flow. Conversely, the size of MW ablation lesions is unaffected by changes in portal venous blood flow. The consistency of the size of MW ablation lesions could translate into a higher local tumor eradication rate than that reported with RF ablation.