Optimal Blood Suppression Inversion Time Based on Breathing Rates and Heart Rates to Improve Renal Artery Visibility in Spatial Labeling with Multiple Inversion Pulses: A Preliminary Study

Hemodynamic study of unenhanced magnetic resonance angiography using spatial labeling with multiple inversion pulses sequence: a phantom study

Background

This study sought to explore the functional relationship between displayed vascular length and blood suppression inversion time (BSP TI) and flow velocity in a phantom, and to provide a theoretical basis for quantitatively assessing vascular hemodynamic responses using unenhanced magnetic resonance angiography (MRA) and spatial labeling with multiple inversion pulses sequence (SLEEK).

Methods

A polyethylene catheter was laid in a long rectangular container filled with pork fat. The entrance of the catheter into the container was connected to a high-pressure syringe filled with normal saline. The high-pressure injector flow rates were set at 0.0, 0.2, 0.4, 0.8, 1.2, 1.6, 2.0, and 2.4 mL/s. SLEEK was performed 19 times for each flow rate with parameter BSP TI values of 50, 75, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900, 1,000, 1,100, 1,200, 1,300, 1,400, 1,600, and 1,800 ms. Maximum intensity projection was employed to reconstruct all SLEEK original images to determine the measurements of the displayed vascular lengths. A regression analysis was undertaken to assess the relationship between the displayed vascular lengths and BSP TI values for each flow rate, and to assess the relationship between the displayed vascular lengths and flow rates at each BSP TI.

Results

The displayed vascular length had a linear relationship with BSP TI for each flow rate (P<0.05) (R2=0.754, 0.941, 0.988, 0.988, 0.977, 0.966, and 0.982 for flow rates of 0.0, 0.2, 0.4, 0.8, 1.2, 1.6, and 2.0 mL/s, respectively). The displayed vascular length also had a linear relationship with flow rate for each BSP TI value (P<0.05) (R2 =0.914, 0.912, 0.834, 0.989, 0.980, 0.996, 0.992, 0.960, 0.975, 0.979, 0.982, 0.981, 0.976, and 0.993 for BSP TI 50, 75, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900, 1,000, and 1,100 ms, respectively). No significant linear relationship was found between displayed vascular length and flow rate when the BSP TI value was 1,200 ms (P>0.05).

Conclusions

Vascular displayed length has a linear relationship to BSP TI for flow ranges from 0.0 to 2.0 mL/s. Vascular displayed length has a linear relationship to flow rate for BSP TI values of 50 to 1,100 ms. Flow rate can be assessed in relation to vascular displayed length.

Non-contrast-enhanced abdominal MRA at 3 T using velocity-selective pulse trains

PURPOSE

Most existing non-contrast-enhanced methods for abdominal MR arteriography rely on a spatially selective inversion (SSI) pulse with a delay to null both static tissue and venous blood, and are limited to small spatial coverage due to the sensitivity to slow arterial inflow. Velocity-selective inversion (VSI) based approach has been shown to preserve the arterial blood inside the imaging volume at 1.5 T. Recently, velocity-selective saturation (VSS) pulse trains were applied to suppress the static tissue and have been combined with SSI pulses for cerebral MR arteriography at 3 T. The aim of this study is to construct an abdominal MRA protocol with large spatial coverage at 3 T using advanced velocity-selective pulse trains.

METHODS

Multiple velocity-selective MRA protocols with different sequence modules and 3D acquisition methods were evaluated. Sequences using VSS only as well as SSI+VSS and VSI+VSS preparations were then compared among a group of healthy young and middle-aged volunteers. Using MRA without any preparations as reference, relative signal ratios and relative contrast ratios of different vascular segments were quantitatively analyzed.

RESULTS

Both SSI+VSS and VSI+VSS arteriograms achieved high artery-to-tissue and artery-to-vein relative contrast ratios above aortic bifurcation. The SSI+VSS sequence yielded lower signal at the bilateral iliac arteries than VSI+VSS, reflecting the benefit of the VSI preparation for imaging the distal branches.

CONCLUSION

The feasibility of noncontrast 3D MR abdominal arteriography was demonstrated on healthy volunteers using a combination of VSS pulse trains and SSI or VSI pulse.

Non-contrast MR angiography using three-dimensional balanced steady-state free-precession imaging for evaluation of stenosis in the celiac trunk and superior mesenteric artery: a preliminary comparative study with computed tomography angiography

OBJECTIVE

Although non-contrast MR angiography (NC-MRA) is well established for the evaluation of renal artery stenosis, its usefulness in the evaluation of other abdominal aortic branches remains to be studied. This study aimed at evaluating the image quality and diagnostic accuracy of NC-MRA using a three-dimensional balanced steady-state free-precession sequence in identifying stenosis in the celiac trunk (CTR) and superior mesenteric artery (SMA) as compared with CT angiography (CTA) as the reference standard.

METHODS

41 patients underwent both NC-MRA and CTA of the abdominal aorta. Two radiologists analyzed the quality of the images (diagnostic vs non-diagnostic) and the performance (accuracy, sensitivity and specificity) of NC-MRA for the identification of arterial stenosis. Kappa tests were used to determine the interobserver agreement and the intermethod agreement between NC-MRA and CTA.

RESULTS

NC-MRA provided diagnostic quality images of the CTR and SMA in 87.8% and 90.2% of cases, respectively, with high interobserver agreement (kappa 0.95 and 0.80, respectively). For stenosis assessment, NC-MRA had a sensitivity of 100%, a positive-predictive value of 50% and a negative-predictive value of 100% for both segments, with accuracies of 88.8% for the CTR and 94.5% for the SMA.

CONCLUSION

NC-MRA is an accurate method for detecting stenosis in the CTR and SMA. Advances in knowledge: Data from this study suggest that MR angiography with balanced steady-state free-precession sequence is a viable non-contrast alternative for stenosis evaluation of these branches in patients for whom a contrast-enhanced examination is contraindicated.