3T improves contrast in first-pass myocardial perfusion imaging at either 0.10 mmol/kg or 0.075 mmol/kg.
Purpose: To determine whether imaging at 3 T could improve and prolong the tag contrast compared to images acquired at 1.5 T in normal volunteers, and whether such improvement would translate into the ability to perform strain measurements in diastole. Materials and Methods:Normal volunteers (N ϭ 13) were scanned at 1.5 T (GE Signa CV/i) and 3.0 T (GE VH/i). An ECG-triggered, segmented k-space, spoiled-gradient-echo grid-tagged sequence was used during cine acquisition. Tag contrast was determined by the difference of the mean signal intensity (SI) of the tagline to the mean SI of the myocardium divided by the standard deviation (SD) of the noise (CNR tag ). Matched short-axis (SA) slices were analyzed. Strain measurements were performed on images using a 2D strain analysis software program (harmonic phase (HARP)). Results:The average CNR tag over the cardiac cycle was superior at 3 T compared to 1.5 T for all slices (3 T: 23.4 Ϯ 12.1, 1.5 T: 9.8 Ϯ 8.4; P Ͻ 0.0001). This difference remained significant at cycle initiation, end-systole, and the end R-R interval (at cycle termination: 3 T ϭ 14.0 Ϯ 11.0 vs. 1.5 T ϭ 4.4 Ϯ 3.5; P Ͻ 0.01). Strain measures were obtainable only in early systole for 1.5 T images, but were robust throughout the entire R-R interval for 3 T images.Conclusion: Imaging at 3 T had a significant benefit for myocardial tag persistence through the cardiac cycle. The improvement allowed strain analysis to be performed into diastole. MYOCARDIAL TAGGING using MRI is an evolving noninvasive technique for assessing and quantifying regional myocardial function and strain in the human heart. Since this technique was first described (1,2), several studies have used MRI tagging to measure regional myocardial function with multiphase myocardial strain in normal and diseased states (3-6). Algorithms that are necessary to quantify strain and regional myocardial function are heavily dependent on the contrast between the tag lines and the myocardium. However, myocardial tagging techniques are limited by the rapid fading of tags, which restricts their application to the systolic phases of the cardiac cycle. Given the increasing recognition of the role of diastolic dysfunction in several cardiac disease states (7), it would be of clinical value to overcome the limitations posed by the early decay tags and extend the analysis of regional myocardial function and strain to the entire cardiac cycle. Several methods, including complementary spatially modulated magnetization (CSPAMM) (8,9) and balanced free precession sequences (10,11) have been employed toward that end. Higher-field-strength imaging is becoming more common and provides another pathway to potentially improve tag persistence through prolonged T1 myocardial recovery and enhanced signal-tonoise ratio (SNR).The aim of this study was to compare tag contrast as a function of time within the cardiac cycle in normal volunteers imaged at both 1.5 T and 3 T using a fast spoiled-gradient-recalled echo sequence with spatial modulation of magnetization. The images...
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