Kurzfassung

For quantitative first-pass myocardial perfusion MR imaging exists the need for a fast and robust pulse sequence to cover the whole human heart with a single heartbeat temporal resolution while maintaining good image quality for quantifying perfusion abnormalities. Rapid, multi-slice, T1-weighted imaging is achieved by using a saturation recovery (SR) preparation pulse in combination with short saturation times (TI) and an ultra fast gradient echo readout like spoiled FLASH, balanced steady...For quantitative first-pass myocardial perfusion MR imaging exists the need for a fast and robust pulse sequence to cover the whole human heart with a single heartbeat temporal resolution while maintaining good image quality for quantifying perfusion abnormalities. Rapid, multi-slice, T1-weighted imaging is achieved by using a saturation recovery (SR) preparation pulse in combination with short saturation times (TI) and an ultra fast gradient echo readout like spoiled FLASH, balanced steady state free precision (bSSFP) or echo-train readout.
Imaging was performed on an 1.5T Siemens Sonata (Siemens Medical Solutions, Germany) using an eight-element phased-array cardiac coil. A total of 24 healthy volunteers were examined by first pass myocardial perfusion imaging at rest. Thereby for each of the three pulse sequences 6 volunteers were examined with and without a twofold TSENSE acceleration, respectively, and finally 6 volunteers were examined with all three sequences using only TSENSE. Furthermore, for each pulse sequence the relationship between signal intensity (SI) and CA concentration was determined, which must be linear to be suitable for (semi-) quantitative analysis of myocardial blood flow, using phantoms with equivalent relaxations times T1 and T2 to myocardium.
In all pulse sequences, the magnetization was prepared using a nonselective saturation pulse. With TSENSE the TI could be decreased from 125ms to 85ms. The parameters TR/TE/α for TurboFLASH were 2.4ms/1.2ms/18°, for TrueFISP 2.2ms/1.1ms/50°, and for Interleaved Gradient EPI (echo train length of 4) 5.8ms/ 1.2ms/35°. The matrix size for all sequences was 128x96 with a field of view (FOV) of 380x285mm2 resulting in a pixel size of 2.97x2.97mm2. No additional temporal filtering for further suppression of aliasing artifacts has been applied. For the volunteer study 40 measurements with 3 slices per heartbeat were acquired during a single breath hold. In all volunteers, 2ml of a Gd-based contrast agent (CA, Magnevist, Schering, Germany) were injected (~0.015mmol/kg BW) in an antecubital vein.
TSENSE introduced a median loss of SNR of 43%, 39% and 23% for TurboFLASH, TrueFISP and Interleaved Gradient EPI, respectively. For the CNR the loss was 43%, 43% and 20%, respectively. Using TSENSE the TrueFISP sequence yielded significant higher SNR- and CNR-values than both of the other sequences, as well as the Interleaved Gradient EPI sequence yielded significant higher values than TurboFLASH. In the TrueFISP images significant more dark banding artifacts appeared in the myocardium than for the other two sequences. No differences were found between the conventional and the TSENSE acquisitions. With TurboFLASH and Interleaved Gradient EPI the images showed significant more image noise than for TrueFISP. TrueFISP yielded significantly the best overall image quality as well as the Interleaved Gradient EPI sequence yielded better results than TurboFLASH.
With TSENSE the acquisition time per image can be decreased and therefore the number of acquired slices can be increased for all sequences for better volume coverage of the heart. The increased linearity of the CA-concentration to signal-intensity relation may provide a more reliable perfusion quantification. With TSENSE the TrueFISP sequence provides the highest SNR and CNR values as well as the best overall image quality and is therefore most suitable for (semi-) quantitative analyses of myocardial perfusion. Because of the shorter acquisition time, a higher linearity, the less sensitivity for dark banding artifacts in the myocardium and fewer losses in SNR and CNR with TSENSE the Interleaved Gradient EPI sequence may advance future clinical perfusion imaging.
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