7 Tesla (T) human cardiovascular magnetic resonance imaging using FLASH and SSFP to assess cardiac function: validation against 1.5 T and 3 T.

We report the first comparison of cardiovascular magnetic resonance imaging (CMR) at 1.5 T, 3 T and 7 T field strengths using steady state free precession (SSFP) and fast low angle shot (FLASH) cine sequences. Cardiac volumes and mass measurements were assessed for feasibility, reproducibility and validity at each given field strength using FLASH and SSFP sequences. Ten healthy volunteers underwent retrospectively electrocardiogram (ECG) gated CMR at 1.5 T, 3 T and 7 T using FLASH and SSFP sequences. B1 and B0 shimming and frequency scouts were used to optimise image quality. Cardiac volume and mass measurements were not significantly affected by field strength when using the same imaging sequence (P > 0.05 for all parameters at 1.5 T, 3 T and 7 T). SSFP imaging returned larger end diastolic and end systolic volumes and smaller left ventricular masses than FLASH imaging at 7 T, and at the lower field strengths (P < 0.05 for each parameter). However, univariate general linear model analysis with fixed effects for sequence and field strengths found an interaction between imaging sequence and field strength (P = 0.03), with a smaller difference in volumes and mass measurements between SSFP and FLASH imaging at 7 T than 1.5 T and 3 T. SSFP and FLASH cine imaging at 7 T is technically feasible and provides valid assessment of cardiac volumes and mass compared with CMR imaging at 1.5 T and 3 T field strengths.

Comparison between eight- and sixteen-channel TEM transceive arrays for body imaging at 7 T.

Eight- and sixteen-channel transceive stripline/TEM body arrays were compared at 7 T (297 MHz) both in simulation and experiment. Despite previous demonstrations of similar arrays for use in body applications, a quantitative comparison of the two configurations has not been undertaken to date. Results were obtained on a male pelvis for assessing transmit, signal to noise ratio, and parallel imaging performance and to evaluate local power deposition versus transmit B(1) (B(1) (+) ). All measurements and simulations were conducted after performing local B(1) (+) phase shimming in the region of the prostate. Despite the additional challenges of decoupling immediately adjacent coils, the sixteen-channel array demonstrated improved or nearly equivalent performance to the eight-channel array based on the evaluation criteria. Experimentally, transmit performance and signal to noise ratio were 22% higher for the sixteen-channel array while significantly increased reduction factors were achievable in the left-right direction for parallel imaging. Finite difference time domain simulations demonstrated similar results with respect to transmit and parallel imaging performance, however, a higher transmit efficiency advantage of 33% was predicted. Simulations at both 3 and 7 T verified the expected parallel imaging improvements with increasing field strength and showed that, for a specific B(1) (+) shimming strategy used, the sixteen-channel array exhibited lower local and global specific absorption rate for a given B(1) (+) .

Initial results of cardiac imaging at 7 Tesla.

This work reports preliminary results from the first human cardiac imaging at 7 Tesla (T). Images were acquired using an eight-channel transmission line (TEM) array together with local B(1) shimming. The TEM array consisted of anterior and posterior plates closely positioned to the subjects' thorax. The currents in the independent elements of these arrays were phased to promote constructive interference of the complex, short wavelength radio frequency field over the entire heart. Anatomic and functional images were acquired within a single breath hold to reduce respiratory motion artifacts while a vector cardiogram (VCG) was used to mitigate cardiac motion artifacts and gating. SAR exposure was modeled, monitored, and was limited to FDA guidelines for the human torso in subject studies. Preliminary results including short-axis and four-chamber VCG-retrogated FLASH cines, as well as, short-axis TSE images demonstrate the feasibility of safe and accurate human cardiac imaging at 7T.

MRI vs. histologic measurement of breast cancer following chemotherapy: comparison with x-ray mammography and palpation.

Twenty consecutive patients with breast cancer were evaluated following chemotherapy using MRI to assess the size of cancer residua and compare these data with subsequent histologic measurements of the viable tumor. This retrospective study also involved assessment of the preoperative size of the malignancy as determined by physical exam and x-ray mammogram. These values were later compared with the histology. The tumor size correlation coefficient between MRI and pathologic analysis was the highest, at 0.93. Physical exam and x-ray mammography (available for 17 patients) produced correlation coefficients of 0.72 and 0.63, respectively, compared to histologic measurement. The accuracy of MRI did not vary with the size of cancer residua. MRI is an accurate method for preoperative assessment of breast cancer residua following chemotherapy. J. Magn. Reson. Imaging 2001;13:868-875.

Applications of high-resolution echoplanar spectroscopic imaging for structural imaging.

Echoplanar spectroscopic imaging (EPSI) was introduced as a fast alternative for spectroscopic imaging and has been recently implemented on clinical scanners. With further advances in gradient hardware and processing strategies, EPSI can be used to obtain spectroscopic images whose spatial resolution parallels that of conventional anatomic images within clinically acceptable acquisition time. The present work demonstrates that high-resolution EPSI can be used to derive structural images for applications in which spectroscopic information is beneficial. These applications are chemical shift (fat-water) imaging, narrow bandwidth imaging, and T2* mapping. In this paper, the EPSI sequence design and processing strategies are detailed and experimental results in normal volunteers are presented to illustrate the potential of using EPSI in imaging anatomic structures.