Feasibility study of non Carr Purcell Meiboom Gill single shot fast spin echo in spinal cord diffusion imaging

The fast spin echo (FPE) sequence is sensitive to the phase of the magnetization, hindering its use in procedures such as diffusion imaging. The current solutions to this problem reduce the available signal by one half. We present the first volunteer study of a sequence which does not suffer from this loss of signal while measuring diffusion coefficients. This work was presented in part during the Eighth Scientific Meeting of International Society for Magnetic Resonance in Medicine. Denver. 2000 (number 1501).     

Subacute myocardial infarction: assessment by STIR T2-weighted MR imaging in comparison to regional function

Purpose Increased T2 signal intensity (SI) can be regularly observed in myocardial infarction. However, there are controversial reports about the relationship of elevated T2 SI to myocardial viability and some authors propose that high T2 SI serves as a sign of irreversible myocardial injury. This study investigates increased T2 SI compared to myocardial function in patients with reperfused subacute myocardial infarction. Preserved function was used as criterion for viability. Methods Ten healthy volunteers and 17 patients with myocardial infarction and patent inlarct related coronary artery were examined on a 1.5 T Magnetom Vision system (Siemens). For T2-weighted MR imaging a breath-hold STIR sequence with dark-blood preparation was used. Cine FLASH 2D imaging was applied to assess myocardial function. Signal-to-noise (S/N) in STIR T2 images was measured in normal and infarcted regions and subsequently identified by two independent observers. Based on a 20 segment model of the left ventricle findings were compared to regional myocardial function. Results Elevated STIR T2 SI was found in all 17 patients and observed in 27% (204/754) of segments. S/N of normal myocardium was 5.1 ±0.7 in volunteers and 4.9 ± 0.8 in patients(P=NS). Infarcted myocardium presented with significantly-increased S/N 12.8 ± 1.9 (P < 0.0001). Significant transmural elevation of T2 SI was noted in 32% of segments with preserved systolic function. Conclusion Increased STIR T2 SI can be observed transmurally in post-ischemic myocardial regions with preserved function. It therefore cannot be used as an exclusive marker for the non-viable region.     

Detection of colorectal liver metastases: prospective comparison of unenhanced and ferumoxides-enhanced magnetic resonance imaging at 1.5 T, dual-phase spiral CT, and spiral CT during arterial portography

The purpose of this study was to compare the efficacy of unenhanced and ferumoxides-enhanced magnetic resonance imaging with that of dual-phase spiral CT and spiral CT during arterial portography (CTAP) for the detection of colorectal liver metastases. Fourteen patients with liver metastases candidates for partial hepatectomy were examined with dual-phase spiral CT, unenhanced and ferumoxides-enhanced MR imaging at 1.5 T, and spiral CTAP. Imaging tests were read blinded, prospectively, quantitating number of lesions excepting CTAP which used US to exclude cysts. Subsequent intraoperative US and pathologic findings were correlated with preoperative imaging results. At surgery, 36 lesions 0.5–13 cm in diameter (mean ±standard deviation, 2.9±2.1 cm) were identified. Dual-phase spiral CT depicted 21/36 (58%); precontrast MR imaging, 19/36 (53%); ferumoxides-enhanced MR imaging, 30/36 (83%); and spiral CTAP, 34/36 (94%) lesions. Ferumoxides-enhanced MR imaging was significantly more sensitive than spiral CT and unenhanced MR imaging (P<0.01). The difference in sensitivity between ferumoxides-enhanced MR imaging and spiral CTAP was not statistically significant (P>0.1). Spiral CTAP, however, depicted nine false-positive lesions (2 hemangiomas, 7 perfusion defects). The positive predictive value was 79% for spiral CTAP and 100% for combined pre- and postcontrast MR imaging. We conclude that ferumoxides-enhanced MR imaging is superior to unenhanced MR imaging and biphasic spiral CT for depiction of colorectal liver metastases. Further investigation is needed to clarify whether MR imaging with use of ferumoxides might replace spiral CTAP for preoperative evaluation of liver resection candidates. Recipient of a Cum Laude award for a scientific exhibit at the 1997 ESMRMB annual meeting.     

Single-shot t1-and t2-weighted magnetic resonance imaging of the heart with black blood: preliminary experience

Purpose: To implement and evaluate two robust methods for T1-and T2-weighted snapshot imaging of the heart with data acquisition within a single heart beat and suppression of blood signal. Methods: Both Tl-and T2-weighted diastolic images of the heart can be obtained with half Fourier single-shot turbo spin echo (HASTE) and turbo fast low-angle shot (turboFLASH) sequences, respectively, in less than 350 ms. Signal from flowing blood in the ventricles and large vessels can be suppressed by a preceding inversion recovery preparing pulse pair (PRESTO). Fifteen volunteers and five patients have been evaluated quantitatively for signal-to-noise ratio (SNR) contrast-to-noise ratio (CNR) and flow void and qualitatively for image quality, artifacts, and black-blood effect. Results: Both PRESTO-HASTE and PRESTO-turboFLASH achieved consistently good image quality and blood signal suppression. In contrast to gradient-echo (GRE) echo-planar imaging techniques, (EPI) HASTE and turboFLASH are much less sensitive to local susceptibility differences in the thorax, resulting in a more robust imaging technique without the need for time-consuming system tuning. Compared to standard spin-echo sequences with cardiac triggering, HASTE and turboFLASH have significantly shorter image acquisition times and are not vulnerable to respiratory motion artifacts. Conclusion: PRESTO-HASTE and PRESTO-turboFLASH constitute suitable methods for fast and high-quality cardiac magnetic resonance imaging (MRI).     

Dynamic snapshot gradient-echo imaging of head and neck malignancies: time dependency and quality of contrast-to-noise ratio

The purpose of this study was to evaluate the time dependency of the contrast-to-noise ratio (CNR) of head and neck malignancies during contrast-enhanced MR imaging. Then we would compare the CNR of dynamic snapshot gradient-echo (SGE) images with conventional spin-echo (SE) and fast spin-echo (FSE) sequences. Fifteen patients with squamous cell carcinomas were examined with T1W-SE, T2W-FSE, contrast-enhanced Gd-TlW-SE, and T1W-SGE sequences, the latter statically and contrast-enhanced dynamically. The CNR for all sequences and adjacent tissues was computed and the time to reach maximal CNR (T_max) was determined for dynamic studies. The CNR was time dependent with two distinct T_max at 6–18 and 60–160 s which corresponded to two different tumor enhancement patterns. Neither enhancement pattern correlated with distinct histologic findings or tumor grading. The CNR improved for the Gd-TlW-SGE images. The improvement was statistically significant in relation to T1W-SE and Gd-TlW-SE images at the floor of the mouth and at the tongue base. The good CNR of the dynamic Gd-TlW-SGE measurements justifies further investigations of this method in order to improve tumor delineation.     

MR imaging of focal liver lesions: comparison between turbo spin-echo and conventional spin-echo pulse sequences

The aim of this study was to compare conventional spin-echo (CSE)T ₂-weighted (T2W) images with turbo spin-echo (TSE) T2W pulse sequences in their ability to detect focal liver lesions. Seventy-eight consecutive patients with focal liver lesions were entered into this study. All patients were imaged using the gradient-echo (GE) sequence with the breath-hold technique forT ₁-weighted (T1W) images, and CSE and TSE sequences for T2W images. Qualitative evaluation included lesion detection (number of lesions detected) and conspicuity (extent of visualization of lesional borders); quantitative evaluation included the signal-to-noise (S/N) ratio and the contrast-to-noise (C/N) ratio. TSE showed the best performance in terms of lesion detection; however, the difference between TSE and CSE was significant only in the case of benign cysts (p<0.01). Conspicuity was higher with TSE and CSE, and lower with GE. The S/N and C/N ratios of the two T2W sequences were also comparable, and better than those of GE. However, the combined use of GE and TSE resulted in improved lesion detection. The results show that, because the acquisition time is greatly reduced with TSE sequences, these should be considered as first-line approach to magnetic resonance imaging of the liver for the study of focal lesions.     

Measurements of T1 and T2 relaxation times of colon cancer metastases in rat liver at 7 T

The purpose of this study was to investigate the magnetic resonance imaging (MRI) characteristics of colon cancer metastases in rat liver at 7 T. A dedicated RF microstrip coil of novel design was built in order to increase the signal-to-noise ratio and, in combination with respiratory triggering, to minimize motion artifacts. T₁- and T₂-weighted MR imaging was performed to follow tumor growth. T₁-weighted images provided a good anatomical delineation of the liver structure, while the best contrast between metastases and normal liver tissue was achieved with T₂-weighted images.Measurements of T₁ and T₂ relaxation times were performed with inversion recovery FLASH and Carr–Purcell–Meiboom–Gill and inversion recovery FLASH imaging sequences, respectively, for quantitative MR characterization of metastases. Both the T₁ and T₂ of the metastases were significantly higher than those of normal liver tissue. Further, an increase in the T₁ relaxation time of the metastases was observed with tumor growth. These findings suggest that quantitative in vivo MR characterization provides information on tumor development and possibly response to therapy, though additional studies are needed to elucidate the correlation between the changes in relaxation times and tumor microenvironment.