T2-weighted Spin-echo Technique Research Articles

Relaxation-Enhanced Angiography without Contrast and Triggering (REACT) for pelvic MR venography in comparison to balanced gradient-echo and T2-weighted spin-echo techniques

Rationale and objectivesTo evaluate the imaging capabilities of the REACT pulse sequence in pelvic venous vessels compared to conventional non-contrast pulse sequences. Materials and methodsIn addition to routine MRI venography, non-contrast enhanced REACT pulse sequence was performed in 4 healthy volunteers and 21 patients with suspected or known deep venous thrombosis and post thrombotic syndrome. Acquired images were independently interpreted by two MRI radiologists. The sequence performance was subjectively evaluated on a four-point scale regarding the delineation of small peripheral, midsize and large proximal venous vessels, the imaging of vascular pathologies, and the degradation due to artifacts. To evaluate statistical differences in diagnostic accuracy Friedman's test with Dunn's correction was used. ResultsREACT depicted the peripheral veins superior to bTFE and T2-TSE with an average score of 3.39 compared to 2.33 in bTFE and 1.77 in T2-TSE. In midsize vessels REACT performed significantly better than T2-TSE (1.94) and bTFE (2.68) with a score of 3.64. For the large proximal vessels REACT (3.39), bTFE (3.33) and T2-TSE (3.56) performed equally without statistical difference. Visibility of venous pathologies was found to be equal between REACT (3.62), bTFE (3.51) and T2-TSE (3.52). The image degradation due to artifacts was rated best in T2-TSE (3.56), followed by REACT (3.39) and bTFE (3.33). ConclusionsREACT is a promising tool for the visualization of the pelvic venous system using magnetic resonance imaging.

MR imaging: its development and the recent Nobel Prize.

HomeRadiologyVol. 231, No. 3 PreviousNext EditorialsMR Imaging: Its Development and the Recent Nobel PrizeStephen J. RiedererStephen J. RiedererAuthor Affiliations1From the MR Laboratory, Mayo Clinic, 200 First Street SW, Rochester, MN 55905. Received January 19, 2004; accepted January 21. Address correspondence to the author (e-mail: [email protected]).Stephen J. RiedererPublished Online:Jun 1 2004https://doi.org/10.1148/radiol.2313040114MoreSectionsFull textPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In References 1 Lauterbur PC. Image formation by induced local interactions: examples employing nuclear magnetic resonance. Nature 1973; 242:190-191. Crossref, Google Scholar2 USA MRI market Mountain View, Calif: Frost and Sullivan Market Research, 2002. Google Scholar3 Mansfield P, Grannell PK. NMR “diffraction” in solids? J Phys C Solid State Phys 1973; 6:L422. Crossref, Google Scholar4 Mansfield P. 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Multiple-slice spin lock imaging of head and neck tumors at 0.1 Tesla: exploring appropriate imaging parameters with reference to T2-weighted spin-echo technique.

Spin lock imaging has been shown to be useful in characterizing head and neck tumors. The purposes of this study were to explore and develop multiple-slice spin lock gradient-echo (SL-GRE) sequences for head and neck imaging and to compare the tumor contrast on SL images to spin-echo (SE) T2-weighted images at 0.1 T. On the basis of measured relaxation times of tumors and head and neck tissues, the authors evaluated with signal equations the effect of imaging parameters on tissue contrast produced by the SL-GRE sequence. In the clinical study, 34 patients with pathologically verified head and neck tumors were imaged with multiple-slice SL-GRE (repetition time 1500 ms/echo time 30 ms) out-of-phase fat/water sequences and compared with T2-weighted SE (repetition time 1500 ms/echo time 120 ms) sequences. The conspicuity of tumors was evaluated by calculating the contrast-to-noise ratios (CNRs). The combination of a short echo time of 30 ms and the length of locking pulses in the range of 10 to 35 ms produced optimal CNRs for head and neck tumor imaging. The measured CNRs and subjective evaluation for tumor detection were satisfactory with both imaging sequences. However, the CNRs between tumors and salivary gland tissues were significantly greater with the SL sequence than with the T2-weighted sequence. The multiple-slice SL-GRE technique provides image contrast comparable to that of SE T2-weighted imaging for head and neck tumors at 0.1 T. With short locking pulse lengths and echo times, wide anatomic coverage and reduced motion and susceptibility artifacts can be achieved. The out-of-phase SL technique is useful in imaging salivary gland tumors.

Effect of mannitol on focal cerebral ischemia evaluated by somatosensory-evoked potentials and magnetic resonance imaging

Mannitol has been used in routine neurosurgical practice for the control of increased intracranial pressure. The effect of mannitol on focal cerebral ischemia was evaluated by somatosensory-evoked potentials (SEP) and magnetic resonance imaging (MRI). The left middle cerebral artery (MCA) was exposed via the superomedial transorbital approach and occluded proximal to the origin of the perforating arteries. Ten cats received mannitol (0.5 g/kg IV) immediately, 6, 12, and 18 hours after MCA occlusion. The other 10 cats received saline solution and served as control. The animals were initially prepared to measure SEP before and 15, 30, and 60 minutes after MCA occlusion. Following SEP measurement, all cats were prepared for MRI. Sequential MRI of both intravoxel incoherent motion (IVIM) and T2-weighted spin echo techniques were obtained at 2, 4, 6, and 24 hours after MCA occlusion. The animals were sacrificed after the last MRIs for histologic study. The SEP amplitude decreased to about 10% at 15 minutes after MCA occlusion and then gradually recovered to 38% at 60 minutes in the mannitol group, and 21% in the control group. In MRI study, IVIM imaging demonstrated ischemic cerebral injury as a sharply demarcated area at 2 hours after MCA occlusion, while T-2 weighted imaging failed to show clear evidence of injury until 2-6 hours. High-signal intensity areas on both IVIM and T2-weighted images were smaller in the mannitol group than those in the control group. Histologic study demonstrated that infarction size was 36.9% +/- 7.7% of the left hemisphere in the mannitol group and 57.3% +/- 5.3% in the control group (p < 0.05). Mannitol is effective for acute cerebral ischemia, and SEP and MRI are useful for monitoring it.

The potential value of magnetic resonance imaging in infertility

The potential value of magnetic resonance imaging as a diagnostic tool in infertility was investigated. Twenty-six women with primary or secondary infertility and symptoms of dysmenorrhoea or menorrhagia were studied prospectively using conventional T1- and T2-weighted spin-echo techniques. Positive diagnoses were obtained in 20 of 26 (76.9%) patients. Of these, 18 (69.2%) had lesions likely to be significantly contributing to infertility. Adenomyosis was detected in 14 patients (53.8%) with 11 showing the diffuse pattern while three had discrete adenomyomas. Cystic lesions typical of endometriosis were detected in seven patients (26.9%), four of these also had evidence of adenomyosis. The endometriotic lesions were also seen at laparoscopy in each case. Five patients (19.2%) had leiomyomas, one in a patient with adenomyosis and endometriosis and one in a patient with endometriosis alone. Only one patient had submucous leiomyomas causing significant distortion of the endometrial mucosa likely to affect fertility. Magnetic resonance imaging is valuable in the investigation of unexplained infertility where it provides a high diagnostic yield particularly if uterine pathology is suspected.

Silicone breast implants in vivo: MR imaging.

This study was designed to evaluate pulse sequences and patient positioning for MR imaging of silicone breast implants in patients. One hundred forty-three patients (281 silicone implants) underwent imaging over a 21-month period. The combination of a T2-weighted fast spin echo technique (SE), T2-weighted fast SE with water suppression, and T1-weighted SE with fat suppression is recommended to reliably differentiate silicone from other breast tissues and to identify intracapsular and extracapsular ruptures or leaks. Seventy of the 143 patients underwent removal of their silicone implants. The sensitivity for detection of silicone implant rupture was 76%, with a specificity of 97%. Positioning the patient prone improved image quality.

Characterization of acute myocardial infarction by magnetic resonance imaging

The T2-weighted spin-echo technique is currently the most frequently used magnetic resonance imaging (MRI) method to visualize acute myocardial infarction. However, image quality is often degraded by ghost artifacts from blood flow, and respiratory and cardiac contractile motion. To enhance the usefulness of this technique for detailed characterization of infarction, a velocity-compensated spin-echo pulse sequence was tested by imaging a flow phantom, 6 normal subjects and 17 patients with acute myocardial infarction. After preliminary studies were performed in 7 patients to determine optimal imaging parameters, a standardized imaging protocol was used in the next 10. The location of myocardial infarction identified by the electrocardiogram and coronary anatomy was correctly identified in 10 of 10 patients. Distribution of the injury within the left ventricle was clearly visualized, and showed that patients often had a mixture of transmural and nontransmural injury. Heterogenous distribution of signal intensity within the infarction suggested the presence of hemorrhage. Papillary muscle involvement was readily apparent. Signal intensity of the infarction (brightest segment) was increased by 89 ± 31% compared with the mean of the remote segments. The myocardial/skeletal muscle ratio was significantly (p < 0.001) increased for the infarction segments compared with that for remote myocardium, allowing quantitative analysis of segmental signal intensity. The MRI wall motion study obtained as part of this protocol demonstrated wall thickening in 58% of the infarction segments and in 6 of 10 patients. This finding suggested the presence of reversibly injured myocardium. In conclusion, the results demonstrate the potential of MRI for detailed tissue characterization after acute myocardial infarction.

Präpontine Liquorpulsationsartefakte im T2-betonten koronaren MRT-Bild

Coronal T2-weighted MRI is the most sensitive imaging modality to detect temporal lobe pathology. However, prepontine artifacts resulting from pulsation of cerebrospinal fluid occasionally simulate temporal lobe lesion. To characterize this artifact we studied 30 patients without temporal lobe pathology in conventional T2-weighted spin-echo technique (0.5 T, SE 1600/70, coronal, horizontal phase encoding). Visual analysis revealed high-intensity artifacts simulating a lesion in five of 30 cases. The present study shows that prepontine artifacts due to pulsation of cerebrospinal fluid are quite frequent (17%) and that these artifacts may result in misinterpretation in the evaluation of temporal lobe epilepsy. By a repeat examination in identical methodology while using vertical phase encoding, all artifacts could be identified and an artifact-free representation of the temporal lobes was achieved.

Gradient-echo imaging of hemorrhage at 1.5 Tesla.

We report in vitro and in vivo MR studies of hemorrhage using the gradient-echo pulse sequence, FISP (steady state free precession) and FLASH (spoiling of transverse magnetization) at 1.5 Tesla. Phantoms containing methemoglobin, ferromagnetic particles, human serum and blood clot were scanned using both spin-echo and gradient-echo techniques. FLASH signal intensities were more sensitive to methemoglobin concentration than high T1-weighted spin-echo images. FISP showed little change in signal intensity with varying concentrations of methemoglobin and a contrast relationship similar to T2-weighted spin-echo techniques. FISP and FLASH showed intensity changes at lower concentrations of ferromagnetic material than T2-weighted spin-echo sequences. In vitro blood clot was less intense when observed by FISP and FLASH sequences than on the T2-weighted spin-echo sequences. Maximum contrast between clot and other blood components occurred at a flip angle of 45 degrees for FLASH and 60 degrees for FISP. FISP and FLASH scans of patients with hemorrhage demonstrated a marked decrease in signal intensity in the region of blood clot. This decrease was more pronounced with the gradient-echo sequences than with T2-weighted spin-echo images. We conclude that FLASH is useful for detecting methemoglobin and that both FISP and FLASH are useful for evaluating hemorrhage because of their sensitivity to methemoglobin.