Contrast on T2-weighted images of the lumbar spine using fast spin-echo and gated conventional spin-echo sequences

A prospective study in 31 patients was designed to compare contrast quantitatively using axial conventional, gated spin-echo T2-weighted (T2W) (SE) (asymmetrical echo TE 30 and 80 ms) and axial dual-echo fast spin-echo (FSE) sequences (TE_eff20 and 120 ms) to image lumbar discs, nerve roots, and cerebrospinal fluid CSF. We used two quantitative measures, percent (%) contrast and contrast-to-noise ratio (CNR), to compare the sequences. The FSE sequence had greater % contrast and CNR on the first and second echo images for both disc and nerve root detection using these scan parameters. An axial FSE sequence, therefore, provided contrast characteristics similar to those of gated axial T2W SE sequence in the lumbar spine, with a 60% saving in acquisition time. The FSE sequence is now our standard axial T2W study for the lumbar spine.     

Malignant hepatic tumor detection with ferumoxide‐enhanced magnetic resonance imaging: Is chemical‐shift‐selective fat suppression necessary for fast spin‐echo sequence?

PURPOSE: To determine whether chemical-shift-selective (CSS) fat suppression is necessary for ferumoxide-enhanced T2-weighted fast spin-echo (FSE) imaging in the detection of malignant hepatic tumors. MATERIALS AND METHODS: Ferumoxide-enhanced magnetic resonance (MR) images obtained in 38 patients with surgically confirmed 61 malignant hepatic tumors (36 hepatocellular carcinomas (HCCs), 25 metastases) were retrospectively reviewed by three independent readers. Three sequences of MR images with CSS fat-suppressed T2-weighted FSE, non-fat-suppressed T2-weighted FSE, and T2*-weighted gradient-recalled-echo (GRE) sequences were randomly reviewed on a segment-by-segment basis in a blind fashion. Observer performance was tested using the McNemar's test and receiver-operating-characteristic (ROC) analysis for the clustered data. Lesion-to-liver contrast-to-noise ratio (C/N) was also assessed. RESULTS: The mean C/N with the CSS fat-suppressed FSE sequence was highest in HCCs, metastases, and tumors overall. Sensitivity was highest with the CSS fat-suppressed FSE sequence in HCC, was highest with the non-fat-suppressed FSE sequence in metastases, and was comparable in tumors overall. Specificity was comparable between the sequences. The area under ROC curve (Az) value was greatest with the CSS fat-suppressed FSE sequence in HCCs, was greatest with the non-fat- suppressed FSE sequence in metastases, and was comparable in tumors overall. The sensitivities and Az values were lower with the GRE sequence than the FSE sequence. CONCLUSION: The CSS fat-suppressed FSE sequence was superior to the GRE sequence in the detection of HCCs, but the non-fat-suppressed FSE sequence was comparable to the GRE sequence. The non-fat-suppressed FSE sequence was superior to the CSS fat-suppressed FSE and GRE sequences in the detection of metastases. Optimal FSE imaging with CSS fat suppression or without aiming for the detection of HCCs or metastases, respectively, outperforms GRE imaging in ferumoxide-enhanced MRI.     

Spinal cord lesions in patients with multiple sclerosis: comparison of MR pulse sequences.

PURPOSETo compare T2-weighted conventional spin-echo (CSE), fast spin-echo (FSE), shorttau inversion recovery (STIR) FSE, and fluid-attenuated inversion recovery (FLAIR) FSE sequences in the assessment of cervical multiple sclerosis plaques.METHODSTwenty patients with clinically confirmed multiple sclerosis and signs of cervical cord involvement were examined on a 1.5-T MR system. Sagittal images of T2-weighted and proton density-weighted CSE sequences, T2-weighted FSE sequences with two different sets of sequence parameters, STIR-FSE sequences, and FLAIR-FSE sequences were compared by two independent observers. In addition, contrast-to-noise measurements were obtained.RESULTSSpinal multiple sclerosis plaques were seen best on STIR-FSE images, which yielded the highest lesion contrast. Among the T2-weighted sequences, the FSE technique provided better image quality than did the CSE technique, but lesion visibility was improved only with a repetition time/echo time of 2500/90; parameters of 3000/150 provided poor lesion contrast but the best myelographic effect and overall image quality. CSE images were degraded by prominent image noise; FLAIR-FSE images showed poor lesion contrast and strong cerebrospinal fluid pulsation artifacts.CONCLUSIONSThe STIR-FSE sequence is the best choice for assessment of spinal multiple sclerosis plaques. For T2-weighted FSE sequences, shorter echo times are advantageous for spinal cord imaging, long echo times are superior for extramedullary and extradural disease. FLAIR-FSE sequences do not contribute much to spinal imaging for multiple sclerosis detection.     

Use of fast spin echo for phase shift magnetic resonance thermometry

PURPOSE: To propose a modified fast spin echo (FSE) magnetic resonance imaging sequence for MR thermometry, employing the proton resonance frequency (PRF) shift by means of MR phase maps. Despite their obvious advantages of speed and high signal-to-noise ratio (SNR), FSE sequences have not until now been used for this purpose due to the restraints imposed by the Carr-Purcell-Meiboom-Gill (CPMG) conditions. MATERIALS AND METHODS: The new FSE combines a new phase modulation scheme that maintains magnetization that ordinarily is destroyed under CPMG conditions, while employing conventional FSE gradient waveforms. The echoes are read in a single shot using 128 readouts in 650 msec, with a phase sensitive preparation using an optional time shift tau before the start of the refocusing gradient waveforms. This feature allows the quantification of temperature dependent phase shifts. We tested the sequence by imaging a heated agar gel phantom while cooling, using different values for tau. RESULTS: There was good correlation between FSE and fiberoptic-based temperature measurements in the phantom(r(2) >or= 0.95). Temperature sensitivity could be adjusted by varying the tau value. CONCLUSION: With the proposed non-CPMG FSE sequence it is feasible to quantify temperature changes by means of the PRF shift.     

MRI of the knee: value of short echo time fast spin-echo using high performance gradients versus conventional spin-echo imaging for the detection of meniscal tears

Objective. Fast spin-echo (FSE) sequences reduce imaging time compared with conventional spin-echo (CSE) sequences, but may result in blurring. High-performance gradients permit shorter interecho spacing and use of the second echo as the effective TE (20 ms); both improvements reduce blurring. This randomized observer study compared a short TE, second-echo FSE sequence obtained using high-performance gradients and a CSE sequence with similar TR/TE for the detection of meniscal tears in the knee. Design and patients. One hundred consecutive MR examinations of the knee using FSE and CSE sequences at 1.5 T were evaluated. The FSE sequence used an effective TE of 20 ms (centered on the second echo at 2 times minimal interecho spacing) and an echo train length of 4. FSE and CSE parameters were otherwise similar. Four independent, masked readers reviewed randomized sagittal FSE and CSE sequences. Results. Cases were assessed for the presence or absence of meniscal tears and, if present, whether tears were medial or lateral and anterior or posterior. Sequence concordance was 93.5% (1496 of 1600 meniscal segments); the intermethod kappa value was 0.78. Sequence quality was graded from 1 to 5. Average quality of CSE images was slightly but statistically significantly preferred by three of the four readers. Conclusion. There was no statistically significant difference between CSE imaging and FSE imaging centered on the second echo (20 ms) using high-performance gradients for the detection of meniscal tears in the knee. There was a small preference for the quality of CSE images. Received: 22 July 1999 Revision requested: 27 October 1999 Revision received: 7 February 2000 Accepted: 21 March 2000     

Single breath-hold T1 measurement using low flip angle TrueFISP.

A method for estimating T1 using a single breath-hold, segmented, inversion recovery prepared, true fast imaging with steady-state precession (sIR-TrueFISP) acquisition at low flip angle (FA) was implemented in this study. T1 values measured by sIR-TrueFISP technique in a Gd-DTPA-doped water phantom and the human brain and abdomen of healthy volunteers were compared with the results of the standard IR fast spin echo (FSE) technique. A good correlation between the two methods was observed (R2=0.999 in the phantom, and R2=0.943 in the brain and abdominal tissues). The T1 values of the tissues agreed well with published results. sIR-TrueFISP enables fast measurements of T1 to be obtained within a single breath-hold with good accuracy, which is particularly important for chest and abdominal imaging.     

Colorectal hepatic metastases: detection with SPIO-enhanced breath-hold MR imaging--comparison of optimized sequences

PURPOSE: To compare the accuracy of four breath-hold magnetic resonance (MR) imaging sequences to establish the most effective superparamagnetic iron oxide (SPIO)-enhanced sequence for detection of colorectal hepatic metastases. MATERIALS AND METHODS: Thirty-one patients with colorectal hepatic metastases underwent T1-weighted gradient-echo (GRE) and T2-weighted fast spin-echo (FSE) MR imaging before and after SPIO enhancement. Four sequences were optimized for lesion detection: T2-weighted FSE, multiecho data image combination (MEDIC), T2-weighted GRE with an 11-msec echo time (TE), and T2-weighted GRE with a 15-msec TE. Images were reviewed independently by three blinded observers. The accuracy of each sequence was measured by using alternative free-response receiver operating characteristic analysis. All results were correlated with findings at surgery, intraoperative ultrasonography, or histopathologic examination. Differences between the mean results of the three observers were measured by using the Student t test. RESULTS: Postcontrast T2-weighted GRE sequences were the most accurate and were significantly superior to postcontrast T2-weighted FSE and unenhanced sequences alone (P <.05). For all lesions that were malignant or smaller than 1 cm, respectively, mean accuracies of postcontrast sequences were 0.082 and 0.64 for T2-weighted FSE, 0.90 and 0.78 for MEDIC, 0.92 and 0.80 for GRE with an 11-msec TE, 0.93 and 0.82 for GRE with a 15-msec TE, and 0.81 and 0.62 for unenhanced sequences. CONCLUSION: Optimized SPIO-enhanced T2-weighted GRE combined with unenhanced T2-weighted FSE MR sequences were the most sensitive. Breath-hold FSE postcontrast sequences offer no improvement in sensitivity compared with unenhanced sequences alone.     

Liver imaging at 3.0 T: diffusion-induced black-blood echo-planar imaging with large anatomic volumetric coverage as an alternative for specific absorption rate-intensive echo-train spin-echo sequences: feasibility study

Institutional Review Board approval and signed informed consent were obtained by all participants for an ongoing sequence optimization project at 3.0 T. The purpose of this study was to evaluate breath-hold diffusion-induced black-blood echo-planar imaging (BBEPI) as a potential alternative for specific absorption rate (SAR)-intensive spin-echo sequences, in particular, the fast spin-echo (FSE) sequences, at 3.0 T. Fourteen healthy volunteers (seven men, seven women; mean age +/- standard deviation, 32.7 years +/- 6.8) were imaged for this purpose. Liver coverage (20 cm, z-axis) was always performed in one 25-second breath hold. Imaging parameters were varied interactively with regard to echo time, diffusion b value, and voxel size. Images were evaluated and compared with fat-suppressed T2-weighted FSE images for image quality, liver delineation, geometric distortions, fat suppression, suppression of the blood signal, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR). An optimized short- (25 msec) and long-echo (80 msec) BBEPI provided full anatomic, single breath-hold liver coverage (100 and 50 sections, respectively), with resulting voxel sizes of 3.3 x 2.7 x 2.0 mm and 3.3 x 2.7 x 4.0 mm, respectively. Repetition time was 6300 msec, matrix size was 160 x 192, and an acceleration factor of 2.00 was used. b Values of more than 20 sec/mm(2) showed better suppression of the blood signal but b values of 10 sec/mm(2) provided improved volume coverage and signal consistency. Compared with fat-suppressed T2-weighted FSE, the optimized BBEPI sequence provided (a) comparable image quality and liver delineation, (b) acceptable geometric distortions, (c) improved suppression of fat and blood signals, and (d) high CNR and SNR. BBEPI is feasible for fast, low-SAR, thin-section morphologic imaging of the entire liver in a single breath hold at 3.0 T.     

Hepatic T2-weighted MRI: A prospective comparison of sequences,including breath-hold,half-Fourier turbo spin echo (HASTE)

The purpose of this study was to quantitatively compare the hepatic contrast characteristics of conventional spin-echo (CSE) and fast spin-echo (FSE) sequences with breath-hold T2-weighted images acquired with half-Fourier turbo spin echo (HASTE). Forty-five patients were examined with a phased-array surface coil. Nineteen patients had focal hepatic lesions, including eight malignant tumors, 10 cavernous hemangiomas, and one hepatic adenoma. Twenty-six patients had no focal hepatic lesions. T2-weighted images with comparable TE were acquired with CSE, FSE, and HASTE pulse sequences. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) for liver, spleen, and lesions were measured. FSE demonstrated significantly better quantitative performance than CSE for liver-spleen CNR (P = .0084). No statistically significant difference was demonstrated between FSE and CSE for liver or spleen SNR. FSE demonstrated clear scan time and resolution advantages over CSE. HASTE performed significantly poorer than CSE and FSE for liver-spleen CNR (P < .0001), liver SNR (P = .0002 for CSE and P < .0001 for FSE), and spleen SNR (P < .0001). Optimized FSE images with a short echo train length performed comparably to CSE images of equivalent TE. Liver-lesion CNR was suppressed on HASTE images, suggesting that long echo train length FSE sequences could diminish solid lesion detection compared to CSE and short echo train length FSE.     

Functional NMR imaging using fast spin echo at 1.5 T

Functional NMR imaging of the brains response to a simple visual task has been performed using a fast spin echo (FSE) imaging sequence at 1.5 T. The FSE method refocuses dephasing effects induced by large-scale susceptibility variations, and permits imaging in regions where macroscopic field gradients produce artifacts in gradient echo sequences. At 1.5 T, gradient echo (GRE) sequences are sensitive to the effects of brain activation, but relatively large effects may arise from large vessels and veins, and these may dominate the effects produced by smaller capillaries. Spin echo (SE) sequences with short echo times are relatively immune to large vessel effects and emphasize the susceptibility induced losses from small capillaries, but the imaging time for these sequences is prohibitive for most functional brain studies. We demonstrate that multislice functional brain imaging may be performed in reasonable imaging times at 1.5 T using an FSE imaging sequence. The FSE sequence with short echo spacing but long effective TE is sensitive to susceptibility induced effects at the capillary level. It is not sensitive to larger scale in homogeneities such as those found in veins and can be used in regions near tissuelair boundaries. Results are shown comparing conventional GRE and FSE images in activation of the visual cortex and these are supported by theoretical calculations and phantom experiments.     

Detection of malignant hepatic tumors with ferumoxides-enhanced MRI: comparison of five gradient-recalled echo sequences with different TEs

OBJECTIVE: The purpose of our study was to compare the detectability of malignant hepatic tumors on ferumoxides-enhanced MRI using five gradient-recalled echo sequences at different TEs. MATERIALS AND METHODS: Ferumoxides-enhanced MRIs obtained in 31 patients with 50 malignant hepatic tumors (33 hepatocellular carcinomas, 17 metastases) were reviewed retrospectively by three independent offsite radiologists. T1-weighted gradient-recalled echo images with TEs of 1.4 and 4.2 msec; T2*-weighted gradient-recalled echo images with TEs of 6, 8, and 10 msec; and T2-weighted fast spin-echo images of livers were randomly reviewed on a segment-by-segment basis. Observer performance was tested using the McNemar test and receiver operating characteristic analysis for the clustered data. Lesion-to-liver contrast-to-noise ratio was also assessed. RESULTS: Mean lesion-to-liver contrast-to-noise ratios were negative and lower with gradient-recalled echo at 1.4 msec than with the other sequences. Sensitivity was higher (p < 0.05) with gradient-recalled echo at 6, 8, and 10 msec and fast spin-echo sequences (75-83%) than with gradient-recalled echo sequences at 1.4 and 4.2 msec (46-48%), and was higher (p < 0.05) with gradient-recalled echo sequence at 8 msec (83%) than with gradient-recalled echo at 6 msec and fast spin-echo sequences (75-78%). Specificity was comparably high with all sequences (95-98%). The area under the receiver operating characteristic curve (A(z)) was greater (p < 0.05) with gradient-recalled echo at 6, 8, and 10 msec and fast spin-echo sequences (A(z) = 0.91-0.93) than with gradient-recalled echo sequences at 1.4 and 4.2 msec (A(z) = 0.82-0.85). CONCLUSION: In the detection of malignant hepatic tumors, gradient-recalled echo sequences at 8 msec showed the highest sensitivity and had an A(z) value and lesion-to-liver contrast-to-noise ratio comparable with values from gradient-recalled echo sequences at 6 and 10 msec and fast spin-echo sequences.     

Effective blood signal suppression using double inversion-recovery and slice reordering for multislice fast spin-echo MRI and its application in simultaneous proton density and T2 weighted imaging

PURPOSE: To design a multislice double inversion-recovery fast spin-echo (FSE) sequence, with k-space reordered by inversion time at slice position (KRISP) technique, to produce black-blood vessel wall magnetic resonance imaging (MRI). MATERIALS AND METHODS: In this sequence, central k-space sampling for each slice is required at inversion time (TI) of the blood signal. To fill the entire k-space, the peripheral lines are obtained less or greater the TI and using a rotating slice order. Blood flow signal suppression was first evaluated using a phantom. Simulation studies were used to investigate FSE image quality. The final sequence was then applied to the rabbit abdominal aorta MRI at 4.7 T. RESULTS: In the flow phantom study, artifacts from slow-flowing water were substantially reduced by the KRISP technique; residual water spins were dephased by the strong phase-encoding gradient required for peripheral k-space. These dephased spins flowed into the slice plane where the center of k-space was being acquired at the TI of the flowing water signal. Multislice black-blood MR images were successfully obtained in the rabbit abdomen using the sequence with the k-trajectory optimized by the simulation study. CONCLUSION: The KRISP technique was effective both in multislice double inversion-recovery FSE and in blood signal suppression.     

Optimizing fast spin echo acquisitions for hepatic imaging in normal subjects

The purpose of this study was to determine which implementations of a T2-weighted fast spin-echo sequence of the liver resulted in observer preference in normal subjects. Five volunteers were scanned with a series of fast spin-echo sequences modified to allow for flow compensation, respiratory triggering (RT), ECG triggering, randomized phase encoding (RPE), breathholding, and echo train length (ETL). Images were compared with conventional 2500/40/80 msec spin-echo images using flow compensation and spatial presaturation by two observers blinded to the specific sequence parameters. All FSE sequences were completed in less than the 12 minutes necessary to perform a conventional spin-echo sequence. The most preferred fast spin-echo sequence employed flow compensation, RT, and used an 8 ETL. Analysis of image preference, signal to noise, and contrast to noise showed that RT was the single most important variable in determining each image response (P < .01, P < .02, P < .01, respectively). There was some evidence that images obtained with an 8 ETL were preferred over those using a 16 ETL (P=.07). No other variables approached statistical significance although one reader preferred images with flow compensation in the frequency direction to those either not flow compensated or flow compensated in the slice direction. Respiratory triggered fast spin-echo images combined with flow compensation in the frequency direction and using ETL=8 can provide image quality equal to conventional spin-echo sequences with significant time savings.     

A motion correction scheme by twin-echo navigation for diffusion-weighted magnetic resonance imaging with multiple RF echo acquisition

In this paper, a series of diffusion-weighted fast spin-echo (FSE) sequences with a new motion correction scheme are introduced. This correction scheme is based on the navigator echo technique. Unlike conventional spin-echo imaging, motion correction for FSE is complicated by the phase oscillation between odd-numbered and even-numbered echoes and the complex phase relationship between spin echo and stimulated echo components. In our approach, incoherent phase shifting due to motion is monitored by consecutive acquisition of two navigator echoes, which provide information on both inter-echo and intra-echo train phase shifts. Applications to both phantom and in vivo studies are presented.     

Musculoskeletal MR imaging: turbo (fast) spin-echo versus conventional spin-echo and gradient-echo imaging at 0.5 tesla

The value of T2-weighted fast spin-echo imaging of the musculoskeletal system was assessed in 22 patients with various neoplastic, inflammatory, and traumatic disorders. Images were acquired with high echo number (i.e., echo train length) fast spin-echo (FSE; TR 2000 ms, effective TE 100 ms, echo number 13, lineark-space ordering), conventional spin-echo (SE; TR 2000 ms, TE 100 ms) and gradient-echo (GRE) sequences (TR 600 ms, TE 34 ms, flip angle 25°). Signal intensities, signal-to-noise ratios, contrast, contrast-to-noise ratios, lesion conspicuousness, detail perceptibility, and sensitivity towards image artifacts were compared. The high signal intensity of fat on FSE images resulted in a slightly inferior lesion-to-fat contrast on FSE images. However, on the basis of lesion conspicuity, FSE is able to replace time-consuming conventional T2-weighted SE imaging in musculoskeletal MRI. In contrast, GRE images frequently showed superior lesion conspicuity. One minor disadvantage of FSE in our study was the frequent deterioration of image quality by blurring, black band, and rippling artifacts. Some of these artifacts, however, can be prevented using short echo trains and/or short echo spacings.     

Can a multiphasic contrast-enhanced three-dimensional fast spoiled gradient-recalled echo sequence be sufficient for liver MR imaging?

OBJECTIVE: The purpose of this study was to determine the accuracy of a multiphasic gadolinium-enhanced three-dimensional (3D) fast spoiled gradient-recalled echo sequence alone in the detection and characterization of focal liver lesions compared with a comprehensive liver evaluation using multiphasic gadolinium-enhanced 3D fast spoiled gradient-recalled echo, T1-weighted, and fat-suppressed fast spin-echo T2-weighted sequences. MATERIALS AND METHODS:A retrospective review of abdominal MR imaging examinations in 61 patients was performed. All MR examinations included unenhanced spin-echo T1-weighted, unenhanced fat-suppressed fast spin-echo T2-weighted, and multiphasic gadolinium-enhanced 3D fast spoiled gradient-recalled echo sequences obtained during successive breath-holds. The liver was evaluated for focal lesions first with the 3D spoiled gradient-recalled echo sequences and then, during a separate sitting, with the T1- and T2-weighted sequences. The usefulness of each sequence in the detection and characterization of lesions was recorded. The gold standard for lesion detection and characterization was all three imaging sequences reviewed together. RESULTS:A total of 114 focal liver lesions were identified, 54 of which were simple cysts. The 3D spoiled gradient-recalled echo sequence alone detected 92 (81%) of the 114 lesions, and the T1- and T2-weighted sequences detected 95 (83%) of the 114 lesions. Of the 60 lesions that were not simple cysts, the 3D spoiled gradient-recalled echo sequence alone detected 58 (97%), and T1- and T2-weighted sequences detected 51 (85%). In 24% of the patients with lesions, the T1- and T2-weighted sequences were found to be helpful for the characterization of lesions. CONCLUSION:A multiphasic contrast-enhanced 3D fast spoiled gradient-recalled echo sequence alone detects most of the clinically relevant focal liver lesions. Additional liver examination using both unenhanced T1- and T2-weighted sequences is helpful for lesion characterization but increases the detection rate only minimally.     

关节软骨损伤MR成像序列的实验研究

目的 评价关节软骨缺损检查的各种MRI扫描序列。材料与方法 选用猪膝关节10只，制成宽度不等，深度为软骨全层的小槽状软骨缺损，MRI序列包括T1加权自旋回波序列（SE-T1），质子和T2加权快速自旋双回波序列（FSE-PD/T2），附加脂肪抑制的质子和T2加权快速自旋双回波序列（FS-FSE-PD/T2），附加脂肪抑制的三维快速扰相梯度回波序列（FS-3D-SPGR），液体衰减反转恢复序列（FLAIR），短TI翻转回波序列（STIR）和T1加权反转恢复序列（IR-TI700）。结果 与常规膝关节检查的FSE-PD/T2序列比较，FS-FSE-PD/T2能够分辨软骨与软骨下骨的界限，可测量软骨缺损厚度和深度；FS-3D-SPGR的软骨信噪比（SNR）和其对软骨下骨，关节液等关节软骨周围组织的对比噪声比（CNR）最高；IR-TI700测量的软骨缺损宽度和深度，与实际测量值的一致性最好，FLAIR和STIR不能清楚分辨软骨和软骨下骨的界限。结论 FS-FSE-PD/T2应作为膝关节检查的常规序列；三维抑脂梯度回波序列仍为关节软骨检查的最佳扫描序列。翻转回波扫描序列在关节软骨检查方面具有潜在的临床价值。     

八次激发SE-EPI在肝脏MRI的应用

目的；比较八次激发SE－EPI与呼吸门控FSE及SSFSE T2WI在肝脏的应用。方法：对14例志愿者及21例肝病患者行上腹部呼吸门控FSE及SSFSE和屏气八次激发SE－EPI扫描。所有T2WI序列均运用脂肪抑制技术。定量分析肝脏、病灶的信噪比及肝脏－病灶的对比噪声比，评价各序列的图像质量及伪影。结果：八次激发SE－EPI与SSFSE及FSE在肝脏及病灶信噪比，肝脏－病灶对比度噪声比和图像质量方面无明显差异（P＞0．05）。其磁敏感伪影较FSE及SSFSE重（P＜0．01），SE－EPI化学位移伪影与SSFSE及FSE相比无明显差别（P＞0．05）。SE－EPI及FSE运动伪影明显比SSFSE重（P＜0．01），但SE－EPI运动伪影与FSE相比无明显差别（P＞0．05）。SE－EPI与FSE及SSFSE的图像质量无明显差别（P＞0．05）。结论：八次激发SE－EPI能够在较短时间里提供较高质量的上腹部T2WI。被检查者在扫描时可自由平静呼吸或屏气，可作为肝脏T2WI的补充序列。     

Comparison between EPI and HASTE for ultra-fast MR imaging of the human brain

Our purpose was to evaluate and compare the performance of ultra-fast single-shot T2-weighted sequences: echo-planar imaging (EPI) versus half-Fourier single-shot turbo spin-echo (HASTE) and to assess the usefulness of their combined reading. Comparative experiments on a phantom as well as a prospective clinical study in 47 patients were done. Axial images acquired with the following methods were compared: (a) HASTE; (b) segmented HASTE (s-HASTE); (c) single-shot spin-echo EPI (SE-EPI); and (d) gradient-echo EPI (GREEPI). Quantitative and qualitative criteria as well as lesion detectability were analyzed against the "gold standard" fast spin-echo (FSE) sequence. For contrast and contrast-to-noise ratio (CNR) between gray and white matter, GRE-EPI was best. The visibility of small markedly hyperintense lesion was best with HASTE and s-HASTE in the clinical study. Small hyperintense lesions were detected equally well with all four sequences, although all performed significantly worse than FSE. The two HASTE variants were better than the EPIs for the extraaxial lesions. The combination of the GRE-EPI and s-HASTE was judged best, and sometimes superior to the FSE image. HASTE or EPI alone cannot substitute for FSE in the screening evaluation of the brain. However, together, EPI and HASTE could provide comparable diagnostic information to that of FSE because their combination compensates for their individual limitations.     

Impact of incidental magnetization transfer effects on inversion-recovery sequences that use a fast spin-echo readout.

Multislice MR images obtained using a fast spin-echo (FSE) readout are strongly affected by magnetization transfer (MT) effects, which will cause a decrease in the observed longitudinal relaxation times for tissues with a large bound water component. This is pertinent for FSE-based inversion-recovery (IR) sequences, as it would be expected to cause a change in the required inversion times. Furthermore, the effect will be greater as the number of slices that are acquired within the repetition time (TR) is increased. A pseudo-3D IR-FSE sequence was used to obtain images of a phantom consisting of thermally crosslinked bovine serum albumin. It was found that increasing the number of slabs acquired per TR period led to a decrease in the inversion time that maximally suppressed the signal from the MT phantom; this was not the case for water. This has important consequences for any IR imaging sequence that uses an FSE readout.