Intracerebral lesion contrast with spin-echo and fast spin-echo pulse sequences.

Fast spin-echo (FSE) magnetic resonance (MR) imaging was compared with conventional, peripherally gated T2-weighted spin-echo (SE) imaging in the detection of high- and low-signal-intensity lesions in the central nervous system. Lesion detectability was determined with percentage of contrast measurements and contrast-to-noise ratios with two different measurements for noise. All three measures of lesion detectability were similar. FSE and SE sequences were quantitatively equivalent in the detection of high-signal-intensity lesions. The SE sequence, however, was superior to the FSE sequence in the detection of small, low-signal-intensity lesions in the central nervous system caused by magnetic susceptibility effects.     

Liliequist membrane: three-dimensional constructive interference in steady state MR imaging

PURPOSE: To evaluate the Liliequist membrane in healthy volunteers by using three-dimensional (3D) Fourier transformation constructive interference in steady state (CISS) magnetic resonance (MR) imaging. MATERIALS AND METHODS: In 31 volunteers, the authors performed 3D CISS MR imaging. They divided the membrane into three segments: the sellar, diencephalic, and mesencephalic segments. MR images were evaluated to identify the segments, superior and inferior attachments, lateral border, and thickness of the Liliequist membrane. RESULTS: Three-dimensional CISS MR imaging depicted the sellar, diencephalic, and mesencephalic segments of the Liliequist membrane in the sagittal plane in 25 (81%), 16 (52%), and five (16%) of the 31 subjects, respectively. Transverse MR imaging depicted these segments in 24 (77%), 10 (32%), and two (6%) subjects, respectively, and coronal MR imaging depicted them in 24 (77%), 12 (39%), and two (6%) subjects, respectively. Clear attachment of the membrane to the dorsum sellae was observed in 22 (88%) of 25 subjects in whom the sellar segment was identified. Clear attachment to the mamillary body was identified in eight (50%) of 16 subjects in whom the diencephalic segment was identified. The Liliequist membrane was attached to the oculomotor nerve on seven (14%) of 50 sides of the lateral border and to the arachnoid membrane around the oculomotor nerve on 28 (56%) sides. In the sagittal plane, the thickness of the membrane was less than one-half the thickness of the third ventricle floor in 22 (88%) of 25 subjects. CONCLUSION: The Liliequist membrane can be visualized by using 3D CISS MR sequences.     

屏气三维快速平衡稳态进动序列对冠状动脉狭窄的诊断效能

目的以普通冠状动脉导管造影为参照,评价屏气三维快速平衡稳态进动(FIESTA)序列对冠状动脉狭窄的显示效能。方法连续33例患者在冠状动脉导管造影检查的3周内接受冠状动脉MR血管成像(CMRA)检查,将冠状动脉狭窄划分成0%、0%~25%、25%~50%、50%~75%,75%~100%共5个级别,对两者判断的结果逐段进行比较。结果CMRA对区分>50%和<50%狭窄的准确度、敏感度和特异度分别为843%、848%和841%,阴性预测值为923%;对区分50%~75%与75%~100%狭窄的准确度、敏感度和特异度均为615%。结论屏气三维FIESTA冠状动脉成像序列对具有血流动力学意义狭窄的排除具有一定的实用价值,但是更细致的分级受限。     

Evaluation of three-dimensional fast spoiled gradient recalled acquisition in the steady state (FSPGR) using ultra magnetic field 3-Tesla MRI for optimal pulse sequences of T1-weighted imaging

The advantage of the higher signal-to-noise ratio (SNR) of 3-Tesla magnetic resonance imaging (3TMRI) contributes to the improvement of spatial and temporal resolution. However, T1-weighted images of the brain obtained by the spin-echo (SE) method at 3T MR are not satisfactory for clinical use because of radiofrequency (RF) field inhomogeneity and prolongation of the longitudinal relaxation time (T1) of most tissues. We evaluated optimal pulse sequences to obtain adequate T1 contrast, high gray matter/white matter contrast, and suitable postcontrast T1-weighted images using the three-dimentional (3D) fast spoiled gradient recalled acquisition in the steady state (FSPGR) method instead of the SE method. For the optimization of T1 contrast, the Ernst angle of the optimal flip angle (FA) was obtained from the T1 value of cerebral white matter with the shortest TR and TE. Then the most appropriate FA, showing the maximum contrast-to-noise ratio (CNR) and SNR, was obtained by changing the FA every 5 degrees at about the level of the Ernst angle. Image uniformity was evaluated by a phantom showing similar T1 and T2 values of cerebral white matter. In order to evaluate the effect of the contrast enhancement, signal intensity was compared by the same method using a phantom filled with various dilutions of contrast media. Moreover, clinical studies using full (0.1 mmol/kg) and half (0.05 mmol/kg) doses of Gd-DTPA were carried out with the most appropriate parameters of the 3D-FSPGR method. These studies indicated that the optimal pulse sequences for obtaining an adequate T1-weighted image of the brain using 3D-FSPGR are 9/2 msec (TR/TE) and 13 degrees (FA).     

Spoiling of transverse magnetization in gradient-echo (GRE) imaging during the approach to steady state

The signal evolution behaviors and corresponding image appearances for different methods of spoiling or refocusing the transverse magnetization in short TR gradient-echo imaging during the approach to steady state were investigated experimentally and using computer simulations based on the Bloch equations. Specifically, ideally spoiled, gradient-spoiled, gradient-refocused, and RF-spoiled pulse sequence configurations were studied. This study showed that, for the gradient-spoiled configuration, the signal evolution is position and phase-encoding order-dependent and, under typical imaging conditions, can deviate substantially from the ideally spoiled signal evolution at some spatial positions, resulting in intensity banding image artifacts. For the gradient-refocused configuration, the signal evolution oscillates toward the steady state and, generally, does not closely approximate that of ideal spoiling, resulting in different image contrast or image blurring. Using RF spoiling, the signal evolution closely approximates the ideally spoiled case for flip angles less than approximately 20° and T₂ values of less than approximately 200 ms and results in relatively artifact-free images. Also, this study showed that, for RF spoiling, an RF-pulse phase-difference increment other than 117°, such as 84°, may be optimal for gradient-echo imaging during the approach to steady state.     

Mr cholangiopancreatography: Comparison between two-dimensional fast spin-echo and three-dimensional gradient-echo pulse sequences

The purpose of our study was to perform a prospective comparative analysis of three-dimensional (3D) steady-state free precession (SSFP) and two-dimensional (2D) fast spin-echo (FSB) imaging in the evaluation of 26 patients with suspected bile duct obstruction. SSFP and highly T2-weighted FSB sequences were obtained for each patient in multiple planes. Both sequences were reviewed independently and results were compared with findings from direct cholangiography (n = 17) or from a combination of sonography and CT (n = 9). The extrahepatic bile duct (EHBD) and intrahepatic bile duct (IHBD) were dilated In 32% and 54% of patients, respectively. The EHBDs were visualized in 44% of patients with SSFP. versus in 96% with FSE. One or more IHBD segments were seen In 42% of the SSFP sequences and in 100% of the FSB sequences. A portion of, or the entire, pancreatic duct was seen in 23% of the SSFP sequences and in 65% of the FSE sequences. Our findings lead us to conclude that T2-weighted FSE sequences are superior to SSFP sequences In visualizing the biliary tree and pancreatic duct and that they should replace gradient-echo sequences in MR Cholangiopancreatography.     

Image contrast and pulse sequences in urinary tract magnetic resonance imaging

Since image contrast in urinary tract proton magnetic resonance imaging (MRI) depends on both intrinsic properties of the imaged tissue and the imaging technique, it is important to understand the principles underlying image production, both while performing urinary tract MRI and when interpreting the images. This paper reviews briefly the major characteristics of tissue that can produce image contrast: mobile proton density, tissue motion, and relaxation times. It also describes the principles by which these factors, together with the choice of pulse sequence, affect image appearance. The specific pulse sequences described include the spin-echo and inversion recovery sequences; the influence of repetition time, echo delay, and inversion time are also described. Although empiric data regarding the best pulse sequences to use for all types and sites of pathology in the urinary tract are not complete, knowledge of the characteristics of normal tissue and the major sorts of pathologic change permit one to make general conclusions about the appropriate choice of pulse sequences.     

Image contrast and pulse sequences in urinary tract magnetic resonance imaging

Since image contrast in urinary tract proton magnetic resonance imaging (MRI) depends on both intrinsic properties of the imaged tissue and the imaging technique, it is important to understand the principles underlying image production, both while performing urinary tract MRI and when interpreting the images. This paper reviews briefly the major characteristics of tissue that can produce image contrast: mobile proton density, tissue motion, and relaxation times. It also describes the principles by which these factors, together with the choice of pulse sequence, affect image appearance. The specific pulse sequences described include the spin-echo and inversion recovery sequences; the influence of repetition time, echo delay, and inversion time are also described. Although empiric data regarding the best pulse sequences to use for all types and sites of pathology in the urinary tract are not complete, knowledge of the characteristics of normal tissue and the major sorts of pathologic change permit one to make general conclusions about the appropriate choice of pulse sequences.     

Efficacy of three-dimensional fast imaging with steady precession dynamic MR imaging in evaluating pancreatic ductal adenocarcinoma.

To compare the diagnostic efficacy of three-dimensional fast imaging with steady precession (3D-FISP) dynamic MR imaging in assessing pancreatic ductal adenocarcinoma with conventional MR imaging and helical CT, 15 patients with surgically proven pancreatic ductal adenocarcinoma were studied. Contrast-to-noise ratio (CNR) of the tumor, tumor detectability, local tumor extension, and vascular involvement were evaluated for all techniques. The results indicate that 3D-FISP dynamic MR imaging may improve the imaging assessment of pancreatic ductal adenocarcinoma.     

Esophageal carcinoma: evaluation with high-resolution three-dimensional constructive interference in steady state MR imaging in vitro

PURPOSE: To determine the usefulness of high-resolution three-dimensional (3D) constructive interference in steady state (CISS) MRI for evaluating mural invasion and morphologic features in esophageal carcinomas. MATERIALS AND METHODS: Twenty-four esophageal specimens with carcinomas were studied with a 1.5-T system using a 4-cm-diameter loop coil. High-resolution 3D-CISS MR images were obtained with a field of view (FOV) of 80 mm, matrix of 256 x 256, and section thickness of 0.5 mm (voxel size of 0.05 mm(3)). 3D-CISS MR images were compared with histopathologic findings, and virtual MR endoscopic images were compared with macroscopic findings at surgery. RESULTS: 3D-CISS MR images clearly depicted the normal esophageal wall as consisting of eight layers, which correlated well with the histologic layers. In 22 of 24 esophageal carcinomas (92%), the depth of mural invasion visualized with 3D-CISS MRI correlated well with the histopathologic staging. In all 24 carcinomas (100%), virtual MR endoscopic images clearly depicted the macroscopic types of the carcinomas, including adjacent lymph node swelling. CONCLUSION: High-resolution 3D-CISS MRI has a high diagnostic accuracy for evaluating mural invasion and macroscopic findings in esophageal carcinomas, and may be applicable to preoperative histopathologic staging and morphologic evaluation.     

High contrast and fast three-dimensional magnetic resonance imaging at high fields

A new three-dimensional imaging strategy based on magnetization prepared ultrafast gradient recalled echo technique that demonstrates pronounced T₁ contrast at high fields is introduced. High-resolution three-dimensional image sets of human brain showing high contrast between white and gray matter areas are presented. The ratio of contrast-to-noise was examined as a function of the relevant parameters in the imaging sequence; calculations based on high-field T₁ values as well as the experimental data demonstrated that maximal contrast-to-noise ratio is attained under the same magnetization preparation conditions both for cortical and subcortical gray matter relative to white matter, leading to approximately equivalent appearance of all gray matter areas in the same image. In addition, the images displayed clear visualization of subtle anatomical structures such as the subthalamic nuclei (ventral tier nuclei, dorsomedial nucleus, and pulvinar) and mammillothalamic tracts.     

Cine MR imaging of heart valve dysfunction with segmented true fast imaging with steady state free precession

PURPOSE: To evaluate the value of cine true fast imaging with steady-state free precession (SSFP) for semiquantitative assessment of valvular dysfunction in the heart and to compare the results to that obtained with a standard breath-hold segmented gradient-recalled echo-planar imaging sequence (GE-EPI). MATERIALS AND METHODS: Twenty-three patients with known valvular dysfunction (main component: 16 with aortic valve stenosis, nine with aortic valve insufficiency, three with mitral stenosis, two with mitral regurgitation, two with tricuspidal regurgitation, and one with pulmonary stenosis) and 23 control subjects with normal valvular function underwent MR imaging on a 1.5-T system (ACS-NT, Philips, Best, The Netherlands). Cine SSFP and GE-EPI images were acquired in identical long-axis views. Images were evaluated for the presence and extent of the signal void arising from the valves and for image quality consensus by two experienced radiologists. Results were compared to those obtained by cardiac catheterization (in 16 patients) or color Doppler (in the remaining seven patients). RESULTS: On SSPF images, the complex flow pattern in valvular regurgitant or stenotic lesions caused signal void within the bright blood pool of the atria or ventricles, similar to GE-EPI, in all patients. Valvular dysfunction was delineated using SSFP with the same high sensitivity (100%) as using the GE-EPI sequence. Results correlated to those obtained by cardiac catheterization or color Doppler ultrasonography (P < 0.001, r = 0.97). However, the jet phenomenon was slightly more pronounced in five patients on GE-EPI. There was no significant signal void in the 23 control subjects with both sequences. In all 46 subjects, the image quality of SSFP images was rated higher (P < 0.05; 2.6 +/- 0.1; using a scale ranging from 0-3) compared to GE-EPI (1.7 +/- 0.1). CONCLUSION: The results of this study suggest that valvular dysfunction can be semiquantitatively assessed using SSFP cine MR imaging.     

Selective missing pulse steady state free precession (MP-SSFP): inner volume and chemical shift selective imaging in a steady state sequence

PURPOSE: To examine new sequences that restrict acquisition of spins to those excited by both of the RF pulses in missing pulse steady state free precession (MP-SSFP) MRI. MATERIALS AND METHODS: New MP-SSFP sequences were created by replacing one of the slice selective pulses (SSPs) with an orthogonal SSP for inner volume imaging, and with a chemical shift selective (CHESS) pulse for chemical shift imaging. The inner volume sequence was applied to a reduced field of view at the center of a resolution phantom; resulting images were evaluated for differences in the aliased signal. The CHESS sequence was applied to volunteers, as well as to and fat, water, and acetic acid phantoms. Results were evaluated with SNR measurements. RESULTS: The inner volume sequence eliminated the aliased signal, while nonselected fat and water levels were suppressed to that of noise by the CHESS sequence. CONCLUSION: Results suggest a novel steady state technique for rapid inner volume or chemical shift imaging.     

Inversion recovery prepared turbo spin echo sequences with reduced SAR using smooth transitions between pseudo steady states.

This study investigates the contrast behavior of 2D inversion recovery (IR) prepared turbo spin echo (TSE) sequences that use RF pulse schemes with variable low flip angles (hyperTSE) to reduce RF power deposition. A framework of equations and calculations for adapting the sequence parameters is presented by which equivalent image contrast is achieved compared to conventional IR-TSE imaging. Although the inversion time (TI) and repetition time (TR) do not need to be changed, the echo time (TE) has to be prolonged such that the effective TE (TE(eff)) is preserved. Measurements in healthy volunteers confirmed this finding for IR-TSE sequences using different TIs: fluid attenuated inversion recovery (FLAIR), gray matter (GM)-white matter (WM)-IR, and short tau IR (STIR). The results demonstrate that hyperTSE sequences enable high-quality IR-prepared imaging with a considerably reduced specific absorption rate (SAR).     

Increased conspicuity of intraventricular lesions revealed by three-dimensional constructive interference in steady state sequences

We describe our preliminary experience with the three-dimensional constructive interference in steady state (3D-CISS) sequence for the evaluation of intraventricular lesions. Cyst walls, extent and margins of tumors, and intratumoral cystic structures were clearly depicted on 3D-CISS images. The 3D-CISS sequence can offer additional information to conventional MR studies to define intraventricular lesions better.     

Improved detection of intraventricular cysticercal cysts with the use of three-dimensional constructive interference in steady state MR sequences

BACKGROUND AND PURPOSE: Before the advent of MR imaging, intraventricular cysts were difficult to diagnose noninvasively. Among the invasive procedures used were contrast ventriculography and CT ventriculography. MR imaging, with its multiplanar imaging capabilities, excellent depiction of tissue contrast, and versatile parameters, is an important tool in the assessment of intraventricular cystic lesions. We investigated the role of three-dimensional constructive interference in steady state (3D-CISS) MR sequences in the evaluation of intraventricular cysticercal cysts. METHODS: The study group comprised 11 patients with intraventricular cysticercal cysts. MR studies included spin-echo (SE) T1-weighted, turbo-SE T2-weighted, and 3D-CISS sequences. All images were obtained on a superconducting 1.5-T MR unit. The routine and 3D-CISS sequences were reviewed and interpreted separately by two neuroradiologists. RESULTS: All patients underwent surgery for excision of intraventricular cysticercal cysts. Eight patients had cysts in the fourth ventricle, two in the lateral ventricle, and one in the third ventricle. SE T1-weighted images showed the cystic wall in nine cases, the scolex in four, and the cystic fluid in two. Turbo-SE T2-weighted images showed the cystic wall and scolex in three and four cases, respectively. The routine sequences did not show the scolex, cystic wall, or cystic fluid together in any of the 11 patients. 3D-CISS images showed the scolex in all 11 patients and the cystic wall and cystic fluid in eight patients each. In seven of the 11 patients, 3D-CISS images showed the scolex, cystic wall, and fluid together. CONCLUSION: The 3D-CISS sequence is more sensitive and specific than routine SE sequences in the diagnosis of intraventricular cysticercal cysts.