磁共振快速成像技术在肺癌分期中的应用

目的:探讨MRI快速成像序列在肺癌分期中的成像质量及其临床应用价值。方法:36例肺癌患者,分别行MRI快速序列成像及CT增强扫描。分析快速序列的伪影,与CT对比分析肿瘤与胸部邻近结构的关系、淋巴结肿大情况。结果:HASTE各项伪影评分均为0,FLASH伪影也低于常规序列。FLASH和true FISP无呼吸伪影,但搏动伪影高于常规序列。与CT对比,在显示胸部邻近结构侵犯方面,HASTE效果可靠,FLASHt、rueFISP因不同程度受伪影影响而效果次之。HASTE和FLASH均可显示纵隔肿大淋巴结。结论:HASTE无伪影,可作为肺癌MRI分期的首选快速成像序列,FLASH则主要用于冠状位成像,trueFISP可以选择应用。     

T1- and T2-weighted imaging at 8 Tesla

In this work, both T1- and T2-weighted fast imaging methods at 8 T are presented. These include the modified driven equilibrium Fourier transform (MDEFT) and rapid acquisition with relaxation enhancement (RARE) methods, respectively. Axial MDEFT images were acquired with large nutation angles, both partially suppressing gray and white matter and permitting the visualization of vascular structures rich in unsaturated spins. Sagittal RARE images, acquired from the same volunteer, were highly T2-weighted, thus highlighting the CSF. At the same time, they provided good visualization of the corpus callosum, cerebellum, and gray and white matter structures. Importantly, both MDEFT and RARE images could be acquired without violating specific absorption rate guidelines.     

Assessment of T2- and T1-weighted MRI brain lesion load in patients with subcortical vascular encephalopathy

Previous cross-sectional studies in patients with subcortical vascular encephalopathy (SVE) have shown little or no correlation between brain lesion load and clinical disability, which could be due to the low specificity of T2-weighted MRI. Recent studies have indicated that T1-weighted MRI may be more specific than T2-weighted MRI for severe tissue destruction. We studied 37 patients with a diagnosis of SVE and 11 normal controls with standardised T1- and T2-weighted MRI. All patients underwent detailed clinical assessment including a neuropsychological test battery and computerised gait analysis. Both the T2- and T1-weighted total MRI lesion loads different between patients and controls different, particularly T1. The ratio of T2-/T1-weighted lesion load was lower in controls than in patients. There was no overall correlation of T1- or T2-weighted lesion load with clinical disability, but group comparison of patients with severe and mild clinical deficits showed different lesion loads. We suggest that T1- and T2-weighted MRI lesion loads demonstrate relevant structural abnormality in patients with SVE. Received: 28 July 1997 Accepted: 24 December 1997     

Endometrial carcinoma in adenomyosis: assessment of myometrial invasion on T2-weighted spin-echo and gadolinium-enhanced T1-weighted images

OBJECTIVE: The aim of our study was to compare T2-weighted and contrast-enhanced dynamic T1-weighted images with histologic findings in assessing the depth of myometrial invasion by endometrial carcinoma in adenomyosis. MATERIALS AND METHODS: We retrospectively reviewed the MRIs of 11 patients who had a total of 12 lesions of endometrial carcinoma within adenomyosis. T2-weighted and contrast-enhanced dynamic T1-weighted images were compared with the histologic findings separately. We assessed the extent of myometrial invasion by endometrial carcinomas. The depth of myometrial invasion seen on MRI was classified as stage S (superficial invasion), stage D (deep invasion), or undetectable. The staging accuracies of each sequence were assessed. The tumor-myometrium contrast-to-noise ratios were calculated for each sequence. RESULTS: The histologic specimens revealed that myometrial invasion was deep in seven of 12 lesions and superficial in five. On T2-weighted images the depth of invasion was underestimated in two lesions and impossible to determine in five lesions. On dynamic T1-weighted images the depth of invasion was overestimated in one lesion and underestimated in one lesion. The staging accuracy on dynamic T1-weighted images (83%) was significantly higher than that on T2-weighted images (42%). The contrast-to-noise ratio was significantly higher on dynamic T1-weighted studies during the early phase (mean +/- SD, 2.68 +/- 0.94) than it was on T2-weighted studies (1.74 +/- 1.05) and during the delayed phase (2.01 +/- 0.86). CONCLUSION: When adenomyosis coexists with endometrial cancer at the same site on T2-weighted images, contrast-enhanced dynamic T1-weighted imaging improves the accuracy of staging.     

Fast MR imaging of liver metastasis using FLASH and FISP--optimal sequences for T1- and T2*-weighted images

This paper deals with a study to obtain the optimal sequence of gradient echo (GE) for T1- and T2*-weighted images similar to T1- and T2-weighted images of spin echo (SE). Two GE sequences, fast low angle shot (FLASH) and fast imaging with steady-state precession (FISP), were performed in 15 cases of liver metastasis in various combination of flip angle (FA), repetition time (TR), and echo time (TE). The optimal combinations were summarized as follows: 1) T1-weighted FLASH image with FA of 40 degrees, TR of 22 msec and TE of 10 msec, 2) T1-weighted FISP image with FA of 70 degrees, TR of 100 msec, TE of 10 msec, 3) both T2*-weighted FLASH and FISP images with FA of 10 degrees, TR of 100 msec and TE of 30 msec. Not only to provide the adequate T1- and T2*-weighted images but also to enable breath-holding MR imaging, GE sequences can optionally take place SE in cases of deteriorated images caused by moving artifacts. Other applications support the re-examination and further detailing when required, conveniently rather in short time.     

Contrast in rapid MR imaging: T1- and T2-weighted imaging

Partial saturation (PS) is an imaging technique that is useful in applications that require rapid image acquisitions (imaging time less than 1 min). Image contrast in PS imaging, as in other magnetic resonance methods, depends on the often conflicting effects of differences in proton density, T1, and T2. Previous analyses of pulse sequence optimization to maximize image contrast have assumed 90 degrees pulses and examined the effects of varying repetition times (TR) and echo times (TE). In this paper we present theoretical calculations and images made with a 0.6 T imager to show that the radiofrequency pulse tip angle alpha, and not the pulse sequence timing parameters, is the most important parameter for producing image contrast. For large tip angles (alpha greater than or equal to 60 degrees), contrast is primarily determined by differences in T1, but for small tip angles (alpha approximately equal to 25 degrees), contrast is primarily due to differences in T2. The T2-weighted images can be produced as quickly as T1-weighted images by using a small pulse angle and a long TE; it is not necessary to use a long TR to reduce the effects of T1 differences. Optimum pulse angles are calculated, and the potential advantages and disadvantages of T2-weighted and T1-weighted PS imaging are discussed.     

Mangafodipir trisodium: effects on T2- and T1-weighted MR cholangiography

The purpose of this study was to determine the effects of mangafodipir trisodium on heavily T2-weighted magnetic resonance cholangiography (MRC) images and on functional T1-weighted MRC. Pre- and post-mangafodipir trisodium heavily T2-weighted MRC and fat-suppressed T1-weighted three-dimensional (3D) gradient-echo MRC images were obtained in a patient with a prior cholecystectomy and a long cystic duct remnant that had apparent biliary stasis. Multiplanar reconstructed images were created. The precontrast T2-weighted MRC showed a long cystic duct remnant and a normal common bile duct (CBD). The postcontrast T2-weighted MRC showed loss of CBD signal, but persistent signal in the cystic duct remnant due to biliary stasis. Post-mangafodipir T1-weighted 3D gradient-echo images showed the main right and left hepatic ducts, but the cystic duct was not depicted. Conventional T2-weighted MRC sequences should not be obtained after administering mangafodipir trisodium because this contrast agent decreases the T2 and therefore the signal intensity of bile within normally functioning bile ducts. Functional MRC images can be acquired by using a post-mangafodipir T1-weighted technique.     

High-contrast 3D neonatal brain imaging with combined T1- and T2-weighted MP-RAGE.

Optimization of magnetization-prepared rapid gradient-echo (MP-RAGE) sequence variations for maximum white matter (WM) versus gray matter (GM) contrast in neonates at 3T was investigated. Numerical simulations were applied to optimize and compare three contrast preparation modules and to assess the effect of phase encoding (PE) order on contrast between WM and thin cortical GM layers. Simulations predict that a new sequence, which combines both T(1)- and T(2)-weighting into the contrast preparation and utilizes an interleaved elliptical-spiral PE order, should provide the strongest contrast between neonatal WM and cortical GM. This sequence was compared to a conventional MP-RAGE acquisition (i.e., T(1)-weighted preparation, centric PE order) for in vivo imaging of seven preterm newborn infants. Regional measurements of the contrast-to-noise ratio (CNR) between WM and GM demonstrated an increase of 50-70% (depending on GM region) using the new sequence, in good agreement with theoretical predictions. This improved contrast resulted in superior WM versus GM discrimination in intensity-based brain tissue segmentations.     

Effect of multislice interference on image contrast in T2- and T1-weighted MR images

Multislice imaging markedly degrades the contrast of T2-weighted MR images as the separation between slices is reduced. Image contrast was measured clinically at 1.5 T and experimentally at 0.15 T as a function of interslice gap width and shown to be in agreement with calculations based on known relaxation times and excitation profiles. Thus, the cause of T2 contrast degradation in multislice sequences is demonstrated. Contrast in T1-weighted sequences is shown to be minimally affected or even slightly enhanced. Selective excitation pulses with better spatial definition will diminish these contrast changes. Since perfect slice profiles can never be achieved, the clinical implications of these findings are discussed for MR imaging. The choice of slice gaps is an important operator-selected parameter in reducing contrast degradation in T2-weighted sequences.     

Clinical utility of optimized three-dimensional T1-, T2-, and T2*-weighted sequences in spinal magnetic resonance imaging

This article reviews the clinical utility of 3D magnetic resonance imaging (MRI) sequences optimized for the evaluation of various intraspinal lesions. First, intraspinal tumors with hypervascular components and arteriovenous malformations (AVM) are clearly shown on contrast-enhanced (CE)-3D T1-weighted gradient-echo (GE) sequences with high spatial resolution. Second, dynamic CE-3D time-resolved magnetic resonance angiography (MRA) shows delineated feeding arteries of intraspinal AVM or arteriovenous fistula (AVF), greatly aiding subsequent digital subtraction angiography (DSA). Third, 3D multiecho T2*-weighted GE sequences are used to visualize intraspinal structures and spinal cord lesions and are sensitive to the magnetic susceptibility of intraspinal hemorrhages. Three-dimensional balanced steady-state free precession (SSFP) and multishot 3D balanced non-SSFP sequences produce contiguous thin images with high signal-to-noise ratio (SNR) in short scanning times. Intraspinal cystic lesions and small nerve-root tumors in subarachnoid space can be viewed using 3D balanced SSFP. Spinal cord myelomalacia and cord compression can be evaluated on fat-suppressed multishot 3D balanced non-SSFP. Finally, a 3D T2-weighted fast spin-echo (FSE) sequence with variable flip angle (FA) refocusing pulse improves through-plane spatial resolution over conventional 2D T2-weighted FSE sequences while matching image contrast.     

Acute cholecystitis at T2-weighted and manganese-enhanced T1-weighted MR cholangiography: preliminary study

Twelve patients with symptoms of acute cholecystitis underwent heavily T2-weighted and mangafodipir trisodium-enhanced T1-weighted magnetic resonance (MR) cholangiography and cholescintigraphy before they underwent cholecystectomy. On T2-weighted MR cholangiographic images, morphologic evidence of outflow obstruction of the gallbladder was definitive in seven patients, equivocal in one, and absent in four. In all 12 patients, biliary dynamics depicted at manganese-enhanced T1-weighted MR cholangiography agreed completely with those depicted at hepatobiliary scintigraphy. T2-weighted MR cholangiography combined with manganese-enhanced T1-weighted MR cholangiography provides not only morphologic information but also functional information about the biliary system.     

High-resolution MR-imaging of the liver with T2-weighted sequences using integrated parallel imaging: comparison of prospective motion correction and respiratory triggering

PURPOSE: To compare high-resolution T2-weighted images of the liver with and without integrated parallel acquisition techniques (iPAT) using either breath-hold sequences in combination with prospective acquisition motion correction (PACE) or respiratory triggering. MATERIALS AND METHODS: Ten volunteers and 10 patients underwent each four different high-resolution fast spin echo (FSE) T2-weighted sequences with 5 mm slice thickness and a full 320 matrix: a multi-breath-hold FSE sequence with and without iPAT and PACE and a respiratory-triggered FSE sequence with and without iPAT. Image quality was rated with a five-point scale by two independent readers. Signal intensity measurements were performed on a water phantom. RESULTS: The sequences with iPAT required a substantially shorter acquisition time without loss of image quality. Overall image quality was rated equal for all sequences by both readers. Image time for nine slices with iPAT was 13 seconds (19 seconds without iPAT) with multi-breath-hold and on average 4:00 minutes (7:02 minutes without iPAT) with respiratory triggering. Imaging with the PACE technique resulted in more correct positioning of the image stacks. CONCLUSION: T2-weighted fast imaging with iPAT is feasible and results in high-quality images within a short acquisition time. Overall image quality is not negatively affected by iPAT.     

Acute myocardial infarction: comparison of T2-weighted and T1-weighted gadolinium-DTPA enhanced MR imaging

Magnetic resonance images were obtained from 32 patients with acute myocardial infarction, using a four-echo technique (echo time (TE) = 30, 60, 90, and 120 ms) pregadolinium(Gd)-DTPA injection and a TE = 30 ms sequence pre- and post-Gd-DTPA. Intensity ratios of infarcted and normal myocardium were calculated, as were contrast-to-noise and signal-to-noise ratios. The four intensity ratios pre-Gd-DTPA were 1.20 +/- 0.15, 1.42 +/- 0.22, 1.78 +/- 0.38, and 1.99 +/- 0.60 for TE = 30, 60, 90, and 120 ms, respectively, and 1.42 +/- 0.19 post-Gd-DTPA (p = NS for post-Gd-DTPA vs TE = 60, p = 0.007 for TE = 90 vs TE = 120, p less than 0.0001 for all other comparisons). The four contrast-to-noise ratios pre-Gd-DTPA were 1.69 +/- 0.97, 2.69 +/- 1.13, 3.17 +/- 1.15, and 2.90 +/- 1.09 for TE = 30, 60, 90, and 120 ms, respectively, and 2.71 +/- 1.26 post-Gd-DTPA (p = NS for post-Gd-DTPA vs TE = 60, 90, and 120, p = NS for TE = 120 vs TE = 60 and 90, p less than 0.01 for all other comparisons). The four signal-to-noise ratios pre-Gd-DTPA were 8.67 +/- 1.47, 6.52 +/- 0.76, 5.20 +/- 0.64, 4.17 +/- 0.53 for TE = 30, 60, 90, and 120 ms, respectively, and 9.17 +/- 1.92 post-Gd-DTPA (p = 0.03 for post-Gd-DTPA vs TE = 30, p less than 0.0001 for all other comparisons). In conclusion, the detectabilities of acute myocardial infarction were similar at TE = 60 ms and at Gd-DTPA enhanced short-TE MR imaging. However, image quality proved to be superior using the Gd-DTPA enhanced short-TE technique.     

Dynamic contrast-enhanced T2*-weighted MRI in patients with cerebrovascular disease

Our purpose was to investigate the potential of dynamic susceptibility contrast-enhanced MRI in assessing regional haemodynamics in patients with cerebrovascular disease. T2^*-weighted FLASH sequences were performed on a control group of 10 healthy subjects, 13 patients with unilateral stenosis or occlusion of the internal carotid artery and 6 patients with acute onset of neurological symptoms, the observed signal intensities being converted into concentration-time curves. A gamma-variate function was fitted to the measured concentration-time curves to eliminate effects of tracer recirculation. In each patient the two cerebral hemispheres were compared and the difference between the mean transit times and the percental change of the regional cerebral blood volume, calculated for each side. Patients with haemodynamically significant unilateral carotid obstruction can be divided into two subgroups: those with good and those with poor collateral supply. Patients with good collateral supply had a slight but not statistically significant increase in mean transit time and cerebral blood volume on the diseased side, whereas those with poor collaterals had a significant increase compared with the control group. In patients with acute onset of neurological symptoms perfusion maps clearly demonstrated the disturbed perfusion at a time when T2-weighted images were still normal. Perfusion imaging is a reliable and noninvasive method of assessing changes in cerebral perfusion in patients with unilateral carotid stenosis. This MR technique permits monitoring of haemodynamic changes during therapy and thus may become an alternative to SPECT and PET scanning. In patients with acute occlusion of a cerebral artery, perfusion imaging reveals the entire perfusion deficit before conventional MRI and thus allows early intervention. Received: 10 April 1996 Accepted: 14 June 1996     

Breast lesions: evaluation with dynamic contrast-enhanced T1-weighted MR imaging and with T2*-weighted first-pass perfusion MR imaging

PURPOSE: To evaluate the diagnostic value of an imaging protocol that combines dynamic contrast-enhanced T1-weighted magnetic resonance (MR) imaging and T2*-weighted first-pass perfusion imaging in patients with breast tumors and to determine if T2*-weighted imaging can provide additional diagnostic information to that obtained with T1-weighted imaging. MATERIALS AND METHODS: One hundred thirty patients with breast tumors underwent MR imaging with dynamic contrast-enhanced T1-weighted imaging of the entire breast, which was followed immediately with single-section, T2*-weighted imaging of the tumor. RESULTS: With T2*-weighted perfusion imaging, 57 of 72 carcinomas but only four of 58 benign lesions had a signal intensity loss of 20% or more during the first pass, for a sensitivity of 79% and a specificity of 93%. With dynamic contrast-enhanced T1-weighted imaging, 64 carcinomas and 19 benign lesions showed a signal intensity increase of 90% or more in the first image obtained after the administration of contrast material, for a sensitivity of 89% and a specificity of 67%. CONCLUSION: T2*-weighted first-pass perfusion imaging can help differentiate between benign and malignant breast lesions with a high level of specificity. The combination of T1-weighted and T2*-weighted imaging is feasible in a single patient examination and may improve breast MR imaging.