Resection of soft tissue sarcomas with intra-operative magnetic resonance guidance.

PURPOSE: To report on a preliminary series of magnetic resonance (MR)-guided sarcoma resections. MATERIALS AND METHODS: Three patients with the skin sarcoma dermatofibrosarcoma protuberans underwent MR-guided resection. RESULTS: The extent of the tumor at MR imaging was greater in each case than suggested by clinical examination. Adequate resection margins were planned using short Tau inversion recovery (STIR) sequences and intra-operative imaging was used to confirm complete tumor excision. Histological examination confirmed clear surgical margins of at least 1 cm in each case. CONCLUSION: We believe this technique may reduce the incidence of specimen margins positive for tumor following resection, and consequently reduce the need for further excisional surgery.     

Primary glioma: diagnosis with magnetic resonance imaging

Seventeen patients with surgically documented primary glial-origin brain tumors were evaluated by magnetic resonance imaging and high-resolution computed tomography. The exclusion of CT ring-enhancing lesions directed the focus of this study toward lower grade tumors that were more difficult to diagnose. The computed tomography abnormalities were often subtle and included areas of low attenuation, mass effect, and focal enhancement. Spin-echo sequences with both heavy T1 and T2 weighting were utilized. Prolonged T1 and T2 values were observed in all tumors. The T2-weighted spin-echo 1000/120 sequence was the most sensitive in tumor detection and was positive in all cases. Magnetic resonance imaging was superior to computed tomography in tumor detection, tumor localization, assessment of tumor extent, and determination of associated changes, ie, brain stem encroachment. All the magnetic resonance sequences used showed an increase in severity of imaging changes with increasing tumor grade. The T2-weighted sequence showed progressive margin irregularity, whereas the T1-weighted (inversion recovery) sequence showed increasing severity of internal tissue changes. The superior resolution of these changes by magnetic resonance imaging may have implications for better assessment of tumor grade in the future than is currently possible with computed tomography.     

Multiparametric tissue characterization of brain neoplasms and their recurrence using pattern classification of MR images

RATIONALE AND OBJECTIVES: Treatment of brain neoplasms can greatly benefit from better delineation of bulk neoplasm boundary and the extent and degree of more subtle neoplastic infiltration. Magnetic resonance imaging (MRI) is the primary imaging modality for evaluation before and after therapy, typically combining conventional sequences with more advanced techniques such as perfusion-weighted imaging and diffusion tensor imaging (DTI). The purpose of this study is to quantify the multiparametric imaging profile of neoplasms by integrating structural MRI and DTI via statistical image analysis methods to potentially capture complex and subtle tissue characteristics that are not obvious from any individual image or parameter. MATERIALS AND METHODS: Five structural MRI sequences, namely, B0, diffusion-weighted images, fluid-attenuated inversion recovery, T1-weighted, and gadolinium-enhanced T1-weighted, and two scalar maps computed from DTI (ie, fractional anisotropy and apparent diffusion coefficient) are used to create an intensity-based tissue profile. This is incorporated into a nonlinear pattern classification technique to create a multiparametric probabilistic tissue characterization, which is applied to data from 14 patients with newly diagnosed primary high-grade neoplasms who have not received any therapy before imaging. RESULTS: Preliminary results demonstrate that this multiparametric tissue characterization helps to better differentiate among neoplasm, edema, and healthy tissue, and to identify tissue that is likely to progress to neoplasm in the future. This has been validated on expert assessed tissue. CONCLUSION: This approach has potential applications in treatment, aiding computer-assisted surgery by determining the spatial distributions of healthy and neoplastic tissue, as well as in identifying tissue that is relatively more prone to tumor recurrence.     

磁共振STIR序列在早期股骨头缺血性坏死诊断中的应用

目的评价磁共振STIR序列对股骨头缺血性坏死(ANFH)早期诊断的临床应用价值。方法对经MRI普查后STIR序列显示不同程度骨髓水肿及关节积液,而常规T1WI及T2WI未明确提示ANFH特征性改变的18例临床高危患者4～6个月后复查,对其影像征象进行分期和对比性分析。结果复查后有14例患者(共25部位股骨头)可诊断为Ⅰ～Ⅱ期ANFH,病变部位与MRI初次检查时STIR序列所显示的骨髓水肿部位基本一致。结论 MRI在检测ANFH病变中具有较高的敏感性,尤其STIR序列对ANFH的早期诊断具有极高的应用价值。     

Whole-heart coronary magnetic resonance angiography: contrast-enhanced high-resolution, time-resolved 3D imaging

OBJECTIVES: To test the feasibility and performance of a 4D magnetic resonance coronary angiography sequence compared with conventional inversion recovery (IR) prepared gradient echo imaging. MATERIALS AND METHODS: A 4D sequence with 100 milliseconds temporal resolution was implemented on a 1.5 T system. Five minipigs were examined after administration of very small superparamagnetic iron oxide particles. Coronary angiographies with an isotropic resolution of 0.82 mm were performed in the pigs using 4D and IR sequences. RESULTS: The 4D sequence allowed visualization of the coronary arteries, the effect of their movement and that of the entire heart without prolonging scan time. The contrast-to-noise ratio of the IR images was on average 38% higher than that of the corresponding 4D phase. CONCLUSIONS: 4D magnetic resonance imaging is superior in that no trigger delay time needs to be determined and an additional whole-heart cine study can be obtained.     

Further technical development in magnetic resonance imaging of the brain in children

Further technical developments implemented in magnetic resonance imaging (MRI) of the brain in children are described. These include the use of longer data collection periods, T2-dependent field echoes, susceptibility mapping, short inversion time inversion recovery sequences, very long echo time spin-echo sequences, and phase mapping techniques to detect tissue perfusion. These techniques are illustrated in selected cases and have increased the range of options available in MR examinations of children.     

Comparison of STIR and spin-echo MR imaging at 1.5 T in 45 suspected extremity tumors: lesion conspicuity and extent

Short inversion time inversion recovery (STIR) imaging and a double-echo spin-echo (SE) sequence at 1.5 T in 45 sequential patients with suspected extremity tumors were compared to assess the number of lesions detected, subjective conspicuity of lesions, approximate volume of abnormality detected in each lesion, and identification of peritumoral brightening in tissues adjacent to each lesion. STIR sequences enabled detection of all 45 lesions; 44 were detected with the SE sequence. Tumor appeared most conspicuous on STIR images in 35 patients (78%) and was most conspicuous on SE images in 10 patients (22%). Peritumoral brightening, which indicated either peritumoral edema or microscopic tumor infiltration, was detected in 20 patients but was detected only with STIR sequences in nine patients. It is concluded that, although STIR and SE sequences are comparable for lesion detection in the extremities, most lesions appear more conspicuous with STIR. STIR may enable detection of a greater volume of abnormality than SE sequences and may therefore have important implications for local staging and surgical and radiation therapy planning.     

Study of focused ultrasound tissue damage using MRI and histology.

This paper reports on an experimental study of in vivo tissue damage in the rabbit brain with focused ultrasound (FUS) using magnetic resonance imaging (MRI) and histopathological analysis. Ten ultrasonic lesions (tissue damage) were created in five rabbits using a focused ultrasound beam of 1.5 MHz, electrical power input to the transducer of 70-85 W, and an exposure duration of 15-20 seconds. T1- and T2-weighted fast spin-echo (FSE) and Fluid attenuated inversion recovery (FLAIR) sequences were used to detect the ultrasonic lesions after treatment. Imaging was performed for 4-8 hours after treatment, after which the animals were immediately sacrificed. Ultrasonic lesion diameter was measured on MRI and histological sections after correction for tissue shrinkage during the histological processing. The T1-weighted images showed lesions poorly, whereas both T2-weighted and FLAIR images showed lesions clearly. The lesion diameters on both T2 and FLAIR imaging correlated well with measurements from histology. The time delay before lesions appeared on T2-weighted imaging was 15 minutes to 1 hour, depending on the exposure location in the brain. J. Magn. Reson. Imaging 1999;10:146-153.     

MR imaging of the liver using short TI inversion recovery sequences

Use of the short inversion time inversion recovery (STIR) sequence in magnetic resonance (MR) imaging of the liver is illustrated in 20 patients. The sequence provides high contrast images of the liver with relatively little degradation due to motion. Lesions appeared more extensive than with X-ray CT in 14 cases and equal in six. Additional areas of presumed atrophy, fatty infiltration, edema, or vascular insufficiency were only seen with MR. The STIR sequence may be valuable in screening of the liver for metastatic disease.     

Use of fluid attenuated inversion recovery (FLAIR) pulse sequences in MRI of the brain.

Fluid attenuated inversion recovery pulse sequences with a long echo time (TE) have been used to image the brain in one volunteer and four patients. The long inversion time used with this sequence suppresses the signal from CSF and the long TE produces very heavy T2 weighting. The marked reduction in flow artefact from CSF and the high T2 weighting enabled anatomical detail to be seen within the brain stem and produced high lesion contrast in areas close to CSF. Lesions were demonstrated with greater conspicuity than with conventional T2-weighted sequences in patients with cerebral infarction, low grade astrocytoma, and diplegia.     

Tissue sodium concentration in human brain tumors as measured with 23Na MR imaging

PURPOSE: To use combined proton (1H) and sodium 23 (23Na) magnetic resonance (MR) imaging to noninvasively quantify total tissue sodium concentration and to determine if concentration is altered in malignant human brain tumors. MATERIALS AND METHODS: Absolute tissue sodium concentration in malignant gliomas was measured on quantitative three-dimensional 23Na MR images with tissue identification from registered 1H MR images. Concentration was determined in gray matter (GM), white matter (WM), cerebrospinal fluid (CSF), and vitreous humor in 20 patients with pathologically proven malignant brain tumors (astrocytoma, n = 17; oligodendroglioma, n = 3) and in nine healthy volunteers. Sodium concentration in tumors and edema was determined from 23Na image signal intensities in regions that were contrast material enhanced on T1-weighted 1H images (tumors) or regions that were only hyperintense on fluid-attenuated inversion recovery (FLAIR) 1H images (edema). Sodium concentrations were measured noninvasively from 23Na images obtained with short echo times (0.4 msec) by using external saline solution phantoms for reference. Differences in mean sodium concentration of all healthy tissue and lesions in patients were tested with a paired t test. Concentration in uninvolved tissues in patients was compared with that in the same tissue types in the volunteers with an independent samples two-tailed t test. RESULTS: Mean concentration (in millimoles per kilogram wet weight) was 61 +/- 8 (SD) for GM, 69 +/- 10 for WM, 135 +/- 10 for CSF, 113 +/- 14 for vitreous humor, 103 +/- 36 for tumor, 68 +/- 11 for unaffected contralateral tissue, and 98 +/- 12 for FLAIR hyperintense regions surrounding tumors. Significant differences (P <.002) in sodium concentration were demonstrated by using a t test for both tumors and surrounding FLAIR hyperintense tissues versus GM, WM, CSF, and contralateral brain tissue. CONCLUSION: 23Na MR imaging with short echo times can be used to quantify absolute tissue sodium concentration in patients with brain tumors and shows increased sodium concentration in tumors relative to that in normal brain structures.     

Diffusion-weighted whole-body MR imaging with background body signal suppression: a feasibility study at 3.0 Tesla

The purpose was to provide a diffusion-weighted whole-body magnetic resonance (MR) imaging sequence with background body signal suppression (DWIBS) at 3.0 Tesla. A diffusion-weighted spin-echo echo-planar imaging sequence was combined with the following methods of fat suppression: short TI inversion recovery (STIR), spectral attenuated inversion recovery (SPAIR), and spectral presaturation by inversion recovery (SPIR). Optimized sequences were implemented on a 3.0- and a 1.5-Tesla system and evaluated in three healthy volunteers and six patients with various lesions in the neck, chest, and abdomen on the basis of reconstructed maximum intensity projection images. In one patient with metastases of malignant melanoma, DWIBS was compared with ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET). Good fat suppression for all regions and diagnostic image quality in all cases could be obtained at 3.0 Tesla with the STIR method. In comparison with 1.5 Tesla, DWIBS images at 3.0 Tesla were judged to provide a better lesion-to-bone tissue contrast. However, larger susceptibility-induced image distortions and signal intensity losses, stronger blurring artifacts, and more pronounced motion artifacts degraded the image quality at 3.0 Tesla. A good correlation was found between the metastases as depicted by DWIBS and those as visualized by FDG-PET. DWIBS is feasible at 3.0 Tesla with diagnostic image quality.     

Correlative MR imaging and histopathology in porcine neurocysticercosis

PURPOSE: To examine whether all the histopathologically seen features of cysticercus cysts excised from brain of swine naturally infected with neurocysticercosis during its evolution are actually visible on magnetic resonance imaging (MRI). MATERIALS AND METHODS: Five swine naturally infected with cerebral cysticercosis were subjected to fast spin-echo (SE) T2, SE T1, fluid attenuated inversion recovery imaging, T1-weighted magnetization transfer (MT), and postcontrast T1-weighted MT sequences on MRI. These animals were sacrificed after imaging and ex vivo imaging of the intact excised brain using the same imaging protocol was also performed. Grossing of these brains was done similar to the ex vivo imaging planes. Numeral density and external appearance of each cyst and scolex were evaluated on each pulse sequence. Amount of pericystic edema, if present, was also assessed. On histopathology, cellular characteristics, inflammatory response, and the extent of edema, if present, in the brain parenchyma around the cysts were graded. Cysts were categorized into viable, early, and late degenerated on histopathology. The MRI features of each cyst were correlated with their histopathologic findings. RESULTS: Out of 31 cysts, eight were found to be viable, 13 early degenerated, and 10 late degenerated on histopathology. T2-weighted imaging demonstrated all the cysts while T1-weighted imaging showed 97% of the cysts. Scolex was seen in 90.3% and 93.5% of the cysts on T2- and T1-weighted images, respectively. Minimal edema (grade I) and inflammation in degenerating cysts present on histopathology was not visible on MRI. All but one of eight degenerated cysts, which showed enhancement on postcontrast MRI, had edema on imaging as well as on histopathology. CONCLUSION: T2-weighted MRI demonstrated all the cysts that were visible on histopathology. Non-enhancement of some of the degenerated cysts along with absence of edema on MRI is likely to underestimate the staging of neurocysticercosis evolution, and these early degenerating cysts may be misdiagnosed as in viable stage.     

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.     

心脏MR反转恢复序列在心肌梗死中的临床应用

目的分析磁共振反转时间(TI)的反转恢复技术的原理及特性,探讨其在心肌梗死中判断心肌存活的临床应用价值及相关注意事项。方法回顾性分析经反转时间的反转恢复技术获得的磁共振心肌梗死图像30例并总结其图像特点。结果在反转时间的反转恢复技术比较其图像质量及心肌与血池对比程度,显示对于坏死心肌判断TI时间的选择,TI=280～320 ms时图像质量最佳。结论在磁共振心肌活性成像的临床应用中,应恰当、合理地选择反转时间的反转恢复技术才能获得最佳的心肌与血池对比的图像,才更利于心肌梗死的诊断与鉴别诊断。     

Contributions of an adiabatic initial inversion pulse and K-space re-ordered by inversion-time at each slice position (KRISP) to control of CSF artifacts and visualization of the brain in FLAIR magnetic resonance imaging

AIM: The aim of this study was to compare the performance of three fluid attenuated inversion recovery (FLAIR) pulse sequences for control of cerebrospinal fluid (CSF) and blood flow artifacts in imaging of the brain. The first of these sequences had an initial sinc inversion pulse which was followed by conventional k-space mapping. The second had an initial sinc inversion pulse followed by k-space re-ordered by inversion time at each slice position (KRISP) and the third had an adiabatic initial inversion pulse followed by KRISP. MATERIALS AND METHODS: Ten patients with established disease were studied with all three pulse sequences. Seven were also studied with the adiabatic KRISP sequence after contrast enhancement. Their images were evaluated for patient motion artifact, CSF and blood flow artifact as well as conspicuity of the cortex, meninges, ventricular system, brainstem and cerebellum. The conspicuity of lesions and the degree of enhancement were also evaluated. RESULTS: Both the sinc and adiabatic KRISP FLAIR sequences showed better control of CSF and blood flow artifacts than the conventional FLAIR sequence. In addition the adiabatic KRISP FLAIR sequence showed better control of CSF artifact at the inferior aspect of the posterior fossa. The lesion conspicuity was similar for each of the FLAIR sequences as was the degree of contrast enhancement to that shown with a T(1)weighted spin echo sequence. CONCLUSION: The KRISP FLAIR sequence controls high signal artifacts from CSF flow and blood flow and the adiabatic pulse controls high signal artifacts due to inadequate inversion of the CSF magnetization at the periphery of the head transmitter coil. The KRISP FLAIR sequence also improves cortical and meningeal definition as a result of an edge enhancement effect. The effects are synergistic and can be usefully combined in a single pulse sequence. Curati, W. L.et al. (2001)Clinical Radiology56, 375-384 Copyright 2001 The Royal College of Radiologists.     

Gd-DTPA-enhanced short repetition time and short inversion time inversion recovery magnetic resonance imaging. Experimental and clinical assessment

To suppress both water and fat signal while retaining the high signal of Gd-DTPA enhancement, magnetic resonance imaging (MRI) of phantoms and 28 patients with mass lesions was done using short repetition time (TR) and short inversion time inversion recovery (STIR) sequences. Optimal STIR pulse sequences of 500 to 1000/80-100/20-30 (TR/TI/TE) were determined by an experimental study. In most instances, a signal bandwidth of +/- 8 kHz was used to increase the signal-to-noise ratio. The authors measured image contrast between lesions and adjacent fatty tissue and compared postcontrast STIR and T1-weighted spin-echo (T1-W SE) images. When the signal intensity of a lesion is 80% of adjacent fatty tissue on postcontrast T1-W SE, short TR STIR images provide better tumor delineation.     

Continuous arterial spin labeling using a train of adiabatic inversion pulses

PURPOSE: To develop a simple and robust magnetic resonance imaging (MRI) pulse sequence for the quantitative measurement of blood flow in the brain and cerebral tumors that has practical implementation advantages over currently used continuous arterial spin labeling (CASL) schemes. MATERIALS AND METHODS: Presented here is a single-coil protocol that uses a train of hyperbolic secant inversion pulses to produce continuous arterial spin inversion for perfusion weighting of fast spin echo images. Flow maps of normal rat brains and those containing a 9L gliosarcoma orthotopic tumor model conditions were acquired with and without carbogen. RESULTS: The perfusion-weighted images have reduced magnetization transfer signal degradation as compared to the traditional single-coil CASL while avoiding the use of a more complex two-coil CASL technique. Blood flow measurements in tumor and normal brain tissue were consistent with those previously reported by other CASL techniques. Contralateral and normal brain showed increased blood flow with carbogen breathing, while tumor tissue lacked the same CO(2) reactivity. CONCLUSION: This variation of the CASL technique is a quantitative, robust, and practical single-coil method for measuring blood flow. This CASL method does not require specialized radiofrequency coils or amplifiers that are not routinely used for anatomic imaging of the brain, therefore allowing these flow measurements to be easily incorporated into traditional rodent neuroimaging protocols.     

Primary bone tumors. MR morphologic appearance correlated with pathologic examinations.

Eighty-three MR studies for primary bone tumors, performed with both spin echo and short time inversion recovery (STIR) sequences, were reviewed. Twenty-six patients underwent surgery within 10 days after MR imaging. Specimens were cut and directly compared with MR images. In the remainder, pathologic slides were compared in order to obtain a better understanding of MR pattern. All MR images were examined with a traditional morphologic approach and, upon comparison with surgical macroslides and with pathology samples, some MR distinctive patterns were identified: the bulky appearance of osteosarcoma surrounded by muscle edema, the multilobular high signal intensity (SI) chondroid lesions, the subtle infiltration of Ewing's sarcoma, rarely accompanied by muscle edema and prone to MR underestimation, the well defined "multiple shells" pattern of giant cell tumor, and the ill defined "storiform" appearance of malignant fibrous histocytoma are all typical MR features strictly corresponding to pathologic findings. The chondroid origin tumors may be identified based on the lobular high SI pattern whereas a benign fibrous lesion was the only one in this series to be distinguished relying on the SI. Peritumoral soft tissue edema was found by the STIR sequence only in malignant tumors (69%) of this series, and particularly in osteosarcoma (96%), chondrosarcoma (83%), and giant cell tumor (100%): this associate finding may further contribute to the diagnosis.