CT-MR image data fusion for computer-assisted navigated surgery of orbital tumors

Purpose

To demonstrate the value of multidetector computed tomography (MDCT) and magnetic resonance imaging (MRI) in the preoperative assessment of orbital tumors, and to present, particularly, CT and MR image data fusion for surgical planning and performance in computer-assisted navigated surgery of orbital tumors.

Materials and methods

In this retrospective case series, 10 patients with orbital tumors and associated complaints underwent MDCT and MRI of the orbit. MDCT was performed at high resolution, with a bone window level setting in the axial plane. MRI was performed with an axial 3D T1-weighted (w) gradient-echo (GE) contrast-enhanced sequence, in addition to a standard MRI protocol. First, MDCT and MR images were used to diagnose tumorous lesions compared to histology as a standard of reference. Then, the image data sets from CT and 3D T1-w GE sequences were merged on a workstation to create CT-MR fusion images that were used for interventional planning and intraoperative image guidance. The intraoperative accuracy of the navigation unit was measured, defined as the deviation between the same landmark in the navigation image and the patient. Furthermore, the clinical preoperative status was compared to the patients’ postoperative outcome.

Results

Radiological and histological diagnosis, which revealed 7 benign and 3 malignant tumors, were concordant in 7 of 10 cases (70%). The CT-MR fusion images supported the surgeon in the preoperative planning and improved the surgical performance. The mean intraoperative accuracy of the navigation unit was 1.35 mm. Postoperatively, orbital complaints showed complete regression in 6 cases, were ameliorated notably in 3 cases, and remained unchanged in 1 case.

Conclusion

CT and MRI are essential for the preoperative assessment of orbital tumors. CT-MR image data fusion is an accurate tool for planning the correct surgical procedure, and can improve surgical results in computer-assisted navigated surgery of orbital tumors.     

Automatic method to assess local CT-MR imaging registration accuracy on images of the head

BACKGROUND AND PURPOSE: Precise registration of CT and MR images is crucial in many clinical cases for proper diagnosis, decision making or navigation in surgical interventions. Various algorithms can be used to register CT and MR datasets, but prior to clinical use the result must be validated. To evaluate the registration result by visual inspection is tiring and time-consuming. We propose a new automatic registration assessment method, which provides the user a color-coded fused representation of the CT and MR images, and indicates the location and extent of poor registration accuracy. METHODS: The method for local assessment of CT-MR registration is based on segmentation of bone structures in the CT and MR images, followed by a voxel correspondence analysis. The result is represented as a color-coded overlay. The algorithm was tested on simulated and real datasets with different levels of noise and intensity non-uniformity. RESULTS: Based on tests on simulated MR imaging data, it was found that the algorithm was robust for noise levels up to 7% and intensity non-uniformities up to 20% of the full intensity scale. Due to the inability to distinguish clearly between bone and cerebro-spinal fluids in the MR image (T1-weighted), the algorithm was found to be optimistic in the sense that a number of voxels are classified as well-registered although they should not. However, nearly all voxels classified as misregistered are correctly classified. CONCLUSION: The proposed algorithm offers a new way to automatically assess the CT-MR image registration accuracy locally in all the areas of the volume that contain bone and to represent the result with a user-friendly, intuitive color-coded overlay on the fused dataset.     

Magnetic resonance findings in chronic osteomyelitis fistula

INTRODUCTION: Osteomyelitis is a common inflammatory process caused by an infection which is usually from gram-positive germs. Acute, subacute and chronic forms can be distinguished both clinically and radiographically, each of them presenting different patterns but which are not always easy to recognize. Besides clinical-laboratory data, imaging methods are also useful to make the diagnosis; in chronic forms, MRI has higher sensitivity in recognizing the active foci and the presence of sinus tracts than the other techniques. MATERIAL AND METHODS: We examined nine patients with suspected chronic osteomyelitis with a sinus tract, all of them submitted to radiographic and MR examinations. MRI was performed with a .5 T magnet using a surface coil for joint studies; T1-weighted SE (TR 300-500, TE 20), T2-weighted GE (TR 500-700, TE 20, FA 35 degrees) and FIR sequences with fat suppression (TR 3000, TE 20, TI 100) were performed on the axial, sagittal and coronal planes. Three patients underwent CT too. RESULTS: Radiography showed the osteostructural changes as osteolytic and osteosclerotic areas. CT depicted not only the changes seen radiographically, but also increased bone marrow density. MRI demonstrated active foci of bone marrow appearing as low-intensity areas in T1, with increased intensity in T2 GE and fat-suppressed FIR images; it also depicted the sinus tracts as areas of decreased signal on T1 and of increased signal on FIR images. CONCLUSIONS: Based on our experience and in agreement with the literature data, we believe that MRI is more useful to diagnose the active foci of bone marrow and the sinus tracts in chronic osteomyelitis, especially with T1-weighted SE and fat-suppressed FIR sequences.     

CT and MR imaging features of oral and maxillofacial hemangioma and vascular malformation

PURPOSE: To present CT and MR images and compare CT and MRI features of oral and maxillofacial hemangioma and vascular malformation. MATERIAL AND METHODS: The clinical materials consisted of nine vascular tumors from nine patients examined by both CT and MR scanners between November 1996 and March 2002. Both CT and MR images were retrospectively evaluated. The following features were evaluated: detectability of the lesion, border of the lesion, tumor margin, inner nature of the lesion, contrast between the lesion and surrounding tissues, degree of CT value or signal intensity of the lesion, enhancement of contrast medium, inner nature of the lesion after contrast medium injection, detectability of phleboliths and detectability of bone resorption. RESULTS: In two patients, we could not detect lesions in any of the CT images because of artifacts from the teeth and/or dental restorations. In contrast, we could detect all lesions on T2-weighted MR images and contrast enhanced T1-weighted MR images. On T2-weighted images with the fat suppression technique, tumors tended to show higher contrast compared to surrounding tissues. CONCLUSION: T2-weighted images with the fat suppression technique and contrast enhanced T1-weighted images with the fat suppression technique were very useful for the detection of vascular lesions. Observation from optional directions (axial, coronal and sagittal images) seemed appropriate for delineating the extension of the tumor. Phleboliths detectability on CT images was superior to that on MR images.     

Computed tomography and magnetic resonance tomography of the normal temporal bone

The normal anatomy of the temporal bone and the inner ear will be described in detail on high resolution computed tomography (HRCT) and magnetic resonance images. The imaging technique of computer tomography--either single detector or multi detector CT--is normally obtained in an axial plane without the intravenous application of contrast material. The images are reconstructed in a high resolution bone window level setting. The coronal images are reconstructed either if used single detector or multi detector CT. Only in some cases a scan in the coronal plane is directly obtained using a single detector CT. MR imaging of temporal bone is usually performed in a head coil. Axial high resolution 3D-T2-weighted sequences either in fast spin echo technique or gradient echo technique--for example CISS-sequence--are obtained, then an axial high resolution T1-weighted sequence before and after the application of gadopentate dimiglumine is performed. HRCT excellently demonstrates the osseous structures of the temporal bone as well as of the inner ear, while MRI excellently depicts soft tissue structures especially those of the inner ear. Due to the susceptibility artifacts MRI is not very suitable for imaging the external auditory canal or the middle ear or the pneumatic system. In conclusion HRCT is so far excellent to delineate the osseous structures of the temporal bone and inner ear while MRI excellently depicts the soft tissue structures of the inner ear, the internal auditory canal and the cerebellopontine angle. Reissner's membrane, the cochlear duct, and the organ of Corti cannot be visualized even using high-resolution MRI. HRCT and MRI are therefore used as complementary methods for imaging the temporal bone.     

MRI of anterior mediastinal tumors.

To compare the abilities of MRI (magnetic resonance imaging) and CT to provide information about anterior mediastinal tumors, we retrospectively evaluated the MR (n = 28) and CT images (n = 25) of patients with anterior mediastinal tumors. T1-weighted and T2-weighted images were obtained with spin echo sequences using cardiac gating. Six of 12 thymomas and seven of nine teratomas showed characteristic findings by MRI, while four of the 10 thymomas and five of the eight teratomas were correctly diagnosed by CT. The other tumors did not show a characteristic MR appearance. All nine malignant tumors were correctly diagnosed as malignant lesions on MR images, while one false positive case and one false negative case were recorded on CT images. We conclude that MRI and CT provide nearly the same information for the evaluation of anterior mediastinal tumors. However, in some cases, only MRI can provide information about malignancy or a specific diagnosis.     

Fusion von MRT-, fMRT- und intraoperativen MRT-Daten Methode und klinische Bedeutung am Beispiel neurochirurgischer Interventionen

The aim of this work was to realize and clinically evaluate an image fusion platform for the integration of preoperative MRI and fMRI data into the intraoperative images of an interventional MRI system with a focus on neurosurgical procedures. A vertically open 0.5 T MRI scanner was equipped with a dedicated navigation system enabling the registration of additional imaging modalities (MRI, fMRI, CT) with the intraoperatively acquired data sets. These merged image data served as the basis for interventional planning and multimodal navigation. So far, the system has been used in 70 neurosurgical interventions (13 of which involved image data fusion--requiring 15 minutes extra time). The augmented navigation system is characterized by a higher frame rate and a higher image quality as compared to the system-integrated navigation based on continuously acquired (near) real time images. Patient movement and tissue shifts can be immediately detected by monitoring the morphological differences between both navigation scenes. The multimodal image fusion allowed a refined navigation planning especially for the resection of deeply seated brain lesions or pathologies close to eloquent areas. Augmented intraoperative orientation and instrument guidance improve the safety and accuracy of neurosurgical interventions.     

CT and MRI characteristics of tumours of the temporal bone and the cerebello-pontine angle

Tumours lesions of the temporal bone and of the cerebello-pontine angle are rare. This tumours can be separated into benign and malignant lesions. In this paper the CT and MRI characteristics of tumours of the temporal bone and the cerebello-pontane angle will be demonstrated. High resolution CT (HRCT) as usually performed in the axial plane are using a high resolution bone window level setting, coronal planes are the reconstructed from the axial data set or will be obtained directly. With the MRI FLAIR sequence in the axial plane the whole brain will be scanned either to depict or exclude a tumour invasion into the brain. After this,T2-weighted fast spin echo sequences or fat suppressed inversion recovery sequences in high resolution technique in the axial plane will be obtained from the temporal bone and axial T1-weighted spin echo sequences before and after the intravenous application of contrast material will be obtained of this region. Finally T1-weighted spin echo sequences in high resolution technique with fat suppression after the intravenous application of contrast material will be performed in the coronal plane. HRCT and MRI are both used to depict the most exact tumorous borders. HRCT excellently depicts the osseous changes for example exostosis of the external auditory canal, while also with HRCT osseous changes maybe characterized into more benign or malignant types. MRI has a very high soft tissue contrast and may therefore either characterize vascular space-occupying lesions for example glomus jugulare tumours or may differentiate between more benign or malignant lesions. In conclusion HRCT and MRI of the temporal bone are excellent methods to depict and mostly characterize tumour lesions and can help to differentiate between benign and malignant lesion. These imaging methods shall be used complementary and may have a great impact for the therapeutic planning.     

Staging of spinal metastasis using special techniques of magnetic resonance imaging

The diagnosis of spine metastasis is a problem of great interest which leaves many questions unanswered. In this field MR imaging plays a fundamental role, as the only technique able to directly demonstrate the changes in bone marrow tissue, bound to tumoral activity. The introduction of gradient-echo (GE) sequences has helped reduce examination time. Moreover, with the accurate choice of pulse-sequence parameters (TR, TE, flip angle) additional information is acquired which is not yielded by conventional spin-echo (SE) sequences. Our study was aimed at evaluating MR sensitivity in the different stages of bone metastatic evolution. The comparative adequacy was evaluated of combined bone scintigraphy and conventional radiology versus MR imaging in 62 patients with vertebral metastases. Time interval between bone scan and/or radiological study and MR exam ranged from 10 days to 8 months. SE and GE T1-weighted images, and SE and GE T2-weighted images on the sagittal plane were employed, and axial images; coronal images were rarely acquired. Metastases were demonstrated by MR imaging at 122 vertebral levels, versus 88 true positives of combined scintigraphy and conventional radiology. Scintigraphic false-positives were observed at 15 vertebral levels, versus 9 with radiography. GE sequences were superior to SE ones in detecting vertebral morphologic lesions and bone marrow involvement thanks to their improved resolution and sensitivity. Moreover, GE sequences demonstrated tumoral bone marrow spread and persistent tumoral activity in the follow-up of spine metastases. Our results point to GE sequences as those of choice because of their higher resolution and sensitivity, which also allow response to treatment to be evaluated.     

MRI of the thorax during whole-body MRI: evaluation of different MR sequences and comparison to thoracic multidetector computed tomography (MDCT)

PURPOSE: To evaluate the accuracy of four MR sequences used as part of a whole-body MRI protocol to detect pulmonary lesions in cancer patients. MATERIALS AND METHODS: A total of 31 oncology patients were imaged in a 1.5T MR scanner (Magnetom Avanto; Siemens Medical Solutions, Germany) for whole-body staging. MR chest imaging included: axial and coronal T2-weighted (T2w)-short-tau inversion-recovery (STIR), axial T2w turbo spin-echo (TSE), and contrast-enhanced (CE) three-dimensional (3D) volumetric interpolated breathhold examination (VIBE). Multidetector computed tomography (MDCT) of the thorax served as the reference standard. The MDCT and MR images were evaluated independently by two radiologists. Comparative analysis was performed per lesion, per lobe, and per patient. Sensitivity, specificity, and predictive values were determined. RESULTS: Compared to MDCT that detected 268 pulmonary lesions ranging from 2 to 75 mm in diameter, the MR sensitivities were 91.1%, 92.5%, 90.8%, and 87.3% for the coronal STIR, the axial STIR, the axial T2w-TSE, and the axial CE 3D-VIBE, respectively. Undetected pulmonary lesions were either calcified or smaller than 10 mm in the axial diameter. With coronal STIR, six false-positive findings were detected; with axial STIR, 14 were detected; with axial T2w-TSE, 10 were detected; and with 3D-VIBE, seven were detected. CONCLUSION: Pulmonary MRI is feasible as part of a whole-body MRI protocol. In our study, STIR images achieved high accuracy compared to chest MDCT for pulmonary lesions of 3 mm in size or larger.     

Comparison of dynamic MRI at 3.0T and MDCT of pancreatobiliary disease: Evaluation with source,MPR, CPR,and MIP images for image quality and hepatic arterial and portal venous vessel conspicuity

Purpose

To compare contrast material‐enhanced three‐dimensional (3D) magnetic resonance imaging (MRI) at 3.0T and multidetector row computed tomography (MDCT) in the same patient with regard to image quality of pancreatobiliary disease and hepatic vascular conspicuity.

Materials and Methods

This study enrolled 32 patients with pancreatobiliary disease who underwent both gadolinium‐enhanced 3D dynamic MRI and multiphasic CT using 16‐MDCT. Data analysis of image quality was performed by two radiologists based on source images, multiplanar reconstruction (MPR), curved planar reconstruction (CPR), and maximum intensity projection (MIP) reconstruction. Determination of image quality was based on a 4‐point image quality rating scale.

Results

The overall image quality of the MRI axial images was superior to that of the axial MDCT images. The MRI protocol yielded an average score of 3.8 points versus 3.5 for the CT imaging. No significant difference was found between 3.0T MRI and MDCT images in MPR or CPR image quality. Image quality for visualization of the distal intrahepatic segmental arteries was significantly improved using MDCT imaging. No significant difference was found between the MDCT and 3.0T MR in portal vein branch image quality.

Conclusion

High‐resolution dynamic contrast‐enhanced MR imaging at 3.0T is a comprehensive technique which provides high image quality in pancreatobiliary disease. J. Magn. Reson. Imaging 2009;29:846–852. © 2009 Wiley‐Liss, Inc.     

Radiologic diagnosis of spondylodiscitis: role of magnetic resonance

PURPOSE: To report the Magnetic Resonance Imaging (MRI) features of acute and chronic spontaneous spondylodiscitis as well as any typical patterns which can be useful for the differential diagnosis between pyogenic and tuberculous forms. MATERIAL AND METHODS: Eleven patients affected with spontaneous spondylodiscitis were selected for the study; they were 7 men and 4 women ranging in age 33-87 years (mean: 64). We excluded the patients with iatrogenic spondylodiscitis. MR images were acquired with a superconductive magnet at 1.5, with the following sequences: sagittal PD and T2-weighted TSE, sagittal T1-weighted SE, axial PD and T2-weighted TSE for the lumbar spine, axial T2-weighted GRE for the cervical and dorsal spine and axial and sagittal T1-weighted SE after contrast agent (gadolinium DTPA) injection. MR images were reviewed by three experienced radiologists and morphological and signal intensity changes of vertebral body and disk were recorded on a standard form. In 9 patients it was possible to compare MR to CT findings. RESULTS: At the time of our observation all patients reported pain at the spine level, associated with fever and weight loss in 50% of cases and with increased values of the inflammatory markers. Three patients had infectious diseases in other organs and 2 were diabetics. Biopsy was performed in two cases only and demonstrated Staphylococcus aureus in one and Mycobacterium tuberculosis in the other patient. MRI allowed the correct diagnosis to be made in all cases, demonstrating the pathological involvement of the paravertebral structures and into the spinal canal earlier and more accurately than CT. A common finding in pyogenic and tuberculous spondylodiscitis was the low signal of the subcortical bone marrow on T1-weighted sagittal images, which enhanced after Gd-DTPA administration and became intermediate or high on T2-weighted images. Moreover, the steady high signal intensity of the disk on T2-weighted images and its contrast enhancement on T1-weighted images is typical for an acute inflammatory process. CONCLUSIONS: Based on our personal experience and literature data, we believe MRI to be the most sensitive technique for the diagnosis of spondylodiscitis in the acute phase, whereas it is comparable to CT in the chronic stage of the disease. At present MRI does not allow to differentiate pyogenic from tuberculous forms.     

Imaging of pancreatic neoplasms: comparison of MR and CT

Thirty-two patients with pathologically proved pancreatic carcinomas or cystadenomas were evaluated with MR images obtained with T1-weighted spin echo (short TR/short TE), inversion recovery, and T2-weighted spin-echo (long TR/long TE) pulse sequences. CT was used as the reference standard to determine the ability of MR to delineate normal and abnormal pancreatic anatomy and thereby to exclude or detect pancreatic malignancy. Short TR/short TE spin-echo sequences were significantly better (p less than .05) than inversion recovery or T2-weighted spin-echo sequences in resolution of both normal and abnormal anatomy. Resolution of pancreatic anatomy correlated (r = .9) with the image signal-to-noise ratio. In seven (22%) of 32 cases, MR visualized pancreatic tumors better than CT did because it showed a signal intensity difference between the tumor and normal pancreatic tissue. Overall, the slight superiority of MR over CT for tumor visualization tended to occur in larger tumors and was not statistically significant. On T1-weighted images, 63% (20 of 32) of pancreatic tumors studied had lower signal intensities than normal pancreatic tissue, whereas on T2-weighted sequences (TE = 60, 120, and 180 msec) only 41% (13 of 32) of tumors had increased signal intensities. Currently available MR imaging techniques offer no significant advantages over CT for evaluating the pancreas for neoplasia.     

Soft-tissue masses of the locomotor system: comparison of MR imaging with CT

Magnetic resonance (MR) images and computed tomographic (CT) scans of histologically characterized soft-tissue masses of the locomotor system in 35 patients were compared for image contrast, demonstration of bone destruction, and display of extent and anatomic relationships of the masses. Subjective criteria for predicting malignancy were tested. T1 measurements were made in a few cases. Intensities of masses relative to those of fat and muscle in spin-echo T1-weighted and highly T2-weighted images were evaluated for correlation with tissue type. Subjective value of using coronal and sagittal images was assessed. Because of its superior inherent image contrast and its ability to provide direct sagittal and coronal images, MR was better than CT in demonstrating size and extent of most tumors and their relationships to vascular and nonvascular structures. However, bone destruction was more difficult to see with MR. Except for fatty tumors, MR was not helpful in identifying tissue type. Subjective criteria were of limited value in distinguishing benign from malignant lesions. Moreover, there is currently no credible evidence that T1 or T2 measurements are helpful in this regard. Study results suggest that MR is superior to CT in evaluating soft-tissue masses of the locomotor system. If an MR examination is performed, CT may not be necessary in certain cases unless bone involvement is suspected.     

Cross-sectional imaging of primary osseous hemangiopericytoma

The aim of this study was to assess cross-sectional imaging features and the value of CT and MRI in primary hemangiopericytoma of bone. In five patients with histologically proven primary osseous hemangiopericytoma CT and MR scans were evaluated retrospectively. Both CT and MRI were available in four patients each. In three patients both imaging techniques were available. On CT primary hemangiopericytoma of bone presents as an expansive lytic lesion with bone destruction and inhomogeneous contrast enhancement. Magnetic resonance imaging depicts osseous hemangiopericytoma as hyperintense lesion on T2-weighted images with intermediate signal intensity on T1-weighted images. Curvilinear tubular structures of signal void in the tumor matrix on T1-weighted images and corresponding hyperintense structures on T2-weighted and on fat-suppressed short tau inversion recovery images were present in three patients. Although cross-sectional imaging findings are non-specific, they add to the diagnosis and provide valuable information about the extent of bone destruction and local tumor spread in patients with primary osseous hemangiopericytoma. While CT demonstrates the extent of bone destruction best, MRI better visualizes medullary and soft tissue extension of the tumor. Curvilinear signal abnormalities support the diagnosis of hemangiopericytoma of bone. This imaging pattern is best visualized on fat-suppressed or contrast enhanced T1-weighted MR images.     

Colloid Cysts of the Third Ventricle: Are MR Imaging Patterns Predictive of Difficulty with Percutaneous Treatment?

BACKGROUND AND PURPOSE: Colloid cysts of the third ventricle are rare benign brain tumors. The purpose of this study was to correlate their patterns on MR images with the probability of success of percutaneous treatment. METHODS: Nineteen patients underwent endoscopic treatment for colloid cysts of the third ventricle. The cases were divided into two groups based on difficulty of the aspiration procedure. We reviewed CT scans and MR images and divided cysts into groups based on their signal intensity on the MR images and their density on CT scans. Intensity and density were correlated with difficulty of aspiration during the endoscopic procedure. RESULTS: The aspiration procedure was difficult in 63% of the cases. Eighty-nine percent of hyperdense cysts on unenhanced axial CT scans were categorized as difficult, and 75% of hypodense cysts were categorized as easy. On T2-weighted MR sequences, 100% of low-signal cyst contents were difficult and nearly 63% of high-signal lesions were easy. There was a significant correlation between the T2-weighted sequences and the CT scans regarding the difficulty of the aspiration procedure. CONCLUSION: T2-weighted MR sequences are useful for predicting difficulty of aspiration during stereotactic or endoscopic procedures. A T2-weighted low-signal cyst is correlated with high-viscosity intracystic contents.     

卵巢卵泡膜-纤维瘤类肿瘤的MDCT和MRI表现分析

目的：探讨卵泡膜-纤维瘤类肿瘤的 MDCT和 MRI表现。方法回顾性分析经术后病理证实的15例(16个)卵泡膜-纤维瘤类肿瘤的 MDCT(12例)和 MRI(8例)表现。结果15例共16个病灶,均为单侧,发生在右侧卵巢10例,左侧卵巢5例,1例为左侧2个肿瘤。肿瘤多为类圆形、巨大病灶呈分叶状;14个肿瘤边界光整,2个边界不清;实性肿块4个,实性为主肿块9个,囊性为主3个。肿瘤最大径在20~220 mm,平均长径为(89±58.29)mm。实性部分CT值等或略低密度,3例病灶内见斑点状钙化,平扫CT值为(40±8)HU。肿瘤实性部分轻度强化,CT值为(49±9)HU。MRI平扫肿瘤实性部分 T1 WI呈等信号5例,呈稍低信号3例;T2 WI为混杂等、稍高及高信号,呈“山间云雾”征象6例,5例见不完整包膜线,5例肿瘤包膜外缘伴随环线状高信号。8例肿瘤实性部分均为轻度延迟强化。肿瘤囊性部分呈长T1长T2信号,无强化。10例有盆腔积液(66.7%),其中13例合并子宫或卵巢其他肿瘤和囊肿(86.7%)。结论卵泡膜-纤维瘤类肿瘤的 MDCT和 MRI有一定的特征,有助于该组肿瘤的诊断和鉴别诊断。     

肝脏炎性肌纤维母细胞瘤的影像表现

目的 探讨肝脏炎性肌纤维母细胞瘤(IMT)的影像表现特征,以提高影像诊断水平.方法 回顾性分析经手术病理证实的12例肝脏IMT的影像表现,其中12例均行CT扫描,2例行MR检查.结果12例单发病灶均位于肝右叶.6例肿块为实性,4例肿块为囊实混合性,2例表现为门静脉周围浸润性病灶.CT图像上呈实性或囊实性低密度影,MR T1WI为低信号,T2WI为略高信号;增强扫描肿块实性部分呈均匀或不均匀中重度强化,囊实混合性病灶周边及灶内实性间隔呈蜂窝样强化.结论CT及MR检查能为临床诊断及鉴别诊断肝脏IMT提供有价值的信息.     

High signal intensity of intervertebral calcified disks on T1-weighted MR images resulting from fat content

Objective To explain a cause of high signal intensity on T1-weighted MR images in calcified intervertebral disks associated with spinal fusion.Design and patients Magnetic resonance and radiological examinations of 13 patients were reviewed, presenting one or several intervertebral disks showing a high signal intensity on T1-weighted MR images, associated both with the presence of calcifications in the disks and with peripheral fusion of the corresponding spinal segments. Fusion was due to ligament ossifications (n=8), ankylosing spondylitis (n=4), or posterior arthrodesis (n=1). Imaging files included X-rays and T1-weighted MR images in all cases, T2-weighted MR images in 12 cases, MR images with fat signal suppression in 7 cases, and a CT scan in 1 case. Histological study of a calcified disk from an anatomical specimen of an ankylosed lumbar spine resulting from ankylosing spondylitis was examined.Results The signal intensity of the disks was similar to that of the bone marrow or of perivertebral fat both on T1-weighted MR images and on all sequences, including those with fat signal suppression. In one of these disks, a strongly negative absorption coefficient was focally measured by CT scan, suggesting a fatty content. The histological examination of the ankylosed calcified disk revealed the presence of well-differentiated bone tissue and fatty marrow within the disk.Conclusion The high signal intensity of some calcified intervertebral disks on T1-weighted MR images can result from the presence of fatty marrow, probably related to a disk ossification process in ankylosed spines.     

Magnetic resonance imaging of musculoskeletal neoplasms

MRI has been shown to be very useful in the work-up of musculoskeletal neoplasms. The lack of ionizing radiation, the superb contrast resolution, and the ability to directly scan the sagittal and coronal planes make MRI a very attractive imaging mode for treatment planning. With spin-echo MRI, maximum contrast between tumor and fatty tissues generally occurs with short TR and TE times (T1-weighted images). Likewise, maximum contrast between tumor and muscle, tendon, or ligaments occurs with long values of TR and TE (T2-weighted images). Early experience suggests that the already exceptional contrast resolution seen with MRI can be improved even more with the administration of intravenous contrast agents. Just as with CT, fatty tumors can usually be easily distinguished from other tissue types with MRI by means of their differential intensity behavior at different pulse sequences. Fluid-filled tumors, such as unicameral bone cysts or aneurysmal bone cysts may be suspected in the same manner, especially if a fluid-fluid level is seen within the lesion. Otherwise, MRI has not been useful so far in noninvasively determining the histologic type of tumors. Our experience and that of others suggests that MRI is equal or superior to CT in the work-up of musculoskeletal neoplasms. This is especially striking when it is remembered that one is comparing an immature MRI technology with a mature CT technology. Although CT presently has a central role in the staging of musculoskeletal tumors, MRI will shortly supplant it in many cases.