MR imaging of the portal venous system: value of gradient-echo imaging as an adjunct to spin-echo imaging.

We evaluated the use of gradient-echo (GRE) as an adjunct to spin-echo (SE) MR imaging of the portal venous system. GRE imaging was performed in 31 subjects, 15 normal volunteers and 16 patients with documented portal venous disease (15 cases) or suspected disease (one case). Eight of 16 patients had venous thrombosis, five had focal thrombus, and three had complete occlusion. Six patients had extrinsic venous compression by tumor. Of the two other patients, one had an arteriovenous fistula and the other a falsely positive angiogram, suggesting portal vein occlusion. In normal subjects, GRE scans had excellent visualization of the portal venous system with high intravascular signal compared with surrounding tissues. Nine (60%) of 15 normal subjects and three patients had an artifact consisting of a curvilinear area of decreased signal that could mimic clot. In three of five patients with focal thrombus, clot was identified on GRE but not on SE images. In all three patients with occlusion, SE and GRE images demonstrated similar findings. In five of the six patients with extrinsic venous compression by tumor, SE and GRE studies showed similar findings. Of the two patients, an arteriovenous fistula was seen on GRE MR in one, and in the other, patency of the left portal vein was seen on SE and GRE images after angiography had suggested portal vein occlusion. Collateral vessels were seen in nine of 16 patients. In five of nine cases, GRE MR demonstrated more extensive collaterals than did SE MR. In summary, GRE MR provides a useful adjunct to standard SE MR imaging. Benefits include high contrast between vascular structures and surrounding tissues, reduced motion artifact, and rapid scanning within a breath-hold.     

Portal hypertension evaluated by MR imaging

Thirteen patients with portal hypertension were examined by magnetic resonance (MR) imaging, using spin-echo sequences, and by visceral angiography. Data from this group were compared with the MR images and angiograms of 20 patients without portal hypertension. MR imaging demonstrated two of three cases of portal vein occlusion and four of five cases of occlusion of the retropancreatic portion of the superior mesenteric vein. Two thirds of the patients with portal hypertension and patent portal veins had marked MR signal within the main portal vein on MR images. Little or no signal was present in the portal veins of the 20 patients without portal hypertension. Our experience indicates that marked intraportal MR signal can be seen in patients with portal hypertension with or without venous occlusion. In some cases the size and distribution of venous collaterals allow one to distinguish between venous occlusion and other causes of portal hypertension. MR images confirmed the patency of distal splenorenal shunts in two patients studied.     

MR imaging of mediastinal lymph nodes: evaluation using a superparamagnetic contrast agent

The purpose of this study was to determine whether intravenous injection of a magnetic resonance (MR) contrast agent, ultrasmall superparamagnetic iron oxide (ferumoxtran-10), can be useful in characterizing lymph nodes in patients with lung cancer. Twelve patients with known or suspected lung cancer were studied. Pre- and postcontrast injection of ferumoxtran-10 MR scans of the chest were obtained. Analysis of the signal intensities and bronchoscopic fine needle aspiration of a single node were performed in each patient. Six of 12 patients had a final diagnosis of lung cancer. T1-weighted images were best for localizing mediastinal lymph nodes. Signal intensity changes before and after contrast were best visualized on T2-weighted and gradient-echo images. All four patients with lung cancer who had nodes positive for malignancy at biopsy had no change in signal intensity of the nodes on T2 images. The signal intensity decreased in the remaining two patients, and the nodes were benign. Of the eight patients with benign disease, five had no change in signal intensity of the nodes. Therefore the sensitivity for tumor involvement of the nodes is 100%, but the specificity is only 37.5%. Ferumoxtran-10 is a contrast agent that can alter the signal intensity of lymph nodes. Lack of signal change may be due to malignant or inflammatory change. Studies in a larger population of lung cancer patients may help to characterize the utility of this agent further. J. Magn. Reson. Imaging 2000;12:899-904.     

Jugular venous thrombosis: MR imaging

Magnetic resonance (MR) imaging of jugular venous thrombosis was investigated in three patients who had symptoms suggestive of this condition; the diagnosis was later confirmed by computed tomography, by venography, and clinically. Bright intraluminal signal intensity was seen throughout the course of the affected jugular vein on MR images in all three patients, in sharp contrast to the lack of signal from the corresponding site in the uninvolved venous system. Temporal changes in signal intensity from the acute to subacute stage of thrombosis were evaluated for one patient. A relative increase in signal intensity for the subacute phase was believed to be related to a decrease in the T1 relaxation time. MR may be the imaging modality of choice in the investigation of venous thrombosis.     

Nuclear magnetic resonance tomography of superior vena cava obstruction

The potential of magnetic resonance tomography (MRT) to demonstrate the mediastinal veins was evaluated retrospectively in 6 patients with superior vena cava obstruction. In each instance, MRT provided detailed information about the extent of venous obstruction and the precise site of the causative oncological pathology. Transaxial images most clearly and unequivocally depicted obstructed superior vena cava. MRT was also able to indicate some secondary effects of superior vena cava obstruction such as slow intravenous flow. The latter could be demonstrated by a significant increase of signal intensity within venous structures proximal to the obstruction. Peripheral venous collaterals in the chest wall were better seen with contrast enhanced computed tomography scans.     

MR imaging of malignant pleural mesothelioma

The magnetic resonance (MR) findings in three patients with malignant pleural mesothelioma are described. All patients had a circumferential pleural mass surrounding the lung on the affected side. These tumors had a signal of intermediate intensity on T1-weighted images. The T2-weighted images showed a slight increase in signal intensity of the mass, with focal areas of very high signal intensity due to pleural fluid. Adenopathy was demonstrated by CT and MR in two patients. The extent of the tumor and its effects on adjacent structures were well appreciated on the coronal MR images.     

Deep venous thrombosis evaluation with limited-flip-angle, gradient- refocused MR imaging: preliminary experience

Sixteen patients (17 lower extremities) were prospectively examined with venography and limited-flip-angle, gradient-refocused magnetic resonance (MR) imaging for the presence or absence of deep venous thrombosis. Thrombosed vessels showed decreased-to-absent signal intensity, while patent vessels had high signal intensity. In 16 of 17 extremities, MR images allowed accurate detection and localization of the thrombi found with venography. In the remaining extremity, MR imaging allowed correct identification of thrombus in the iliac and femoral veins but incorrectly demonstrated clot in the calf and popliteal veins. MR imaging with limited-flip-angle, gradient-refocused pulse sequences appears to be a sensitive, noninvasive means of detecting deep venous thrombosis.     

Neck neoplasms: MR imaging. Part II. Posttreatment evaluation

Thirty-three patients who had undergone prior surgery and/or radiation therapy for malignant neoplasms of the neck were studied with magnetic resonance (MR) imaging. Twenty-seven of these patients were also evaluated with computed tomography (CT). Ten patients were healthy posttreatment volunteers, and 23 had documented tumor recurrence. MR images better demonstrated normal muscular landmarks, especially in patients with obliterated fat planes. Areas of posttreatment fibrosis or scarring were low in signal intensity with all MR pulse sequences. However, in three patients, high signal intensity from postradiation edema of the supraglottic area mimicked neoplasm. In patients with recurrent tumor, MR imaging was superior to CT in defining the relationship of tumor and muscle and in demonstrating vascular anatomy when no intravenous contrast material was given during the CT examination. In two patients tumor and fibrosis were separated on MR images because of signal intensity differences. CT scans, however, showed adjacent bone and cartilage anatomy better. Our data indicate that an MR examination may be helpful in patients in whom CT is indeterminate either because of anatomical distortion or suboptimal demonstration of vascular anatomy.     

Mediastinal lymphoma: quantitative changes in gadolinium enhancement at MR imaging after treatment

PURPOSE: To compare changes in gadolinium enhancement at magnetic resonance (MR) imaging with outcome in mediastinal lymphoma after treatment. MATERIALS AND METHODS: Thirty-one patients with bulky mediastinal lymphoma (17 with Hodgkin disease, 14 with non-Hodgkin lymphoma) underwent serial MR imaging before and up to 50 months after treatment, with routine follow-up (including computed tomography). Signal intensity ratios between masses and muscle were calculated on T1-weighted, T2-weighted, and contrast material-enhanced T1-weighted spin-echo MR images. The percentage enhancement and signal intensity ratios of mediastinal masses on T2-weighted MR images were calculated at diagnosis and during and after treatment. RESULTS: Twenty-one patients with persistent complete remission had a mean percentage enhancement of residual masses (4%; range, -26% to 40%) that was significantly lower than that of initial masses (78%; range, 41%-124%). Although the mean signal intensity ratio of residual masses on T2-weighted images was significantly lower than that of initial masses, an increase in this ratio was observed in four patients after treatment. In seven patients with relapse, the percentage enhancement value of the residual mass was as high as that of the initial mass. CONCLUSION: Gadolinium enhancement of lymphomatous masses of the mediastinum decreased markedly after treatment in patients in continuous complete remission but not in patients with relapse.     

Mediastinal masses: MR imaging

Seventy-five patients with mediastinal masses were imaged with magnetic resonance (MR). Results were analyzed with regard to the ability of MR to demonstrate the masses, their morphology, and their encroachment or displacement of blood vessels and airways. T1 values were determined in 53 patients and T2 values in 59. Hydrogen density and percentage of contrast relative to muscle and fat were also obtained in 53 and 59 patients, respectively. MR images were compared with computed tomography (CT) scans, which were available in 45 patients. MR depicted all masses and demonstrated compromise of vessels and cardiac chambers owing to the inherent contrast between the masses and cardiovascular structures. Bronchogenic carcinoma had very long relaxation values for T1 and T2, while chronic inflammatory processes had intermediate values for T1 and T2, thus appearing less intense than bronchogenic carcinoma on T2-weighted images. Other neoplasms demonstrated T1 and T2 values between these two disease groups. Masses appeared less homogeneous on MR images than on CT scans, and vascular compromise was better assessed with MR. Thus, MR imaging is a completely noninvasive technique for the evaluation of mediastinal masses. While the anatomic information is comparable to that produced by CT, MR provides some insight into the composition of the mass.     

MR imaging of rotator cuff tears]

A total of 115 patients with clinical symptoms and signs suggesting rotator cuff tears underwent MR imaging with a 1.5-Tesla system. The body coil was used as the receiver coil in 24 patients and a single 10 cm surface coil in 91. Arthrography or MR imaging with intra-articular Gd-DTPA (MR arthrography) was performed in 95 of the 115. T2-weighted images with the body coil showed high signal intensity lesions in rotator cuffs in only seven of the 10 patients who had tears demonstrated by arthrography or MR arthrography. On the other hand, T2-weighted images with the surface coil demonstrated high signal intensity lesions in cuffs in all 27 patients who were diagnosed to have tears by arthrography or MR arthrography. In 12 patients, T2-weighted images with the surface coil showed high signal intensity lesions in cuffs, while arthrography and MR arthrography did not show tears. Surgery was performed in four of the 12 patients and partial tears were confirmed. A single 10 cm surface coil, 3 mm slice thickness and 2.5 second repetition time seem to account for the fine visualization of cuff tears by the T2-weighted images. These results suggest that T2-weighted images obtained with the surface coil are superior to arthrography and MR arthrography.     

CT and MR imaging of advanced Zollinger-Ellison syndrome

The CT and magnetic resonance (MR) findings in 13 patients with advanced Zollinger-Ellison syndrome are described. In eight patients (62%) one or more primary tumors were found with both methods. All patients with proven liver metastases (n = 7) were identified by MR. Computed tomography was positive in six of these patients. Three patients with lymph node metastases were identified on CT and MR and one patient had bone metastases. Computed tomography and MR were inferior to selective arteriography in the detection of multiple lesions of the pancreas in a patient with multiple endocrine neoplasia-I syndrome. On the T1-weighted MR images, the primary tumors demonstrated no consistency with regard to their signal intensity relative to the adjacent pancreatic parenchyma. All gastrinomas had an increased relative signal intensity on the T2-weighted images with the exception of a calcified tumor. Liver and lymph node metastases had a low signal intensity on the T1-weighted images and an increased signal intensity on the T2-weighted images. The signal intensity of primary tumors and metastases was independent of size. In conclusion, MR was able to detect abnormalities based on its outstanding lesion/normal tissue contrast, whereas CT diagnosis was based mostly on contour distortion. For the current technique, MR is considered at least equal to CT.     

MR imaging of superior sulcus carcinoma

Magnetic resonance (MR) imaging was performed in 10 patients with biopsy proven superior sulcus carcinomas to determine the extent of local tumor invasion. Chest wall invasion or extension into the base of the neck was demonstrated in five patients. This finding was facilitated by the contrast between the bright signal intensity of tumor and the low signal intensity of muscle on T2-weighted images. In three patients, MR clearly depicted direct invasion of the mediastinum. This finding was facilitated on the MR image because of inherent contrast between the mediastinal fat and tumor. Coronal and sagittal images showed the relationship of tumor to the subclavian artery and brachial plexus in all cases. Encasement of the artery was confirmed in two cases and brachial plexus involvement in three. However, MR failed to detect evidence of rib destruction in five patients in whom rib involvement was confirmed by other studies. Magnetic resonance appears to be a useful imaging modality in determining the extent of local disease and, therefore, the selection of patients for surgical resection. Multiplanar imaging and contrast between tumor and muscle and tumor and fat allow assessment of invasion of the mediastinum and base of the neck, subclavian artery, and brachial plexus.     

MR evaluation of large intracranial aneurysms using cine low flip angle gradient-refocused imaging

MR imaging has proved to be useful in evaluating large intracranial aneurysms. The parent artery and patent lumen can be identified as flow voids and differentiated from thrombus. However, in the presence of slow flow, even-echo rephasing, and motion artifact, increased intraluminal signal may be present, which may be difficult to distinguish from thrombus. Aneurysms are also dynamic lesions and exert pulsatile mass effect on adjacent structures. Further definition of vascular anatomy and physiology may aid in therapeutic planning and assessment. Cine MR is a new technique using a movie loop of sequential GRASS (gradient-recalled acquisition in the steady state) images obtained during various points in the cardiac cycle. The combination of GRASS images and cardiac gating thus allows cinegraphic display of vascular structures. A comparison of this method with routine T1- and T2-weighted MR imaging and angiography was made in a group of 13 patients with intracranial aneurysms greater than 1.5 cm in diameter. Eight of these patients underwent transvascular detachable balloon occlusion. With cine MR, flowing blood has high intensity due to flow-related enhancement. Turbulent and high-velocity flow can be recognized on the basis of signal loss, which occurs during systole. Thrombus demonstrated variable signal intensity, which remained unchanged during the cardiac cycle. Compared with routine MR sequences, there was less image degradation from phase-encoding artifacts and improved visualization of the neck of the aneurysm. Pulsatile mass effect was uniquely assessed. After transvascular embolization, cine MR demonstrated improved conspicuity of acute thrombus and higher contrast between flowing blood and the occlusion balloon when compared with routine MR. Confirmation of flow within the parent vessel, residual aneurysm lumen, and distal arterial branches is possible. If the parent vessel was occluded, cine MR yielded greater information than angiography. Cine MR provides additional anatomic and physiologic data in the evaluation and assessment of therapy of intracranial aneurysms. Information can be obtained that is not available with either routine MR or angiography. The inherent limitations of this new technique include partial-volume artifacts, less than optimal flow-related enhancement or spatial resolution, and poor data acquisition due to cardiac arrhythmias.     

Accuracy of pre- and postcontrast 3D time-of-flight MR angiography in patients with acute ischemic stroke: correlation with catheter angiography

BACKGROUND AND PURPOSE: 3D time-of-flight (TOF) MR angiography (MRA) is insensitive to slow flow; however, the use of MR imaging contrast agents helps to visualize slow-flow vessels and avoids overestimation of vascular occlusion. The purpose of this study was to correlate pre- and postcontrast 3D TOF MRA with the results of conventional angiography during endovascular reperfusion therapy and to determine the accuracy of postcontrast 3D TOF MRA. MATERIALS AND METHODS: Thirteen patients who underwent endovascular reperfusion therapy for acute ischemic stroke were retrospectively analyzed. MR imaging techniques included single-slab 3D TOF MRA with and without contrast, as well as perfusion-weighted imaging. Angiography during reperfusion therapy was used as a standard of reference. Affected arteries were divided into segments either proximal or distal to the lesion, and pre- and postcontrast MRA signals were graded as absent, diminished or narrowed, or normal. RESULTS: In 2 of 5 patients with arterial stenosis and 6 of 8 patients with complete occlusion, MRA signal intensity proximal to each lesion was absent, indicating a proximal pseudo-occlusion on precontrast MRA. Postcontrast MRA demonstrated an arterial signal intensity proximal to the stenotic or occlusive lesions in all 13 patients. Arterial signal intensity distal to the occlusion was identified on postcontrast MRA in 7 of 8 patients having complete occlusion, and the extent of occlusion on postcontrast MRA was similar to results of conventional angiography. CONCLUSION: In this small series, postcontrast 3D TOF MRA more accurately delineated the extent of stenotic or occlusive arterial lesions than precontrast MRA.     

MR imaging in the management of thoracic malignancies

CT remains the modality of choice for evaluating patients with a thoracic malignancy. In specific cases MR imaging can provide useful information that cannot be obtained with CT, and thus is useful as a problem solving tool. Advantages of MR imaging include superb demonstration of vessels and vessel/mass relationships, direct multiplanar imaging capability, and the potential for tissue characterization. MR imaging is useful in staging the patient with lung cancer when vascular or mediastinal invasion is in question. Its specific applications in surgical planning include the question of chest wall invasion, brachial plexus involvement, and transgression of the diaphragm, pericardium, or lung apex. Multiplanar imaging is useful in radiation therapy planning, displaying lesion extent in a coronal or sagittal format rather than on multiple axial images. Multiplanar capability also resolves problem areas for CT such as the aortopulmonic window, subcarinal region, and lesions at the cervicothoracic or thoracoabdominal junction. Structures such as the trachea and superior vena cava can be evaluated in their plane of anatomic orientation. Routine spin-echo and fast (GRASS) imaging of mediastinal vessels is useful in the evaluation of venous thrombosis as a result of catheters or tumors. The diagnosis and follow-up are obtained without the use of intravenous contrast material or radiation. When CT cannot evaluate vessels adequately because of surgical clip artifacts or postoperative distortion of anatomy, MR imaging is useful in the determination of vessel patency as well as identification of tumor recurrence. Cardiac masses are very well demonstrated by MR imaging. A unique feature of MR imaging is its potential for tissue characterization and ability to assess disease activity. Lymphoma evaluation is an active area of research. MR imaging can evaluate the radiated patient for tumor response and recurrence. Fibrous tissue remains of low signal intensity on T2-weighted images, whereas tumor has increased signal intensity. MR imaging may detect tumor recurrence before an increase in the size of a residual lymphoma mass and before clinical recurrence is evident. The area of increased signal can also serve as a guide to the appropriate site for biopsy to confirm recurrence. In addition, MR imaging can help characterize some adrenal and liver masses, potentially helping to avoid more invasive diagnostic procedures. At the current time MR spectroscopy does not have a clinical role in thoracic malignancies, but it may be a powerful tool in the future for diagnosis and management.     

Cholesterol granuloma of the petrous apex: MR and CT evaluation

We reviewed the clinical, CT, and MR findings in seven consecutive patients who had a total of nine cholesterol granulomas. Preoperative MR scans were available for five of the seven patients; two patients were studied with MR after treatment only (one had a recurrent lesion and the other was asymptomatic at the time of study). Preoperative CT scans were available for all patients, except one patient who was examined after developing a symptomatic recurrence. All lesions were detected by both imaging methods. Seven preoperative lesions (five patients) and one symptomatic recurrence (one patient) demonstrated increased signal intensity of both T1- and T2-weighted MR images. Three surgically drained lesions (three patients) showed a marked reduction in signal intensity on T1-weighted images. Pre- and postoperative lesions had different patterns of signal intensity on the chemical-shift images, which were obtained in two instances. The MR appearance of cholesterol granuloma differs from that of most other lesions that occur in the petrous apex. CT did not differentiate between pre- and postoperative lesions in all cases, while MR demonstrated a dramatic change on T1-weighted images and chemical-shift studies. Our findings indicate that MR is more specific than CT in suggesting the correct diagnosis of cholesterol granuloma and that MR appears to be the technique of choice in the follow-up of previously treated patients.     

Chordomas of the skull base: MR features.

PURPOSE: To characterize the MR features of skull base chordomas with regard to signal intensity, size, position, extension, and Gd-DTPA enhancement. PATIENTS AND METHODS: The MR imaging studies of 28 patients with surgically proven chordomas of the skull base were retrospectively reviewed. Twenty-two of these patients received intravenous administration of Gd-DTPA. RESULTS: On short TR/short TE images, chordomas generally had low to intermediate signal. On long TR/long TE images, chordomas generally had very high signal that was heterogeneous in 79%. After Gd-DTPA administration, all chordomas demonstrated some degree of contrast enhancement. In most cases, enhancement was demonstrated throughout most of each tumor in a heterogeneous pattern. Chordomas were associated with MR findings of displacement and encasement of vessels, and frequent extension into adjacent structures such as the cavernous sinus, sella, nasopharynx, and hypoglossal canal. CONCLUSION: The MR characterization of the position and extent of these neoplasms played an important role in determining the optimal surgical approaches for gross total tumor resection.     

Routine MR imaging of the internal carotid artery siphon: angiographic correlation with cervical carotid lesions

This study correlates the appearance of the cavernous segment of the carotid artery on MR images with the presence of significant stenosis or occlusion of the cervical carotid artery as seen on angiograms in 100 patients who had brain MR imaging and arteriography within a 1-week period. Four patients demonstrated isointense signal within the carotid artery's cavernous segment; two of these findings correlated with complete carotid occlusion as seen angiographically, while partial compromise was seen angiographically in the other two. Four other patients had variable signal intensity and irregularity of the luminal outline in the carotid siphon, correlating with angiographic evidence of atheromatous disease in three patients and of dissection in one patient. The demonstration of normal signal void within a normal-appearing cavernous segment of the internal carotid artery in the remaining 92 patients correlated with absence of significant stenosis within the cervical segment in 86 patients. In the remaining six, significant disease of the internal carotid artery was found. Isointensity within the intracranial carotid artery can indicate either complete occlusion or very slow flow. Therefore, angiography is still necessary to completely exclude potentially treatable disease that produces very slow flow leading to isointensity. The presence of normal flow void in the intracranial segment does not exclude significant compromise of the cervical segment of the carotid artery.     

MRI在良、恶性胸膜肿瘤鉴别诊断中的价值

目的：探讨磁共振成像在良、恶性胸膜肿瘤鉴别诊断中的作用。方法：对45例胸膜肿瘤患者（良性8例,恶性37例）进行了CT和MRI检查。评估分析良、恶性胸膜肿瘤的CT和MRI形态学特点及其分别在T1WI、T2WI和增强T1WI上的信号特点。结果：在CT图像上,共出现弥漫性胸膜增厚30例（恶性29例,良性1例）,纵隔胸膜受累28例（恶性27例,良性1例）、环绕或不规则胸膜增厚23例（恶性22例,良性1例）,胸壁或膈肌浸润9例（全部为恶性）;在MRI上,共出现弥漫性胸膜增厚32例（恶性31例,良性1例）,纵隔胸膜受累29例（恶性27例,良性2例）、环绕或不规则胸膜增厚24例（恶性23例,良性1例）,胸壁或膈肌浸润1例（全部为恶性）。根据前述形态学特点,CT与MRI对诊断胸膜恶性肿瘤总的敏感性分别为83．8％和86．5％,总特异性均为62．5％。结论形态学及信号特点,MRI对诊断良、恶性肿瘤病变的敏感性为97．3％,特异性为100％。结论：单纯依据其形态学特点,MRI对胸膜肿瘤的发现与诊断价值与CT相仿。但当MR信号与形态学特点结合时,其对良、恶性胸膜肿瘤的鉴别诊断价值则明显优于CT。