Unenhanced MRI Research Articles

Gadolinium-enhanced 3D magnetic resonance angiography of the thoracic vessels.

MAGNETIC RESONANCE IMAGING has long been recognized as a useful tool for the non-invasive evaluation of the thoracic vasculature. Unlike computed tomography and conventional angiography, MRI is not associated with the concerns related to ionizing radiation exposure or to contrast-related nephrotoxicity. MRI is also capable of oblique image acquisition and multiplanar reformation, which aids the illustration of the thoracic vessels, inherently intertwined and complex in their arrangements. In addition, MRI using cine technique affords cardiac referenced data that enables dynamic assessment of blood flow, yielding information comparable to an echocardiogram. Gadolinium (Gd)-enhanced three-dimensional (3D) magnetic resonance angiography (MRA) is a newer technique that provides high-resolution (ie, 3D) data very quickly and is well suited for the depiction of intrathoracic vessels. Improvements in gradient technology now allow a Gd-enhanced 3D MRA to be performed during a 20–40 second breath-hold. Because it relies on T1-shortening effects of circulating Gd-chelate contrast media and not inherent flow characteristics, Gdenhanced 3D MRA can often depict pathologic vascular segments that are not adequately visualized using unenhanced flow-based MRI techniques. In addition, Gdenhanced 3D MRA provides volumetric data that can be processed for multiplanar reformation (MPR) and maximum intensity projection (MIP) viewing. In this article, the technical considerations and potential applications for Gd-enhanced 3D MRA of the systemic and pulmonary vessels within the chest will be discussed and illustrated. Traditionally, T1-weighted spin-echo and gradientecho pulse sequences have been employed for delineation of vascular pathology within the chest (1–10). The combination of T1-weighted spin-echo and gradientecho images can often provide the information necessary for the assessment of simple clinical queries such as patency of a vessel (Fig. 1) or delineation of a vascular ring (Fig. 2). These techniques, however, rely on flowing blood (ie, the movement of blood during the acquisition period) for their illustration of vascular structures. This flow dependency makes these techniques prone to flowrelated image artifacts, thereby frequently limiting their clinical utility. On spin-echo pulse sequences, vessels are characterized by their dark lumina. The black appearance of blood, also known as flow void, on spin-echo imaging occurs secondary to the wash-out of blood prior to the refocusing pulse and sampling of the echo. The washout may be incomplete if the echo time is too short, the vessel courses primarily within the imaging plane, or the blood flow is too slow. Incomplete wash-out results in the persistence of signal within the vessel lumen, which may result in the masking of underlying luminal pathology such as an intimal tear or the erroneous simulation of a vascular occlusion or thrombosis. A superior black blood effect is achieved by using preparatory pulses such as a double inversion pulse to null blood signal for more effective suppression even when the blood flow is slow. Unlike spin-echo imaging, time-of-flight (TOF) and phase contrast (PC)-MRA depict flowing blood with bright signal intensity. TOF imaging relies on the wash-in or in-flow effect of unsaturated protons; PC imaging relies, on the phase shift experienced by moving protons traveling along the gradient field (7–13). Both TOF and PC imaging provide higher intra-vascular signal-tonoise ratios than spin-echo pulse sequences. These ‘‘bright blood’’ pulse sequences (ie, TOF and PC imaging) often show intraluminal abnormalities (Fig. 1b) not clearly identified on black blood spin-echo images. However, should blood flow be slow, turbulent, or complex, vascular signal on gradient-echo images becomes unreliable. Disturbances in blood flow can often result in signal loss, which can result in the underestimation of vessel patency, overestimation of a stenosis, or even simulation of a vascular occlusion. 1Department of Radiology, University of Michigan Medical Center, Ann Arbor, Michigan 48109-0030. 2MR Research Division, Department of Radiology, Uniformed Services University, Bethesda, Maryland 20814. 3Cornell University, New York, NY 10021 Contract Grant Sponsor: Whitaker Foundation, GE. *Address reprint requests to: M.R.P., Cornell University, MRI Division, 416 East 55th Street, New York, NY 10021. Received June 29, 1999; Accepted July 13, 1999. JOURNAL OF MAGNETIC RESONANCE IMAGING 10:758–770 (1999)

Hepatic MRI with SPIO: detection and characterization of focal liver lesions.

A variety of parenterally administered iron oxides have been developed for contrast-enhanced MRI of the liver. Two different classes of iron oxides are currently clinically approved or in phase 3 trials: superparamagnetic iron oxides (SPIO) with a high R2/R1 relaxivity ratio and short blood half-life (AMI-25 and SH U 555 A), and ultrasmall paramagnetic iron oxides (USPIO) with a lower R2/R1 relaxivity ratio and longer blood half-life (AMI-227). All iron oxides significantly increase tumor-to-liver contrast and allow detection of more lesions than unenhanced MRI on T2-weighted images at a field strength of 0.2-1.5 T. Malignant lesions without phagocytic cells exhibit constant signal on T2-weighted accumulation phase images with all three iron oxides. All iron oxides cause a signal decrease of benign lesions with either phagocytic cells or a significant blood pool on T2-weighted accumulation phase images. The signal decrease of benign lesions is proportional to the Kupffer cell activity or tumor vascularity and is useful for lesion characterization. Another enhancement feature for the differentiation of benign from malignant lesions is ring enhancement of malignant lesions (metastases) on T1-weighted enhanced images either during the perfusion phase with SH U 555 A or during the accumulation phase with AMI-227, which is attributed to the blood pool effects of the compounds. Differentiation of lesions and vessels is easier on enhanced images with angiographic effects than on unenhanced images. Iron oxides improve the quality of two-dimensional MR angiography techniques of the portal venous system by decreasing background signal (liver tissue with all iron oxides) and increasing intravascular signal (AMI-227). The use of iron oxides for hepatic MRI provides an alternative to the existing multistep diagnosis with CT, CT portography, MRI and biopsy.

Pancreatic Carcinoma

Our goal was to determine the value of MRI in the assessment of vascular invasion in the preoperative staging of pancreatic carcinoma. In 53 consecutive patients with an established diagnosis of pancreatic ductal adenocarcinoma, SE T1-weighted and breath-hold gradient echo images at 0.5 T were obtained before and after bolus injection of Gd-DTPA. Major peripancreatic vessels were evaluated for the presence of (a) no tumor invasion, (b) contiguity with tumor, and (c) tumor encasement. All patients subsequently underwent surgery. Results of unenhanced and contrast-enhanced MRI studies were compared with the histologic findings in the resected specimens in 34 cases and with the surgical findings in 19 nonresected cases. In six patients, pathologic examination showed the presence of tumor confined to the pancreas with no vascular invasion. With MRI, five of these cases were correctly evaluated; in the remaining case, tumor-vessel contiguity was erroneously diagnosed. In 21 patients, tumor contiguity with adjacent vessels was found at pathologic examination. At MRI, 16 of these cases were correctly assessed, and 5 were understaged as tumors confined to the pancreas. Of the remaining 26 patients, 7 had vascular encasement by tumor at pathologic examination of the resected specimen; the other 19 patients had unresectable tumors encasing the adjacent vessels at surgical evaluation. MRI detected vascular encasement in 21 of these 26 cases; in the other 5, tumor contiguity was incorrectly diagnosed. The overall accuracy of MRI for determining vascular invasion was 79%. MRI is a helpful method for preoperative assessment of vascular involvement due to pancreatic carcinoma.

Differential diagnosis of truly suprasellar space-occupying masses: synopsis of clinical findings, CT, and MRI

This review demonstrates the features of truly suprasellar masses in modern imaging based on the clinical, CT, and MRI findings of 42 patients with suprasellar masses in correlation to the histologic findings. The radiologic examinations were evaluated retrospectively to determine if diagnosis can be made based on specific imaging patterns. The most frequent clinical findings of space-occupying suprasellar masses were visual disturbances, diabetes insipidus, and symptoms and signs of occlusive hydrocephalus. There were no clinical features specific for any of the observed masses. Craniopharyngiomas were the most frequent tumors. They appeared in two different forms, as cystic and as solid enhancing masses. The cystic tumors could not be differentiated from cystic hamartomas or cystic gliomas by CT or MRI. The solid craniopharyngiomas were similar to meningiomas and hamartomas. In craniopharyngiomas of adults calcifications were not common. In CT and especially in MRI gliomas were characterized by the diffuse infiltration of the adjacent brain tissue or optic nerve. Except for meningiomas, all lesions were highly variable in appearance, making a reliable characterization by CT and MRI difficult in many cases. However, administration of contrast media in some cases resulted in a better tumor delineation. Compared with unenhanced MRI the enhanced scans did not increase diagnostic efficacy for neoplasms, but were helpful in the differentiation from inflammatory diseases. The MRI technique was superior to CT in demonstrating the anatomic relationships, thus facilitating evaluation of origin and extent of the lesions. The CT technique, of course, was more reliable in the detection of calcifications. Both CT and MRI are not tissue-specific, however,and suprasellar tumors as well as many other neoplasms cannot be classified using only one of these imaging techniques.To optimize the diagnostic strategy both imaging modalities should be used with close regard to patient history, physical examination, and clinical parameters.

Correlation between Gd-enhanced MR imaging and histopathology in treated and untreated 9L rat brain tumors.

Gadolinium-based MR imaging contrast agents cause signal enhancement of intracerebral tumors on T1-weighted MR images because they cross the compromised blood-brain barrier, increasing the T1 relaxation rate of extracellular water. Tumor extent measured by Gd-enhanced MR imaging often does not agree with T2-weighted MRI or biopsy measurements, due to possible peritumoral barrier defects or infiltration of tumor cells beyond the region of enhancement. In this study, the 9L rat brain tumor model was used to measure the correlation between tumor size measured by Gd-enhanced and unenhanced MRI and histological measurements. There was excellent agreement between Gd-enhanced MRI measurements and histology. Morphological features of untreated 9L intracranial tumors and those treated with radiation and/or cisplatin were compared with histological features. No significant change in intracranial tumor size was detected in the treated animals up to 7 days following treatment, despite substantial tumor necrosis evident on histological analysis.

Imaging of renal cell carcinoma with gadolinium-enhanced magnetic resonance: radiological and pathological study.

The use of gadolinium-DTPA enhanced MR imaging (Gd-MR) in detecting and staging of large and small renal neoplasm was investigated in 61 patients with 66 renal cell carcinoma confirmed at surgery. The purpose of the study was also to evaluate the signal intensity of the lesions and to correlate the contrast-enhanced pattern to the pathological components and architecture of the surgical specimens. Forty-four tumors were larger than 3 cm and 22 lesions were smaller than 3 cm. Unenhanced MRI detected all large lesions (44/44) and 63% (14/22) of small lesions, while Gd-MRI detected all large and small neoplasms (100%). The overall staging accuracy was 79 and 87% for plain MRI and Gd-MRI, respectively, but both modalities led to an overstaging of the disease. Enhanced MRI was an excellent staging modality for the evaluation of tumor vascular extension and tumor spread to adjacent structures. The most frequent Gd-MRI pattern of small RCC was hyperintensity, while large lesions were mostly hypointense. The presence of fibrohyaline components seemed responsible for the hyperintense pattern. No specific contrast-enhanced MRI pattern was observed according to the tumor architecture (alveolar, tubular or papillar) of noncystic lesions. On the contrary, cystic lesion appeared as an area of low signal intensity and the use of contrast media improved detection and characterization. The inhomogeneous signal intensity increased the detectability of the lesion.

Detection of focal liver lesions with superparamagnetic iron oxide: value of STIR and SE imaging.

We assessed the value of superparamagnetic iron oxide (SPIO) particles on the detection of focal liver lesions by MRI. Twenty patients with one to five focal liver lesions, primarily detected with ultrasonography and/or contrast-enhanced CT, were evaluated further with unenhanced and iron oxide-enhanced MRI at 1.0 T. Superparamagnetic iron oxide particles were administered intravenously as a slow infusion. Then T1-, T2-, and proton density-weighted SE images were obtained. In addition, the performance of a short TI inversion recovery (STIR) sequence was evaluated. The iron oxide contrast medium had marked effects on liver signal-to-noise (S/N) and tumor-to-liver contrast-to-noise (C/N) ratios but only minimal effects on tumor S/N ratios in cases of malignant tumor foci. Lesion-to-liver contrast, expressed as differences between the tumor and liver S/N ratios, improved very significantly after SPIO infusion with all four pulse sequences. Contrast enhancement of the liver parenchyma was best in T2-weighted SE images, but the tumor-to-liver C/N values were highest with the postcontrast STIR sequence. The SPIO enhancement revealed a number of additional focal lesions (31%), also foci under 1 cm in diameter. In three benign focal lesions, SPIO infusion produced a definite reduction in the S/N ratio of the lesions in contrast to the minimal change measured in malignant foci. The favorable performance of the STIR sequence contradicts the disappointing results previously obtained at 0.6 T. Superparamagnetic iron oxide is a promising new contrast medium for MR examinations of the liver, increasing the conspicuity and reducing the detectability threshold of focal hepatic lesions.

Breast MRI as an adjunct in the diagnosis of a carcinoma partially obscured on mammography

The role of unenhanced breast MRI as an adjunct to mammography in the diagnosis of a breast carcinoma presenting as architectural distortion partially obscured by dense tissue on film-screen mammography is illustrated.

Prevalence of Incidental Intraspinal Lipoma of the Lumbosacral Spine As Determined by MRI

The prevalence and appearance on MRI of lipomas of the filum terminale was studied in a random population referred to MRI for evaluation of the lumbosacral spine. The MRI scans of 100 patients selected at random were retrospectively reviewed. The study sought to determine the frequency and MRI appearance of incidental filum lipomas in a random population. Postmortem studies have reported a 4%-6% incidence of occult fibrolipomas of the filum terminale in what were thought to be otherwise normal spinal cords. The improved resolution of MRI imaging allows the detection of small amounts of fat associated with the filum terminale that heretofore had not been demonstrated on radiologic imaging examinations. The lumbosacral spine unenhanced MRI scans of 100 patients not previously operated upon were selected at random and were retrospectively reviewed by two of the authors (EB and JCM). Of the 100 MRI examinations reviewed, four patients were found to have small lipomas of the filum terminale. No spinal dysraphism or cord tethering were present in these four patients. Their clinical symptoms were related to disc herniation in two patients, spinal stenosis in one, and discitis in one. The lipomatous tissue was hyperintense to cerebrospinal fluid (CSF) on T1-weighted images and hypointense to CSF on T2-weighted images. Incidental lipomas of the filum terminale were present in 4% of 100 lumbosacral spine MRI examinations in a random population.

MR imaging of late onset orbital rhabdomyosarcoma with intracranial extension

Today, patients with alveolar rhabdomyosarcoma have a favorable prognosis with a survival rate of more than 80%, due to modern radiotherapy. However, those patients with secondary meningeal involvement are still afflicted with a mortality rate of 90% unless a different therapeutic approach is taken. We report a case of a young adult with invasion of the tumor into the anterior cranial fossa. MRI aided in the assessment of the intracranial tumor spread and allowed for a direct visualization of the meningeal membranes. The signal characteristics of the tumor and the adjacent tissue in unenhanced and postcontrast MRI is discussed. MRI was clearly superior to CT and indicative for the choice of treatment.

Quantitative MRI changes in gadolinium‐DTPA enhancement after high‐dose intravenous methylprednisolone in multiple sclerosis

In 12 patients with definite multiple sclerosis who received a total of 21 courses of high-dose (1 gram daily for 10 consecutive days) intravenous methylprednisolone, we performed MRI of the brain with and without gadolinium-DTPA before and after treatment. On the initial MRI, there was a total of 98 enhancing lesions, 93 of which were also represented on the unenhanced images. After treatment, 13 patients improved clinically, and 78 of the lesions lost enhancement but remained visible on the unenhanced images. There were six new enhancing lesions on the second MRI. Thus, the blood-brain-barrier integrity improved after high-dose IV methylprednisolone, which correlated well with the clinical improvement. The lesions remaining visible on the unenhanced images indicate an incomplete histologic recovery at the time of the second scan, and also demonstrate that unenhanced MRI alone is not sufficient to monitor disease activity in the short term in multiple sclerosis.

Serial study of gadolinium‐DTPA MRI enhancement in multiple sclerosis

We performed serial baseline and gadolinium (Gd)-DTPA-enhanced MRI in 4 patients with definite multiple sclerosis. Studies were performed every month for a total of 4 scans. We obtained short TR/short TE sequences at 10 and 60 minutes after Gd-DTPA injection. All patients had multiple hyperintense lesions seen on baseline MRI with long TR/short and long TE. There was Gd-DTPA enhancement in new, enlarging, and preexisting lesions that were unchanged in size. The enhancing lesions were always seen on T2-weighted images. There was no difference in enhancement between the 10- and 60-minute studies. Six of 85 preexisting lesions enhanced whereas all new or enlarging lesions enhanced. Enhancement persisted in only 1/3 of the new or enlarging lesions, suggesting that MR enhancement is a transient phenomenon due to local temporary blood-brain barrier breakdown. Our data indicate that Gd-DTPA enhancement monitoring is more sensitive than unenhanced MRI for detecting disease activity in MS.

Gadolinium-DTPA-enhanced magnetic resonance imaging in childhood brain tumors.

Gadolinium DTPA (Gd-DTPA) is a paramagnetic blood-brain barrier contrast agent for MRI that has been used primarily in adults. During May through October 1987, 17 children between the ages of 3 and 18 years with brain tumors underwent MRI examinations, before and after Gd-DTPA (11 gliomas, 4 medulloblastomas, 1 craniopharyngioma, and 1 child with neurofibromatosis and no pathologic diagnosis). We compared T1 and T2 Gd-DTPA-enhanced MRI with concurrent unenhanced MRI and enhanced CT, and then correlated this with the clinical and pathologic findings. Gd-DTPA enhanced tumors in all 7 patients with newly diagnosed tumors and enhanced tumors in 7 of 10 patients without clinical evidence of progressive disease at the time of the study. In the 7 new patients, Gd-DTPA defined tumor margins in all, and demonstrated internal tumor architecture (vessels, necrosis, and cysts) in 5. Areas believed to represent surgical scars showed varying degrees of enhancement. Leptomeningeal tumor spread, including spinal, not seen on pre-Gd-DTPA MRI or on contrast CT, was evident in 2 patients. Gd-DTPA enhancement obscured hemorrhage within the tumor (methemoglobin) in 2 patients. There were no significant side effects. These results suggest that Gd-DTPA-enhanced MRI (1) is safe in children, (2) demonstrates the extent and character of tumors better than unenhanced MRI and enhanced CT, and (3) may allow for noninvasive imaging of leptomeningeal disease, including the spine, not previously demonstrated by any other noninvasive neuroimaging technique.

46 CONTRAST ENHANCED MRI

An osmotic model of blood-brain barrier (BBB) disruption was studied by magnetic resonance (MR) imaging (0.5 T) in 17 canines. The animals were killed after imaging and the lesions confirmed on gross pathology by the presence of Evans blue dye. No accompanying cerebral edema was demonstrated on histologic examination. The disrupted BBB could be identified in only one of five control animals on unenhanced MRI, despite the use of calculated T1 and T2 images. In a second group of five animals, the area of abnormal vascular permeability was consistently demonstrated after IV injection of 0.25 mmol/kg Gd DTPA. The time course of enhancement was evaluated in four additional animals. The brain tissue concentration of the gadolinium ion responsible for the observed enhancement was determined by ion coupled plasma analysis in the last three canines. In a study of pulse techniques, spin echo sequences with both short TRs and TEs (ie, SE 500/30) and inversion recovery techniques proved to be most efficacious for the detection of contrast enhancement. However, contrast could be demonstrated on more T2 weighted sequences.

The use of GD DTPA as a perfusion agent and marker of blood-brain barrier disruption

To provide contrast enhancement in magnetic resonance imaging, a new class of compounds has been developed, the paramagnetic metal ion chelates. Gadolinium (Gd) DTPA, a prototype of this class, shows a sufficiently high in vivo stability and low toxicity for use in initial clinical trials. This type of agent, designed for rapid clearance by glomerular filtration, allows the assessment on MRI of renal function, alterations in tissue perfusion, myocardial ischemia, and perhaps most significantly disruption of the blood-brain barrier (BBB). Research at Vanderbilt has demonstrated these applications, with particular emphasis in three areas. Tissue perfusion changes, such as those produced by ligation of the arterial blood supply to portions of the spleen and kidney, cannot easily be detected on unenhanced MRI. These acute tissue infarcts can be readily identified following the administration of Gd DTPA. The question of field strength dependence of Gd DTPA has been addressed by experimentation at 0.15, 0.5, and 1.5 tesla. Furthermore, the ability to detect an alteration of the BBB, when present without associated edema, has been demonstrated with the application of control enhancement. The use of contrast agents in MRI will enhance both the sensitivity and specificity of magnetic resonance imaging.

The Association of Venous and Cavernous Angioma - Case Report and Review of Literature

Isolated cavernous and venous angiomas are common vascular cerebral malformations but their association is less frequent. Presence of venous angioma enhances the risk of bleeding from cavernous angioma. Also, this association is important for surgical planning. While early extirpation of cavernous angioma is recommended, the associated venous angioma has to be preserved due to the possible venous infarction. We report a case of venous angioma associated with cavernous angioma revealed by magnetic resonance imaging after the administration of contrast material, which was not visualised on unenhanced MRI images. The importance of contrast administration in the diagnosis of venous angioma in a close vicinity of cavernous is emphasised in this report.