Intrauterine contraceptive devices: MR imaging

To assess the safety of magnetic resonance (MR) imaging in women who have an intrauterine contraceptive device (IUD) in place, in vitro and in vivo studies were performed at both 0.35 and 1.5 T. Two commonly used IUDs were tested, one all of plastic, the other with a coil of copper wire on it. Specifically, the study assessed possible motion of the IUD in the magnetic field, potential of the IUD to heat up during two spin-echo imaging sequences commonly used in MR imaging of the pelvis (2,000/30 and 60 [repetition time, msec/echo time, msec], and 500/30), and the appearance on MR images of the IUD devices. A retrospective review of MR images of the pelvis in six women who had an IUD in place was also performed. Results show that an IUD does not move under the influence of the magnetic field, does not heat during spin-echo sequences commonly used for pelvic imaging, and does not produce artifacts in vitro or in vivo. Patients with either type of IUD can be safely imaged with MR, and MR images of the pelvis are not degraded by the presence of an IUD.     

Cerebral MR imaging in intravascular lymphomatosis.

MR imaging data were reviewed retrospectively in four male patients (32 to 74 years old) with histologically confirmed intravascular lymphomatosis (IVL), a rare, aggressive form of non-Hodgkin lymphoma. MR findings included infarct-like lesions (n = 2), focal parenchymal enhancement (n = 3), dural/arachnoid enhancement (n = 2), and, in one case, nonspecific, patchy foci of increased signal in the white matter on long-TR images. All patients had multifocal lesions. Knowledge of the spectrum of MR imaging features in this unusual disorder may aid in diagnosis and potentially enhance the role of imaging in following response to therapy.     

Autoperfused balloon catheter for intravascular MR imaging

An intravascular magnetic resonance (MR) imaging catheter for high-resolution imaging of vessel walls was developed. The catheter design is based on an autoperfusion balloon catheter that allows passive perfusion of blood during balloon inflation. The blood enters a central lumen through multiple sideholes of the catheter shaft proximal to the balloon. A remotely tuned, matched, and actively decoupled, expandable single-loop radiofrequency coil was mounted onto the balloon to receive intravascular MR signals. The autoperfusion rate through the catheter was determined experimentally relative to perfusion pressure. The catheter concept was evaluated in vitro on human femoral artery specimens and in vivo in the internal carotid artery of two pigs. The proposed catheter design allowed for maintained blood perfusion during the acquisition of high-resolution intravascular images. During perfusion, image quality remained unaffected by flow, motion, and pulsatility artifacts. The availability of an autoperfused intravascular catheter design can be considered an important step toward high-resolution atherosclerotic plaque imaging in critical vessels such as the carotid and coronary arteries.     

In vivo intravascular MR imaging: transvenous technique for arterial wall imaging

PURPOSE: To determine, in vivo, the potential for transvenous magnetic resonance (MR) imaging of the arterial wall and to assess appropriate MR pulse sequences for this method. MATERIALS AND METHODS: MR imaging was performed on 19 vessels (right renal artery, N = 9; left renal artery N = 2; external iliac artery, N = 4; abdominal aorta, N = 4) in nine swine. The animals were either low-density lipoprotein receptor knockout (N = 5) or Yucatan mini-pigs fed an atherogenic diet for 6 to 11 weeks (N = 4). The intravascular MR coil/guide wire (IVMRG) (Surgi-Vision, Gaithersburg, MD) was introduced via the external iliac vein into the inferior vena cava (IVC). The following electrocardiograph-gated MR pulse sequences were obtained: T1-weighted precontrast with and without fat saturation and T1-weighted postcontrast with fat saturation. Two observers scored wall signal and conspicuity and classified the vessel as normal, abnormal, or stented. Images were compared with histopathologic findings. RESULTS: The T1-weighted precontrast without fat saturation, T1-weighted precontrast with fat saturation, and T1-weighted postcontrast images correlated with histopathologic findings in 12 of 15 vessels, eight of 10 vessels, and 14 of 16 vessels, respectively. Abnormal histopathologic findings included: arterial wall thickening (N = 3), arterial dissection (N = 2), focal fibrous plaque (N = 2), adherent thrombus (N = 1). The T1-weighted postcontrast images were not compromised by artifacts and had the highest score for vessel wall signal and conspicuity. T1-weighted precontrast images were compromised by chemical shift artifact and poor blood suppression. Negligible artifacts were created by the platinum stent. CONCLUSION: The T1-weighted fat saturated postcontrast pulse sequence was superior to other sequences for transvenous MR imaging of the arterial wall.     

MR evaluation of pulmonary interstitial and intravascular fluids

Serial dilutions of sheep plasma and red blood cells were made yielding blood samples of various hematocrits (Hcts). These samples were studied at bore temperature (34 degrees C) in a 0.25 T pulsed NMR analyzer for differences in T1 and T2. An inverse relationship between Hct and T1 was demonstrated (P less than .001); no change was detected in T2 with Hcts from 0% to 88%. Plasma and lung lymph samples were also obtained from chronically instrumented, unanesthetized sheep to determine the effects on T1 and T2 of increasing hydrostatic pressure and altering capillary permeability in the lungs. Normal baseline lung lymph T1 was longer than the concurrent plasma T1. T1 of lung lymph was inversely proportional to the lymph/plasma protein ratio. Edema induced by elevation of hydrostatic pressure lengthens T1, whereas increased capillary permeability shortens T1. T2s were unchanged in plasma and lymph in the baseline state with hydrostatic edema, and with increased capillary permeability.     

Chiari II malformation: MR imaging evaluation

The purpose of this study was to explore the value of high-detail MR imaging in the diagnosis of the Chiari II malformation. Twenty-four patients with known Chiari II malformation as diagnosed by CT scanning were evaluated with cranial MR scans. Two patients also had spine scans. The sagittal-plane images were the most informative, and abnormalities of the telencephalon, diencephalon, mesencephalon, rhomboencephalon, upper spinal cord, and mesencephalon were shown extremely well. We found MR to be an easy and accurate method for demonstrating the abnormalities of the Chiari II malformation, and it is our procedure of choice.     

Venous clots: evaluation with MR imaging

In vitro and in vivo studies were performed to determine the proton relaxation and imaging characteristics of static blood and acute and organized clot in canine jugular veins. In vivo, it was found that two inversion recovery sequences using a short inversion time (100 msec) demonstrated better differentiation of signal intensity of intravascular clot from surrounding soft tissues than did standard T1- and T2-weighted sequences. In vitro, quantitative measurements showed marked reduction of both T1 and T2 relaxation time of acute clot compared with stagnant blood. In addition, the T1 relaxation time, and to a lesser extent the T2 relaxation time, shortened as the clot aged, indicating a potential role for magnetic resonance imaging in determining the age of venous thrombi.     

Gallbladder carcinoma: evaluation with MR imaging

Magnetic resonance (MR) images of 19 patients with histologically proved gallbladder carcinoma were retrospectively reviewed to determine the appearance of the primary tumor, and to assess the ability of MR imaging to demonstrate the various modes of tumor spread beyond the gallbladder. The primary tumor, as well as tumor spread beyond the gallbladder, was hyperintense on T2-weighted images and hypointense on T1-weighted images when compared with the liver parenchyma. Liver invasion and metastasis could be depicted by MR imaging with both sequences, unless the tumors were small or the extent of invasion was minimal. Duodenal invasion was difficult to evaluate because of motion artifacts, paucity of fat, and partial volume effects. T1-weighted images readily demonstrated extension of the tumor to the hepatoduodenal ligament and para-aortic region with good contrast between tumor and surrounding tissue. The extent of tumor extension to the blood vessels was also easily evaluated because of flow void in the vasculature. MR imaging can help determine the extent of gallbladder carcinoma and can contribute to the staging of this disease.     

Suprasellar lesions: evaluation with MR imaging

The authors retrospectively evaluated the characteristics on magnetic resonance (MR) images of 59 suprasellar lesions and compared them with computed tomography (CT) scans in 55 of the cases in which CT was performed. A diverse number of lesions were included: 17 pituitary adenomas; eight optic or hypothalamic gliomas; six craniopharyngiomas; six vascular anomalies; four lesions with extension into the suprasellar space; three metastases; two each of meningioma, hamartoma, germinoma, sarcoid granuloma, and teratoma; and one each of lymphoma, optic tract hematoma, cerebrospinal fluid-borne metastasis, pituitary hyperplasia, and sphenoid sinus mucocele. MR enabled characterization of lesions containing hemorrhage, fat, flowing blood, mucus, and cyst and allowed more specific diagnoses than CT in 6% of cases. MR was equivalent to CT in allowing lesions to be detected and in 20% of cases more accurately defined altered perisellar anatomy. Vascular abnormalities can be better evaluated with MR, and use of angiography can be avoided in some cases.     

Renal allografts: evaluation by MR imaging

The value of magnetic resonance (MR) imaging in assessing renal transplants was prospectively studied in 45 patients with 46 allografts. Four allografts were imaged at two different times, and separate diagnoses were given for both examinations. Therefore, this study was based on 50 proved diagnoses: nine normally functioning allografts, four allografts with acute tubular necrosis (ATN), 29 with acute rejection, one with chronic rejection, five with cyclosporin nephrotoxicity, and two with local inflammation secondary to adjacent abscess. Twenty-seven of the allografts had concomitant fluid collections. Normal renal structures with preservation of corticomedullary contrast (CMC) on T1-weighted images were demonstrated in all the normally functioning allografts. Decreased or absent CMC on T1-weighted images, reflecting a long T1 relaxation time for cortex, was found to be the most consistent sign of acute renal allograft rejection (27/29). No abnormalities on on MR images were observed in allografts compromised by cyclosporin nephrotoxicity. Hydronephrosis of the renal allograft was easily diagnosed with MR. Perirenal abscess (three cases) and perirenal hematomas (five cases), because of their higher MR signal intensity on T1-weighted images (TR = 0.5 sec, TE = 28 msec), could be differentiated from clinically insignificant postoperative fluid seromas (seven cases), lymphoceles (11 cases), and urinoma (one case).     

Cirrhosis: CT and MR imaging evaluation

In this article, we present the CT and MR imaging characteristics of the cirrhotic liver. We describe the altered liver morphology in different forms of viral, alcoholic and autoimmune end-stage liver disease. We present the spectrum of imaging findings in portal hypertension, such as splenomegaly, ascites and varices. We describe the patchy and lacelike patterns of fibrosis, along with the focal confluent form. The process of hepatocarcinogenesis is detailed, from regenerative to dysplastic nodules to overt hepatocellular carcinoma. Different types of non-neoplastic focal liver lesions occurring in the cirrhotic liver are discussed, including arterially enhancing nodules, hemangiomas and peribiliary cysts. We show different conditions causing liver morphology changes that can mimic cirrhosis, such as congenital hepatic fibrosis, "pseudo-cirrhosis" due to breast metastases treated with chemotherapy, Budd-Chiari syndrome, sarcoidosis and cavernous transformation of the portal vein.     

Shoulder instability: evaluation with MR imaging

Instability of the glenohumeral joint is a common cause of chronic shoulder pain and disability. One or more episodes of subluxation or dislocation may result in a tear, detachment, or attenuation of the glenoid labrum, stripping of the joint capsule from the scapula, or trauma to the tendons or muscles of the rotator cuff. A series of 27 shoulders examined with magnetic resonance (MR) imaging showed changes of glenohumeral instability, which were confirmed with open or arthroscopic surgery. MR imaging was capable of displaying common types of pathologic conditions resulting from instability, including labral trauma, capsular detachment, and retraction of the subscapularis muscle. MR imaging is a valuable diagnostic tool for the evaluation of glenohumeral instability.     

Wallerian degeneration: evaluation with MR imaging

Twenty-three patients who underwent routine magnetic resonance (MR) imaging of the brain were found to have signal or structural abnormalities corresponding to white matter tracts. Images were evaluated for anatomic and MR signal characteristics of the involved tract, associated primary lesions, and, when possible, changes in MR signal and anatomic structures with time. Images from 20 patients demonstrated a thin band of abnormal signal contiguous with the primary lesion and conforming to the known anatomic pathway of a white matter tract. Cerebral infarction was the most common associated primary disorder (n = 17). Neoplasms (n = 2), demyelinating (n = 1) and posthemorrhagic (n = 2) conditions, and an idiopathic movement disorder (n = 1) were associated with white matter tract signal abnormalities that were indistinguishable from those seen with infarction. Signal abnormality corresponding to the corticospinal tract was the type most commonly seen. No change in signal characteristics was seen with time (six cases) or following contrast material administration (two cases). The authors conclude that MR imaging provides a sensitive method of evaluating wallerian degeneration in the living human brain.