Hemorrhagic and nonhemorrhagic stroke: diagnosis with diffusion-weighted and T2-weighted echo-planar MR imaging

PURPOSE: To determine if diffusion- and T2-weighted echo-planar magnetic resonance (MR) imaging can be used to detect acute hemorrhagic stroke and to differentiate hemorrhagic from nonhemorrhagic stroke. MATERIALS AND METHODS: A total of 118 examinations (diffusion- and T2-weighted MR imaging) in 19 patients with 27 nonhemorrhagic strokes and in six patients with seven hemorrhagic strokes were performed. The ratios of apparent diffusion coefficient and of signal intensity on T2-weighted MR images in lesions to those in contralateral control areas were calculated. RESULTS: Decreased ADC was shown in lesions of acute (0-3 days) hemorrhagic stroke, as well as in lesions of acute nonhemorrhagic stroke. Hypointense areas were seen on T2-weighted MR images in patients with acute hemorrhagic stroke, in contrast to normal to increased signal intensity in those with acute nonhemorrhagic stroke. Apparent diffusion coefficient tended to remain decreased in hemorrhagic stroke lesions even 100 days after onset, in contrast to the increased coefficient in nonhemorrhagic stroke lesions at the late chronic stage (31 days or older). CONCLUSION: Diffusion- and T2-weighted echo-planar MR imaging can be used to detect and distinguish between acute hemorrhagic and nonhemorrhagic stroke.     

Increased-contrast, high-spatial-resolution, diffusion-weighted, spin-echo, echo-planar imaging

An insertable head gradient coil with a maximum gradient amplitude of 45 mT/m and a rise time of 150 musec along all three major axes was used to collect high-spatial-resolution, single-shot, spin-echo, echo-planar, diffusion-weighted magnetic resonance images with b values ranging from 0 to 2,200 sec/mm2. Improvements in spatial resolution allowed better visualization of large white matter tracts and their relation to adjacent anatomic structures. Excellent contrast and anatomic detail were revealed for most structures in the brain when a sufficient number of acquisitions were collected.     

Osteogenic sarcoma: noninvasive in vivo assessment of tumor necrosis with diffusion-weighted MR imaging

PURPOSE: To evaluate diffusion-weighted magnetic resonance (MR) imaging for detecting tumor necrosis in an animal model of osteogenic sarcoma. MATERIALS AND METHODS: Twelve rats with osteogenic sarcoma underwent T1-weighted unenhanced and gadolinium-enhanced spin-echo and diffusion-weighted spin-echo MR imaging. Histologic correlation was performed. Signal intensities, T2 relaxation times, normalized apparent diffusion coefficients, and relative signal intensity increases were calculated. RESULTS: On diffusion-weighted images, necrotic tumor showed low signal intensity (mean normalized apparent diffusion coefficient, 0.46 +/- 0.20 [1 standard deviation]), indicating rapid diffusion of water molecules as a result of loss of membrane integrity, while viable tumor showed high signal intensity (mean normalized apparent diffusion coefficient, 0.16 +/- 0.05; P < .0001). Differences in the T2 relaxation times and relative signal intensity increases between viable and necrotic tumor were not statistically significant. CONCLUSION: Normalized apparent diffusion coefficients are more accurate in differentiating between viable and necrotic tumor than are T2 relaxation times or relative signal intensity increases on contrast-enhanced images. Signal intensity overlap between viable and necrotic tumor on gadolinium-enhanced images may be caused by the small molecular size of the agent, which permeates the interstitial space freely, thereby also enhancing necrosis. Diffusion-weighted MR imaging depicts differences in diffusion and, ultimately, in membrane integrity between viable and necrotic tumor and may be used to monitor tumor viability during treatment.     

Dynamic MR imaging of splenic tumor

Inflammatory pseudotumor and hemangioma of the spleen are rare benign tumors, and MRI findings of splenic diseases have been reported only rarely. We recently observed three patients with inflammatory pseudotumor and hemangioma of the spleen. Abdominal ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI) and angiography demonstrated within the enlarged spleen. MRI and dynamic MRI after administration of gadolinium DTPA provide the characterization of the splenic tumor.     

MR imaging of the liver: comparison between single-shot echo-planar and half-Fourier rapid acquisition with relaxation enhancement sequences

We previously reported the case of a human chronic Bordetella bronchiseptica respiratory infection, due to contact with infected rabbits. Lipopolysaccharides of the human isolates, of one rabbit isolate and of isolate from other origins were analyzed with sera from infected mice, rabbit and human. Antigenicity and length of the lipopolysaccharide molecules varied between isolates. We showed a progressive loss of O-chain during infection, associated with an enhanced susceptibility of the isolates to the bactericidal effect of normal serum. This observation suggests the existence of an intracellular niche which selects for strains with distinct lipopolysaccharide types.     

Breath-hold MR cholangiopancreatography with three-dimensional, segmented, echo-planar imaging and volume rendering

End-expiration, 21-second breath-hold, three-dimensional magnetic resonance (MR) cholangiopancreatography (MRCP) was developed with segmented echo-planar imaging. In 15 healthy subjects and 14 randomly selected patients undergoing liver studies, three-dimensional MRCP images were obtained and volume rendered. In 15 (100%) healthy subjects and 13 (93%) patients, clear depiction of biliary, hepatic, and pancreatic ducts (with lumen diameter of at least 2 mm) was possible with good signal-to-noise ratio.     

Elimination of eddy current artifacts in diffusion-weighted echo-planar images: the use of bipolar gradients

Small gradient fields resulting from incompletely canceled eddy currents can cause geometric distortion in echo-planar images. Although this distortion is negligible in most echoplanar applications, the large gradient pulses used in diffusion-weighted echo-planar imaging can result in significant image distortion. In this report, it is shown that this distortion can be significantly reduced by the application of bipolar gradient waveforms. Both bipolar diffusion-sensitizing gradients and an inverted gradient preparatory pulse were examined for minimizing the eddy currents responsible for these distortions.     

Beyond anatomy: MR imaging as a molecular diagnostic tool

Technical advances in software and hardware make MR imaging competitive with CAT scanning as an anatomic imaging tool. Although anatomic relationships remain important, increased understanding of cell structure and function is rapidly moving us toward diagnosis and treatment at the cellular level. By virtue of its reliance on nuclear magnetic spin moment, MR imaging is responsive to real time physico-chemical characteristics of cells and tissues being imaged. This intrinsic advantage of MR imaging is being rapidly developed through the use of targeted imaging agents and magnetic resonance spectroscopy. Imaging agents that target specific cell populations have been prepared by using monoclonal antibodies, liposomes, and short peptides bound to chelates containing paramagnetic atoms. Using magnetic resonance spectroscopy, the chemical composition of tumors can be analyzed and compared with normal tissues in vivo and in vitro. Areas of possible clinical usefulness for magnetic spectral analysis include: (1) in vitro or in vivo characterization of lesions as benign or malignant, (2) differentiation between in situ and invasive carcinomas, (3) determination of responsiveness to specific chemotherapeutic regimens before their institution, (4) study of in vivo drug metabolism by neoplasms, and (5) assessment of response to therapy and of residual disease at the completion of therapy. Early experiences in these parallel fields show great promise, with widespread clinical applications expected in the near future.     

Intraperitoneal abscesses: diagnostic accuracy of and appearances at MR imaging

PURPOSE: Transverse retubularization of small ileal segments has been described as a new time and labor saving variation of the Mitrofanoff principle in a dog model with good functional results. We report our initial clinical experience with this technique. MATERIALS AND METHODS: From May 1996 through January 1997 a new technique of channel formation for intermittent catheterization was applied in 9 children (1 to 16 years old) and 7 adults (18 to 56) with various abnormalities of the lower urinary tract. The new method was used in primary reconstruction of the lower urinary tract and in revision procedures. An ileal segment 2 cm. long was excised. The bowel wall was opened longitudinally about 1 cm. from the mesentery. The resulting rectangle was retubularized over a 14F catheter in transverse direction. The longer portion of the tube was implanted submucosally into the native bladder, the augmented bladder or an intestinal reservoir. The shorter portion was used to form the stoma. In 4 patients we created a double tube. RESULTS: Of the patients 13 (81%) are completely continent day and night with easy catheterization postoperatively. In 2 cases of tunnel failure continuous leakage required reimplantation of the intact ileal tube to achieve continence. Minor leakage with bladder fullness in an 11-year-old boy could be obviated by adjusting the interval of catheterization. CONCLUSIONS: With the advantage of constant availability, minimal loss of bowel, relative simplicity (no mesentery interfering with implantation, high tube mobility), minimized risk of stone formation (no staples), reliable continence (no leak point) and easy catheterization (longitudinal folds), this straightforward technique is an excellent second choice use of the Mitrofanoff principle.     

Insulinoma associated with liver lesions: value of MR imaging

We report on a middle-aged woman who presented with clinical and biochemical findings of insulinoma. Preoperative evaluation by ultrasound, CT, and angiography located the pancreatic lesion but also revealed two focal liver lesions. The latter were interpreted as metastases. MR imaging with injection of superparamagnetic iron oxide particles not only localized the insulinoma but proved to be the only noninvasive technique capable to exclude presence of liver metastases preoperatively. This reversed management to minimal laparoscopic surgery. Recent literature of preoperative imaging evaluation of insulinoma and focal liver lesions is discussed.     

MR imaging in children with nonperforated acute appendicitis: value of unenhanced MR imaging in sonographically selected cases

OBJECTIVE: The aim of this study was to describe the MR appearance of acute appendicitis and to determine the value of MR imaging for diagnosis of acute appendicitis. SUBJECTS AND METHODS: Forty-five children (28 girls, 17 boys), 7-16 years old (mean age, 13 years old), with clinically diagnosed acute appendicitis underwent independently graded compression sonography by two radiologists. MR imaging was performed when sonography revealed acute appendicitis (observer 1, 16 [36%] patients; observer 2, 18 [40%] patients), was inconclusive (observer 1, two [4%] patients; observer 2, one [2%] patient), and was interpreted as normal (observer 1, two [4%] patients; observer 2, one [2%] patient) (n = 20). Axial T1-weighted turbo spin-echo sequences, T2-weighted turbo spin-echo sequences in the axial and coronal planes, and fat-suppressed short inversion time inversion recovery turbo spin-echo sequences in the axial plane (4-mm slice thickness) were obtained and evaluated independently by two radiologists. The ability to see acute appendicitis with MR imaging was evaluated, the appearance and morphologic changes were described, and the most accurate sequence was determined. All children in whom MR imaging was performed underwent surgery. RESULTS: MR imaging revealed acute appendicitis in all cases (100%) by both observers. On T2-weighted ultra turbo spin-echo images, acute appendicitis appeared with a markedly hyperintense center, a slightly hyperintense thickened wall, and markedly hyperintense periappendiceal tissue. Unenhanced axial T2-weighted spin-echo imaging was the most sensitive sequence. CONCLUSION: In this study group, MR imaging was a valuable technique for depiction of acute appendicitis.     

Low incorporation of soleus tendon: a potential diagnostic pitfall on MR imaging

Head pain is one of the main presenting symptoms of internal carotid artery (ICA) dissection, usually in association with ischemic and/or local signs such as Horner's syndrome, lower cranial nerve palsies, or tinnitus. In rare cases, head pain remains isolated and mimics other conditions. We report a patient who suffered isolated prolonged orbital pain as the only sign of intrapetrous ICA dissection. Early recognition of such unusual facial pain may be crucial in decreasing the risk of secondary cerebral or retinal ischemia.     

Studies on utility of MR T2-weighted images using multishot echo-planar imaging for hepatic mass lesions

MR T2-weighted images using multishot echo-planar imaging (EPI) and fast spin-echo (FSE) sequences were obtained in 22 patients with hepatic masses. Multishot EPI sequences included eight-shot breath-hold EPI and 16-shot EPI without breath-hold, while FSE sequences included nonfat-suppressed respiratory-triggered FSE, fat-suppressed respiratory-triggered FSE, and nonfat-suppressed breath-hold FSE. Signal-to-noise ratio, contrast-to-noise ratio and artifacts were compared between EPI and FSE images of 47 hepatic masses. In evaluating solid tumors, EPI provided image quality equal or superior to that of FSE, whereas in the evaluation of nonsolid tumors FSE showed better image quality than EPI. In conclusion, it was demonstrated that in the evaluation of hepatic solid tumors T2-weighted eight-shot breath-hold EPI can replace both nonfat-suppressed respiratory-triggered FSE and breath-hold FSE, and it was suggested that eight-shot breath-hold EPI can replace fat-suppressed respiratory-triggered FSE to reduce patient discomfort and increase examination throughput.     

"Whiplash" injury of the cervical spine: value of modern diagnostic imaging

"Whiplash injuries" are frequent sequelae of motor vehicle accidents. While conventional imaging methods such as X-ray, including special and functional lateral projections, continue to be the first-choice evaluation methods, they frequently do not reveal injuries to the soft tissues. Cross-sectional methods such as CT and MRT may therefore be indicated for further workup in given clinical situations. In this paper the role of the entire spectrum of imaging methods is reviewed. Emphasis is placed on so-called functional CT, which allows detection of rotational instabilities of the upper cervical spine. These are difficult to evaluate clinically or by standard imaging studies, yet they may be a frequent cause of chronic whiplash syndrome. Furthermore, some results of morphologic studies of the alar ligaments by MRT are presented. Although experience to date is limited, it is likely that MRT of the occipitocervical junction region due to its potential to reveal exquisite anatomical detail, will gain in importance in the future.     

In vivo echo-planar imaging of rat spinal cord

An integrated approach to echo-planar imaging of rat spinal cord in vivo with a small field of view (FOV) is presented. This protocol is based on a multishot interleaved echo-planar imaging (EPI) sequence and includes: 1) use of an inductively coupled implantable coil for improved signal-to-noise ratio (SNR); 2) three-dimensional (3D) automatic shimming of the magnetic field over the spinal cord; and 3) post-acquisition data processing using a multireference scan for minimizing image artifacts. Some of the practical issues in implementing this protocol are discussed. This imaging protocol will be useful in characterizing the spinal cord pathology using techniques that are otherwise time-consuming, such as diffusion tensor imaging.     

Bronchial carcinoid tumor: demonstration by dynamic inversion recovery turbo-flash MR imaging

A 38-year-old woman was referred to our hospital following the discovery of a right hilar mass on chest radiograph. Retrospectively, a hilar mass could be seen on a chest X-ray which had been obtained 5 years earlier. A coronal dynamic inversion recovery turbo-FLASH gadolinium-enhanced sequence was performed, demonstrating the right lesion which enhanced during the systemic arterial phase indicating an arterial supply from the bronchial arterial circulation. The surgical and pathological findings were a bronchial carcinoid tumor, with foci of bone formation.     

Segmented three-dimensional echo-planar flow imaging of the cervical carotid arteries

PURPOSE: To implement and assess the application of segmented three-dimensional echo-planar MR imaging time-of-flight flow sequences for studying the anatomy of the cervical carotid arteries at 1.5 T. METHODS: The 3-D echo-planar sequences were segmented along the in-plane phase-encoding direction. Echo train lengths (ETLs) of 3 and 5 and signal bandwidths of +/-25, +/-33, and +/-50 KHz were tested along with a conventional (ETL = 1) 3-D MR flow study in six healthy volunteers and in five patients with known arteriosclerotic disease involving the carotid bifurcation as confirmed by conventional angiography. The volunteer data were used to rank the techniques with respect to vessel dimension, vessel/background contrast, and quality by four trained neuroradiologists. For the patient studies, the percentage of stenoses was measured for all MR studies and compared against the conventional angiographic data using the criteria of the North American Symptomatic Carotid Endarterectomy Trial. RESULTS: Using Wilcoxon's test statistic and a significance level of .05, we found that the conventional MR flow examination was better than the segmented techniques and that the segmented techniques with ETL of 3 were superior to their counterparts with ETL of 5. For the ETL of 3 techniques, the high-bandwidth studies were inferior to their lower bandwidth counterparts; however, there was no significant difference between the performance of the medium- and low-bandwidth sequences. The patient data revealed that the segmented techniques consistently overestimated the severity of stenosis; however, in no instance did any of the segmented examinations erroneously indicate the presence of disease. CONCLUSIONS: The reduction in acquisition time and the zero false-positive rate we obtained suggest that segmented 3-D echo-planar MR flow techniques may be used as a screening/locating study for cervical carotid artery disease.     

Time-of-flight MR angiography of the portal venous system: value compared with other imaging procedures

A simple method for determination of mimosine and 3,4-dihydroxypyridine (3,4-DHP) in plasma and milk was developed. Milk and plasma, with tyrosine as internal standard, were deproteinized using 9% trichloracetic acid and extracted with diethyl ether. Metabolites were separated by isocratic high-performance liquid chromatography, with 0.02 M orthophosphoric acid (pH 2.5) at 0.5 ml/min and a Hypersil ODS microbore column. Mimosine, 3,4-DHP and tyrosine were detected at 275 nm. The recovery of the mimosine added to the plasma samples was 101.6 +/- 2.3% and 103.3 +/- 1.0% for milk samples. 3,4-DHP recovery for plasma samples was 101.2 +/- 0.9% and for milk samples 100.8 +/- 1.4%. The reproducibility of the method was evaluated by analyzing six plasma samples and six goat milk samples. The analyses yielded relative standard deviations of 2.65 and 2.82%, respectively.