3D time of flight MR angiography: acquisition with small field of view and low phase encodes.

The aim of the study was to evaluate and compare the image quality of the 3D TOF MRA acquired with a small FOV and low phase encodes with those MR angiographic images acquired with standard pulse sequence parameters. Twenty patients who were referred to our institution for MR imaging of the brain and strictly satisfied the selection criteria were included in this study. Apart from the routine protocol for MR imaging of the brain, 3D TOF MRA of the circle of Willis with a small FOV and a standard FOV were performed. The image quality of all MRA was evaluated by two independent observers who were blind to the pulse sequence parameters. From the standard FOV MRA, 22.5, 12.5, and 5% of the patients were graded as mild, moderate, and severe stenosis of the internal carotid artery, respectively. On the contrary, no apparent stenosis was observed from the small FOV MRA with low phase encodes. Regarding the reduction in MR artifacts and acquisition time achieved with the small FOV 3D TOF MRA with low phase encodes, this might be a useful MR angiographic technique to be used in routine clinical practice.

Diffuse axonal injury: detection of changes in anisotropy of water diffusion by diffusion-weighted imaging.

Myelinated axons of white matter demonstrate prominent directional differences in water diffusion. We performed diffusion-weighted imaging on ten patients with head injury to explore the feasibility of using water diffusion anisotropy for quantitating diffuse axonal injury. We showed significant decrease in diffusion anisotropy indices in areas with or without signal abnormality on T2 and T2*-weighted images. We conclude that the water diffusion anisotropy index a potentially useful, sensitive and quantitative way of diagnosing and assessing patients with diffuse axonal injury.

Moyamoya syndrome in a child with Down syndrome.

Moyamoya syndrome has been reported in association with Down syndrome. In paediatric patients, the usual presentation is that of ischaemic stroke. We report a 9-year-old boy with Down syndrome and moyamoya syndrome who presented with acute-onset left hemiparesis. This is the first such reported case in Hong Kong. There is growing evidence that the chromosomal abnormalities in patients with Down syndrome may contribute to a vulnerability for the development of moyamoya syndrome. A high index of suspicion is necessary to make the correct diagnosis. Medical and surgical management strategies for this disease are discussed. Surgical intervention should proceed without delay, if indicated, to prevent further neurological deterioration. A multidisciplinary approach is recommended for the rehabilitation of these patients.

Syphilitic myelitis with diffuse spinal cord abnormality on MR imaging.

Syphilitic myelitis is a very rare manifestation of neurosyphilis. The MRI appearance of syphilitic myelitis is not well documented and only a few cases have been reported. We present a 52-year-old woman with acute onset of paraplegia. Magnetic resonance imaging of the spine showed diffuse high signal intensity in the whole spinal cord on T2-weighted images. Focal enhancement was observed in the dorsal aspect of the thoracic cord on T1-weighted gadolinium-enhanced images. To our knowledge, diffuse spinal cord abnormality in syphilitic myelitis has not been reported in the international literature. Disappearance of the diffuse high-signal lesions with residual focal enhancement was noted after antibiotic therapy. The patient suffered significant neurological deficit despite improvement in the MR images. In this article we present the imaging findings and review the literature of this rare condition.

Tumefactive demyelinating lesions by combined perfusion-weighted and diffusion weighted imaging.

Tumefactive demyelinating lesion may sometimes mimic intracranial neoplasm or abscess and pose a diagnostic problem both clinically and radiologically. The diagnosis is even more complicated since multiple sclerosis is relatively uncommon among Chinese and due to low incidence of oligoclonal protein in the cerebrospinal fluid. We present a Chinese lady with tumefactive demyelinating lesion, which mimic cystic neoplasm and cerebral abscess. The use of perfusion and diffusion weighted imaging obviated unnecessary surgical biopsy.

Evaluation of cerebral abscesses by diffusion-weighted MR imaging and MR spectroscopy.

Cerebral abscess may sometimes mimic necrotic tumor and cystic metastases both clinically and radiologically. The imaging findings may be indistinguishable on conventional magnetic resonance imaging. Although recent studies have shown that cerebral abscess displays restricted diffusion on diffusion-weighted imaging (DWI), it is not pathognomic. Necrotic tumor and cystic metastases may occasionally have restricted diffusion on DWI. Since the urgency of surgical intervention and approach of surgery is different, MR Spectroscopy may be used in conjunction with DWI in establishing the correct diagnosis.

Digital subtraction in gadolinium-enhanced MR imaging of the brain: a method to reduce contrast dosage.

The aim of the study was to investigate the feasibility of using digital subtraction in contrast-enhanced MR imaging of the brain to reduce the MR contrast dosage without jeopardizing patient care. Fifty-two patients with intracranial lesions, either intra-axial or extra-axial, detected by computerized tomography were selected for contrast-enhanced MR imaging with half-dose and full-dose of gadopentetate dimeglumine. The half-dose unsubtracted, full-dose unsubtracted, and half-dose subtracted MR images were visually assessed by counting the number of enhancing brain lesions in the images and quantitatively analyzed by computing their lesion contrast-to-background ratios (CBR). The visual conspicuity of the half-dose subtracted MR images was comparable to that of the full-dose unsubtracted MR images ( p>0.05), whereas the CBR of the half-dose subtracted images was approximately two to three times higher than that of the full-dose unsubtracted images. The half-dose subtracted T1-weighted spin-echo images might be able to replace the conventional standard-dose T1-weighted spin-echo images in MR imaging of the brain.

Acute vertebral body compression fractures: discrimination between benign and malignant causes using apparent diffusion coefficients.

Diffusion weighted MRI was performed on patients with acute vertebral body compression. The usefulness of the apparent diffusion coefficient (ADC) in differentiating between benign and malignant fractures was evaluated. A total of 49 acute vertebral body compression fractures were found in 32 patients. 25 fractures in 18 patients were due to osteoporosis, 18 fractures in 12 patients were histologically proven to be due to malignancy, and 6 fractures in 2 patients were due to tuberculosis. Signal intensities on T(1) weighted, short tau inversion recovery (STIR) and diffusion weighted images were compared. ADC values of normal and abnormal vertebral bodies were calculated. Except for two patients with sclerotic metastases, benign acute vertebral fractures were hypointense and malignant acute vertebral fractures were hyperintense with respect to normal bone marrow on diffusion weighted images. Mean combined ADCs (ADC(cmb); average of the combined ADCs in the x, y and z diffusion directions) were 0.23 x 10(-3) mm(2) s(-1) in normal vertebrae, 0.82 x 10(-3) mm(2) s(-1) in malignant acute vertebral fractures and 1.94 x 10(-3) mm(2) s(-1) in benign acute vertebral fractures. The differences between ADC(cmb) values were statistically significant (p<0.001). The ADC is useful in differentiating benign from malignant acute vertebral body compression fractures, but there may be overlapping ADC values between malignant fractures and tuberculous spondylitis.

Clinics in diagnostic imaging (76). Left extradural-intradural lumbar neurofibroma.

A 62-year-old woman presented with weight loss, anoexia and back pain. She was found to have a palpable left abdominal mass. Radiographs, CT and MR imaging revealed a large left 3rd lumbar neurogenic tumour with both intra- and extradural components. A neurofibroma was excised and the diagnosis was confirmed histopathologically. The patient has no recurrence at six years follow-up. The pathological classifications, clinical and imaging features of neurogenic tumours are discussed. With the knowledge of characteristic imaging features, these tumours can be differentiated from other types of intradural-extramedullary tumours.

Reversible MRI changes of hypothalamus in a multiple sclerosis patient with homeostatic disturbances.

Multiple sclerosis (MS) patients occasionally present with homeostatic disturbances suggestive of hypothalamic dysfunction; however, the hypothalamus often appears normal on imaging, apart from confirmation in a few necropsy studies. In this article we describe a Chinese woman with atypical clinical presentation. She presented with relapsing symptoms and signs consistent with hypothalamic dysfunction including hyperprolactinema, syndrome of inappropriate secretion of anti-diuretic hormone (SIADH), hypersomnolence and temperature dysregulation. Serial MRI depicted the atypical reversible changes in the hypothalamus, correlating with the observed homeostatic abnormalities.

Discrimination of an infected brain tumor from a cerebral abscess by combined MR perfusion and diffusion imaging.

The aim of this study was to investigate the signal characteristics of the abscess wall and tumor wall on diffusion-weighted and perfusion-weighted images and thus to evaluate the feasibility of using combined MR diffusion and perfusion imaging to differentiate pyogenic cerebral abscess from infected brain tumor. The tumor wall of various types of cystic or necrotic brain tumor was significantly hyperintense relative to that of cerebral abscess wall on both diffusion-weighted images and regional cerebral blood volume maps. Sixteen patients who had cerebral masses with large cystic or necrotic cavities were imaged to generate diffusion-weighted images and regional cerebral blood volume maps using single-shot echoplanar imaging (EPI) pulse sequences. Apart from qualitative analysis, apparent diffusion coefficients (ADC) as well as regional cerebral blood volume (rCBV) ratios were calculated from the abscess wall and peripheral tumor wall and comparison was made by using Student's t-test. The tumor wall of various types of cystic or necrotic brain tumor had significantly lower ADCs relative to those of the abscess wall (P<0.005) and thus appeared relatively hyperintense on diffusion-weighted images. The mean rCBV ratio relative to normal white matter (2.90+/-0.62) of the peripheral tumor wall of various types of cystic or necrotic brain tumor were significantly larger than the mean rCBV ratio (0.45+/-0.11) of the pyogenic cerebral abscess wall (P<0.001) by Student's t-test. It is concluded that the combined MR diffusion and perfusion imaging might be capable of differentiating an infected brain tumor from a pyogenic cerebral abscess.