Optimizing MRI of small joints and extremities.

Obtaining optimal images of small joints using magnetic resonance imaging (MRI) can be technically challenging. The aim of this review is to outline the practical aspects of MRI of small joints, with reference to the underlying physical principles. Although the most important contribution to successful imaging of small joints comes from the magnet field strength and design of the receiver coil, there are a number of factors to balance including the signal-to-noise ratio, image resolution, and acquisition times. We discuss strategies to minimize artefacts from movement, inhomogeneity, chemical shift, and fat suppression. As with all MRI, each strategy comes at a price, but the benefits and costs of each approach can be fine-tuned to each combination of joint, receiver coil, and MRI machine.

Pitfalls and artefacts in performance and interpretation of contrast-enhanced MR angiography of the lower limbs.

Peripheral contrast-enhanced MR angiography is widely used for anatomical imaging of the arterial system of the lower limb. There are several pitfalls in the planning, acquisition, and interpretation of these studies that can result in the loss of important diagnostic information, as well as artefacts that can be misinterpreted as disease entities. This review illustrates the range of these potential sources of error and how to avoid them.

Optimization of metal artefact reduction (MAR) sequences for MRI of total hip prostheses.

AIM: To describe the relative contribution of matrix size and bandwidth to artefact reduction in order to define optimal sequence parameters for metal artefact reduction (MAR) sequences for MRI of total hip prostheses. METHODS AND MATERIALS: A phantom was created using a Charnley total hip replacement. Mid-coronal T1-weighted (echo time 12ms, repetition time 400ms) images through the prosthesis were acquired with increasing bandwidths (150, 300, 454, 592, and 781Hz/pixel) and increasing matrixes of 128, 256, 384, 512, 640, and 768 pixels square. Signal loss from the prosthesis and susceptibility artefact was segmented using an automated tool. RESULTS: Over 90% of the achievable reduction in artefacts was obtained with matrixes of 256x256 or greater and a receiver bandwidth of approximately 400Hz/pixel or greater. Thereafter increasing the receiver bandwidth or matrix had little impact on reducing susceptibility artefacts. Increasing the bandwidth produced a relative fall in the signal-to-noise ratio (SNR) of between 49 and 56% for a given matrix, but, in practice, the image quality was still satisfactory even with the highest bandwidth and largest matrix sizes. The acquisition time increased linearly with increasing matrix parameters. CONCLUSION: Over 90% of the achievable metal artefact reduction can be realized with mid-range matrices and receiver bandwidths on a clinical 1.5T system. The loss of SNR from increasing receiver bandwidth, is preferable to long acquisition times, and therefore, should be the main tool for reducing metal artefact.

Comparison of levodopa with carbidopa, and levodopa with domperidone in Parkinson's disease.

In a comparison of the effects of domperidone and carbidopa during levodopa treatment, 20 patients with idiopathic Parkinson's disease were treated with fixed dose regimens of either levodopa 500 mg-domperidone 20 mg or levodopa 100 mg-carbidopa 25 mg; each for 8 weeks. Clinical response, incidence of side effects, and plasma levodopa concentration resulting from each treatment were compared. Overall, in the dosages used, Parkinson's disease was less well controlled with levodopa-domperidone than with levodopa-carbidopa. In eight subjects there was a severe deterioration 2 to 7 days after changing from a fixed dose of levodopa-carbidopa to levodopa-domperidone. In nine subjects who completed the trial, the clinical response, occurrence of dyskinesias and of nausea and vomiting, were similar with both treatments, although peak plasma levodopa concentration and levodopa bioavailability were greater on levodopa-domperidone than on levodopa-carbidopa.

Technetium-99m hexamethylpropyleneamineoxime labelled leucocyte scanning in the initial diagnosis of Crohn's disease.

The technetium hexamethylpropyleneamineoxime labelled white cell scan (WCS) is not widely used as a screening test for Crohn's disease primarily because, though sensitive, it is perceived as being insufficiently specific. A series of 42 patients screened for Crohn's disease by this method was analysed retrospectively. The sensitivity was 100% and specificity 91%. This performance was maintained in a subgroup of these patients with very low prevalence of disease. If appropriate criteria for interpretation are used the WCS is a specific as well as a sensitive screening test for Crohn's disease.

CT appearances of external ear canal cholesteatoma.

External ear canal cholesteatoma (EECC) is rare in ear, nose and throat (ENT) practice. Two cases, one bilateral, are described. Computed tomography demonstrates the extent of bony involvement. Erosion of the external canal should not be overlooked when reviewing CT of the petrous bone in cases of discharge from the ear. EECC may necessitate surgery and delay in the diagnosis of EECC can result in progressive bony destruction.

Evaluation of head examinations produced with a mobile CT unit.

Recent years have seen the development of mobile CT units, designed for use in operating theatres, intensive care units and accident and emergency departments. One such unit is the Tomoscan M (Philips, Utrecht, The Netherlands). It operates with a maximum tube voltage of 130 kV, and a maximum tube current of only 50 mA. This study tested whether acceptable quality CT images of the brain could be produced on the mobile unit with these parameters. 44 consecutive normal head examinations performed on the mobile scanner were compared with 35 examinations from two conventional CT units. Two independent readers scored the examinations for noise and artefact. CT dose index (CTDI) values for the three CT units were obtained in free air as an estimate of patient dose. Differences in artefact score between CT units were generally small, but noise scores were worse when using the Tomoscan M with a 2 s slice time. The lowest CTDI values were obtained with the Somatom DRH (Siemens, Erlangen, Germany) unit and the highest with the SR 7000 (Philips, Utrecht, The Netherlands), with values from Tomoscan M, in all except one case, falling between these values for the protocols used in the study. The measured scattered radiation doses from the Tomoscan M are presented.

Symptomatic intracranial involvement by mycosis fungoides.

Involvement of the central and peripheral nervous system by mycosis fungoides is rare and usually occurs in the presence of widespread cutaneous and visceral disease. We describe a patient with mycosis fungoides, previously confined to the skin, who developed intracranial parenchymal disease with no evidence of systemic involvement.

Deficiency of 17 alpha-hydroxylase associated with absent gonads.

A phenotypic female presented initially at the age of 17 years with amenorrhoea and delay of sexual development. Karyotype was male, 46 XY, and as gonads were absent, a diagnosis of congenital anorchia was made. The patient was treated with oestrogen. At the age of 23 years, she re-presented with tall stature and hypertension. She then had normal female habitus but absent pubic and axillary hair. Re-investigation showed that sex steroids and cortisol were absent and established the diagnosis as 17 alpha-hydroxylase deficiency. Treatment with hydrocortisone rapidly corrected the hypertension. Ultrasound examination confirmed the absence of gonads but showed that a small uterus was present. Measurement of serum cortisol is important for recognition of such patients, but further measurements of sex steroids, particularly progesterone, are needed to prove the diagnosis. We have found no previous reports of absent gonads in 17 alpha-hydroxylase deficiency. The association remains unexplained.

Evaluation of thermal and vibration sensation in diabetic neuropathy.

Sensory evaluation of diabetic neuropathy was undertaken by a new technique for assessment of thermal sensitivity. The method is simple and reproducible, and the mean normal value of the lateral border of the foot was 6.0 degrees C (3.6-9.8 degrees C, 95% confidence limits). Four groups of patients with diabetic neuropathy were examined: 22 with neuropathic ulcers and/or Charcot joints (groups 1 and 2); all showed severe abnormalities (range 10.8- greater than 30 degrees C), frequently more than three times the upper limit of normal. In contrast thermal sensitivity in 15 patients with painful neuropathy (group 4) varied from normal to grossly abnormal (range 3.9- greater than 30 degrees C) confirming this form of neuropathy as a distinct entity. The majority of those 10 patients with autonomic neuropathy alone (group 3) had abnormal thermal sensitivity (range 6.4- greater than 30 degrees C). Comparison of thermal sensitivity (a small fibre modality) with vibration perception threshold (a large fibre modality) showed that thermal sensitivity is sometimes selectively affected, especially in those with painful neuropathy, suggesting that the small fibres are more vulnerable in diabetes. Frequent involvement of the hands confirms the "stocking and glove" distribution of diabetic neuropathy. We conclude that impairment of thermal sensitivity is the rule in symptomatic diabetic neuropathy and its assessment provides a simple quantitative measurement suitable for long-term studies of its natural history.

The use of antibiotic prophylaxis in radiology departments for patients at high-risk of infective endocarditis.

Patients with a prosthetic heart valve, or a history of endocarditis are at particular risk of developing infective endocarditis during a bacteraemia which may follow many gastrointestinal and genito-urinary radiological procedures. The current British Society for Antimicrobial Chemotherapy guidelines (1992) do recommend antibiotic prophylaxis for these high-risk patients prior to instrumentation of the gastrointestinal or genito-urinary tracts. Routine antibiotic prophylaxis for patients with damaged native valves or heart murmurs is recommended prior to dental procedures only. A questionnaire enquiring about prescribing practice prior to several radiological investigations known to be associated with bacteraemia was sent to 192 radiology departments and 126 replied. Only 38 of the 126 respondents have a prescribing policy for antibiotic prophylaxis in high-risk groups. Fifty-eight departments employ antibiotic prophylaxis prior to one or more of the procedures named in the questionnaire, but only 30 of these have mechanisms for identifying at-risk patients. Forty-eight departments keep recommended antibiotics in the department.

Magnetic resonance imaging features of pituitary yttrium-90 rod implantation.

Intersellar implantation of yttrium-90 rods was a common treatment for a variety of pituitary tumours in the 1960s and 1970s. The magnetic resonance (MR) imaging features in three patients with implants (two for growth hormone-secreting and one for prolactin-secreting pituitary adenomas) are presented: the implants appeared as low signal cylinders with no image distortion, in contradistinction to CT where the implants generate beam hardening and back projection artefacts. Confident evaluation of the pituitary fossa for residential tumour and sequelae of therapy could be made on MR. It is the imaging technique of choice in the follow-up of patients treated with yttrium-90 implants.

Arteriovenous fistula at the site of balloon dilatation complicating femoropopliteal angioplasty.

We describe an arteriovenous fistula (AVF) at the site of balloon dilatation immediately after percutaneous transluminal angioplasty (PTA) of the femoropopliteal artery. This occurred during an otherwise uncomplicated angioplasty with a good clinical result. The AVF closed spontaneously within 2 months as monitored by color duplex ultrasound. This uncommon complication of PTA is not widely recognized.

Complications of the ileal pouch: is the pouchogram a useful predictor?

A series of ileal pouchograms from 25 consecutive patients has been analysed retrospectively. Ileal pouchography may demonstrate abnormalities which delay closure of the covering ileostomy. The aim was to determine whether disruption of the ileoanal anastomosis and/or leak at pouchography correlated with pelvic sepsis after ileostomy closure. Disruption of the stapled ileoanal anastomosis is a sensitive (88%) but not specific predictor (57%) for subsequent pelvic sepsis. The predictive value of a negative test is high (89%). Leak of contrast from the anastomosis is specific (81%) but not sensitive (56%) for pelvic sepsis. No significant relationship was demonstrated between width of the presacral space and the presence of pelvic sepsis. No significant relationship was demonstrated between diameter of the ileoanal anastomosis and symptoms of stricture. The presence of anastomotic disruption or leak at pouchography prior to ileostomy closure are useful predictors of potential pelvic sepsis.

MRI of the brain in HIV-positive patients: what is the value of routine intravenous contrast medium?

Our purpose was to assess the value of routine administration of intravenous gadolinium-DTPA (Gd-DTPA) for cranial MR in a series of human immunodeficiency virus (HIV)-positive patients. Two radiologists retrospectively reviewed 150 consecutive examinations of 104 patients. All patients underwent unenhanced and contrast-enhanced images. Each radiologist independently assessed first the unenhanced images alone and then the pre- and postinjection images together. Then both reviewed the complete study and produced a consensus report. The history, investigations and management were collated separately and were unknown to the radiologists. Contrast-enhanced T1-weighted images showed new focal abnormalities, not seen on the T2-weighted or unenhanced images in 15 (14 %) patients, but almost always in the context of abnormal unenhanced images. In only 2 patients (2 %) did contrast medium reveal abnormalities when the unenhanced study had been considered normal. In only 1 of these (1 %) was the new finding, cytomegalovirus diffuse ependymal enhancement, of clinical importance, although the diagnosis of encephalitis was made on routine examination of cerebrospinal-fluid. The other revealed a toxoplasma lesion in a patient known to have resolving disease. Meningeal disease not suspected on the unenhanced images was shown in 2 patients (2 %). In these case the unenhanced images were abnormal in other respects. Intravenous Gd-DTPA was helpful to the radiologist in making a radiological diagnosis in 11 patients (11 %), usually by improving characterisation of a lesion seen on the unenhanced images. The contribution of intravenous Gd-DTPA in this series does not warrant recommending its use in every case.