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Biomedical subjects

I D Wilkinson

Publications and source records attributed to I D Wilkinson.

At least 55 records · Page 3Linked to original sources
PubMed2001

Detection of subarachnoid haemorrhage with magnetic resonance imaging.

OBJECTIVES: To measure the sensitivity and specificity of five MRI sequences to subarachnoid haemorrhage. METHODS: Forty one patients presenting with histories suspicious of subarachnoid haemorrhage (SAH) were investigated with MRI using T1 weighted, T2 weighted, single shot fast spin echo (express), fluid attenuation inversion recovery (FLAIR), and gradient echo T2* sequences, and also by CT. Lumbar puncture was performed in cases where CT was negative for SAH. Cases were divided into acute (scanned within 4 days of the haemorrhage) and subacute (scanned after 4 days) groups. RESULTS: The gradient echo T2* was the most sensitive sequence, with sensitivities of 94% in the acute phase and 100% in the subacute phase. Next most sensitive was FLAIR with values of 81% and 87% for the acute and subacute phases respectively. Other sequences were considerably less sensitive. CONCLUSIONS: MRI can be used to detect subacute and acute subarachnoid haemorrhage and has significant advantages over CT in the detection of subacute subarachnoid haemorrhage. The most sensitive sequence was the gradient echo T2*.

Adult↗
PubMed2001

Cerebral arteriovenous malformations: comparison of novel magnetic resonance angiographic techniques and conventional catheter angiography.

OBJECTIVE: To investigate the potential of novel magnetic resonance (MR) angiographic techniques for the assessment of cerebral arteriovenous malformations. METHODS: Forty patients who were about to undergo stereotactic radiosurgery were prospectively recruited. Three-dimensional, sliding-slab interleaved ky (SLINKY), time-of-flight acquisition was performed, as was a dynamic MR digital subtraction angiography (DSA) procedure in which single thick slices (6-10 cm) were obtained using a radiofrequency spoiled Fourier-acquired steady-state sequence (1 image/s). Sixty images were acquired, in two or three projections, during passage of a 6- to 10-ml bolus of gadolinium chelate. Subtraction and postprocessing were performed, and images were viewed in an inverted cine mode. SLINKY time-of-flight acquisition was repeated after the administration of gadolinium. Routine stereotactic conventional catheter angiography was performed after MR imaging. All images were assessed (in a blinded randomized manner) for Spetzler-Martin grading and determination of associated vascular pathological features. RESULTS: Forty-one arteriovenous malformations were assessed in 40 patients. Contrast-enhanced (CE) SLINKY MR angiography was the most consistent MR imaging technique, yielding a 95% correlation with the Spetzler-Martin classification defined by conventional catheter angiography; MR DSA exhibited 90% agreement, and SLINKY MR angiography exhibited 81% agreement. CE SLINKY MR angiography provided improved nidus delineation, compared with non-CE SLINKY MR angiography. Dynamic information from MR DSA significantly improved the observation of early-draining veins and associated aneurysms. CONCLUSION: CE SLINKY MR angiographic assessment of cerebral arteriovenous malformations offers significant advantages, compared with the use of non-CE SLINKY MR angiography, including improved nidus demonstration. MR DSA shows promise as a noninvasive method for dynamic angiography but is presently restricted by limitations in both temporal and spatial resolution.

Adult↗
PubMed2001

In vivo measurement of cerebral blood flow: a review of methods and applications.

This article reviews the concepts of cerebral blood flow for the clinician involved in the management of patients with carotid stenosis and/or ischaemic stroke. Methods of assessing cerebral blood flow in vivo using nuclear medicine, magnetic resonance and X-ray computed tomography are described. Applications of magnetic resonance and X-ray computed tomographic methods are reviewed and illustrated by examples from the authors' radiological practice.

Blood Flow Velocity↗
PubMed2001

Multimodality MR imaging depiction of hemodynamic changes and cerebral ischemia in subarachnoid hemorrhage.

BACKGROUND AND PURPOSE: Subarachnoid hemorrhage (SAH) is a common and serious neurologic emergent condition. We tested the hypothesis that multimodality MR imaging depicts changes in cerebral blood flow SAH, before any surgical or endovascular intervention, and that the frequency of these changes increases with time after ictus. METHODS: We prospectively examined 37 patients with suspected SAH and three with symptoms of acute stroke but who subsequently had SAH. Routine CT and multimodality MR imaging were performed within 18 h of presentation. Standard MR imaging, diffusion-weighted MR imaging, time-of-flight MR angiography, and dynamic first-pass gadolinium-enhanced MR perfusion imaging were performed. Images were reviewed for abnormalities in cerebral blood flow, ischemia, and infarction. Nine patients did not have SAH at CT and CSF investigations. Of 31 patients with proved SAH, 13 were examined during the acute stage (within 4 d of ictus) and 18, during the subacute stage (4-14 d after ictus). RESULTS: MR imaging showed alteration in cerebral blood flow parameters in 16 of 31 patients before surgery or endovascular treatment. The frequency of blood flow changes and associated complications increased with worsening clinical grade and increasing time after ictus. CONCLUSION: Multimodality MR imaging provides information not available from CT in patients with SAH. MR imaging shows oligemic and ischemic areas in SAH before surgery or endovascular treatment. MR imaging is a simple noninvasive method of assessing cerebral blood flow and its complications in SAH. It can be performed in a clinical environment.

Adult↗
PubMed2001

Brain MR perfusion imaging in humans.

PURPOSE: To evaluate any possible advantages of high-concentration gadolinium chelates in the human brain thin-slice MR. MATERIAL AND METHODS: Thirty-six patients were allocated into six groups. Three groups had perfusion imaging performed using 7-mm-thick slices and the other three groups had 4-mm-thick slices. One group who had 7-mm slices and one group of 4-mm slices had 0.5 M gadolinium (20 ml) whilst other groups received the high-concentration gadolinium (1.0 M: 10 ml and 20 ml). The time-intensity curves were analysed for maximum signal reduction and signal-to-noise measurements. RESULTS: Twenty ml of the 1.0-M agent produced significantly increased maximum signal change and improvement in signal-to-noise when compared to 20 ml of 0.5 M. There was no significant difference between the maximum signal change when 20 ml of 0.5 M and 10 ml of 1.0 M agents were compared. There was no significant difference between the maximum signal changes when 7-mm and 4-mm slice thickness using the same dosing regimens. CONCLUSION: Four-mm slice thickness perfusion imaging can be performed with high-concentration gadolinium in the human brain and we discuss the advantages of this.

Adolescent↗
PubMed2000

The prevalence of viral hepatitis (HAV, HBV and HCV) in the Christchurch community.

AIM: To determine the prevalence of hepatitis A (HAV), hepatitis B (HBV) and hepatitis C (HCV) in adults randomly selected from the Christchurch community. METHODS: A list of names was randomly generated from the Christchurch electoral roll and subjects were sequentially contacted and invited to participate. A blood sample was taken and tested for hepatitis A (IgG anti-HAV antibody), hepatitis B (HBsAg and anti-HBc) and HCV (anti-HCV antibody) using Abbott Elisa kits. Subjects positive for HBsAg were also tested for HBeAg/HBV DNA. Those positive for anti-HBc were tested for anti-HBs. HCV antibody positive samples were tested for HCV RNA using PCR. RESULTS: 1064 subjects (30.3% of those invited) participated in the study. The prevalence of HAV antibodies was 27.9%, and increased with age. The overall prevalence of HBV markers was 42/1064 (4.2%), and of these 0.3% were HBsAg positive and 3.9% were considered immune. No gender or ethnic differences in these proportions were observed. The seroprevalence of HVC antibody was 3/1064 (0.3%), two of whom were also PCR positive for HCV RNA. CONCLUSION: In the Christchurch community there was a high prevalence of antibodies to HAV, which increased with age. The prevalence of HBsAg and antibody to HCV were both low at 0.3%.

Adult↗
PubMed2000

Comparison of Doppler ultrasound, magnetic resonance angiographic techniques and catheter angiography in evaluation of carotid stenosis.

AIM: To compare the accuracy of ultrasound and two magnetic resonance (MR) angiographic techniques with catheter angiography in assessing atherosclerosis at the carotid bifurcation. MATERIALS AND METHODS: Forty patients with symptomatic carotid stenosis were studied by Doppler ultrasound, time-of-flight MR angiography, contrast-enhanced MR angiography and conventional catheter angiography. The degree of stenosis found on ultrasound and MR angiography was compared with the results of catheter angiography. Four different assessment methods were conducted for the MR angiographic data. Kappa, sensitivity and specificity (with confidence intervals) values were calculated for the US and MR angiography results compared to catheter angiography. RESULTS: Catheter angiography showed 12 internal carotid artery occlusions (15%), 34 severe (44%), 12 moderate (15%) and 20 mild stenoses (26%), using NASCET criteria. Ultrasound showed 65% sensitivity and 95% specificity in detecting surgically amenable lesions, whilst the MR angiographic techniques had sensitivities varying from 82-100%, and specificities from 95-100%.A moderate kappa value was calculated for the US data, whilst all MR techniques were found to show very good agreement with catheter angiography. CONCLUSION: This data suggests that MR angiography is more accurate than Doppler ultrasound in defining surgical lesions and has comparable accuracy to catheter angiography. The use of contrast-enhanced MR angiography is useful in certain situations but is not essential in all cases.

Aged↗
PubMed2000

Acute neuromedical and neurosurgical admissions. Standard and ultrafast MR imaging of the brain compared with cranial CT.

PURPOSE: To evaluate the role of standard and ultrafast MR brain imaging and compare the information with CT. MATERIAL AND METHODS: This was a prospective study of 114 patients with acute neurological symptoms and signs. CT brain examinations consisted of axial non-enhanced images. MR imaging consisted of standard spin-echo/fast spin-echo sequences and a series of rapid techniques including echoplanar and single shot fast spin-echo sequences. RESULTS: Using standard MR methods, 41% of the patients had all five sequences of good technical quality, while using ultrafast methods 81% of the patients had good technical quality examinations in all five sequences. In 3% of the cases, ischaemic stroke was incorrectly reported on CT. In 24% of the cases, MR gave extra diagnostic information not reported on CT and in a further 8%, one neuroradiologist reported the abnormality in agreement with the MR, whilst the other neuroradiologist reported the CT as normal. In 2 cases, subarachnoid haemorrhage was missed on MR. Subarachnoid haemorrhage was not shown on the ultrafast sequences. CONCLUSION: MR can be used to image acute neurological admissions with a high success rate, particularly using ultrafast methods. In many cases, MR provided extra information of direct clinical relevance not shown on CT.

Acute Disease↗
PubMed2000

Unilateral leptomeningeal enhancement after carotid stent insertion detected by magnetic resonance imaging.

BACKGROUND AND PURPOSE: Percutaneous transluminal angioplasty combined with vascular stenting is currently being assessed in the treatment of patients with symptomatic, severe carotid stenosis. The immediate cerebral hemodynamic effects resulting from stenting are not fully understood. This article describes a novel finding: abnormal leptomeningeal enhancement after stenting shown by MRI. METHODS: Fourteen patients with symptomatic severe carotid bifurcation stenosis underwent MRI within 4 hours before and within 3 hours after attempted carotid stenting. Twelve patients were successfully stented. Part of the MR investigation consisted of the acquisition of T1-weighted images before and after administration of the contrast agent Gd-DTPA, both before and after the procedure. RESULTS: All 12 patients who underwent successful stenting did not have abnormal enhancement of the leptomeninges before stenting but developed unilateral enhancement following intervention but before the second injection of contrast agent. No contrast enhancement was detected in the 2 patients who had the angiographic procedure but were not stented. CONCLUSIONS: These findings suggest that abnormal changes to the leptomeningeal vasculature occur during carotid stenting which are not associated with sudden development of neurological symptoms. The anatomic distribution of the enhancement suggests that it is a consequence of the sudden change in brain hemodynamics secondary to the improvement in carotid flow after stenting.

Aged↗
PubMed1999

The assessment of postmortem brain volume; a comparison of stereological and planimetric methodologies.

We compared two methods of estimating the volume of 10 formalin-fixed brains using MRI. MRI was performed and total brain volume was then assessed using two distinct techniques: a stereological point-counting technique based on the Cavalieri principle, and an edge-tracing technique. The total brain volumes obtained using these two techniques were similar and correlated closely with each other (r = 0.97). Both methods could be optimised to a similar degree while maintaining the coefficient of error at an acceptably low level. However, the stereological assessment of brain volume required between 20 min and 30 min per brain, depending on the number of points per sampling grid, compared with 1 h per brain using the planimetric method. Thus, while planimetric and stereological approaches yield very similar results, the stereological method has the advantage of greater speed and, therefore, efficiency.

Aged↗
PubMed1999

Changes in articular synovial lining volume measured by magnetic resonance in a randomized, double-blind, controlled trial of intra-articular samarium-153 particulate hydroxyapatite for chronic knee synovitis.

OBJECTIVE: Magnetic resonance techniques have recently been investigated as tools with which to monitor inflammatory joint disease. Our aim was to use a contrast-enhanced T1-weighted protocol to monitor the short-term changes in knee synovial lining volume in a double-blind, randomized, controlled trial of intra-articular samarium-153 particulate hydroxyapatite (Sm-153 PHYP). METHODS: Twenty-four out-patients with chronic knee synovitis, from a cohort who had been recruited to a long-term clinical efficacy trial, were recruited for this study. Patients received either intra-articular Sm-153 PHYP combined with 40 mg triamcinolone hexacetonide or 40 mg intra-articular triamcinolone hexacetonide alone. Synovial lining volumes were calculated from three-dimensional T1-weighted contrast-enhanced images made before and after contrast enhancement with thresholding and pixel counting, immediately before and 3 months after treatment. RESULTS: Paired pre- and post-treatment magnetic resonance data were obtained for 18/24 (75%) patients. There was no significant difference in mean pre-treatment synovial volume between the two treatment groups (139 vs 127 ml). A mean reduction in synovial lining volume was detected in the Sm-153 PHYP/steroid-treated group (139 to 110 ml, P = 0.07) and in the steroid-treated group (127 to 58 ml, P < 0.001). The reduction was significantly greater in the steroid-treated group (-61% vs -23%, P < 0.05). CONCLUSIONS: Short-term changes in articular synovial lining in response to intra-articular treatment for chronic synovitis may be monitored by magnetic resonance imaging. After 3 months, a greater mean reduction in synovial lining volume had occurred in response to intra-articular steroid alone compared to combined Sm-153 PHYP/steroid injection.

Adult↗
PubMed1998

Magnetic resonance imaging, thallium-201 SPET scanning, and laboratory analyses for discrimination of cerebral lymphoma and toxoplasmosis in AIDS.

OBJECTIVES: To compare the results of magnetic resonance imaging (MRI) and thallium-201 (201Tl) SPET scanning with laboratory analyses including CSF DNA detection, brain biopsy, and necropsy in the discrimination of cerebral lymphoma and toxoplasmosis in patients with AIDS. METHODS: A retrospective study of 32 patients infected with HIV who had focal CNS lesions on MRI as a result of either lymphoma or toxoplasmosis. RESULTS: 18 patients had lymphoma, 12 had toxoplasmosis, and two had both. Toxoplasma IgG antibodies were detected in only seven patients--four with toxoplasmosis, two with lymphoma, and one with both diagnoses. Epstein-Barr virus DNA was detected in CSF of all six patients with lymphoma and none of two with toxoplasmosis. MRI showed multiple lesions in 23 patients, appearances did not discriminate between lymphoma and toxoplasmosis; nine patients had single lesions, of these eight had lymphoma (p = 0.044, two tailed Fisher's exact test) 201Tl SPET showed accumulation in 17 with lymphoma and six with toxoplasmosis (p = 0.034, two tailed Fisher's exact test). Of nine patients with single lesions on MRI and 201Tl SPET with focal accumulation eight had lymphoma. 201Tl SPET uptake ratios of > or = 2.9 were only seen with lymphoma. CONCLUSION: Knowledge of patients' toxoplasma serostatus does not aid discrimination between lymphoma and toxoplasmosis. Single lesions on MRI with focal accumulation of 201Tl strongly suggest lymphoma. Multiple lesions on MRI with 201Tl SPET uptake ratios > or = 2.9 also suggest lymphoma; uptake ratios less than 2.1 do not aid discrimination. Detection of Epstein-Barr virus DNA in CSF is highly sensitive and specific for cerebral lymphoma.

AIDS-Related Opportunistic Infections↗
PubMed1998

Short echo-time proton magnetic resonance spectroscopy in regions of severe HIV-related diffuse white matter abnormality on MRI.

The purpose of this study was to determine whether short echo-time proton magnetic resonance spectroscopy (H-MRS) could detect mobile lipid resonances attributable to myelin breakdown products in the deep cerebral white matter of patients with AIDS who have severe diffuse/patchy white matter hyperintensity on T2-weighted magnetic resonance imaging (MRI). Seven patients with AIDS and clinical HIV-associated dementia complex (HADC) and 12 male controls were studied at 1.5T using a single 8 ml voxel, gradient localised, stimulated echo acquisition mode (STEAM) spectroscopy sequence. Spectra were acquired at an echo time of 20 ms with a repetition time of 5000 ms. No spectroscopic peaks were identified at 0.9 ppm and 1.3 ppm (corresponding to lipid resonances) in 6 of the 7 patients with AIDS or in any of the controls. Lipid resonances were identified in 1 patient who had been taking anti-retroviral therapy for 8 weeks. Follow up MRI/H-MRS, performed after a further 14 weeks of anti-retroviral therapy, showed partial resolution of white matter hyperintensity and lipid resonances were not detectable. These data suggest that mobile lipids are only rarely detected by H-MRS in patients with HADC and abnormalities on MRI and that their presence may be transitory.

AIDS Arteritis, Central Nervous System↗
PubMed1997

Magnetic resonance imaging of the brain and cerebral proton spectroscopy in patients with systemic lupus erythematosus.

OBJECTIVE: To investigate the prevalence and extent of cerebral changes in patients with systemic lupus erythematosus (SLE) by magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). METHODS: SLE patients (47 women) and controls (25 women) underwent 1.5T MRI. A semiautomated segmentation technique calculated cerebrospinal fluid (CSF) and brain volumes. Proton MRS of the frontal and parieto-occipital white matter yielded metabolite ratios of N-acetyl groups (NA), choline, and creatine. RESULTS: Compared with the control group, the SLE patients more often had cerebral atrophy on MRI (32% versus 0%), confirmed by an increase in the CSF to intracranial volume ratio. The patients also had old infarcts and hemorrhages (8.5% versus 0%) and more small white matter lesions (23% versus 8% had > 5 such lesions). MRS showed relative reduction of NA peaks. Although no patient was studied when acutely ill, prior neurologic involvement was related to abnormal findings. CONCLUSION: MRI and MRS are helpful in the investigation of cerebral complications of SLE. There are chronic changes which may be ischemic in nature. Their precise cause, consequences, and prevention are current challenges.

Adult↗
PubMed1997

High magnetic susceptibility coatings for visualisation of optical fibres on a specialised interventional MRI system.

The aim of this study was to develop methods of visualising optical fibres on MRI scans for monitoring interstitial laser therapy. Scans were performed on a specialised MRI extremity scanner at 0.17 T. Optical fibres of 0.4 mm diameter used for delivering laser energy were coated with iron particles from a superferromagnetic contrast agent. MR images of the fibres were acquired using gradient echo sequences (TR/TE = 300/10, 1 mm in-plane, 3 mm slice) and assessed for fibre visibility. Coated fibres could be resolved as lines 2 +/- 1 mm wide using the gradient echo sequence. Uncoated fibres were invisible on the sequences used for in vivo therapy monitoring due to partial volume averaging. It is concluded that optical fibre visualisation by MRI may be improved by coating with ferromagnetic particles. Biocompatibility requires further assessment, but direct coating appears to be a promising method for fibre visualisation in MR-guided laser therapy.

Contrast Media↗
PubMed1997

Cerebral volumes and spectroscopic proton metabolites on MR: is sex important?

One of the factors that may influence the selection of appropriate controls for MR studies of the brain is gender. This study compared calculated intracranial volumes and proton spectroscopic metabolite ratios obtained from male and female volunteers. Thirty-two males (mean age = 36; range = 30-53 yr) and 19 females (mean age = 39; range = 26-53 yr) underwent investigation at 1.5T. Brain, cerebrospinal fluid (CSF), and intracranial (ICV = brain + CSF) volumes were measured by the CLASS technique on data acquired using an axial dual spin-echo imaging sequence (TE = 20/90 ms, TR = 3500 ms). Proton spectra (TE = 135 ms, TR = 1600 ms) were acquired from an 8 ml cubic region placed in parieto-occipital white matter. The mean male and female brain, CSF and ICV were significantly different (p < .005). However, the mean CSF/ICV ratios of the two groups were not significantly different. The N-acetyl/choline and choline/creatine metabolite ratios of the two groups were significantly different (p < .05). When comparing proton metabolite ratios and absolute brain volumes between groups, gender is an important factor. CSF/ ICV ratios do not appear to depend on gender.

Adult↗
PubMed1997

The measurement of R2, R2* and R2' in HIV-infected patients using the prime sequence as a measure of brain iron deposition.

Brain iron deposition was assessed at 1.5 T in the caudate nucleus, globus pallidus and frontal and parieto-occipital white matter in 28 human immunodeficiency virus (HIV)-infected patients and 15 control subjects with a new Partially Refocussed Interleaved Multi-Echo sequence by measuring 1/T2, 1/T2* and 1/T2' (i.e., R2, R2* and R2'). There were significant differences in the R2 and R2* of the caudate nucleus (p < 0.0001 and p < 0.05) and the R2, R2* and R2' of the globus pallidus (p < 0.01, p < 0.005 and p < 0.05) in HIV-infected patients compared to control subjects. There was a trend for higher values of R2, R2* and R2' in the globus pallidus and caudate nucleus in HIV-infected patients with later stage HIV disease. These results suggest that there is greater iron deposition in the basal ganglia of HIV-infected patients compared with control subjects, with a predilection for the globus pallidus. The relationship between iron deposition in the brain and various parameters of severity of HIV infection remains uncertain.

AIDS Dementia Complex↗