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Biomedical subjects

A Coulthard

Publications and source records attributed to A Coulthard.

At least 37 records · Page 2Linked to original sources
PubMed1999

Partial volume effects in MRI studies of multiple sclerosis.

We have estimated the accuracy of volume measurements of multiple sclerosis (MS) lesions made using magnetic resonance imaging (MRI) for lesions of comparable diameter to the image slice thickness. We used a phantom containing objects of known volume and obtained images using a range of slice thicknesses. Measurements on the phantom were used to assess a theoretical model, which was then employed to investigate the effects of image dimensions and geometry upon volume measurement accuracy. We observed measured volume to be dependent upon slice thickness. Thin slices gave the most accurate estimate of volume. As slice thickness increased relative to object diameter, the error in the volume measurement increased (to as much as 100%), the volume measured being dependent on the position of the object relative to the slice center. Using a signal intensity threshold value of 50% to outline objects gave results closest to the actual volume. As expected, a lower threshold value tended to give higher volume estimates (up to 100% larger), as did a semi-automated local edge detection technique. For accurate volume measurement, the slice thickness should be no more than a fifth of anticipated object diameter. For typical MS lesions (7 mm in diameter), this implies using a 1.5-mm slice thickness. For serial studies, a repositioning error of 1 mm could lead to differences in the volume measurement of individual lesions of up to 12% between studies for lesions of typical MS size and 5-mm slice thickness. These results emphasize the need for accurate patient repositioning, relatively thin slices, for regular quality assurance checks to ensure that pixel size and slice position are correct and stable over time, and that lesion outlining is performed in a consistent fashion. We would recommend the use of a 3D sequence with 1 mm cubic voxels for accurate measurements of MS lesions.

Humans↗
PubMed1999

A comparison of two methods for measuring the signal to noise ratio on MR images.

The signal to noise ratio (SNR) is one of the important measures of the performance of a magnetic resonance imaging (MRI) system. The object of this study was to compare a single acquisition method, which estimates the noise from background pixels, with a dual acquisition method which estimates the noise from the subtraction of two sequentially acquired images. The dual acquisition method is more exact, but is slower to perform and requires image manipulation. A comparison between the two methods gave a good correlation, and a regression equation of SNRsingle = 1.1 + 0.94 SNRdual. The single acquisition method is therefore appropriate for use in a quality assurance programme, since it is quicker and simpler to perform and is a good indicator of the more exact measure.

Magnetic Resonance Imaging↗
PubMed1999

Extrinsic cerebral venous sinus obstruction resulting in intracranial hypertension.

We report the case of a 70-year-old man reporting with headache and visual disturbances who was being treated for prostate cancer. Investigations showed him to have intracranial hypertension caused by venous sinus obstruction. Patients with metastatic disease and raised intracranial pressure in the absence of focal signs should be considered as possible cases of venous outflow obstruction.

Aged↗
PubMed1999

MRI appearances of the axilla in treated breast cancer.

Differentiation between recurrent axillary disease and changes due to radiotherapy or surgery has major implications for management in patients following breast cancer treatment, but clinical examination of the axilla may be difficult. This study was undertaken to correlate the MRI appearances of the axilla following breast cancer treatment with clinical outcome. 74 women with treated breast cancer were evaluated by MRI (0.5 T) and the appearances defined by consensus. Outcome was assessed by long-term clinical follow-up. 62 women had symptoms related to the axilla while 12 were scanned to stage the axilla. None of the axillary staging group had abnormal MRI appearances and none of these subsequently developed recurrence. The 62 symptomatic women were subdivided according to MRI appearances. 22 had normal axillary appearances, 18 had an axillary mass and 22 women had abnormal axillary appearances (rated mild, moderate and severe) in the absence of a mass. Normal axillary appearances on MRI excluded recurrent disease as the cause of symptoms with a specificity of 94.7% and a positive predictive value (PPV) of 95.5%. The presence of an axillary mass was commonly but not exclusively due to recurrent disease (sensitivity 68.4%, specificity 88.4%, PPV 72.2%). Sensitivity for diagnosis of axillary recurrence was increased to 89.5% with a specificity of 76.7% if the criteria for recurrent disease were taken as either the presence of an axillary mass or severe axillary changes in the absence of a mass lesion.

Adult↗
PubMed1999

Quantitative analysis of MRI signal intensity in new variant Creutzfeldt-Jakob disease.

High signal intensity within the posterior thalamus (pulvinar nucleus) has been noted on MRI in patients with new variant Creutzfeldt-Jakob disease (nvCJD). In this study MRI examinations from three patients with proven nvCJD were compared with MRI examinations from a control group of 14 age-matched subjects with no neurological abnormalities. Mean signal intensity from seven target areas (periaqueductal tissue, posterior thalamus, dorsomedial thalamus, anterior thalamus, putamen, caudate head and frontal white matter) was calculated in each case. Absolute signal intensity measurements were not significantly different between the groups. Patients with nvCJD showed significantly higher signal intensity within dorsomedial thalamus, posterior thalamus and periaqueductal region than control patients when these measurements were normalized to the signal intensity of normal appearing white matter. Highly significant differences in posterior thalamus/putamen signal intensity ratio (PPR) and posterior thalamus/caudate ratio (PCR) were observed between the groups. For proton density images, PPR and PCR were greater than 1 for all nvCJD patients and less than 1 for all control patients. Both PPR and PCR are simple to calculate and offer a simple, non-invasive indicator of nvCJD.

Adolescent↗
PubMed1998

A distinct low-level mechanism for interaural timing analysis in human hearing.

The detection of phase or timing differences, and amplitude differences between the two ears are cues for the spatial analysis of sound by humans. Previous physiological and anatomical studies of animals suggest that phase and amplitude differences between the ears may depend on different pathways, though human psychophysical studies suggest that interaural phase and amplitude differences between the two ears may be coded in the same way. Here we describe detailed psychophysical analysis of a subject with multiple sclerosis affecting the brain stem. He has a complete deficit in the detection of phase between the ears with preserved detection of interaural amplitude. The results prove that a distinct mechanism exists in humans for interaural phase detection.

Acoustic Stimulation↗
PubMed1998

Cerebral venous sinus thrombosis: a late sequel of invasive fibrous thyroiditis.

Riedel's invasive fibrous thyroiditis (IFT) is a rare disease of unknown etiology characterized by a dense fibrosis involving the thyroid gland and its surrounding tissues. Clinically, patients present with a stony hard goiter frequently associated with compressive symptoms. Involvement of the surrounding neck structures by IFT can lead to various clinical sequelae. We report the case of a 55-year-old woman with known IFT who developed thrombosis in the right internal jugular vein that progressed to the right sigmoid, transverse, and superior sagittal sinuses. IFT could have predisposed to cerebral venous sinus thrombosis by causing venous stasis, vascular damage and possibly a hypercoagulable state. To our knowledge, this is the first report of cerebral venous sinus thrombosis that developed as a complication of IFT.

Cerebral Veins↗
PubMed1998

Familial cavernous angiomas masquerading as multiple sclerosis.

We report here two cases of cavernous angioma, in the proband and her father, with quite different clinical presentations. The proband presented with a brainstem syndrome, mimicking multiple sclerosis, while the father had a history of mild epilepsy. Both patients were managed conservatively. The cases also demonstrate the utility of magnetic resonance imaging in the diagnosis of cavernous angioma.

Adult↗
PubMed1997

Natural behavior polymorphism due to a cGMP-dependent protein kinase of Drosophila.

Naturally occuring polymorphisms in behavior are difficult to map genetically and thus are refractory to molecular characterization. An exception is the foraging gene (for), a gene that has two naturally occurring variants in Drosophila melanogaster food-search behavior: rover and sitter. Molecular mapping placed for mutations in the dg2 gene, which encodes a cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG). Rovers had higher PKG activity than sitters, and transgenic sitters expressing a dg2 complementary DNA from rover showed transformation of behavior to rover. Thus, PKG levels affected food-search behavior, and natural variation in PKG activity accounted for a behavioral polymorphism.

Animals↗
PubMed1997

The intramuscular arterial anatomy of the long head of biceps femoris muscle.

We have previously shown that the neurovascular anatomy and length of the long head of biceps femoris (LHBF) is suitable for its possible use in the creation of a dynamic perianal myoplasty to restore faecal continence. If intramuscular arterioarterial anastomoses exist between a muscle's vascular pedicles then the delay procedure, i.e. ligating the vascular pedicles to the transposed section of the muscle, 4-6 wk before transposition, can be used to improve blood flow to the distal part of the transposed muscle. The intramuscular arterial anatomy of 20 biceps femoris muscles was shown by dissection (14) or radiographically (6). The mean entry point of the upper major vascular pedicle to the LHBF was 12 cm (S.D. 3.3) and the mean length of the LHBF was 36.8 cm (S.D. 1.8). Therefore the ratio between upper major vascular pedicle entry point and muscle length in 95% of specimens was 0.33 (0.2). In the present study intramuscular arterioarterial anastomoses were found between the arterial pedicles to the nontransposed and transposed sections of the LHBF and between the long and short heads of this muscle. Using the delay procedure would therefore theoretically allow the intramuscular arterioarterial anastomoses between the arterial pedicle to the nontransposed and transposed sections of the LHBF to open up enhancing blood flow to the distal part of the myoplasty.

Aged↗
PubMed1996

Magnetic resonance angiographic assessment after extracranial-intracranial bypass surgery.

Extracranial-intracranial (EC-IC) bypass operation may be performed to augment the distal cerebral circulation. The bypass patency is usually assessed postoperatively with conventional cerebral angiography. Six patients are reported in whom the bypass patency was assessed using magnetic resonance angiography (MRA): Two had intracavernous carotid aneurysms, three had base of skull tumours encompassing the internal carotid artery, and one had occlusion of the right internal carotid artery with poor collateral reserve as confirmed by an acetazolamide stimulation test. Postoperative conventional cerebral angiography was also obtained in three patients for comparison. The MRA correlated reasonably well with conventional cerebral angiography in showing bypass patency, although conventional cerebral angiography was superior in demonstrating small vessels; MRA has the added advantage of showing the relative flow contribution and flow direction under physiological conditions by using targeted presaturation pulses.

Adult↗