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Biomedical subjects

A P Carter

Publications and source records attributed to A P Carter.

At least 19 recordsLinked to original sources
PubMed1998

MRA of the intracranial circulation in asymptomatic patients with sickle cell disease.

BACKGROUND: MR angiography (MRA) provides a mechanism for non-invasively studying blood flow, thus providing a new opportunity to study the intracranial circulation in asymptomatic sickle cell disease (SCD) patients. Although conventional angiography is the gold standard for the depiction of vascular anatomy, this is too invasive for an asymptomatic population. OBJECTIVE: To establish the range of appearances in asymptomatic SCD patients and to correlate brain MRI results (either sub-clinical abnormalities or normal brain parenchyma) with the MRA findings. MATERIALS AND METHODS: Brain MRI and MRA of the intracranial circulation was performed on 22 patients (13 male and 9 female, median age 7.5 years, range 1.3-20 years). Fourteen were homozygous SS and eight were SC. The median haematocrit at the time of MRI was 25.9 (range 13.8-33.3). RESULTS: On MR imaging, four patients had infarcts in eight vascular territories (six anterior and two posterior). In 3/4 of anterior vascular territories with infarction, long ( >/= 6 mm) segments of abnormal signal were seen at the internal carotid artery bifurcation with associated reduced distal flow. Short focal areas of abnormal signal were commonly seen where vessels branched, bifurcated or curved and were not associated with infarcts. These areas probably represent turbulence-related dephasing secondary to high velocity flow found in SCD. CONCLUSION: Long segments ( >/= 6 mm) of abnormal signal with reduced distal flow correlated with sub-clinical infarction.

Adolescent↗
PubMed1997

Carotid MRA--what advantages do the turbo field-echo and 3D phase-contrast sequences offer?

Our purpose was to investigate some of the newer MR angiography (MRA) techniques for studying the carotid arteries. Forty-two arteries in seven asymptomatic, healthy volunteers were studied using five MRA sequences: two conventional time-of-flight sequences, 2D time-of-flight (2DTOF) and 3D time-of-flight (3DTOF); 2D and 3D magnetisation-prepared, segmented time-of-flight sequences (2DTFE and 3DTFE); and a 3D phase contrast angiography (3DPCA) sequence. A protocol that could be realistically employed in a routine clinical situation was chosen. 2DTOF had significantly (P < 0.05) better signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) than 2DTFE. 3DTOF demonstrated better SNR than 3DTFE but 3DTFE demonstrated better CNR than 3DTOF. 3DPCA provided maximal anatomical coverage. No one sequence provided optimal anatomical coverage, accurate demonstration of the carotid bulb and maximal SNR and CNR. The combination of 3DPCA and a 3D inflow sequence was best. 2DTOF sequences are useful when only one brief sequence is practicably feasible.

Adult↗
PubMed1997

Fast spin echo vs conventional spin echo in cervical spine imaging.

The major attraction of fast-spin-echo (FSE) imaging is reduced acquisition time; however, careful review of the literature reveals many weaknesses: phase-encoded blurring, truncation artefact, bright fat signal, reduced magnetic susceptibility and increased motion artefact. Our aim was a prospective, blinded comparison of FSE and conventional spin echo (CSE) in the cervical spine. Both sequences were performed in 43 patients (19 males and 24 females; mean age 45 years, range 15-66 years). Twenty-eight patients were studied at 1.5 T and 15 at 0.5 T. Typical sequence parameters were: at 1.5 T, TR/TE 2000/90 CSE and 3000/120 FSE, and at 0.5 T, 2200/80 CSE and 2800/120 FSE. Time saved on the FSE was used to increase the matrix and the number of acquisitions. Two neuroradiologists evaluated the images for pathology, artefacts, disc signal intensity, thecal sac compression and image quality. Ten patients had cord lesions; 2 (20 %) were missed on CSE. In 4 of 10 patients with moderate/severe thecal sac compression, the degree of stenosis was apparently exaggerated on CSE. The mean degree of confidence for the CSE sequences was 1.8 and for the FSE 1.1, where 1 is optimal. For cervical spine imaging, FSE should be preferred to CSE.

Artifacts↗
PubMed1997

Cerebral infarction in patients with AIDS.

PURPOSE: To establish the frequency, distribution, and pathogenesis of cerebral infarction as confirmed with MR imaging in a cohort of patients with acquired immunodeficiency syndrome (AIDS). METHODS: We reviewed all (71) abnormal cranial MR studies obtained at our institution in human immunodeficiency virus (HIV)-positive patients over a 2-year period and recorded the number and distribution of ischemic lesions, any associated abnormalities, and the MR angiographic findings, where available. Patients' charts were studied for relevant clinical data, biochemical and culture results, and potential etiologic factors. RESULTS: Twenty-two infarcts were seen in 13 of the 71 patients. Of these 22, the basal ganglia area was affected in 15, the middle cerebral artery territory in two, and the vertebrobasilar territory in five. Five patients had concomitant evidence of infection, six others used cocaine or were intravenous drug abusers. MR angiography was performed in eight patients; two of these had multiple lesions consistent with vasculitis, two had isolated lesions that corresponded with their parenchymal infarct, and four had normal findings. CONCLUSIONS: The frequency of infarction was 18%, higher than previously reported. The pathogenesis of infarction was multifactorial. Underlying infectious causes were identified in 39% of patients. Two patients had an idiopathic vasculitis.

AIDS Dementia Complex↗
PubMed1996

MR appearances of the temporal evolution and resolution of infectious spondylitis.

OBJECTIVE: We undertook this study to document the MR appearances of evolving or resolving infectious spondylitis. MATERIALS AND METHODS: A retrospective review was carried out of all patients with infectious spondylitis who had undergone MR imaging from 1991-1993 at Boston University Hospital and Boston City Hospital Imaging Foundation. The study population consisted of 25 patients (seven females and 18 males). There was a bimodal age distribution with peaks at 34 and 59 years old (age range, 25-81 years old). The causative organism was isolated in 20. Sixteen had Staphylococcus aureus, two had mycobacterium tuberculosis, and two had gram-negative bacilli. Follow-up MR imaging was performed in 20. Nine had two studies, three had three, five had four, two had five, and one had six. The median length of follow-up was 8 weeks (range, 2-104 weeks). Follow-up MR appearances were correlated with clinical outcome. RESULTS: Early imaging revealed atypical appearances. Fourteen of 20 (70%) improved; the first sign of response to treatment was a reduction in the inflammatory soft tissue (8/14, 57%). Changes in the bones or discs concurrently progressed in six of eight patients (75%) including involvement of a new disc level in four (50%). A definitive sign of healing was a peripheral rim of high T1 signal in bone (5/14, 36%). Gadolinium enhancement persisted long after resolution of changes in the soft tissues, for up to a median of 17.5 weeks (range, 8-80 weeks). A subgroup of six IV drug users showed unique radiologic features. CONCLUSION: The early appearances of infectious spondylitis may be atypical. Resolution of soft-tissue change and fat deposition in the bone marrow are reliable signs of healing. Bone or disc changes can progress despite clinical improvement. Gadolinium enhancement can increase and persist after symptom resolution.

AIDS-Related Opportunistic Infections↗
PubMed1996

Magnetization transfer contrast MR in lesions of the head and neck.

PURPOSE: To compare lesion-to-background contrast with and without magnetization transfer (MT) in lesions of the head and neck. METHODS: Twenty lesions (16 malignant, 4 benign) were evaluated in 17 patients (11 men, 6 women; mean age, 58 years; age range, 39-76 years). In 13 patients, MR imaging was performed at 0.1 T with continuous-wave, off-resonance MT; in 4 patients, MR imaging was performed at 1.5 T with on-resonance, binomial MT prepulses. Fifteen sequences were conducted before the administration of gadopentetate dimeglumine; 13 were conducted after the administration of that contrast material. The ratio of signal intensity with the MT pulses (Ms) to signal intensity without the MT pulses (Mo) was calculated, as were the lesion-to-background contrast and the contrast-to-noise ratios. RESULTS: Ms/Mo showed both wide variability and considerable overlap among different lesion types. Images from MT sequences showed better contrast than those from non-MT sequences in 23 of 28 lesions (12 of 15 before and 11 of 13 after the administration of contrast material). The mean contrast improvement percentages (+/- standard deviation) were 165.5% (+/- 58%) on unenhanced images and 186.6% (+/- 84.8%) on contrast-enhanced images. The mean improvements in contrast-to-noise ratios were 156% (+/- 60%) on unenhanced images and 171.6% (+/- 98.1%) on contrast-enhanced images. CONCLUSION: MT improved contrast between nodes or tumors showing an MT effect and background tissue (usually fat) not showing an MT effect. MT also improved contrast between contrast-enhanced neoplastic lesions and background tissue that showed an MT effect.

Adult↗
PubMed1995

Is transcranial Doppler a worthwhile addition to screening tests for cerebrovascular disease?

PURPOSE: Carotid duplex imaging has become the standard diagnostic evaluation for patients with suspected cerebrovascular disease. Transcranial Doppler ultrasonography expands the noninvasive diagnostic capabilities to the intracranial circulation. The purpose of this study was to evaluate the results of routine transcranial Doppler studies on patients referred for noninvasive cerebrovascular evaluation. METHODS: A total of 670 patients had routine transcranial Doppler examinations as part of their noninvasive cerebrovascular evaluation. Patients were categorized clinically and according to their severity of extracranial internal carotid artery stenosis (< 50%, 50% to 79%, 80% to 99%, occlusion). Transcranial Doppler examinations were classified as normal or abnormal (intracranial stenosis, collateral pathway, > 30% velocity difference normal or abnormal (intracranial stenosis, collateral pathway, > 30% velocity difference between sides, flow reversal, and velocities +/- SD from normal). RESULTS: Forty-eight percent of the patients were women, and 52% were men. The average age was 65.5 years. Fifty-four percent of the patients were white, 42% were black, 3% were Hispanic, and 1% were other. Forty-eight percent presented with hemispheric symptoms, 34% had no symptoms, and 18% had nonhemispheric symptoms. Forty-five percent (304 of 670) had an interpretable transcranial Doppler examination. The ability to insonate the basal cerebral arteries through the temporal bone was significantly reduced in women (p < 0.0001), black patients (p < 0.0001), and older patients (p < 0.0001). The results of forty-four percent of interpretable examinations were normal, 19% demonstrated side-to-side velocity differences, 13% showed collateral pathways, 11% showed velocities +/- 2 SD, 10% showed an intracranial stenosis, and 4% showed reversed flow pattern. Although 56% of the patients had notable findings, no patient had their diagnostic or therapeutic plan altered by the transcranial Doppler results. CONCLUSION: Less than 50% of the patients referred for first-time cerebrovascular examination had access for an interpretable transcranial Doppler examination. Though the number of positive findings is reasonably high, no material impact on diagnostic or treatment plans was seen in the patients in this series. These results indicate that selection criteria for examination of the intracranial arteries should be refined and that transcranial Doppler scanning should not be incorporated as part of the "routine" noninvasive cerebrovascular examination.

Aged↗
PubMed1994

The piezoelectric pulse sensor device: a prospective evaluation.

The goal of this prospective study of the piezoelectric pulse sensor device was to determine its technical applications and its ability to detect lower extremity occlusive arterial disease. Ten extremities (five volunteers) were evaluated to assess the ability to place the sensor in the correct anatomic position on a foot without a palpable pulse during cuff occlusion so that pulsatile flow would be detected following cuff deflation; its sensitivity as an end-point detector for pulsatile perfusion; and whether there is a linear qualitative pulse wave response with increasing perfusion pressures. Forty extremities (20 patients) with suspected occlusive arterial disease were studied to evaluate its capability of detecting perfusion as compared with the presence of a palpable pulse, an audible Doppler signal, and a foot volume waveform. The placement of the sensor on 10 normal limbs with temporary arterial occlusion resulted in a recordable waveform following cuff deflation in 100% of the dorsalis pedis arteries and in 10% of the posterior tibial arteries. The piezoelectric pulse sensor was as sensitive for detecting pulsatile perfusion as an audible Doppler signal and demonstrated a linear change in the waveform's amplitude and shape with incremental changes in perfusion pressure. In the 40 extremities with ankle/brachial indices ranging from 0.00 to 1.35, there was uniform agreement between pulse volume and Pulse Check waveforms. The piezoelectric pulse sensor is a sensitive method for monitoring lower extremity arterial perfusion when supplied by the dorsalis pedis artery; however, it is inadequate for the posterior tibial artery.(ABSTRACT TRUNCATED AT 250 WORDS)

Arterial Occlusive Diseases↗
PubMed1994

A new approach to alcoholism detection in primary care.

This article describes a model that brings together the chemical dependency, mental health, and primary care services of a staff model HMO for the purpose of establishing a primary care clinic-based program to assist physicians in early detection of chemical dependency and frequent psychiatric disorders. The model creates a partnership between a master's-level professional social worker (MSW) and a designated family physician from the clinic. Their focus is on provider education, consultation, and on assisting patients with referrals to the appropriate services. Parameters of success include changes on referral patterns, use of the MSW's services, and clinic satisfaction. In addition, there are indications that early intervention has had a positive impact on subsequent use of other health care system's resources.

Alcoholism↗
PubMed1994

MR angiography of normal pelvic arteries: comparison of signal intensity and contrast-to-noise ratio for three different inflow techniques.

OBJECTIVE: Two-dimensional (2D) time-of-flight (TOF) MR angiography has been the standard technique for evaluating arteries of the lower extremity. However, this technique is limited by artifacts resulting from vessel pulsation, as well as by relatively poor vessel-to-background contrast. The purpose of this study was to evaluate two cardiac-gated inflow techniques to determine whether they exhibited better contrast and signal performance than the standard technique of 2D TOF MR angiography of the iliac arteries. SUBJECTS AND METHODS: Fourteen subjects who had no clinical evidence of vascular disease had standard 2D TOF, gated 2D TOF, and gated 2D turbo field-echo MR angiography. Images were evaluated for signal-intensity ratio, signal-to-noise ratio, and contrast-to-noise ratio, in addition to qualitative evaluation. RESULTS: Turbo field-echo MR angiography exhibited significantly higher signal-intensity, signal-to-noise, and contrast-to-noise ratios than did either gated or standard MR angiography for all vessel segments. We found no significant difference between gated and standard 2D TOF techniques for any vessel segment. Qualitative features of turbo field-echo MR angiography included improved visualization of horizontal vessel segments compared with the standard 2D TOF technique, less effective venous saturation compared with either the gated or standard 2D TOF technique, and increased ghosting artifacts compared with the gated 2D TOF technique. CONCLUSION: Two-dimensional turbo field-echo MR angiography exhibits improved signal and contrast for evaluation of normal iliac segments compared with standard or gated 2D TOF MR angiography. This technique should replace standard 2D TOF MR angiography for evaluation of the iliac arteries.

Adult↗
PubMed1990

Magnetic resonance imaging of pathologic conditions of the Achilles tendon.

The advent of magnetic resonance imaging (MRI) has improved imaging of the Achilles tendon. Various pathologic conditions of the Achilles tendon and their MRI characteristics are described. The superior resolution of the tendon provided by MRI can aid in the diagnosis of Achilles tendon disorders, which include complete or partial rupture of the tendon as well as postoperative assessment of tendinous healing, tendinitis and tenosynovitis, and various tumors of the Achilles tendon.

Achilles Tendon↗
PubMed1989

Magnetic resonance imaging in a family with hereditary cerebral arteriovenous malformations.

Because of a family history of neurologic problems and the documentation of three vascular lesions in one patient, we evaluated 18 members representing three family generations with magnetic resonance imaging. Of these, eight were normal, two had abnormalities probably not related to arteriovenous malformation, one scan was suboptimal, and the remaining eight had evidence of hemorrhagic lesions characteristic of arteriovenous malformation. Four of these patients had multiple lesions, and three patients with lesions had no neurologic symptoms. The findings suggest an autosomal dominant mode of inheritance in this unique case of familial cerebral arteriovenous malformation.

Adult↗
PubMed1987

A clinically effective breast cancer screening program can be cost-effective, too.

The logistics of complying with current American Cancer Society breast cancer screening recommendations in a large health maintenance organization, serving more than 50,000 women age 40 or older, are described. An alternative screening approach estimated to be at least as health-effective as the American Cancer Society recommendations has been developed and appears to solve the problem and is financially feasible. Cost-effectiveness depends on optimal use of mammography and health-care personnel resources. The authors show how the start-up and maintenance costs of an organized program can be offset by future cost savings resulting from reduced long-term disability in patients diagnosed at Stages 0-1 as opposed to Stages 2 and later. Careful selection of the delivery model before implementation can make a breast cancer screening program cost-effective as well as health-effective.

Adult↗
PubMed1986

Intracranial histiocytosis X: a case report.

A case of intracranial histiocytosis X that presented radiologically with thickening of the pituitary stalk is presented. The radiologic findings, including a blush seen on angiography, are described.

Adult↗
PubMed1985

An improved radioimmunoassay for the anabolic agent hexoestrol, using a monoclonal antibody.

A monoclonal antibody was raised against hexoestrol coupled to bovine serum albumin. The antibody cross-reacted with the stilbenes, diethylstilboestrol (10%) and dienoestrol (4%), but had no cross-reaction (less than 0.01%) with other anabolic agents. A radioimmunoassay method using the monoclonal antibody has been validated and used to measure residues of hexoestrol in the urine of treated cattle. The limit of detection was 0.6 pg/ml urine at the 95% confidence limit. The results were compared with those obtained using polyclonal antibodies. Although there was a good correlation between the results, the use of monoclonal antibody gave more reliable results than those obtained with available polyclonal antibodies. The monoclonal antibody, because of its quality and theoretically limitless supply, is very suitable for use in large scale screening or monitoring programmes for regulating the use of hexoestrol.

Animals↗
PubMed1985

Interobserver discrepancies in distance measurements from lumbar spine CT scans.

Lumbar spine computed tomographic (CT) scans of 10 patients were examined independently at two levels by five experienced radiologists. At each level the minimum midline sagittal diameter was measured, and at each intervertebral space the left foramen was measured for its minimum diameter. Statistically significant differences were found between the measurements of different observers, differences that in a number of cases could have led to disagreement over whether or not stenosis was present. There were reasonably strong correlations between different observers' readings of midline sagittal diameters but generally not of foraminal diameters. Reasons for discrepancies between observers in spine CT measurements are reviewed briefly.

Diagnostic Errors↗
PubMed1984

Computed tomography of aqueous humour outflow pathways.

The anterior chamber of adult Rhesus monkeys (Macaca mulatta) was perfused with a radio-opaque contrast medium (Amipaque; mol. wt 789 daltons) at controlled intraocular pressure (IOP), and its subsequent distribution examined by computed tomography. In the living monkey no contrast medium was detectable outside the anterior chamber, even after prolonged (8 hr) perfusion. However, if the animal was then killed, and the IOP maintained artificially at its previous level, opacity appeared immediately throughout the anterior segment. Subsequent scans showed the contrast medium to diffuse into the anterior orbital tissues, and to move posteriorward through the globe wall and extraocular muscles. None entered the vitreous body and very little progressed behind the point at which the extraocular muscles exited from Tenon's capsule. Elevation of IOP did not appear to accelerate this posterior diffusion. It is inferred that in vivo contrast medium passing into the posterior, non-conventional aqueous drainage pathway is cleared immediately by the circulating blood in the uvea and possibly also the extraocular muscle. Tenon's capsule may provide a barrier to further intra-orbital diffusion.

Animals↗