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Biomedical subjects

W M Kelly

Publications and source records attributed to W M Kelly.

29 records · Page 2Linked to original sources
PubMed1984

Beam attenuation devices for digital subtraction angiography.

A set of three contoured and beveled aluminum filters was constructed for routine use in a variety of digital subtraction angiography (DSA) applications. These adjustable devices are designed to compensate for the uneven x-ray penetration that occurs in many radiographic fields and may otherwise lead to video camera saturation, a major source of artifact in DSA. We have used this simple yet versatile adjunct in more than 200 DSA examinations with uniformly satisfactory results. Major advantages include elimination of the procedural delays that may be associated with more conventional approaches (such as the use of a bolus technique) and avoidance of misregistration artifact when pixel-shifting is used.

Angiography↗
PubMed1984

ECG-synchronized DSA exposure control: improved cervicothoracic image quality.

An electrocardiogram (ECG)-synchronized x-ray exposure sequence was used to acquire digital subtraction angiographic (DSA) images during 13 arterial injection studies of the aortic arch or carotid bifurcations. These "gated" images were compared with matched "ungated" DSA images acquired using the same technical factors, contrast material volume, and patient positioning. Subjective assessments by five experienced observers of edge definition, vessel conspicuousness, and overall diagnostic quality showed overall preference for one of the two acquisition methods in 69% of cases studied. Of these, the ECG-synchronized exposure series were rated superior in 76%. Linear intensity gradients across vessel margins generally showed improved or unchanged edge definition in the gated subtraction images as compared with their ungated pairs. These results, as well as the relatively simple and inexpensive modifications required, suggest that routine use of ECG exposure control can facilitate improved arterial DSA evaluations of suspected cervicothoracic vascular disease.

Adult↗
PubMed1983

Acquired immunodeficiency syndrome: neuroradiologic findings.

Central nervous system complications depicted by CT in ten patients with acquired immunodeficiency syndrome are described. Three patients had multifocal intra-axial enhancing lesions representing atypical brain abscesses (two with toxoplasmosis, one with candidiasis). A fourth patient with multifocal "ring" lesions whose biopsy was interpreted as suggestive of toxoplasmosis responded poorly to treatment. Following his death three months later of Pneumocystis carinii pneumonia, autopsy revealed primary intracerebral immunoblastic lymphoma. One patient had Kaposi sarcoma involving the right frontal lobe (seen as an enhancing mass on the CT scan). CT findings in the remaining five patients revealed mild to moderate enlargement of cerebrospinal fluid spaces (including ventricles and basal cisternae) as a result of cryptococcal meningitis in three patients and "aseptic" meningitis in two. The two patients in whom early biopsy confirmed toxoplasmosis responded well to anti-infective therapy, resulting in dramatic clinical recoveries.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Spatial misregistration of vascular flow during MR imaging of the CNS: cause and clinical significance.

Spatial misregistration of signal recovered from flowing spins within vascular structures is a common phenomenon seen in MR imaging of the CNS. The condition is displayed as a bright line or dot offset from the true anatomic location of the lumen of the imaged vessel. Its origin is the time delay between application of the phase- and frequency-encoding gradients used to locate spins within the plane of section. The principal condition necessary for the production of spatial misregistration is flow oblique to the axis of the phase-encoding gradient. Flow-related enhancement (entry slice phenomenon), even-echo rephasing, and gradient-moment nulling contribute to the production of the bright signal of spatial misregistration. Familiarity with the typical appearance of flow-dependent spatial misregistration permits confirmation of a vessel's patency; identification of the direction of flow; estimation of the velocity of flow; and differentiation of this flow artifact from atheromas, dissection, intraluminal clot, and artifacts such as chemical shift.

Brain↗
PubMedDate not supplied

Effect of multislice interference on image contrast in T2- and T1-weighted MR images.

Multislice imaging markedly degrades the contrast of T2-weighted MR images as the separation between slices is reduced. Image contrast was measured clinically at 1.5 T and experimentally at 0.15 T as a function of interslice gap width and shown to be in agreement with calculations based on known relaxation times and excitation profiles. Thus, the cause of T2 contrast degradation in multislice sequences is demonstrated. Contrast in T1-weighted sequences is shown to be minimally affected or even slightly enhanced. Selective excitation pulses with better spatial definition will diminish these contrast changes. Since perfect slice profiles can never be achieved, the clinical implications of these findings are discussed for MR imaging. The choice of slice gaps is an important operator-selected parameter in reducing contrast degradation in T2-weighted sequences.

Adult↗
PubMedDate not supplied

Posterior pituitary ectopia: an MR feature of pituitary dwarfism.

Using high-field-strength, 1.5-T, high-resolution MR, we identified the following complex of neurohypophyseal abnormalities in each of five pituitary dwarfs: (1) severe hypoplasia or total absence of the infundibulum; (2) absence of the posterior pituitary bright spot in its normal location; and (3) a 3-8-mm tissue nodule at the median eminence exhibiting lipidlike signal on T1-weighted images. On the basis of its signal features and the clinical absence of diabetes insipidus in these patients, the median eminence nodule appears to represent an ectopic and functional posterior pituitary gland. We propose that this anatomic derangement is the end result of a localized defect of developmental origin, possibly ischemic in nature, and involving principally the infundibular stem. Thus, human growth hormone deficiency could result from perinatal disruption of the peri-infundibular hypophyseal portal system, which in turn impairs anterior pituitary function through deprivation of direct delivery of crucial hypothalamic-releasing factors. Finally, we suggest that the trophic influence of continued axonal neurosecretion at the median eminence engages proliferation of rest cell pituicytes; a process that induces formation of an ectopic and functional posterior pituitary gland, complete with its characteristic bright spot.

Adolescent↗