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Biomedical subjects

A S Mark

Publications and source records attributed to A S Mark.

At least 55 records · Page 3Linked to original sources
PubMed1987

The utility of principal component analysis for the image display of brain lesions. A preliminary, comparative study.

Principal component analysis (PCA), a common tool from multivariate statistical analysis, has been implemented into the computer display system of a MR imaging device. PCA allows the calculation of images in which the information in a defined region of interest inherent in the basic acquired images is condensed. PCA image calculation has been applied to acquired MR studies of 13 patients with brain lesions. The appearance of the brain lesions on the resultant PCA images was scored in comparison to the acquired images before and after administration of Gd-DTPA as well as to other calculated images including T1, T2, hydrogen density, and contrast-optimized images. The conspicuity of a lesion and the number of distinguishable components within a lesion were slightly superior on PCA than on the acquired images. PCA is an analytical tool for MR imaging that should be helpful in revealing information that is inherent in, but not readily visible on, standard acquired MR images.

Brain Neoplasms↗
PubMed1987

Magnetic resonance imaging of the TMJ disc in asymptomatic volunteers.

Forty-two temporomandibular joints (TMJs) in 21 asymptomatic volunteers were visualized by magnetic resonance imaging (MRI). The subjects, 12 males and nine females, were between 23 and 43 years of age and had no history of TMJ pain, joint noise, limited opening, or previous treatment for TMJ disorder. A cephalometric head-holder was designed to position the TMJ in an accurate and reproducible manner and multisection parasagittal images were obtained perpendicular to the longitudinal axis of the condyle. MR images depicted anterior disc position in 32% of the asymptomatic joints (8/24 males, 5/18 females). Anterior disc position in asymptomatic subjects may be a predisposing factor to TMJ dysfunction or simply an anatomic variant whose prevalence must be considered when evaluating TMJ dysfunction.

Adult↗
PubMed1987

Gated acquisition of MR images of the thorax: advantages for the study of the hila and mediastinum.

Gated and nongated magnetic resonance (MR) scans of the chest were compared in five normal volunteers and 20 patients with chest disease to determine possible advantages of gated MR for delineation of noncardiac mediastinal anatomy. In order to compare gated and nongated images of the chest using similar imaging parameters, five spin-echo sequences were obtained in each of five normal volunteers: TR: 1000 msec, TE: 30 msec; gated to every heart beat (TR approximately 1000 msec, TE: 30 msec); TR: 2000 msec, TE: 30 msec; gated to every other heart beat (TR approximately 2000 msec), TE: 30 msec; TR: 500 msec, TE: 30 msec. In the 20 patients, the gated images were gated to every heart beat and the nongated images were obtained using a TR of 2000 msec, both with a TE of 30 msec. The noise in the periphery and in the center of the gated and nongated images at the level of the carina was compared in the five normal volunteers, using the signal intensity of the posterior chest wall as a control. There was 92% +/- 44% greater noise in the central region and 63% +/- 60% greater noise in the peripheral region on the nongated studies (TR: 1000 msec), than on the studies gated to every heart beat. In three of the five volunteers, the measured noise was greater on the nongated long TR (2000 msec) images than on the images gated to every other heart beat. However, the mediastinal structures below the level of the aortic arch were much better defined on the gated images in all five subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Changes in size and magnetic resonance signal intensity of the cerebral CSF spaces during the cardiac cycle as studied by gated, high-resolution magnetic resonance imaging.

In 1966, du Boulay demonstrated the pulsatile nature of CSF flow in the cerebral aqueduct by using air cineventriculography, which disturbs normal CSF dynamics by replacing part of the incompressible CSF with air. To investigate this phenomenon noninvasively, 35 normal volunteers were studied using high-resolution, cardiac-gated MR imaging. Specifically, we wished to document changes in size and configuration of the CSF spaces and the incidence and magnitude of signal loss (an indication of CSF motion) in these spaces as they related to time in the cardiac cycle. Changes in size and configuration were measurable in the third ventricle only (size increased during systole in seven of the 35 volunteers). Except for the lateral ventricles, some loss in signal intensity was seen in all CSF spaces at least during systole in all 35 volunteers--findings consistent with those of du Boulay. However, contrary to du Boulay's observations, asymmetric loss of signal, consistent with pulsatile CSF flow, was demonstrated at the level of the foramen of Monro in 15 of the 35 volunteers. Based on the pattern of flow void at the level of the foramen of Monro and on the expansion of the third ventricle during systole, we propose a theory of synchronous CSF flow at the foramen of Monro and aqueduct, which unifies our MR findings with du Boulay's cineventriculographic observations.

Adult↗
PubMed1987

Intrauterine contraceptive devices: MR imaging.

To assess the safety of magnetic resonance (MR) imaging in women who have an intrauterine contraceptive device (IUD) in place, in vitro and in vivo studies were performed at both 0.35 and 1.5 T. Two commonly used IUDs were tested, one all of plastic, the other with a coil of copper wire on it. Specifically, the study assessed possible motion of the IUD in the magnetic field, potential of the IUD to heat up during two spin-echo imaging sequences commonly used in MR imaging of the pelvis (2,000/30 and 60 [repetition time, msec/echo time, msec], and 500/30), and the appearance on MR images of the IUD devices. A retrospective review of MR images of the pelvis in six women who had an IUD in place was also performed. Results show that an IUD does not move under the influence of the magnetic field, does not heat during spin-echo sequences commonly used for pelvic imaging, and does not produce artifacts in vitro or in vivo. Patients with either type of IUD can be safely imaged with MR, and MR images of the pelvis are not degraded by the presence of an IUD.

Female↗
PubMed1987

Adenomyosis and leiomyoma: differential diagnosis with MR imaging.

To assess the capability of magnetic resonance (MR) imaging to enable differentiation of adenomyosis from leiomyoma, a prospective study was performed in 21 premenopausal patients with a strong clinical suggestion of adenomyosis. Histologic findings from hysterectomy (19 patients) and biopsy specimens (two patients) showed that eight patients had adenomyosis (three focal, five diffuse) and 12 had leiomyomas (five of the 12 also had microscopic foci of adenomyosis); one patient had a normal uterus. All eight cases of adenomyosis were correctly diagnosed from MR images. On T2-weighted MR images, diffuse adenomyosis appeared as a thickening of the junctional zone, whereas focal adenomyosis appeared as a low-signal-intensity mass poorly marginated from the adjacent myometrium. Ten of the 12 leiomyomas were correctly diagnosed from MR images. In the other two cases of leiomyoma, differentiation between focal adenomyosis and leiomyoma was not possible. Microscopic foci of adenomyosis were not demonstrated with MR imaging.

Adult↗
PubMed1987

Human brain motion and cerebrospinal fluid circulation demonstrated with MR velocity imaging.

Present theory holds that pulsatile pressure of cerebrospinal fluid (CSF) is driven by the force of expansion of the choroid plexus. Alternate theories postulating that a possible movement of the brain is involved in pumping CSF have not, to the authors' knowledge, been substantiated heretofore. In this study, in vivo, quantitative magnetic resonance (MR) imaging methods were developed to show reproducible magnitudes and directions of CSF flow. Measurements were obtained with a new MR velocity imaging technique at high resolution (0.4 mm/sec), requiring 64 cardiac cycles per image. Twenty-five healthy volunteers and five patients were studied. Observations of pulsatile brain motion, ejection of CSF out of the cerebral ventricles, and simultaneous reversal of CSF flow direction in the basal cisterns toward the spinal canal, taken together, suggest that a vascular-driven movement of the entire brain may be directly pumping the CSF circulation. The authors describe what they believe to be the first observations and measurements of human brain motion, which occurs in extensive internal regions (particularly the diencephalon and brain stem) and is synchronous with cardiac systole.

Adolescent↗
PubMed1987

Coronary artery bypass graft patency: noninvasive evaluation with MR imaging.

A noninvasive means of determining coronary artery bypass graft (CABG) patency in symptomatic patients would be an important clinical asset. The accuracy of magnetic resonance (MR) imaging was evaluated for this purpose. Multiphasic electrocardiographically gated MR imaging examinations were performed in 25 patients with a total of 72 grafts. Transverse images of the heart at ten anatomic levels were obtained at five or six phases of the cardiac cycle. The MR images were read blindly to determine CABG patency versus occlusion, and these results were compared with those of coronary angiography performed within 2 months before the MR imaging. MR imaging correctly disclosed 43 patent grafts and 13 occluded grafts (predictive accuracy, 78%). Patency and occlusion were incorrectly diagnosed from MR imaging findings in five and four CABGs, respectively. CABG status could not be determined in seven (10%) grafts because the grafts were visualized at only one anatomic level. Thus, the accuracy of a definitive MR imaging evaluation was 91% (43 of 47 grafts) for patency determination and 72% (13 of 18 grafts) for occlusion determination. MR imaging appears to be a useful method for the noninvasive evaluation of CABGs.

Adult↗
PubMed1987

MR imaging of the prostate gland: normal anatomy.

MR images of the male pelvis in 55 subjects were analyzed retrospectively for depiction of the zonal anatomy of the prostate gland as related to different repetition (TR) and echo (TE) times, slice thickness, plane of imaging, chronologic age of the patient, and different magnetic field strengths. With imagers operating at 0.35 and 1.5 T, T2-based tissue-contrast images were needed for the demonstration of the internal anatomy of the prostate gland. The display of zonal anatomy was improved when continuous 0.5-cm slices were used. Evaluating sequential sections, the peripheral, central, and transition zones could be differentiated. The peripheral zone showed higher signal intensity than either the central or transition zone and was discerned in the coronal, sagittal, and transverse planes. The central zone was of low signal intensity and was well displayed in the coronal and sagittal planes. The central zone was seen in 31 of the 32 young men (aged 25-35 years) but in only eight of the 23 older men (aged 40 years and older). The transition zone had intrinsic MR parameters similar to the central zone, and the two could be distinguished from each other only by the knowledge of their respective anatomic location. The low-intensity transition zone blended with the periurethral glands and the preprostatic sphincter. The transition zone was of homogeneous low signal intensity in young men but varied in size and signal intensity in older men. Such a detailed display of the prostate zonal anatomy offers a unique potential for the evaluation of prostatic physiology and disease.

Adult↗
PubMed1986

Sonographic evaluation of the rejecting ureter.

In 10 mongrel dogs, the sonographic features of the pelvocaliceal system and ureteral peristalsis during acute rejection were correlated with the electromyographic (EMG) findings and histologic appearance. There were significant alterations of the ureteral dynamics during rejection as demonstrated by changes in the pressure tracings, the progressive decrease of electrical activity of the ureteral muscle, and decreased peristalsis with pelvicaliectasis as demonstrated on real-time ultrasound. The sonographic changes of peripelvic and periureteral thickening corresponded to histologic changes of edema and inflammatory infiltrate with disruption of the muscular layer. In the presence of clinical and sonographic findings of kidney rejection, the demonstration of hydronephrosis and thickened pelvic wall should be considered as another measure of the rejection process.

Animals↗
PubMed1986

CT of subpulmonic pleural effusions and atelectasis: criteria for differentiation from subphrenic fluid.

The ability to distinguish intrathoracic from intraabdominal fluid collections has important therapeutic implications. In the setting of peridiaphragmatic fluid collections CT accurately distinguishes between pleural and subphrenic fluid collections in most cases. Subpulmonic effusions represent a potential pitfall to CT diagnosis, however, because the atelectatic basilar lung segments appear on axial CT sections as a curvilinear band density that simulates the hemidiaphragm. Fluid found anterior to this "pseudodiaphragm" will erroneously be diagnosed as subphrenic unless the atelectatic lung is recognized as such. New CT observations are reported that allowed confident diagnosis in 18 consecutive cases of subpulmonic effusions. The atelectatic lung was distinguished from the diaphragm because the atelectatic band appeared thickened (17 of 18 cases), tapered laterally (14 of 18), was interrupted rather than continuous (17 of 18), and could be followed in contiguous cephalad sections into lung that was confidently recognized by the presence of gas bubbles or air bronchograms (12 of 18).

Adult↗
PubMed1986

Gated magnetic resonance imaging of the intracranial cerebrospinal fluid spaces.

The pulsatile nature CSF flow in the cerebral aqueduct has been demonstrated by du Boulay using air cineventriculography, a technique which disturbs normal CSF dynamics. To investigate this phenomenon non-invasively, we studied 35 normal volunteers using high-resolution, cardiac-gated magnetic resonance imaging (MRI). Specifically, we wished to document changes in size, configuration and signal intensity of the CSF spaces as they related to time in the cardiac cycle. Results show that changes in size and configuration were measurable in the third ventricle only (size increased during systole in 7 of the 35 volunteers). Except for the lateral ventricles, some loss in signal intensity was seen in all CSF spaces at least during systole, in all 35 volunteers-findings consistent with du Boulay's. However, contrary to du Boulay's observations, asymmetric loss of signal, consistent with pulsatile CSF flow, was demonstrated in the foramen of Monro in 15 of the 35 volunteers. Based on the pattern of signal void at the level of the foramen of Monro and on the expansion of the third ventricle during systole we propose a theory of synchronous CSF flow at the foramen of Monro and aqueduct, which unifies our MRI findings with du Boulay's cineventriculographic observations.

Adult↗
PubMed1985

Computerized tomographic assessment of graft incorporation after aortic reconstruction.

Computerized tomographic scanning is being used with increasing frequency for the detection of abdominal aortic prosthetic complications. Although computerized tomography remains a very precise method for direct imaging of the retroperitoneal space, the interpretation of a postoperative computerized tomographic scan is limited by the absence of any information on the normal appearance of the routine uncomplicated aortic graft. To study the normal tissue incorporation of aortic grafts, 29 patients were evaluated with periodic postoperative computerized tomographic scans. Seventeen patients had aortoiliac occlusive disease and 12 had aneurysmal disease. No patients who had reoperation were included and all patients had a normal postoperative course. Computerized tomographic scans were obtained in the early (mean 7 days), intermediate (mean 48 days), and late (mean 102 days) postoperative periods. A variable amount of perigraft hematoma was always present on the initial computerized tomographic scan. Perigraft air was seen in only four patients in the early study. Graft incorporation appeared complete in these patients by 48 days, although minimal hematoma persisted in one patient. This study provides baseline data on the appearance and timing of aortic graft incorporation which should facilitate subsequent computerized tomographic detection of aortic graft complications.

Aged↗
PubMed1985

Immunologically oriented concept of the genesis of acquired immunodeficiency syndrome.

An immunologically oriented concept of the genesis of acquired immunodeficiency syndrome is presented in which the central event is the lack of cytotoxic T8 cells. An interlocking system wherein the T4 (helper) cells do not synthesize interleukin-2 to generate the cytotoxic cells due to the lack of functional thymosin as well as the lack of interleukin-1 from the macrophages is postulated. The transmissible agent which sets the cascade of immunologic imbalance into play replicates only in the thymic epithelium and subverts thymosin synthesis. The T8 cells in the syndrome are exclusively H2 positive and functionally suppressor. The macrophage which phagocytizes the effete thymic epithelium hematogenously spreads the transmissible agent to others. Kaposi's sarcoma is considered to be an integral component of the immunologic disarray in that angiogenesis is proposed to require two essential events - endothelial cell proliferation and movement of those cells. Under normal circumstances although the activated macrophage elaborates a monokine that has endothelial cell proliferative inducing capacity the cells are held in situ by a lymphokine that prevents movement. The lymphokine is considered to be IL-2. Eight predictions of the model which are experimentally testable are presented.

Acquired Immunodeficiency Syndrome↗
PubMed1985

Detection of abdominal aortic graft infection: comparison of CT and in-labeled white blood cell scans.

Aortic graft infections are a rare but potentially lethal complication of aortic graft surgery. If the infection is limited to the groin, local therapy and preservation of the graft may be possible in some cases, whereas infections extending into the retroperitoneum require removal of the graft and revascularization of the lower limbs. The diagnosis and assessment of the extent of a graft infection is difficult on clinical grounds. A prospective study compared CT and indium-labeled white blood cell (In-WBC) scans in the diagnosis of aortic graft infection. Five patients with aortic graft infection and three patients without aortic graft infection were studied by both methods. CT correctly detected the retroperitoneal extension of the infection in three patients with groin infection; In-WBC scans diagnosed the extension only in one patient. Both CT and In-WBC were positive in two patients with aortic graft infection but no groin infection. Both studies were negative in the three patients without evidence of aortic graft infection. The study suggests that CT is more sensitive than In-WBC in evaluating the extent of aortic graft infection and should be the imaging method of choice.

Aorta, Abdominal↗
PubMed1984

Immunoperoxidase evaluation of lymph nodes from acquired immune deficiency patients.

Immunoperoxidase evaluation of cryostat sections from acquired immune deficiency syndrome (AIDS) or prodromal nodes indicated that the majority (75%) had T8 dominance as contrasted to reactive hyperplasia nodes of unknown origin which had 80% T4 dominance. The cells in the AIDS nodes in the interfollicular and medullary sinuses areas marked intensely for Ia as opposed to sparse scattering in the comparative group. Finally, the follicles in the study group as opposed to the comparative group demonstrated hypervariability both in size and shape as outlined by a thin mantle zone of BA-1 positive cells. On the basis of the above three immunological criteria it is considered as highly likely that an AIDS node can be distinguished as such as opposed to the conventional characterization of 'reactive hyperplasia'.

Acquired Immunodeficiency Syndrome↗
PubMed1981

Computed tomography of the normal larynx during quiet breathing and phonation.

Computed tomography scans of the larynx were obtained during quiet breathing and during phonation in 10 volunteers having no neck or larynx abnormalities. The subglottic and glottic laryngeal cavity and soft tissues showed symmetry from side to side. At the supraglottic level, the pliable aryepiglottic folds and pyriform sinuses appeared moderately asymmetric and variable during quiet breathing. Phonation made them more symmetric. Phonation also allowed accurate determination of vocal cord function. The laryngeal cartilages were symmetric in their degree of calcification and had clearly visible centers of dense calcification. Computed tomography is a highly precise method for demonstrating the structures of the larynx.

Humans↗