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Biomedical subjects

P D Lester

Publications and source records attributed to P D Lester.

At least 19 recordsLinked to original sources
PubMed1992

Esophagogastric ring: why and when we see it, and what it implies: a radiologic-pathologic correlation.

Schatzki first reported a ring-like structure at the esophagogastric mucosal junction in 1953. There is still no uniform agreement as to its exact location, etiology, or clinical importance. We found an esophagogastric ring in 15% to 18% of 22,368 patients having routine upper gastrointestinal examinations. It was present only in patients with cephalad displacement of the esophagogastric junction and only in those who had sharply and circumferentially marginated transition of esophagogastric mucosal junction. It is postulated that the esophagus shortens on vagal stimulation by contracture of the longitudinal esophageal muscle, which causes a mucosal infolding at the esophagogastric junction. In a small group of these patients, fibrosis apparently develops in this region and results in a fixed organic circumferential diaphragm, which may cause obstructive symptoms. These concepts affect therapeutic alternatives.

Barium Sulfate↗
PubMed1988

Systemic mastocytosis and mastocytosis-like syndrome: radiologic features of gastrointestinal manifestations.

Mastocytosis is a disorder of unknown etiology characterized by an abnormal proliferation of tissue mast cells, and/or by degranulation of abnormally behaving mast cells that show no proliferation, but release myriad active metabolites. This results in a wide spectrum of signs and symptoms that fluctuate considerably. The presently available diagnostic tests vary in their specificity and sensitivity. We have evaluated the role of radiologic studies in 78 confirmed cases of systemic mastocytosis and/or mastocytosis-like syndrome, including barium meal and small bowel follow-through (UGI-SBFT).

Adolescent↗
PubMed1988

Properties of electromagnetic field focusing probe.

The electromagnetic field focusing (EFF) apparatus consists of a radio frequency generator, solenoidal coil, and a hand-held or catheter probe. Applications such as aneurysm treatment, angioplasty, and neurosurgery in various models have been reported. The probe is operated in the near field (within one wavelength of an electromagnetic field source) of a coil inducing eddy currents in biological tissues, producing maximal convergence of the induced current at the probe tip. The probe produces very high temperatures depending on the wattage selected for the given radio frequency of output power. The high temperature can be used in cutting, cauterizing, or vaporizing. The EFF probe is comparable to different types of lasers and to bipolar and monopolar cautery. The EFF probe can be used with catheters or endoscopes. Objectives of this study were to determine what the thermal properties of the EFF probe are and how instrument parameters can be varied to obtain different temperatures in the tissue near the probe tip. In this study an F2 catheter was used as an insulated sheath and the tip of the guide wire was used as the probe tip. Different powers, wave forms, coil-to-probe distances, and probe-tip lengths were tested on a phantom that simulates tissue electrical properties. Some of the experiments were conducted under normal saline to simulate treatment of tissue with body fluids such as blood vessels or brain tissue under normal physiologic conditions. It is concluded that the EFF probe has the advantages of easy manipulation, relative safety, cost effectiveness, and a high degree of spatial control.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocoagulation↗
PubMed1988

Electromagnetic field focusing probe (EFFP)--a new angioplasty tool.

An electromagnetic field focusing probe (EFFP) consists of a radiofrequency generator, solenoidal coil, and a hand-held or catheter probe. The probe is operated in the near field (distance within one wave length of an electromagnetic field source) of a coil, which induces eddy current in a biological tissue. The induced eddy current is converged maximally at the tip of the probe upon contact of the tip with the tissue. The probe produces very high temperatures depending on the wattage selected. In this study, the EFFP was used to evaporate atheromatous plaques in human cadaver abdominal aorta specimens, which were then studied histologically. Gas produced by this technique was analyzed and the volume found to be related to power delivered, but in such small amounts as to be of no embolic significance. While temperature varied with wattage and time of application, it was maximal at the probe tip and easily controlled, resulting in clean obliteration of plaque.

Angioplasty, Balloon↗
PubMed1988

Precision surgery with an electromagnetically induced current convergence probe application in aneurysm treatment, angioplasty, and brain tumor resection in in vivo and in vitro models.

A hand-held probe, or one introduced through a catheter, rapidly produces an extremely high, tissue-vaporizing temperature in a precisely defined manner enabling surgeons or interventional radiologists to perform angioplasty, thrombose aneurysms, and vaporize tumors. The probe is operated in a near field of an inductive coil, and the current induced in the biologic tissue is converged maximally at the tip of the probe at the resonance frequency of both the inductor and the probe, producing a maximum temperature in excess of 1400 degrees C. Radio-frequency power controls the probe-tip temperature. The operation of the probe is comparable to that of a CO2 or YAG laser and is complementary to laser-surgical techniques. The low cost relative to lasers and simplicity of the device including its disposable components make the prospect of commercialization of this device promising.

Aneurysm↗
PubMed1987

Electromagnetically induced focused heat in the treatment of surgically created aneurysm models.

A hand-held radiofrequency (rf) probe of a novel design based on the principle of the induced current convergence was used to treat aneurysm models using focused hyperthermia. Aneurysms were created surgically in rats by a side-to-side anastomosis between the inferior vena cava and the abdominal aorta or by grafting a donor abdominal aorta from one rat onto the abdominal aorta of another rat. Aneurysms were treated by inserting the 0.3-mm diameter probe tip into the fundus and applying the power for brief periods (0.5-1.5 sec) using a foot pedal. Collapse of the fundus was observed as the result of the heat-induced thrombosis. Thermal distribution in the immediate vicinity of the probe as well as the heating rate were measured in a uniformly dielectric phantom and in rat vessels. The aneurysms were histologically examined immediately, three days, and three weeks after the treatment. Complete obliteration of the aneurysms and patency of the parent arteries were confirmed. Partial integrity of the vessels around the lesion was also confirmed.

Animals↗
PubMed1986

Magnetic Resonance Imaging (MRI) stereotaxis using the Patil System. A technical note.

Magnetic Resonance Imaging (MRI) scanning would prove useful for lesions that are not visualized on computed tomography (CT) scan or are better defined on MRI scan. The problem of reference marker visualization can be overcome by coating them with mineral oil or by placing paramagnetic fluid filled rods on them. The unique construction of the Patil System permits its use even in a strong magnetic field. The technique of MRI stereotaxis using this stereotaxic system without any modification is described.

Brain Diseases↗
PubMed1986

Magnetic resonance imaging in childhood intracranial masses.

Magnetic Resonance Imaging (MRI) was compared with computerized tomography (CT) in 40 pediatric and adolescent patients with intracranial mass lesions as part of an ongoing project to determine the potential of MRI as a primary and definitive imaging modality. Multiplanar, multisequence MRI surpassed CT in providing mass localization, extent of involvement, and delineating the relationship to adjacent vital structures. Further development of MRI is encouraged to overcome current inconsistencies in pathologic characterization in order for this new technology to be employed not only as a primary screening modality but also as a definitive diagnostic test.

Adolescent↗
PubMed1986

MRI in infants and children with spinal dysraphism.

Magnetic resonance imaging (MRI) of the spine was used in 37 infants and children to assess the potential of this new technology to evaluate suspected lumbosacral dysraphic myelodysplasia. Eighteen of these patients had correlative metrizamide myelotomography and metrizamide computed tomography (CT). MRI using a spin-echo pulse sequence with short repetition times (TR) and echo delay times (TE) affords optimal delineation of normal and abnormal spinal cord morphology in the lumbosacral region. Coronal projections usually provide an adequate demonstration of the normal conus medullaris for screening purposes; however, multiplanar acquisitions are necessary for more complete delineation of the dysraphic myelopathy. The sensitivity of MRI compares favorably with metrizamide tomography and CT, although these procedures provide somewhat better specificity. These results suggest that MRI is a reliable, noninvasive procedure to screen patients for lumbosacral dysraphism.

Adolescent↗
PubMed1986

Noninvasive tumor volume measurement using magnetic resonance (MR) imaging and an open sided saddle coil.

A magnetic resonance (MR) imaging scanner operated at 0.5 T with a specially constructed receiving coil was used to measure volumes of primary spontaneous tumors in rats and guinea pigs. The coil was used to improve the signal to noise ratio (S/N) of the MR images of tumors in these small animals. The tumor volume was determined by the summation of the volume of contiguous slices or ellipsoid approximation. The accuracy of the volume measurement was better when the numerical integration was used in calculating the slice volume. The open sided saddle (OSS) coil used as the receiving coil gave better S/N than that of the standard head coil.

Animals↗
PubMed1985

Dependence of magnetic resonance image (MRI) intensity values on relaxation times, pulse intervals and other signal attenuation factors.

Magnetic resonance image (MRI) pixel intensities were investigated using a phantom containing several uniform size chambers filled with solutions of known relaxation times, as well as head scans of patients and volunteers. Intensities were measured with a variety of pulse intervals typically used for imaging with spin echo, (SE) and inversion recovery (IR) sequences at 0.15 Tesla using the back projection (R-THETA) method, and at 0.27 Tesla using the 2-dimensional Fourier transform (2DFT) technique. The results were compared with the calculated dependence of MRI signal intensity on relaxation times and pulse interval parameters using the well known functions containing exponential forms. The experimental and the calculated pixel intensity time dependence did not always agree. We infer that factors other than the conventional functions for T1 and T2 signal decay are important. These factors may include the attenuation of the radiofrequency (RF) signals through inhomogenious lossy dielectric materials (e.g., tissues and organs), the location (coordinate) of the portion of the sample to be imaged relative to the RF coils, and the timing and amplitude of gradient pulses relative to the RF input and the detected signals. The flow velocity and diffusions are also important determinants of the signal from blood vessels and body fluids. We point out the necessity for further investigation toward more comprehensive understanding of MRI intensities.

Adenoma↗
PubMed1984

Technical artifacts in magnetic resonance imaging.

Various artifacts of Magnetic Resonance Imaging (MRI) typically associated with currently available imaging techniques such as projection reconstruction and two-dimensional fourier transform (2D-FT) are described and illustrated. Examples of MRI artifacts were obtained with an imaging unit with a super conducting magnet operated at .15 Tesla and .27 Tesla with corresponding proton resonance frequency of 6.4 MHz and 11.25 MHz. The .15 Tesla images were obtained using projection reconstruction and the .27 Tesla using the 2D-FT method. Instrument related artifacts include those due to direct current (DC), projection, gradient offset, active shimming, phase encoding, and pulse sequencing. Other often encountered artifacts are related to the patient. These include those due to motion, ferromagnetic effect, and tissue contents. The cause of these artifacts and how (if possible) they may be eliminated or minimized is discussed.

Diagnostic Errors↗
PubMed1984

Focused hyperthermia with a magnetic resonance imaging (MRI) unit and an interstitial grounded probe.

The feasibility of using a commercial magnetic resonance imaging (MRI) scanner to do either imaging or hyperthermic treatment was demonstrated. Radiofrequency (RF) induced focal heating of phantoms and animal tissues was performed using a MRI scanner as the RF power source and a grounded interstitial probe as a device to produce hyperthermia via eddy current convergence. In the therapeutic mode, a pulse width of 900 microseconds and interval of 50 ms were used to give 2% duty cycle (closest simulation to continuous wave (CW) mode without bypassing imaging filters). Temperature in the vicinity of the grounded probe was measured with a field nonperturbing fluoroptic probe. Temperatures increased 4.5 degrees C in 5 minutes in a dielectrically uniform phantom, 3.1 degrees C in 6.7 minutes in rats' leg muscles, and 5.0 degrees C in 6.0 minutes in rats' peritoneum. The MRI of the phantom with the grounded probe and the fluoroptic probe was obtained using spin echo sequences. The potential advantage of this approach is visualization of deep-seated tumors and hyperthermic treatment with minimal modification of the MRI scanner.

Animals↗
PubMed1983

Clinical evaluation of unsharp masking and slit scanning techniques in chest radiography.

Conventional, unsharp masking, and slit-mask (combining slit radiography and unsharp masking) techniques were compared in a clinical nodule detection study in cancer patients who were at risk for metastatic lung disease. Unsharp masking improved detection rates for nodules located in poorly penetrated areas of the chest (25% vs. 52%), with no difference in detection rates for other areas of the image and no change in false-positive detection rates. Results with the slit-mask technique did not differ significantly from those obtained with conventional techniques. In general, the differences in nodule detection rates noted between different techniques in the clinical study were less than had been observed in earlier phantom-nodule detection studies. Possible reasons for these findings are discussed.

Clinical Trials as Topic↗
PubMed1982

Neonatal pneumopericardium.

The clinical data and radiographs of 50 neonates with pneumopericardium (PPC) were reviewed. Most of these neonates were premature, low-birth-weight infants with hyaline membrane disease who required ventilatory assistance. The presence of other extraventilatory air prior to (or concurrent with) PPC, the use of cardiopulmonary resuscitation with intracardiac drug administration, and improper endotracheal tube placement were contributory factors. However, it was not possible to determine why some infants progressed to PPC and others, with similar disease and predisposing conditions, did not. The primary radiographic sign of PPC is the "halo" sign, which was apparent in 96% of these cases. When this sign was not present, other signs, such as the "pericardial line" sign, were helpful. The overall mortality was 72%. Thirty-three per cent of the fatalities were related to PPC; however, the long-term prognosis is probably more closely related to the severity of underlying lung disease or other complications than to PPC.

Drainage↗
PubMed1981

Effectiveness of chest tube evacuation of pneumothorax in neonates.

This is a retrospective review of the effectiveness of 149 chest tubes placed in attempts to evacuate 91 pneumothoraces among 57 infants. Forty-four percent of initial evacuation attempts were ineffective; 42% of total chest tubes throughout the clinical courses were ineffective. The largest number of these ineffective chest tubes lay posterior in the pleural cavity. Fifty-six percent of posterior tubes were ineffective whereas only 4% of anterior tubes were ineffective. Other causes for failure included tubes which had perforated the lung, diaphragm, or mediastinum or were lying subcutaneously. On some occasions, chest tubes were mistakenly used to evacuate intrathoracic air which was actually a pulmonary pseudocyst or pneumomediastinum. Two thoracostomy sites were chosen: the superior and lateral. Eighty-five percent of chest tubes inserted through the superior approach lay anteriorly in the pleural cavity whereas only 47% of the laterally inserted tubes lay anteriorly. Superior thoracostomy tubes were significantly more effective than lateral tubes because of their more frequent anterior location. There were also fewer complications with superior thoracostomy tubes. Whereas only 10% of superiorly inserted tubes encroached upon the mediastinum, 32% of lateral tubes did so. To be effective, chest tubes should be placed anteriorly in the pleural space; this location is more often achieved via the superior thoracostomy approach.

Female↗