Biomedical subjects

C P Davis

Publications and source records attributed to C P Davis.

At least 19 recordsLinked to original sources

PubMed1998

Diagnostic impact of four postprocessing techniques in evaluating contrast-enhanced three-dimensional MR angiography.

OBJECTIVE: The purpose of this study was to determine the added diagnostic value of various three-dimensional (3D) data viewing techniques when analyzing contrast-enhanced 3D MR angiography. MATERIALS AND METHODS: Twenty patients (mean age, 62 years) with symptomatic peripheral vascular disease were assessed with breath-hold, contrast-enhanced 3D MR angiography and catheter angiography, which served as the standard of reference. After an initial interpretation of the 3D MR angiographic data sets based only on standardized maximum intensity projections (MIP), the diagnostic gain of the stepwise addition of interactive multiplanar reformations, shaded-surface displays (SSD), and virtual intraarterial endoscopy (VIE) images was calculated. Time required for each step of postprocessing was measured. RESULTS: Pathologic changes were revealed by catheter angiography in 60 vascular segments (50 severe stenoses, seven aneurysms, and three occlusions). The average postprocessing times were MIP, 8 min (range, 5-12 min); multiplanar reformations, 9 min (range, 3-11 min); SSD, 15 min (range, 8-25 min); and VIE, 40 min (range, 18-63 min). Addition of multiplanar reformations to MIPs resulted in the greatest gain of diagnostic accuracy, from 92% to 96%, and diagnostic confidence. When analysis was based on all four techniques, receiver operating characteristic curve analysis revealed only minimal improvements in diagnostic confidence, whereas diagnostic accuracy remained unchanged at 96%. CONCLUSION: Accurate and time-effective analysis of contrast-enhanced 3D MR angiography should be based on MIP algorithms and multiplanar reformations. Additional evaluation with VIE or SSD techniques is time-consuming and provides little diagnostic gain.

Adult↗

PubMed1998

Expression of zonula occludens and adherens junctional proteins in human venous and arterial endothelial cells: role of occludin in endothelial solute barriers.

OBJECTIVE: The purpose of this study was to correlate the expression of occludin and VE-cadherin with the solute barrier properties of arterial and venous endothelial monolayers. METHODS: Immunofluorescent confocal and traditional microscopy were used to determine junctional protein localization in endothelium in vivo and in vitro respectively, and western and northern analysis used to determine protein and gene expression levels. Permeability of endothelial monolayers was examined under normal, low calcium, and cytochalasin-D treatment conditions. Antisense oligonucleotide experiments for occludin were performed to determine the contribution of occludin to solute barrier. RESULTS: Occludin protein in endothelial monolayers is more concentrated in arterial junctions than in venous junctions both in vivo and in vitro. Arterial endothelial cells express 18-fold more occludin protein and nine times more occludin mRNA compared to venous endothelial cells. In vivo, both endothelial cells demonstrate VE-cadherin staining; and in vitro, only venous endothelial cells express VE-cadherin protein and mRNA. Occludin antisense experiments suggest that both arterial and venous barrier properties are due to these different amounts of occludin expression. Venous barrier was remarkably sensitive to low extracellular calcium, while arterial barrier was more sensitive to cytochalasin-D. CONCLUSIONS: These findings suggest strongly that arterial and venous endothelial barrier reflects the level of expression of different adhesion molecules and that modulation of these proteins, especially occludin, may regulate the level of endothelial solute barrier.

Antigens, CD↗

PubMed1997

Coronary flow and coronary flow reserve measurements in humans with breath-held magnetic resonance phase contrast velocity mapping.

Objective evidence for coronary lesion significance can be obtained with ischemic stress testing. Since flow-limiting stenoses have already undergone compensatory vasodilatation to maintain flow, the response to vasoactive stimulation is dampened. The degree of response limitation is reflected by the coronary flow reserve (CFR). Absolute volume flow rates can be accurately and noninvasively measured with MRI techniques. The purpose was to assess the ability to measure coronary volume flow rate noninvasively, and characterize the effect of pharmacologic stress on coronary flow quantitatively by using ultrafast, breath-held segmented k-space phase-contrast-MR imaging (PC-MRI). Ten healthy volunteers were examined by using ultrafast breath-held PC-MRI. Coronary volume flow rates were measured in the anterior descending coronary artery (LAD) at rest and following intravenous administration of dipyridamole. CFR was determined based on these data. Mean LAD volume flow rates increased from 38 +/- 11 ml/min before application of dipyridamole to 169 +/- 42 ml/min. The mean CFR amounted to 5.0 +/- 2.6 (median = 4.15). This study demonstrates the feasibility of breath-held PC-MRI to noninvasively quantify coronary volume flow rates over the cardiac cycle. Pharmacologically induced changes in volume flow rate and thus CFR can be quantitated.

Adult↗

PubMed1997

New approach to patency and flow assessment after left internal thoracic artery hypoperfusion syndrome with additional saphenous vein graft to the left anterior descending artery with phase-contrast magnetic resonance angiography.

OBJECTIVE: Perioperative and early postoperative flow reduction of a left internal thoracic artery conduit is a rare complication of myocardial revascularization and may lead to the potentially fatal left internal thoracic artery hypoperfusion syndrome. It has been advocated that an additional vein graft be placed to the distal left anterior descending artery to provide sufficient myocardial perfusion. Some evidence exists, however, that this high-flow vein might lead to competing or even backward flow through the internal thoracic artery. METHODS: In the past 2 years, 21 patients received an additional vein graft to the distal left anterior descending artery for left internal thoracic artery hypoperfusion syndrome. Nineteen of these patients were available for magnetic resonance imaging. Early (< 6 months) and late (> 12 months) postoperative flow measurements, both in the left internal thoracic artery and in the saphenous vein grafts, were performed by means of conventional and a segmented k-space phase-contrast magnetic resonance angiography technique. RESULTS: Early magnetic resonance examinations indicated that all conduits had adapted to the coronary flow type with predominant diastolic perfusion. Patency rate both at the early and at the late study was 100%. No concurrent flow, flow reversal, or steal phenomena were observed. Mean flow rates were 49.2 ml/min for the left internal thoracic artery and 72.6 ml/min for the saphenous vein graft. CONCLUSION: On the basis of the flow data obtained with magnetic resonance angiography, the use of an additional saphenous vein graft as the treatment of choice in left internal thoracic artery hypoperfusion syndrome does not lead to occlusion of the artery. Conduit flow adaptation to the diastolic predominance occurs in the first 6 months after operation.

Coronary Vessels↗

PubMed1997

MR angiography of patients with peripheral arterial disease before and after transluminal angioplasty.

OBJECTIVE: This study was performed to evaluate the feasibility of using MR angiography for following up patients who have undergone interventional therapy of the infrapopliteal vascular bed. SUBJECTS AND METHODS: Fourteen patients with peripheral vascular disease underwent MR imaging before and after percutaneous transluminal angioplasty (PTA) using a two-dimensional time-of-flight technique (TR/TE, 33/3.9; section thickness, 2.9 mm). As the gold standard, selective digital subtraction angiography was obtained for all evaluated extremities before and after PTA. For data analysis, the distal peripheral arterial system was divided into 11 segments: the popliteal artery; the tibioperoneal trunk; and the proximal, mid, and distal portions of the three trifurcation vessels. Each segment was characterized as normal, mildly diseased, moderately diseased, severely diseased, or occluded. RESULTS: We found overall agreement between the two techniques in 110 segments (71%) and 123 segments (80%) on data obtained before and after PTA, respectively. Before PTA, our interpretation of MR angiograms overestimated 14 lesions (9%). After PTA, we overestimated five lesions (3%) on MR angiograms. We underestimated lesion severity in 30 cases (19%). The high incidence of agreement between the two techniques was reflected by the high Kendall's tau-beta values of .83 and .87 for data obtained before and after PTA, respectively. CONCLUSION: The excellent depiction of the PTA-induced morphologic changes suggests great potential for the use of MR angiograms during interventional follow-up.

Aged↗

PubMed1996

Ultra-high-speed MR imaging.

Conventional magnetic resonance imaging (MRI) has been shown to provide excellent morphological images of the body organs, particularly structures undergoing little physiologic motion. Nevertheless, the clinical usefulness of MRI has been hampered by long acquisition times, high cost of scanning because of limited patient throughput, and image artifacts due to patient motion. With recent technical developments, several ultrafast scanning techniques capable of acquiring images in a breath-hold now find their introduction into clinical use. The system improvements are potentially useful for a vast range of applications hitherto not accessible to MR imaging. Among these are functional brain imaging, realtime imaging of cardiac motion and perfusion, fast abdominal imaging, improved MR angiography, and potentially real-time monitoring of interventional procedures. Whereas some ultrafast techniques can be performed on conventional scanners, echo-planar imaging, the fastest currently available data acquisition strategy, requires specially designed hardware. This article provides an overview of the technical advances in ultrafast MRI and discusses potential applications and the possible future impact on body scanning.

Humans↗

PubMed1996

[Virtual intravascular endoscopy in the renal arteries: a new way of observing 3-D-MIR angiography data sets].

PURPOSE: To determine the potentials and limitations of a recently developed algorithm for virtual intravascular endoscopy (VIE) based on 3-dimensional (3-D) magnetic resonance (MR) data sets. METHOD: The data from 6 patients derived from gadolinium-enhanced MR angiography of the renal arteries were reviewed. All patients had unilateral or bilateral renal arterial pathologies (stenoses n = 2, aneurysms n = 4). Imaging was performed on a 1.5-T scanner using a 3-D gradient-echo MR sequence. The imaging parameters were as follows: TR/TE/flip angle 3.9/1.9/40 degrees, matrix 256 x 192, slice thickness 1.5 to 2 mm, FOV 32 cm, and 48 slices. Image acquisition time was 28 seconds under apnoeia conditions. A total of 60 ml 0.5 molar Gd-DTPA was injected during the scan. RESULTS: 3-D data sets could be obtained in all patients and postprocessed for VIE. The intraluminal vessel wall was depicted with high clarity in all cases. All pathologies that were not intraparenchymal could be easily seen. Limitations to the technique include the image quality of the original data set, use of the ideal threshold to minimise intraluminal artifacts, and a complicated prescription sequence. CONCLUSIONS: We have shown that VIE can be consistently performed in the renal arteries using MR data sets acquired with a contrast enhanced 3-D gradient-echo technique. It provides a hitherto unused approach to viewing 3-D vascular MR data sets.

Adolescent↗

PubMed1996

Serial myoglobin levels for patients with possible myocardial infarction.

OBJECTIVES: To determine the sensitivity and specificity of a new myoglobin assay for acute myocardial infarction (AMI), considering both the total amount of serum myoglobin and its percentage change over 2 hours. METHODS: A prospective, observational test performance study for the recognition of AMI was done using serial myoglobin assays of 42 admitted chest pain patients at a large, urban teaching hospital ED. Myoglobin testing was performed at presentation (time 0) and at 1 and 2 hours after arrival. A myoglobin level > 100 micrograms/L (ng/mL) or a change > or = 50% from baseline (increase or decrease) any time during the 2-hour period was considered positive. Patients and their physicians were blinded to the myoglobin results. The managing clinician's final diagnosis of the presenting event was used as the diagnostic criterion standard. RESULTS: The sensitivity of the myoglobin technique for detection of AMI in the first hours in the ED was 13/14 (93%; 95% CI: 66-100%). The 1 patient who had a false-negative test had evidence of AMI on the ECG and an initially abnormal creatine kinase-MB (CK-MB) assay. The specificity was 22/28 (79%; 59-92%). However, of the 6 patients who had "false-positive" myoglobin tests, all had serious illness: significant cardiac disease (n = 4), in-hospital death (n = 1), or deep venous thrombosis (n = 1). CONCLUSION: Myoglobin level determinations are sensitive tests to detect AMI during the first 2 hours of a patient's stay in the ED and may complement current clinical tools.

Adolescent↗

PubMed1996

Human aorta: preliminary results with virtual endoscopy based on three-dimensional MR imaging data sets.

PURPOSE: To determine the feasibility of use of magnetic resonance (MR) imaging data sets to perform virtual intraarterial endoscopy (VIE). MATERIALS AND METHODS: Seven female and 14 male patients (aged 9-86 years [mean, 42 years]) with various pathologic aortic conditions underwent three-dimensional gadolinium-enhanced spoiled gradient-echo MR imaging. With prototype software, VIE postprocessing algorithms (based on ray casting) were applied to the imaging data sets. Findings at conventional angiography were used as the standards of reference. RESULTS: The vessel wall was seen from the inside in each case, and the following pathologic conditions were depicted clearly: the two lumina in a congenial double aortic arch and the single lumen after correction, vessel narrowing in coarctations, characteristics of Leriche syndrome, stenoses, occlusions, and the true and false lumina of dissections. CONCLUSIONS: Limitations of VIE include the image quality of the original data set, the threshold chosen to minimize intraluminal artifacts, and the inherent smoothing of vessel walls.

Adult↗

PubMed1996

Breath-hold, contrast-enhanced, three-dimensional MR angiography.

Breath-hold gadolinium-enhanced three-dimensional magnetic resonance (MR) angiography was performed with a high-performance gradient MR imaging system in 10 volunteers with no history of vascular abnormalities (breath-hold interval, 28 seconds; repetition time, 4.0 msec; echo time, 1.9 msec; 0.4 mmol gadoterate meglumin per kilogram of body weight). High-resolution three-dimensional time-of-flight angiograms of the aorta, renal arteries, pulmonary arteries, pelvic arteries, and portal venous system were successfully acquired in all cases.

Adolescent↗

PubMed1995

[MRI venous angiography of the abdomen].

The assessment of abdominal vessels by conventional methods is invasive and frequently does not yield an accurate diagnosis, particularly in evaluation of the portal venous system. MR angiography is non-invasive and is well suited to the examination of abdominal veins. Both vessel morphology and intravascular flow patterns can be characterized with this method. Clinical indications include portal hypertension, portal vein thrombosis, portosystemic shunts as well as assessment of congenital anomalies, thrombus and tumor propagation into the inferior vena cava and the renal veins. In the future MR angiography is likely to evolve into the modality of choice for non-invasive evaluation of abdominal venous structures.

Abdomen↗

PubMed1995

Kidney transplantation in diabetic patients using cyclosporine. Five-year follow-up.

OBJECTIVE: To review our center's experience with kidney transplantation in diabetic recipients; specifically, to compare long-term (5-year) patient and graft survival rates between diabetic and nondiabetic recipients overall and according to donor source using cyclosporine-based immunosuppression. DESIGN: A retrospective review of all kidney transplants performed over the 7-year period from 1987 to 1993. SETTING: A large urban tertiary care referral center with a long history of kidney transplantation and care of the diabetic patient. PATIENTS: All patients receiving a kidney transplant, either alone or simultaneously with a pancreas transplant, were reviewed. MAIN OUTCOME MEASURES: Actuarial patient and graft survival, serum creatinine levels, and causes of late graft loss. RESULTS: There was no significant difference in actuarial 5-year patient or kidney graft survival between diabetic and nondiabetic recipients overall or when analyzed by donor source. There was no significant difference in mean serum creatinine levels at 5 years between diabetic and nondiabetic recipients overall or between diabetic and nondiabetic cadaveric recipients. While chronic rejection was the major cause of late graft loss in nondiabetic recipients, death with a functioning graft, principally due to cardiovascular disease, was the major cause of graft loss in diabetic recipients. CONCLUSIONS: With cyclosporine-based immunosuppression, diabetic kidney transplant recipients have 5-year patient and graft survival rates and allograft function comparable to nondiabetic recipients. Given the high mortality of diabetic patients receiving dialysis, kidney transplantation is the treatment of choice for end-stage diabetic renal disease.

Actuarial Analysis↗

PubMed1995

Evaluation of ultrafast phase-contrast imaging in the thoracic aorta.

PURPOSE: Two ultrafast phase-contrast (PC) data acquisition strategies, multishot echo-planar imaging (EPI)-PC and segmented k-space fast gradient-echo PC (FASTCARD-PC) were evaluated with regard to their measurement accuracy. MATERIALS AND METHOD: Flow measurements of the ascending and descending aorta were acquired in 10 healthy volunteers with an electrocardiogram (ECG)-triggered eight-shot EPI-PC sequence (TR/TE/flip 16/7.4/45 degrees, 32-ms flow-phase interval, 2 x 2 mm in plane resolution), and FASTCARD-PC (six k-lines per band, TR/TE/flip 11/6.1/45 degrees, 132-ms flow-phase interval, 2 x 1 mm in plane resolution). These were compared to flow-volume data acquired with conventional cine-PC (TR/TE/flip 24/7/45 degrees, 48-ms flow-phase interval, 2 x 1 mm in plane resolution). Using cine-PC as a gold standard, the measurement accuracy of FASTCARD-PC and EPI-PC were determined. RESULTS: Both EPI-PC and FASTCARD-PC significantly reduced data acquisition times compared to cine PC. EPI-PC flow measurements correlated well with aortic cine-PC flow-volume determinations (r = 0.98). Reflecting poorer temporal resolution, FASTCARD-PC measurements were less accurate (p < 0.05), evidenced by poor correlation with cine-PC data (r = 0.62). CONCLUSION: Ultrafast PC measurements are possible. In contrast to the segmented k-space PC technique, which is limited in temporal resolution, multishot EPI-PC provides high measurement accuracy in pulsatile vessles while keeping the image acquisition interval short enough for a comfortable breath-hold.

Adult↗

PubMed1995

Ketorolac versus meperidine-plus-promethazine treatment of migraine headache: evaluations by patients.

This study was designed to compare and contrast the speed and efficacy of meperidine (75 mg)/promethazine (25 mg) intramuscularly to ketorolac (60 mg) intramuscularly, in a double-blind study in reducing the symptoms of migraine headache. Forty-two patients who presented to the emergency department between July 1992 and February 1993, with previous diagnoses of migraine headache, were considered for this study. Patients subjectively evaluated parameters of their migraine headaches (eg, pain and nausea) using a numeric scale and were later asked to reevaluate these same parameters at 30, 60, and 360 minutes after a single intramuscular injection of either ketorolac (60 mg) or meperidine (75 mg)/promethazine (25 mg). Sixty-eight percent of patients given meperidine/promethazine responded whereas 55% of patients given ketorolac responded. The responder group showed a statistically significant reduction in headache within 30 minutes with both drug regimens. There was no statistically significant difference between the number of responders in either group. The responders from both groups had relief that lasted 6 hours after injection. In the nonresponder groups, most of the patients withdrew within 1 hour after treatment. As determined by patient response to treatment of their migraine headaches, there was no statistically significant difference between the ketorolac and the meperidine/promethazine groups.

Adult↗

PubMed1995

Mycoplasma pneumoniae and Mycoplasma genitalium mixture in synovial fluid isolate.

A mycoplasma cultured from synovial fluid specimens from a patient with pneumonia and subsequent polyarthritis was identified initially as Mycoplasma pneumoniae. In retrospective studies, the culture was shown also to contain Mycoplasma genitalium. In this paper, the laboratory techniques employed in the identification and separation of the two species are presented, and evidence to implicate postinfectious autoimmunity is provided. An increasing number of reports of M. genitalium in human tissue sites and difficulties in isolation and identification of the organism in the clinical laboratory suggest the need for more extensive application of rapid and specific detection systems for both M. genitalium and M. pneumoniae in the clinical laboratory.

Animals↗

PubMed1995

Real-time biplanar needle tracking for interventional MR imaging procedures.

PURPOSE: To evaluate real-time biplanar tracking of a specially designed needle with magnetic resonance (MR) imaging guidance. MATERIALS AND METHODS: The needle is made of polyetheretherketone and has a miniature radio-frequency coil incorporated into the tip. Tracking software on two workstations is used to compute three-dimensional coordinates of the coil and to display the position as a moving symbol in two imaging planes. Validation of needle tracking was performed in a harvested human liver. T2-weighted fast spin-echo images were used to target a 1-cm cyst. Success of needle placement was confirmed with aspiration and with updated gradient-recalled-echo images. RESULTS: The cyst was successfully targeted from different approaches. Tracking procedures were monitored in real time simultaneously on two separate images. CONCLUSION: Real-time biplanar needle tracking may prove to be useful for both diagnostic and therapeutic interventional MR imaging procedures.

Artifacts↗

PubMed1995

In vivo reduction of bacterial populations in the urinary tract of catheterized sheep by iontophoresis.

PURPOSE: Iontophoresis kills microbes in vitro and, therefore, may be a useful method for eliminating microbial populations associated with catheter-induced urinary tract infections in vivo. MATERIALS AND METHODS: Catheters were modified to deliver current to platinum electrodes in the catheter tip. Female sheep were catheterized with this iontophoretic catheter and left ambulatory. In 5 sheep (experimental group) 400 microA was applied to the catheter and withheld in 4 sheep (control group) for 20 to 21 days. The animals were then sacrificed. During the study, types and concentrations of bacteria, and physical and chemical characteristics of the urine samples were determined. RESULTS: Throughout the study, bacteria levels were reduced in urinary tracts of the experimental group (10(3) to 10(4) microbes per ml.) compared with the control group (10(7) microbes per ml.), without extensive alterations to urine chemistry or the sheep urinary tract. CONCLUSIONS: Since iontophoresis safely reduced bacterial populations in catheterized sheep, this technology may reduce or eliminate nosocomial, catheter-induced urinary tract infections in humans.

Animals↗

PubMed1995

[Fast and ultra-fast MRI imaging of the heart].

Conventional magnetic resonance imaging (MRI) is capable of providing satisfactory morphological images of the heart and the surrounding structures. It has further evolved into a well accepted modality for functional cardiac studies such as flow quantification and volumetry. MRI has, however, been hampered by long image acquisition times. This combined with its non-real-time nature and the limited spatial resolution hs made it difficult to extend MRT to the study of small cardiac structures. Recent technical improvements have made breath-held or real-time MRI feasible and thus laid the foundations for further applications in the field of cardiovascular imaging, notably MR coronary angiography, imaging of cardiac valve leaflets, as well as first-pass perfusion studies. Moreover ultrafast MR techniques may eventually replace conventional data acquisition strategies and thus drastically increase patient throughput by shortening acquisition time. This article provides an overview of the technical advances in MRI and their application to the cardiovascular system and discusses possibilities of combined ultrafast and interventional strategies.

Echo-Planar Imaging↗