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PubMed1987

Rapid scan magnetic resonance angiography.

The change in phase of transverse spin magnetization induced by macroscopic spin motion in the direction of an applied magnetic field gradient is used to generate projection angiograms. The method can provide a quantitative measure of laminar and pulsatile flow. Cardiac synchronization is not required provided that data are acquired at many points in the cardiac cycle. The use of short TR and a large number of excitations provides better suppression of stationary tissue and patient motion artifacts than is possible with cardiac gated studies. In addition to improvements in image quality, a substantial shortening of scan time is obtained.

Angiography↗
PubMed1988

Fast limited flip angle MR subtraction angiography.

A fast MR angiography method is introduced that is capable of generating difference images of blood vessels in scan times of 10-20 s. This is an order of magnitude faster than many previous methods. The fundamental concept of this approach is to use cardiac gating and acquire several phase encodings at least twice during each cardiac cycle using limited flip angles (LFAs) and repetition times in the 20 to 50 ms range. The encodings acquired during diastole are subtracted from those acquired during systole to generate the difference image. The contrast in the difference image is due both to the influx of unsaturated spins and to the loss of phase coherence of systolic blood moving at high velocity along a magnetic gradient. The systolic peak of the cardiac cycle is determined during reconstruction by shifting the systolic and diastolic "windows" until the difference signal is maximized. Ghost artifacts due to pulsatile flow are eliminated by a phase reordering technique similar in concept to those developed for suppression of breathing artifacts. Arteries in thick slices are successfully imaged and initial in vivo results are presented.

Angiography↗
PubMed1993

Quantitative measurement of velocity at multiple positions using comb excitation and Fourier velocity encoding.

An MR imaging technique that simultaneously acquires Fourier velocity encoded data from multiple stations is described. The technique employs a comb excitation rf pulse that excites an arbitrary number of slices. As the Fourier velocity phase encoding gradient pulse is advanced, the phase of each slice is the comb is advanced by a unique amount. This causes the signals from the spins in a particular slice to appear at a position in the phase encoding direction, which is the sum of the spin velocity and an offset arising from the phase increment given to that excitation slice. Acquisition of spin velocity information occurs simultaneously for all slices, permitting the calculation of wave velocities arising from pulsatile flow. These wave velocities can then be used to determine vessel distensibility.

Fourier Analysis↗
PubMed1996

Temporally resolved 3D phase-contrast imaging.

A conventional 3D phase contrast acquisition generates images with good spatial resolution, but often gives rise to artifacts due to pulsatile flow. 2D cine phase contrast, on the other hand, can register dynamic flow, but has a poor spatial resolution perpendicular to the imaging plane. A combination of both high spatial and temporal resolution may be advantageous in some cases, both in quantitative flow measurements and in MR angiography. The described 3D cine phase contrast pulse sequence creates a temporally resolved series of 3D data sets with velocity encoded data.

Electrocardiography↗
PubMed1998

FID-based lung MRI at 0.5 T: theoretical considerations and practical implications.

Pulse sequences based on FID signals and projection reconstruction (PR) were investigated for lung MRI at 0.5 T and evaluated for artifacts caused by: (1) k-space mismapping due to either delay or distortion of the readout gradient waveform, (2) cardiac motion and pulsatile flow, and (3) respiratory motion. Nonstructured artifacts were described, simulated, and experimentally confirmed for the first time. Nonstructured artifacts did not impair the demonstration of structures of high signal-to-noise ratio (SNR) but generated quantitative errors in the image intensity analysis over the lung parenchyma. The use of FID-based PR techniques for lung MRI is not justified at 0.5 T.

Artifacts↗
PubMed2006

Incoherent artefact correction using PPI.

Multiple coils provide extra information about a patient which is frequently used to shorten exam times. This review looks at how the extra information might be used to reduce incoherent artefacts arising from physiological processes such as motion or pulsatile flow.

Algorithms↗
PubMed1996

ePTFE coating with fibrin glue, FGF-1, and heparin: effect on retention of seeded endothelial cells.

In an attempt to improve the resistance of seeded endothelial cell (EC) to desquamation due to shear stress, we evaluated the effect of coating expanded polytetrafluoroethylene (ePTFE) grafts with fibrin glue (FG) containing fibroblast growth factor 1 (FGF1) and heparin on the retention of EC exposed to pulsatile flow ex vivo. Five pairs of ePTFE grafts (30 microm internodal distance, 4 mm internal diameter, 7 cm long) were coated with either FG/FGF-1/heparin (fibrinogen 32.1 mg/ml, thrombin 0.32 U/ml, FGF-1 11 ng/ml, heparin 250 U/ml) or fibronectin (FN) (20 microgram/ml). Canine jugular vein endothelial cells (Factor VIII, passages 5-7), were radiolabeled with indium-111 (100 microCi/1 million cells). Cell seeding (3 x 10(5) cells/cm2) was achieved by four successive inoculations of cells separated by 90 degree graft rotations. After overnight incubation (37 degrees C), pairs of FG and FN grafts (5 cm long) were simultaneously perfused ex vivo with culture media containing 10% fetal bovine serum (120/80 mm Hg, 90 cc/min, 60 pulsations/min). During the 1-hr perfusion, perfusate samples were taken at 0, 5, 15, 30, and 60 min to determine radioactivity loss. Pre- and postperfusion whole graft radioactivity data were compared to estimate cell retention and confirmed by histologic evaluation. Mean adherent radioactivity on FG-coated grafts (96 +/- 5%) was significantly higher (P = 0.0029, Student's t test) than on FN-coated grafts (85 +/- 3%). Maximum radioactivity loss in perfusate was seen after 5 min, with lower sustained loss thereafter. The improved retention of seeded EC on ePTFE grafts coated with FG containing FGF-1 and heparin compared to FN will need to be confirmed for longer durations of perfusion and using in vivo models.

Animals↗
PubMed1997

Rapid postincubation endothelial retention by Dacron grafts.

Defining the most appropriate conditions for strengthening the retention of endothelial cells (ECs) by small-diameter prosthetic endothelialized grafts is indispensable to their clinical application. The incubation time after seeding is one of the most important factors in EC retention. The effects of different postincubation times (0, 2, 4, 8, 16, 24, and 36 hr) on EC monolayers on two different types of graft, fibronectin-coated expanded polytetrafluoroethylene (ePTFE) and collagen-coated knitted Dacron grafts (4 mm x 5 cm) were examined. In situ counting of ECs on the grafts was performed by light microscopy. The percentage cell retention was calculated by dividing the cell counts for grafts exposed to pulsatile flow for 90 min by those for control grafts. To characterize the EC coverage of the grafts, scanning electron microscopy was also performed. The average cell density of control grafts ranged from 5.59 +/- 1.1 to 6.69 +/- 1.5 x 10(4) cells/cm2 and did not differ according to the kind of graft or incubation time. The knitted Dacron grafts showed the maximal cell retention (88 +/- 5%) after incubation for 8 hr, whereas ePTFE grafts did so after 24 hr (83 +/- 6%). Scanning electron microscopic examination after incubation for 8 hr revealed that the density of human ECs on the surfaces of ePTFE and Dacron grafts differed, although there was no morphological difference between the ECs on the two types of graft. Knitted Dacron grafts achieved a high percentage retention in a shorter time than ePTFE grafts.

Blood Vessel Prosthesis↗
PubMed2002

Investigating cervical spinal cord structure using axial diffusion tensor imaging.

This study describes a new technique for Diffusion Tensor Imaging (DTI) that acquires axial (transverse) images of the cervical spinal cord. The DTI images depict axonal fiber orientation, enable quantification of diffusion characteristics along the spinal cord, and have the potential to demonstrate the connectivity of cord white matter tracts. Because of the high sensitivity to motion of diffusion-weighted magnetic resonance imaging and the small size of the spinal cord, a fast imaging method with high in-plane resolution was developed. Images were acquired with a single-shot EPI technique, named ZOOM-EPI (zonally magnified oblique multislice echo planar imaging), which selects localized areas and reduces artefacts caused by susceptibility changes between soft tissue and the adjacent vertebrae. Cardiac gating was used to reduce pulsatile flow artefacts from the surrounding cerebrospinal fluid. Voxel resolution was 1.25 x 1.25 mm(2) in-plane with 5-mm slice thickness. Both the mean diffusivity (MD) and the fractional anisotropy (FA) indices of the cervical spinal cord were measured. The FA index demonstrated high anisotropy of the spinal cord with an average value of 0.61 +/- 0.05 (highest value of 0.66 +/- 0.03 at C3), comparable to white matter tracts in the brain. The diffusivity components parallel and orthogonal to the longitudinal axes of the cord were lambda( parallel) = (1648 +/- 123) x 10(-6) mm(2)s(-1) and lambda( perpendicular) = (570 +/- 47) x 10(-6) mm(2) s(-1), respectively. The high axial resolution allowed preliminary evaluation of fiber connectivity using the fast-marching tractography algorithm, which generated traces of fiber paths consistent with the well-known cord anatomy.

Algorithms↗
PubMed1988

Correlation of laser-Doppler-velocity measurements and endothelial cell shape in a stenosed dog aorta.

Laser-Doppler-velocity measurements were carried out in an elastic 1:1 true-to-scale silicone rubber model of a dog aorta with stenosis. The model was constructed from a cast of a severely stenosed dog aorta (71% of its area). The stenosis in the dog aorta was prepared by wrapping a cotton band around the aorta. This band was tightened until the presence of a thrill or a bruit was felt distal to the band. Twelve weeks later the animal was sacrificed and a cast was prepared from the aorta. From this vascular cast, the cross-sectional area was calculated. Endothelial cell geometry and orientation was studied using computerized analysis to determine the cell area and shape index. An elastic silicone rubber model was prepared from the cast to measure the velocity profiles and to estimate the local wall shear stress. Velocity measurements were done at steady and pulsatile flow using a Newtonian aqueous-glycerol solution and a non-Newtonian blood-like fluid. From those velocity measurements the velocity gradients near the wall were determined and the shear stress calculated. The flow distal to the stenosis separates from the wall at physiological conditions. The endothelial cells are smaller and more elongated in the throat; distal to the stenosis they are larger and rounder. The shape index distribution along the stenosed aorta is correlated with the level of wall shear stress. It is shown that even low changes in the wall shear stress have an influence on the orientation of the endothelial cells.

Animals↗
PubMed1988

Interdependence of pharmacologically-induced and endothelium-mediated coronary vasodilation in antianginal therapy.

Recent advances in the understanding of vascular physiology have furnished new aspects in the treatment of angina pectoris by various vasodilators. Upon stimulation by various factors (viscous drag from increased flow, pulsatile stretch, ADP/ATP, norepinephrine, serotonin), the coronary endothelium releases a vasodilator called endothelium-derived relaxant factor (EDRF). This factor has recently been shown to probably be nitric oxide (NO), which is identical to the active compound of nitroglycerin. EDRF (NO) dilates both large epicardial arteries and also coronary resistance vessels. It also has a strong platelet antiaggregant effect. The predominant effect of Ca2+ antagonists is on resistance vessels, increasing myocardial perfusion and viscous drag acting upon the endothelial lining. This, in turn, stimulates EDRF (NO) release in epicardial arteries and dilation. This additional nitrate-like effect augments the direct vasodilator effect of Ca2+ antagonists. Lack of normal endothelial function results in diminished capacity to dilate, and sometimes even in a shift from dilator to constrictor effects, paralleled by an increased tendency for platelet adhesion, activation, and thrombosis, which is still enhanced when plasma low density lipoprotein (LDL) is augmented. EDRF release, vasodilator capacity, and antiaggregant effects are reduced when LDL is high. Nitrates have a direct, endothelium-independent dilator effect, particularly on large coronary arteries, which seems even more pronounced when the endothelium is absent, but only when the vessel segment is still compliant. Therefore nitrates may particularly be effective in vessels with deficient EDRF release.

Angina Pectoris↗
PubMed1988

MR imaging of syringobulbia with giant syrinx.

Syringobulbia with a large syrinx was revealed by MR imaging. The syrinx extended from the medulla to vertebral level T10. We suspect that this giant syrinx may be produced by a congenital meningioma at C7, generating pulsatile flow in the original syrinx and causing a giant syrinx.

Aged↗
PubMed1976

The effects of VIP on intestinal motility: study on ex vivo perfused isolated canine jejunal loops.

The effects of VIP on intestinal motility were studied on isolated canine jejunal loops ex vivo perfused at normothermia, under pulsatile flow with heparinized, oxygenated and nonrecirculated canine whole blood, by means of an intraluminal balloon. VIP was administered intraarterially either by 1 min injections or by long-time infusions. The results showed that for arterial concentrations of the polypeptide ranging between 25 pg/ml and 300-500 pg/ml a fast but short-lasting relaxant effect was observed. For higher concentrations VIP usually produced a biphasic response: The relaxant effect is followed by an increase of the basal muscular tone often accompanied, for concentrations higher than about 25 ng/ml, by a marked and transient increase in amplitude of the intestinal rhythmic contractions. During long-time infusions a biphasic response was also observed but both effects were of short duration. A cholingeric origin of the secondary contracting phase was expected but could not be demonstrated because, at blood concentrations at which atropine affected the biphasic response, not only was the contractile effect abolished but also the initial relaxing phase. It is suggested that the secondary contraction may be a "rebound excitation" of myogenic nature or a result of noncholingeric excitatory fiber stimulations. The short-lasting relaxant effect observed under the present experimental conditions, even during long-time infusion of the polypeptide, fails to argue for an important physiological role of VIP as an hormonal inhibitor of intestinal motility. The biphasic response, however, might have a physiological significance in so far as the aboral propulsion of the intestinal content requires a muscular inhibition which rapidly changes to contraction.

Animals↗
PubMed1992

A simple technique of renal transplant preservation during aortic reconstruction.

Various methods of insuring renal transplant perfusion during aortic reconstruction have been described but these are often complex and troublesome. Although short periods of warm ischemia are probably well tolerated, reinstitution of pulsatile flow is more desirable. A simple method of rapidly restoring renal perfusion during aortic reconstruction is described.

Anastomosis, Surgical↗
PubMed1993

Duplex Doppler examination of renal allografts in children: correlation between renal blood flow and clinical findings.

We reviewed the diastolic blood flow (DBF), pulsatility index (PI), and resistive index (RI) in 211 duplex Doppler ultrasound examinations of 63 pediatric renal transplant recipients. We correlated our findings with the clinical diagnosis, independently determined at the time of ultrasound examination. DBF, evaluated in 202 examinations, was found to be decreased, absent, or reversed in acute rejection (kappa = 0.4, p < 0.01) and acute tubular necrosis (ATN) (kappa = 0.3, p < 0.01). The PI and RI were evaluated in 87 and 78 ultrasound examinations respectively. The range of normal PI and RI values in recipients between six and 18 years of age were similar to those reported in adults. However, normal PI and RI values were somewhat higher in recipients less than six years of age who had received adult donor allografts. Overall, the PI was greater than 1.5 in acute rejection (kappa = 0.3, p < 0.05) and ATN (kappa = 0.3, p < 0.01), but not in chronic rejection (kappa < 0, p = NS). The RI was greater than 0.7 in chronic rejection (kappa = 0.3, p < 0.05) and ATN (kappa = 0.3, p < 0.05), but not in acute rejection (kappa = 0.03, p = NS). We conclude that the PI and RI vary in pediatric recipients of renal allografts and are not associated with a specific clinical diagnosis.

Adolescent↗
PubMed1994

Modulation of pumping function of gastric body and antropyloric contractions.

Gastric and antropyloric phasic contractions control transpyloric pulsatile flow, the major mechanism of gastric emptying. Both the occurrence and patterning of phasic gastric contractions are highly modulated by intestinal feedback mechanisms, with resultant variation in gastric emptying. The observed patterns of these contractions can only be plausibly explained by the action of neural influences on gastric motility. These influences derive from several mechanisms driven by intestinal feedback, central nervous system controls, and higher centers, with transmission of signals via intrinsic enteric pathways and extrinsic nerves. It is suggested that the occurrence and patterning of gastric phasic contractions depend on the spatial specificity and local modulation of the intensity of neural stimulation of gastric muscle. The resultant strength of contraction determines the occurrence and timing of lumen occlusion relative to adjacent regions. The timing of lumen occlusion in adjacent regions may be the major determinant of mechanical outcome.

Animals↗
PubMed1989

Solid state line scan cameras for measuring strain in soft tissues and implants.

The line scan camera, or LSC, is an inexpensive and easily applied technique for optical strain measurement of soft biomaterials. The LSC is based on a linear array of photodiodes; in gauging applications, where measurements between dark/light interfaces are important, the digital nature of the array can be exploited. Advantages of the LSC include low cost, high frequency response, applicability to front- or back-lighted samples, insensitivity to stray and nonuniform lighting as well as to accidental overexposure, ease and linearity of calibration, and lack of temperature sensitivity. With the 1024 element arrays used herein, the relative resolution is theoretically limited to 1 part in 1024, or 0.1%; in practice, the relative resolution is somewhat poorer. LSCs have been successfully used in mechanical tests to measure the diameter of arteries and compliant vascular grafts, the longitudinal strain of vascular grafts, and the dynamic diameter of elastic tube models of graft/artery systems in pulsatile flow visualization experiments.

Animals↗
PubMedDate not supplied

Hepatic artery infusion and chemoembolization in the management of liver metastases.

Hepatic metastases rather than the primary neoplasm usually dictate the course of the disease and patient's survival. For unresectable disease, intraarterial infusion of chemotherapy, embolization, and chemoembolization are viable alternatives. Intraarterial therapy for hepatic metastases is based on the dual blood supply of the normal liver (portal vein, 75%, and hepatic artery, 25%) and that of the tumors (hepatic artery, 90%). Intraarterial infusion delivers a higher concentration of chemotherapy, whereas chemoembolization adds ischemia and increased contact time with the tumor. Selective vascular occlusion for infusion, redistribution of the blood supply and pulsatile flow enhance the delivery of therapeutic agents to the liver.

Antineoplastic Agents↗