The effect of hypothermic pulsatile perfusion on glomerular epithelial surface structures studied by scanning electron microscopy.
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Cadaver↗
Biomedical subjects
L Axel
Publications and source records attributed to L Axel.
Flow limits of Kedem-Katchalsky equations for fluid flux.
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Diffusion↗
Elimination of Nyquist ghosts in MRI by using fast linogram imaging.
Timing inaccuracies between the even and odd echoes lead to the formation of Nyquist ghosts in conventional (blipped) echo-planar imaging (EPI). A fast radial scanning method based on the linogram sampling geometry was designed and implemented. No ghosting effects are seen with this scheme, and correction for timing inaccuracies is performed using simple postprocessing steps before reconstruction.
Artifacts↗
Determination of global function and regional mechanics of dynamic cardiomyoplasty using magnetic resonance imaging.
This study used tissue tagged magnetic resonance (MR) to assess regional strain and generate pressure-volume (PV) loops in a canine model of cardiomyoplasty (CMP). Three dogs with rapid ventricular pacing induced heart failure underwent dynamic CMP chronic cardiac assistance for 1 year. At the end of the study period, we performed a MR study with the myostimulator "on" and "off" and recording of left ventricular (LV) pressure. We determined the short axis displacement (D) and maximal and minimal principal strains (lambda1 and lambda2) by quantitative two-dimensional regional spatial modulation of magnetization visualization utility image analysis. LV PV loops were generated by combining the LV volume data from the MR images with the LV pressure recorded during imaging. Muscle stimulation produced a leftward shift of the LV PV loops in two of the three dogs, and an increase in LV peak pressure and dp/dt max. In contrast, short axis lambda1 and lambda2 did not change significantly (p = NS). D increased significantly in the anterolateral, posterolateral, and posteroseptal regions (p < 0.05) but did not change for the septal region (p = NS). Flap stimulation augments LV function in the absence of short axis strain change; this suggests that dynamic CMP exerts its main action along the long axis of the heart.
Animals↗
Dynamic cardiomyoplasty decreases myocardial workload as assessed by tissue tagged MRI.
The effects of dynamic cardiomyoplasty (CMP) on global and regional left ventricular (LV) function in end-stage heart failure still remain unclear. MRI with tissue-tagging is a novel tool for studying intramyocardial motion and mechanics. To date, no studies have attempted to use MRI to simultaneously study global and regional cardiac function in a model of CMP. In this study, we used MRI with tissue-tagging and a custom designed MR compatible muscle stimulating/pressure monitoring system to assess long axis regional strain and displacement variations, as well as changes in global LV function in a model of dynamic cardiomyoplasty. Three dogs underwent rapid ventricular pacing (RVP; 215 BPM) for 10 weeks; after 4 weeks of RVP, a left posterior CMP was performed. After 1 year of dynamic muscle stimulation, the dogs were imaged in a 1.5 T clinical MR scanner. Unstimulated and muscle stimulated tagged long axis images were acquired. Quantitative 2-D regional image analysis was performed by dividing the hearts into three regions: apical, septal, and lateral. Maximum and minimum principal strains (lambda, and lambda2) and displacement (D) were determined and pooled for each region. MR LV pressure-volume (PV) loops were also generated. Muscle stimulation produced a leftward shift of the PV loops in two of the three dogs, and an increase in the peak LV pressure, while stroke volume remained unchanged. With stimulation, lambda1 decreased significantly (p<0.05) in the lateral region, whereas lambda2 increased significantly (p<0.05) in both the lateral and apical regions, indicating a decrease in strain resulting from stimulation. D only increased significantly (p<0.05) in the apical region. The decrease in strain between unassisted and assisted states indicates the heart is performing less work, while maintaining stroke volume and increasing peak LV pressure. These findings demonstrate that the muscle wrap functions as an active assist, decreasing the workload of the heart, while preserving total pump performance.
Animals↗
Assessment of synchronized direct mechanical ventricular actuation in a canine model of left ventricular dysfunction.
Direct mechanical ventricular actuation (DMVA) is an experimental procedure that provides biventricular cardiac assistance by intracorporeal pneumatic compression of the heart. The advantages this technique has over other assist devices are biventricular assistance, no direct blood contact, pulsatile blood flow, and rapid, less complicated application. Prior studies of nonsynchronized DMVA support have demonstrated that a subject can be maintained for up to 7 days. The purpose of this study was to determine the acute hemodynamic effects of cardiac synchronized, partial DMVA support in a canine model (RVP) of left ventricular (LV) dysfunction. The study consisted of rapidly pacing seven dogs for 4 weeks to create LV dysfunction. At the conclusion of the pacing period, the DMVA device was positioned around the heart by means of a median sternotomy. The animals were then imaged in a 1.5 T whole body high speed clinical MR system, with simultaneous LV pressure recording. Left ventricular pressure-volume (PV) loops of the nonassisted and DMVA assisted heart were generated and demonstrated that DMVA assist shifted the loops leftward. In addition, assist significantly improved pressure dependent LV systolic parameters (left ventricular peak pressure and dp/dt max, p < 0.05), with no diastolic impairment. This study demonstrates that DMVA can provide synchronized partial assist, resulting in a decrease in the workload of the native heart, thus having a potential application for heart failure patients.
Animals↗
A simple way to estimate the size of a pneumothorax.
An approximate formula relating the volume of a pneumothorax to the decrease in linear dimensions of the lung is presented. For a small pneumothorax, the fractional volume occupied by pneumothorax is three times the fractional decrease in linear dimensions of the lung. These relationships were demonstrated with a simple phantom.
Humans↗
Measurement of cardiac output by computed transmission tomography.
The capability of computed tomography (CT) scanning to measure cardiac output was explored using ten anesthetized dogs, and the results were compared with those obtained by thermodilution. Dynamic CT scans were performed at the level of the aortic root while small peripheral intravenous boluses of contrast medium were injected. Time/density curves were generated using a gamma variate fitting program. These were used to estimate cardiac output by applying indicator dilution principles. CT results correlated favorably (r = 0.86) with those of thermodilution. This feasibility study indicates the utility of CT for obtaining physiologic measurements of cardiac function and should encourage further studies to develop the potential of CT for cardiovascular diagnostic purposes.
Animals↗
Tissue mean transit time from dynamic computed tomography by a simple deconvolution technique.
In order to calculate the mean transit time of tissue, such as brain, from dynamic computed tomography performed after a bolus injection of intravenous contrast material, the time dependence of the input of contrast material to the tissue must be "deconvolved" from the observed time course of the tissue contrast enhancement. If the approximate shape of the curve of the response of the tissue to an instantaneous injection of contrast material is assumed, the width of this curve that gives the best fit to the observed tissue response can be used to find a value for the tissue mean transit time. Applying this technique to dynamic CT scans of two normal volunteers yielded values comparable to those in the literature by other techniques. The method has the advantages of being simple to implement, relatively insensitive to noise and the details of the assumed curve shape, and not requiring any curve fitting to correct for recirculation.
Blood Circulation↗
Functional imaging of the liver. New information from dynamic CT.
In order to assess their potential usefulness in conjunction with dynamic CT scans of the liver, functional images of several variables related to blood flow were created from dynamic CT scans of 15 patients with a variety of liver diseases. Seven of the patients received intra-arterial and intravenous boluses of contrast; the other eight received intravenous boluses alone. Intra-arterial contrast injections yielded superior functional images, but useful functional images could also be created from studies with intravenous boluses. Although respiratory motion artifacts caused some problems, images that can be interpreted in terms of effective distribution volume, transit time, and blood flow were successfully created. Functional imaging of the liver can provide a useful display of regional physiologic differences.
Breast Neoplasms↗
MR imaging of venous and arterial flow by a selective saturation-recovery spin echo (SSRSE) method.
Flow velocity imaging studies have been conducted by means of a selective saturation-recovery spin echo technique, and the dependence of signal amplitude on interpulse interval, echo delay, slice-selection gradient, and flow velocity was evaluated experimentally. The simple theory predicting a steady increase of signal intensity with increasing interpulse interval until this latter equals the transit time could be verified in phantoms and was shown to permit measurement of blood flow velocity in venous structures such as the femoral vein. The flow phantom experiments further showed that the final intensity, attained when inversion time (TI) = transit time, decreases with increasing flow velocity, an effect that cannot be explained by influx of spins between the 90 degree detection pulse and the 180 degree refocusing pulse. This signal reduction is due to slice-selection gradient-induced phase shifts across the pixel, caused by the intralumenal velocity gradient, leading to destructive interference of the spin isochromats. The velocity distribution can be mapped by plotting signal intensity as a function of interpulse interval for pixels in different radial positions. To highlight arterial flow, gating is required with the acquisition delay selected such that the interpulse period TI falls in a time zone of slow flow within the cardiac cycle. By subtracting images recorded with different acquisition delays, flow images showing arterial enhancement only can be obtained, as illustrated for the femoral artery in the thigh.
Blood Flow Velocity↗
MR imaging of double aortic arch.
Magnetic resonance was used to demonstrate a double aortic arch in a patient initially noted to have a right aortic arch on chest radiography.
Aorta, Thoracic↗
MR flow imaging by velocity-compensated/uncompensated difference images.
The phase shifts acquired by motion of excited spins along magnetic field gradients can result in decreased signal intensity from blood vessels in conventional magnetic resonance images. The imaging technique can be modified with the use of additional gradient pulses so as to either compensate these phase shifts and increase the signal from the vessels or augment the phase shift and decrease the signal, without altering the signal from stationary tissues. Making a difference image from images made with and without sensitization to motion will cancel out the stationary tissues, leaving an image of the vessels alone. The technique does not require cardiac gating, shows veins as well as arteries, and can be performed in an interleaved manner to avoid registration errors due to patient motion.
Animals↗
MR imaging of normal extrahepatic bile ducts.
Abdominal scans of 48 patients without evidence of biliary tree or pancreatic head pathology were retrospectively evaluated to determine how often the normal common bile duct (CBD) could be visualized, as well as to determine which projections and pulse sequences optimized its visualization. Axial sequences with long repetition time (TR) and for echo time (TE) intervals (2,000-2,500 and 60-80 ms, respectively) were the most useful, identifying the normal CBD in 15 of 30 diagnostic studies. Axial sequences using short TR/TE intervals (300-800 and 20-25 ms, respectively) were less informative, identifying the CBD in only eight of 30 studies. Coronal studies were not useful, identifying the CBD in only one of 10 long TR/TE pulse sequences.
Bile Ducts↗
Correlation of cine MR imaging with two-dimensional pulsed Doppler echocardiography in valvular insufficiency.
Eight adults with known valvular insufficiency were studied with cine magnetic resonance (MR) imaging. Our cine MR uses cardiac synchronization of a rapid small flip angle pulse sequence on a 1.5 T MR system. Eleven regurgitant lesions (including aortic, mitral, and tricuspid valves) were imaged with both cine MR and two-dimensional pulsed Doppler echocardiography (2-DPDE). In each case of significant regurgitation the jet of valvular insufficiency was easily seen as a discrete area of low signal with cine MR. Not only was the regurgitant jet identified but also its relative severity agreed well with the 2-DPDE results. In two patients the regurgitant lesions were identified on cine MR prior to 2-DPDE. In addition to the regurgitant jet, chamber enlargement and wall thickening were also well demonstrated. Cine MR is a promising modality for both the detection and semiquantification of valvular insufficiency.
Aortic Valve Insufficiency↗
MR imaging of focal nodular hyperplasia of the liver.
The magnetic resonance appearance of three lesions of focal nodular hyperplasia observed in two patients is reviewed. All three lesions demonstrated isointensity with the liver on the short repetition time (TR) and echo time (TE) spin echo images. One lesion also showed a central area of low signal intensity that pathologically corresponded to a scar. The long TR and TE images had a varied appearance, from mixed high signal intensity to predominantly isointense with the liver. The histopathology for each lesion was carefully reviewed. The primary microscopic difference between the lesion that was predominantly isointense with liver on the long time TR and TE images and the other two, which were of mixed high signal intensity on the long time TR and TE images, was the former's relative lack of fibromuscular obliteration of septal blood vessels in the scar. Focal nodular hyperplasia can have at least two possible appearances at 1.5 T; in these three lesions there was consistent isointensity with the liver on the short TR and TE images.
Adult↗
Cine MR imaging in aortic stenosis.
The potential of cine magnetic resonance (MR) imaging for the assessment of aortic stenosis (AS) was investigated in 17 patients. The severity of AS was graded by continuous wave Doppler ultrasound as severe in 10 of 17 patients and as moderate in the remaining 7 patients. Cine MR demonstrated a flow disturbance proximal and/or distal to the aortic valve plane in all 17 patients. This flow disturbance was seen as a signal void with four typical features: (a) a high-velocity jet phenomenon distal to the valve plane during systole, closely related to the stenotic orifice (8 of 17); (b) a turbulent systolic signal void in continuity with the jet, which propagated for a variable extent into the aorta (17 of 17); (c) a signal void just proximal to the valve plane during systolic ejection, reflecting prestenotic acceleration of blood flow (5 of 17); and (d) a void at the valve plane due to valvular calcifications (14 of 17). The following features or a combination thereof appeared to correlate with more severe grades of AS as visualized on cine MR display: (a) identification of narrow high-velocity jet phenomenon; (b) extensive propagation of the turbulent signal void into the aorta; and (c) presence of a prestenotic acceleration effect. Assessment of the severity of AS with cine MR is still limited. However, cine MR can identify the presence of AS and several flow phenomena that correlate with more severe degrees of stenosis.
Aortic Valve Stenosis↗