Biomedical subjects

D N Firmin

Publications and source records attributed to D N Firmin.

At least 55 records · Page 3Linked to original sources

PubMed1996

Computation of flow pressure fields from magnetic resonance velocity mapping.

Magnetic resonance phase velocity mapping has unrivalled capacities for acquiring in vivo multi-directional blood flow information. In this study, the authors set out to derive both spatial and temporal components of acceleration, and hence differences of pressure in a flow field using cine magnetic resonance velocity data. An efficient numerical algorithm based on the Navier-Stokes equations for incompressible Newtonian fluid was used. The computational approach was validated with in vitro flow phantoms. This work aims to contribute to a better understanding of cardiovascular dynamics and to serve as a basis for investigating pulsatile pressure/flow relationships associated with normal and impaired cardiovascular function.

Algorithms↗

PubMed1996

A comparison of left ventricular myocardial velocity in diastole measured by magnetic resonance and left ventricular filling measured by Doppler echocardiography.

Abnormal diastolic left ventricular function is an early marker for myocardial disease and may be impaired even when global systolic function is normal. Subendocardial function is affected early in ischaemic heart disease and by altering left ventricular long axis motion, may contribute to abnormal transmitral pressure gradients. Regional myocardial long axis velocity in diastole measured by magnetic resonance was compared with left ventricular filling measured by Doppler echocardiography in 25 patients with coronary artery disease. Fifteen patients also underwent magnetic resonance assessment at the time of onset of early diastolic blood flow. The onset of diastolic long axis velocity preceded flow across the mitral valve by a mean of 46 ms. Mean long axis myocardial velocity correlated with peak early filling velocity (E) (r = 0.73, P < 0.001), early deceleration (r = -0.73, P < 0.001), and the early to late filling ratio (E/A) ratio (r = 0.6, P < 0.01). Maximum myocardial long axis velocity also correlated with peak early filling velocity (r = 0.56, P < 0.01), early deceleration rate (r = 0.63, P < 0.001), and the E/A ratio (r = 0.53, P < 0.01). The variability of long axis velocity around the ventricle correlated inversely with peak early filling, (r = -0.7, P < 0.001), early deceleration (r = -0.56, P < 0.01), and the E/A ratio (r = -0.48, P < 0.02). Peak atrial filling velocity did not correlate with any measure of long axis myocardial velocity. We conclude that early diastolic long axis myocardial velocity has a significant effect on left ventricular filling.

Adult↗

PubMed1996

Magnetic resonance coronary angiography in heart transplant recipients.

BACKGROUND: Magnetic resonance angiography (MRA) using segmented k-space fast low-angle shot imaging has recently been used to demonstrate the proximal coronary arteries in healthy subjects and in patients with coronary artery disease. We assessed the sensitivity and specificity of coronary MRA in heart transplant recipients and investigated the feasibility of coronary MRA in patients with metallic sutures and clips in the chest. MATERIALS AND METHODS: Sixteen cardiac transplant patients aged 57.2 +/- 7.9 years (mean +/- SD) were recruited. Forty-eight arterial segments were evaluated, including the left main artery (LMA), left anterior descending artery (LADA) and right coronary artery (RCA). We excluded the left circumflex artery which could not be imaged accurately. The average time between heart transplant operation and MRA was 6 years, whereas that between MRA and X-ray angiography was 4 months. The coronary MRA was interpreted by two experienced investigators who were blinded to the coronary X-ray angiography results. Similarly, the coronary X-ray angiography results were interpreted by two experienced investigators blinded to the MRA results. The coronary arterial segments were classified by MRA as being normal or as having an amount of disease that was significant (> 50% lesion) or insignificant (< 50% lesion). RESULTS: There were 28 true-negative, five true-positive, four false-negative and six false-positive results. Of the 28 true-negative cases, 13 were in the LMA, six in the LADA and nine in the RCA. There was one false-positive LMA, two false-positive LADA and three false-positive RCA stenoses. There were four false-negative results in the LADA and one in the RCA. Clips precluded evaluation in one LMA, one LADA and one RCA. One LMA and one LADA were not evaluated as a result of poor images. One false-positive RCA stenosis was caused by a metallic clip. Three of the false-negative LADA stenoses had lesions in the distal third of the artery. The sensitivity, specificity, negative and positive predictive values were generally poor for the left coronary artery. The best results were for the RCA (sensitivity 100%, specificity 75%, positive predictive value 50% and negative predictive value 100%). The specificity in the left coronary arteries (LMA and LADA) was 86%, but the other indicators were all poorer. For the RCA, LMA and LADA combined, the overall sensitivity was 56%, specificity 82%, predictive accuracy 45% and negative predictive value 88%. In three patients, < 50% RCA lesions were seen in the MRA data, which were all confirmed by angiography. No < 50% lesions were seen in the LMA or in the LADA by MRA or by X-ray angiography. CONCLUSION: Coronary MRA using the segmented fast low-angle shot technique is feasible in heart transplant recipients but the sensitivity and specificity of this method are limited. Further developments in coil design, rapid imaging techniques and respiratory monitoring methods are necessary to improve the accuracy of coronary MRA.

Aged↗

PubMed1996

Assessment of coronary artery stenosis by magnetic resonance imaging.

OBJECTIVE: The findings of magnetic resonance and x-ray angiography were compared for assessment of coronary artery stenosis in this validation study. BACKGROUND: Magnetic resonance angiography of the coronary arteries has recently been described, but there has been no comparison with x-ray angiography of localisation or assessment of important characteristics of coronary stenosis. METHODS: A breath hold, segmented k-space, 2D gradient echo imaging technique incorporating fat suppression was used in 39 patients (55 coronary stenoses) with known coronary artery disease. RESULTS: Overall, 47 stenoses (85%) were assessed by magnetic resonance (29 of 33 stenoses in the left anterior descending artery, one of one in the left main stem, 14 of 17 in the right coronary artery, and three of four in the left circumflex artery were detected). There was close agreement between magnetic resonance and x-ray angiography for the distance of the stenosis from the arterial origin (magnetic resonance mean (SD) 27 (16) mm versus x-ray angiography 27 (16) mm, P = NS, mean difference -0.2 mm). The distance to 39 stenoses (83%) agreed to within 5 mm, with increased scatter for more distal stenoses. The severity of magnetic resonance signal loss, assessed visually at the site of stenosis, varied significantly according to the percentage diameter stenosis (F = 30, P < 0.0001); stenosis severity with severe signal loss was 89 (7)%, with partial signal was 70 (16)%, and with irregular wall only 37 (11)%, with significant differences among the three groups (P < 0.001). A significant correlation was found between the proportional magnetic resonance signal loss at the stenosis and the percentage diameter stenosis severity (r = -0.67, P < 0.0001). The length of stenosis measured by magnetic resonance (6 (3) mm) was greater than by x-ray angiography (5 (2) mm, P < 0.006, mean difference +1.1 mm). Spearman's rank test showed that there was significant overestimation of stenosis length by magnetic resonance as stenosis severity increased (rs = 0.34, P < 0.02). CONCLUSIONS: Accurate localisation of coronary stenosis and a qualitative assessment of stenosis severity are possible by magnetic resonance, but stenosis length is overestimated as severity increases, probably because of disturbed patterns of flow with turbulence distal to severe stenoses. Reasonable results for the detection of coronary artery stenosis by magnetic resonance were achieved in this highly selected population, but further progress in imaging techniques is necessary before moving towards appreciable clinical application.

Angina Pectoris↗

PubMed1995

Magnetic resonance velocity vector mapping of blood flow in thoracic aortic aneurysms and grafts.

Magnetic resonance imaging with multidirectional cine velocity mapping was used to study relationships between aortic blood flow patterns and the geometry of thoracic aortic aneurysms and grafts. Ten patients with 13 thoracic aortic aneurysms, single or multiple, or grafts (4) participated in the study. The causes of disease were atherosclerosis (4), Marfan's syndrome (2), trauma (1), and unknown (1), and there were two dissections. Spin-echo imaging and cine velocity mapping in 10 mm thick slices with vertical and horizontal velocity encoding were done. Maps of the two velocity components were processed into multiple computer-generated streaks whose orientation and length corresponded to velocity vectors in the chosen plane. The dynamic arrow maps were compared with previously reported aortic arrow maps from normal subjects. The forward flow occupied the entire lumen in the normal aorta in systole and small vortices were only present in the sinuses of Valsalva. Atherosclerotic aneurysms in the ascending aorta were located at the anterior right and had oblique, eccentric jet flows that created a large secondary vortex in the aneurysm. Patients with Marfan's syndrome had a central jet and two large vortices, one on each side. All other aneurysms, dissections, and grafts had irregular flows and vortices not seen in normal subjects. Magnetic resonance imaging with multidirectional velocity mapping is a powerful noninvasive tool to assess morphologic features and disturbed blood flow in aortic aneurysms and grafts. Recognizably altered flow patterns were found to be associated with altered vessel geometry. The significance of this requires further investigation.

Adult↗

PubMed1995

Assessment of magnetic resonance velocity mapping of global ventricular function during dobutamine infusion in coronary artery disease.

BACKGROUND: Magnetic resonance imaging (MRI) is a versatile technique for examination of the cardiovascular system but only recently has assessment of myocardial ischaemia in coronary artery disease (CAD) become possible, for example by demonstrating abnormalities of regional ventricular contraction during stress. Global ventricular function during stress was assessed by MRI of aortic flow, which has not been previously attempted. DESIGN: Variables measured by MRI reflecting the effect of ischaemia on global ventricular function during dobutamine stress were correlated with thallium-201 myocardial perfusion tomography. PATIENTS: 10 normal controls and 25 patients with CAD. SETTING: Tertiary cardiac referral centre. METHODS: Novel MRI sequences and analysis systems were used to measure the following variables during staged dobutamine infusion to 20 micrograms/kg/min: stroke volume, cardiac output, cardiac power output, peak flow, peak flow acceleration, aortic back flow, and flow wave velocity. Heart rate, blood pressure, double product, and maximum tolerated dobutamine dose were also measured. Multiple regression analysis was used to compare changes during stress with 201TI tomography. RESULTS: All parameters except for stroke volume and diastolic blood pressure increased in the controls. In the patients with CAD a significant relation was shown between the extent of reversible ischaemia and the change in peak flow acceleration (P < 0.00001), peak flow (P = 0.002), cardiac power output (P = 0.036), maximum dobutamine dose (P = 0.039), and systolic blood pressure (P = 0.04). Peak flow acceleration accounted for 58.4% of the variation in reversible ischaemia, and after allowing for this, only cardiac power output remained independently predictive adding a further 4.2% to the model (adjusted r2 = 0.626). A decrease in peak flow acceleration with an increase in dobutamine infusion indicated moderate or severe ischaemia (chi 2 = 10.2, P = 0.017). CONCLUSION: MRI may be used to assess variables of aortic flow during stress, which includes acceleration with high temporal resolution. Peak flow acceleration was the most sensitive indicator of the effect of ischaemia on global ventricular function.

Adult↗

PubMed1994

Real time blood flow imaging by spiral scan phase velocity mapping.

The work describes the development of a novel sequence that uses rapid spiral k-space sampling, combined with phase velocity mapping, for real time flow velocity imaging. The performance of the technique is assessed on phantoms for both through-plane and in-plane flows. The flow measurements compared well with those measured using a bucket and stopwatch. One advantage of the technique is that flow related signal loss is minimal due to the early acquisition of the center of k-space data. Flow artifacts were observed for in-plane flow and these were understood with the aid of computer simulations. In vivo studies involved cine velocity mapping in normal volunteers; aortic blood flow waveforms acquired by spiral scanning in two cardiac cycles compared well with data from a conventional gradient-echo sequence. Potential applications of the method are demonstrated by studying the response of aortic flow to physical exercise and the real time monitoring of aortic flow during a valsalver maneuver.

Algorithms↗

PubMed1994

Regional myocardial velocity imaged by magnetic resonance in patients with ischaemic heart disease.

OBJECTIVE: To assess the pattern of global and regional left ventricular long axis motion during early diastole in patients with ischaemic heart disease with and without myocardial infarction using magnetic resonance velocity mapping. DESIGN: Prospective study of 26 patients with a history of myocardial infarction (age 29-78, mean 55 years) and 21 patients with coronary artery disease without infarction (age range 39-71, mean 58 years). Values were compared with a control group (19 controls, age 35-76, mean 52 years) with a low likelihood of cardiovascular disease. RESULTS: Regional long axis velocity varied with time and position around the ventricle. All measurements were taken at the time of maximum early diastolic long axis velocity. Patients with coronary artery disease without infarction had lower values for maximum (mean (SD)) (99 (30) v 125 (33) mm/s, P < 0.05) and mean peak early diastolic wall motion (63 (13) v 82 (22) mm/s, P < 0.05) than controls. The coefficient of variation showed greater inhomogeneity of relaxation in patients than in controls (38 (18)% v 27 (10)%). All values were lower in patients with previous infarction than in patients with coronary artery disease without infarction and normal subjects. In patients with previous myocardial infarction the maximum (mean (SD)) early diastolic velocity was 80 (22) mm/s (P < 0.01 compared with controls and P < 0.05 compared with patients without infarction) and the mean (SD) velocity was 47 (18) mm/s (P < 0.01 compared with controls). The coefficient of variation was greater (52 (33)%) than for controls (P < 0.05) and patients with coronary artery disease without infarction. 18 of 26 patients with previous myocardial infarction and 13 of 21 patients with coronary artery disease without infarction had regional abnormalities corresponding to areas of fixed or reversible ischaemia on exercise electrocardiography or thallium myocardial perfusion tomography. CONCLUSIONS: Magnetic resonance velocity mapping can be used to assess regional long axis myocardial velocity. Ischaemic heart disease causes alterations in the patterns of left ventricular long axis velocity during early diastole.

Adult↗

PubMed1994

Technical note: rapid measurement of left ventricular mass by spin echo magnetic resonance imaging.

Magnetic resonance (MR) imaging provides an accurate measurement of left ventricular mass but imaging time can be up to 45 min. We tested a more rapid multislice spin echo technique on 16 volunteers without evidence of heart disease. Multislice short axis spin echo images were acquired in up to three sets of five, clustered around end systole. Total imaging time was 15 min. Myocardial areas were summed and specific gravity was assumed. Comparison was made with multiple single acquisitions timed to end systole. There was good agreement between the two measurements of left ventricular mass. Mean (+/- standard deviation (sd), range) values were 212 g (+/- 41.71, 152 to 311) by the multislice method and 213 g (+/- 44.26, 155 to 317) by the single slice method. The mean difference (+/- sd of difference) between measurements was -1.72 +/- 14.89 g (95% confidence interval for limits of agreement was +/- 14%). We have therefore established a more rapid and accurate method of measuring left ventricular mass.

Adult↗

PubMed1993

Magnetic resonance imaging of coronary arteries: technique and preliminary results.

BACKGROUND: Coronary artery imaging is an important investigation for the management of coronary artery disease. The only reliable technique presently available, x ray contrast angiography, is invasive and is associated with a small morbidity and mortality. Alternative non-invasive imaging would be useful, but the small calibre and tortuosity of the coronary vessels, and cardiac and respiratory motion create formidable imaging problems. OBJECTIVE: The development of rapid magnetic resonance imaging of the coronary arteries. PATIENTS: 21 healthy controls and five patients with coronary artery disease established by x ray contrast angiography, of whom two had undergone bypass grafting. METHODS: Magnetic resonance imaging was performed with gradient echoes and a segmented k-space technique, such that a complete image was acquired in 16 cardiac cycles during a breathhold. The signal from fat was suppressed and images were acquired in late diastole to reduce artefact from cardiac motion. An imaging strategy was developed for the proximal arteries, including longitudinal imaging from oblique planes defined according to the origins and the continuation of the arteries in the atrioventricular grooves or interventricular sulcus. RESULTS: Of the 26 subjects studied, 22 were imaged successfully. Identification of the artery was possible for the left main stem, left anterior descending, right coronary, and left circumflex arteries respectively in 95%, 91%, 95%, and 76%. The arterial diameter at the origin could be measured in 77%, 77%, 81%, and 63%. The mean (SD) arterial diameter in each case (4.8 (0.8), 3.7 (0.5), 3.9 (0.9), and 2.9 (0.6) mm) was not significantly different from reference values. The mean length of artery visualised was 10.4 (5.2), 46.7 (22.8), 53.7 (27.9), and 26.3 (17.5) mm. In 12 healthy men the total coronary area was 30.9 (9.2) mm2 and the ratio compared with body surface area was 16.4 (4.4) mm2m2 (both p = NS compared with reference values). In seven patients in whom x ray contrast coronary angiography was available, the proximal arterial diameter was 3.9 (1.1) mm measured by magnetic resonance and 3.7 (1.0) mm by x ray contrast angiography (p = NS). The mean difference between the measurements was 0.2 (0.5) mm, and the coefficient of variation was 13.7%. All five occluded coronary arteries were identified, as were all three vein grafts. In two patients insertion of the graft into the native arteries was identified. CONCLUSIONS: Magnetic resonance coronary angiography is feasible. Good results were obtained by a breath-hold, fat suppression technique, gated to late diastole. Arterial occlusions and vein grafts were readily identified. Further studies are required to establish its value in the detection of coronary stenosis and to develop the measurement of coronary flow velocity which could be used to quantify the severity of the stenosis.

Coronary Angiography↗

PubMed1993

Age-related changes of human aortic flow wave velocity measured noninvasively by magnetic resonance imaging.

We have used magnetic resonance imaging with cine velocity mapping to measure flow wave velocity in the thoracic aorta of 20 healthy volunteers of different ages. We have also studied the relationship between propagation of flow wave velocity and regional aortic compliance. Aortic flow velocity increased linearly with age (r = 0.87), and there was a significant difference between the youngest decade [age 10-19, mean velocity 4.3 +/- 0.7 (SD) m/s] and the oldest decade studied (age 50-59, mean velocity 7.2 +/- 0.2 m/s). Flow wave velocity (m/s) was negatively correlated with ascending aortic compliance (microliter/mmHg) (r = -0.75). Magnetic resonance imaging is a noninvasive method for measurement of aortic flow wave velocity that is an important parameter in assessing arterial wall mechanics and blood flow dynamic.

Adolescent↗

PubMed1993

Magnetic resonance jet velocity mapping in mitral and aortic valve stenosis.

BACKGROUND: Magnetic resonance (MR) phase-shift velocity mapping is an established method for measurement of nonturbulent intravascular flow. Shortening the echo time of the MR sequence to 3.6 msec allowed application of the technique to turbulent jet flow. The objective of this study was validation of MR jet velocity mapping in patients with cardiac valve stenosis. METHODS AND RESULTS: We used a 0.5-T Picker MR machine to measure peak poststenotic jet velocity in 15 consecutive patients recruited with known valve disease (six mitral stenosis, three of these restudied after valvoplasty, and 11 aortic stenosis). On the same day as the MR study, these patients underwent independent Doppler echocardiographic measurement of peak jet velocity. The results of 10 further MR investigations of aortic stenosis are also reported and compared with Doppler studies performed within 6 months. Of the 29 MR studies, 28 (97%) produced interpretable velocity maps, the one failure being attributed to misplacement of the imaging slice in a case of severe aortic stenosis. Agreement between MR and Doppler measurements of peak jet velocity in the recruited group was as follows: n = 18; range, 1.4-6.1 m/sec; mean, 3 m/sec; mean of differences (MR-Doppler), 0.23 m/sec; standard deviation of differences, 0.49 m/sec. CONCLUSIONS: In vivo MR peak jet velocity measurements agree well with those made by Doppler ultrasound. The technique, which is not subject to restricted windows of access and has potential for further refinements, could contribute to improved evaluation of stenoses, especially at locations where ultrasonic access is limited.

Aortic Valve Stenosis↗

PubMed1993

Helical and retrograde secondary flow patterns in the aortic arch studied by three-directional magnetic resonance velocity mapping.

BACKGROUND: Helical and retrograde secondary flows have been recorded in the aorta, but their origins and movements in relation to the arch have not been clarified. We set out to do this using magnetic resonance velocity mapping. METHODS AND RESULTS: Three-directional phase contrast cine magnetic resonance velocity mapping was used to map multidirectional flow velocities in the aortas of 10 healthy volunteers. Computer processing was used to visualize flow vector patterns in selected planes. Right-handed helical flows predominated in the upper aortic arch in late systole, being clearly recognizable in 9 of the 10 subjects. Nonaxial components of velocity in this region reached 0.29 m/s (+/- 0.05 m/s) as axial velocities declined from a peak of 1.0 m/s (+/- 0.1 m/s). Helical flow patterns in the upper descending aorta varied between subjects, apparently depending on arch curvature. End-systolic retrograde flow originated from regions of blood with low momentum, usually along inner wall curvatures. Flow studies in a curved tubular phantom showed right-handed helical flow in the upper "arch" when the inflow section was positioned to simulate ascending aortic curvature, and retrograde flow occurred along the inner wall at end systole during pulsatile flow. CONCLUSIONS: Helical and retrograde streams are consistent features of intra-aortic flow in healthy subjects that result, at least in part, from the curvature of the arch and the pulsatility of flow in it. They may have significance in relation to circulatory dynamics and the pathogenesis of atheroma in the arch.

Adult↗

PubMed1991

Magnetic resonance morphological, chemical shift and flow imaging in peripheral vascular disease.

We have used magnetic resonance imaging to study the aorto-iliac region in 13 patients with peripheral disease. Five healthy volunteers were studied for comparison. Magnetic resonance spin-echo imaging, chemical shift imaging to determine lipid content of atheroma, phase-shift velocity mapping and quantitative flow studies were obtained and the findings compared with radiological angiograms. The velocity profiles study showed an increased velocity at the site of a stenosis in eight patients who had iliac artery disease. Quantitative flow measurements made in both iliac arteries and the aorta in five patients and five volunteers showed a flow ratio in both iliac arteries less than 0.85 in patients with a stenosis of one iliac artery and a ratio greater than 0.85 in the volunteers. In one patient studied before and after angioplasty, flow improved post-angioplasty. The flow curve showed a characteristic distortion in diseased vessels compared with healthy vessels. In the chemical shift images of aortic atheroma five were classified as fibrous and three were lipid rich. This preliminary study showed the potential of magnetic resonance to assess non-invasively the morphology, composition and the haemodynamic significance of atheroma. This could be important in the study of the progression of peripheral vascular disease and its response to pharmacological and surgical intervention and in the planning treatment of lesions.

Adult↗

PubMed1991

Valve and great vessel stenosis: assessment with MR jet velocity mapping.

For measurement of poststenotic jet velocities with magnetic resonance (MR) imaging, the authors reduced the echo time (TE) of the field even-echo rephasing (FEER) velocity mapping sequence from 14.0 to 3.6 msec, so minimizing the problem of MR signal loss from turbulent fluid. In vitro use of rotating disk and stenotic flow phantoms confirmed that the 3.6-msec TE sequence enables accurate measurement of jet velocities of up to 6.0 m/sec (r = .996). Peak jet velocity measurements were made with MR imaging in 36 patients with stenosis of native heart valves (n = 9), conduits (n = 19), or Fontan connections (n = 2) or with aortic coarctation (n = 6). Peak velocity measurements made with MR imaging agreed well with measurements made with Doppler ultrasound (US), which were available in 18 cases (standard deviation = 0.2 m/sec). Velocity mapping with fast-echo MR imaging is likely to have considerable importance as a noninvasive means of locating and evaluating stenoses, particularly at sites inaccessible to US, but care must be taken to prevent errors caused by malalignment, signal loss, phase wrap, or partial-volume effects.

Adult↗

PubMed1991

Magnetic resonance imaging: a method for the assessment of changes in vascular structure and function.

A brief review is made of the history of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). The advantages and disadvantages of MRI are discussed with particular reference to methods of studying the vascular system. Techniques developed to study separately sclerosis and atherosis, the two components of atherosclerotic disease, are discussed in more detail. Finally, in vitro and in vivo results are presented to demonstrate the great wealth of information already available from the NMR signal and hence its considerable potential for the study of vascular disease in the future.

Aorta↗

PubMed1991

Magnetic resonance characterization of pulmonary arterial blood flow after single lung transplantation.

Magnetic resonance imaging has been used to study pulmonary arterial anatomy and to measure pulmonary arterial blood flow in patients with single lung transplantation. Nine patients and nine control subjects matched for age and sex were studied. The anatomy of the main pulmonary artery and its main branches, as well as the site of arterial anastomoses, was identified and measurements of their diameters were taken. There were no significant differences in diameters of these vessels between the patients and the control subjects. Arterial blood flows to the transplanted lung were 2.07 +/- 0.45 L/min/m2 in the group with right lung transplantation and 2.43 +/- 0.60 L/min/m2 in those with left lung transplantation compared with 1.22 +/- 0.22 L/min/m2 and 1.27 +/- 0.41 L/min/m2 in the control group, respectively. The ratio of blood flow in the transplanted and the native lungs in all patients studied was 2.8 +/- 0.83:1. The flow profile in the artery of the transplanted lung showed a wide forward flow during systole and most of diastole, whereas that of the native lung showed a narrow early systolic peak and a reverse flow in most of diastole. These differences in the volume and pattern of flow in the transplanted lung are most likely related to the relative resistance in the native and the transplanted lung and could constitute an additional index for monitoring the condition of patients with lung transplantation and help in the understanding of the physiology of the denervated pulmonary vascular bed.

Adult↗

PubMed1990

The application of phase shifts in NMR for flow measurement.

A brief overview of the history of the application of phase shifts in NMR, and in particular NMR imaging, is presented. The imaging methods include direct phase mapping, Fourier flow imaging (where the flow data are Fourier transformed into one dimension of an image), and alternative methods, where flow-related phase shifts are utilized for flow measurement from the magnitude of the signal. A discussion then follows of the principal errors that can affect the accuracy of the various flow imaging techniques, with particular reference to the phase mapping methods that have been used extensively in our institution. The results from a number of experiments are included to illustrate the extent of the errors and methods of removing or minimizing these effects are suggested.

Blood Circulation↗