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Biomedical subjects

A de Roos

Publications and source records attributed to A de Roos.

At least 91 records · Page 5Linked to original sources
PubMed1997

Variability of splanchnic blood flow measurements using MR velocity mapping under fasting and post-prandial conditions--comparison with echo-Doppler.

BACKGROUND/AIMS: The aim was to study the reproducibility of magnetic resonance velocity mapping, when measuring portal vein and superior mesenteric artery blood flow, under fasting and post-prandial conditions. Magnetic resonance flow measurements for the portal vein were compared with echo-Doppler measurements in the right portal vein. METHODS: Eight healthy volunteers were studied on two occasions, separated by 1 week. Blood flow in the portal vein and superior mesenteric artery was measured repeatedly under basal fasting conditions. On one occasion measurements were also made after a meal. Every magnetic resonance measurement was followed by an echo-Doppler measurement in the right portal vein. Correlations between flow values were calculated using Pearson's r. Variability components were assessed using ANOVA. RESULTS: Intra-individual variability was approximately 7% for portal vein flow measurements using magnetic resonance velocity mapping. This variability did not increase after 1 h, 1 week and after a meal. Values of flow measured in the portal vein and superior mesenteric artery using magnetic resonance velocity mapping correlated well (r = 0.80, p < 0.001). Fasting portal flow as measured with magnetic resonance velocity mapping was 1.2 l/min (range 0.96-1.6 l/min). Variability in echo-Doppler measurements was comparable to the variability of magnetic resonance velocity mapping, and flow measurements obtained with the two techniques correlated well (r = 0.74; p < 0.001). CONCLUSIONS: Magnetic resonance velocity mapping accurately measures blood flow in the portal vein with low variability and should be preferred when absolute flow values are necessary. Echo-Doppler measurement of the right portal vein has a low variability and can be used to study changes in flow.

Adult↗
PubMed1997

Quantitative analysis of cardiovascular MR images.

The diagnosis of cardiovascular disease requires the precise assessment of both morphology and function. Nearly all aspects of cardiovascular function and flow can be quantified nowadays with fast magnetic resonance (MR) imaging techniques. Conventional and breath-hold cine MR imaging allow the precise and highly reproducible assessment of global and regional left ventricular function. During the same examination, velocity encoded cine (VEC) MR imaging provides measurements of blood flow in the heart and great vessels. Quantitative image analysis often still relies on manual tracing of contours in the images. Reliable automated or semi-automated image analysis software would be very helpful to overcome the limitations associated with the manual and tedious processing of the images. Recent progress in MR imaging of the coronary arteries and myocardial perfusion imaging with contrast media, along with the further development of faster imaging sequences, suggest that MR imaging could evolve into a single technique ('one stop shop') for the evaluation of many aspects of heart disease. As a result, it is very likely that the need for automated image segmentation and analysis software algorithms will further increase. In this paper the developments directed towards the automated image analysis and semi-automated contour detection for cardiovascular MR imaging are presented.

Blood Flow Velocity↗
PubMed1997

Ischemic heart disease: value of MR techniques.

BACKGROUND: The cardiovascular applications of magnetic resonance (MR) techniques in coronary artery disease have increased considerably in recent years. Technical advantages of MR imaging are the excellent spatial resolution, the characterization of myocardial tissue, and the potential for three-dimensional imaging. These characteristics allow the accurate assessment of left ventricular mass and volume, the differentiation of infarcted from normal tissue, and the determination of systolic wall thickening and regional wall motion abnormalities. METHODS: In addition to the conventionally used spin-echo and cine-echo techniques, newer techniques such as myocardial tagging, ultrafast MR imaging and MR coronary angiography have been developed. These newer techniques allow a more accurate assessment of ventricular function (tagging), myocardial perfusion (ultrafast imaging), and evaluation of stenosis severity (MR coronary angiography). Particularly early detection and flow assessment of stenosed coronary arteries and bypasses by MR angiography would constitute a major breakthrough in cardiovascular MR imaging. Apart from the MR imaging techniques, cardiac metabolism may be well assessed using MR spectroscopy. This provides unique information on the metabolic behaviour of the myocardium under conditions stress-induced ischemia. However, the definite niche of cardiac MR spectroscopy has still to be settled. CONCLUSION: Currently, MR techniques allow the evaluation of anatomy and function (accepted use), perfusion and viability (development phase), and coronary angiography (experimental phase). A particular strength of MR imaging is that one single MR test may encompass cardiac anatomy, perfusion, function, metabolism and coronary angiography. The replacement of multiple diagnostic tests with one MR test may have major effects on cardiovascular healthcare economics and would outweight the cost inherent to the MR angiography procedure.

Coronary Disease↗
PubMed1997

Assessment of regional left ventricular wall parameters from short axis magnetic resonance imaging using a three-dimensional extension to the improved centerline method.

RATIONALE AND OBJECTIVES: Short-axis magnetic resonance images of the cardiac left ventricle, acquired in multiple slices and phases, may be used for the quantitative assessment of regional wall parameters. Conventional two-dimensional (2-D) methods for wall thickness measurement rely on information within one imaging plane, which may result in overestimation of the true thickness depending on the local direction of myocardial wall with respect to the imaging plane. METHODS: To perform wall thickness measurements truly perpendicular to the myocardial wall, a three-dimensional (3-D) wall thickness calculation algorithm has been developed based on the 2-D improved centerline method. An evaluation was performed on left ventricular-shaped software phantoms, and on the magnetic resonance (MR) imaging data obtained from 20 healthy individuals. RESULTS: The 3-D method applied to software phantoms with an angulation within 20 degrees of the true short-axis orientation demonstrated only a 1.6% overestimation of wall thickness at the mid to low slices, and a 10.6% error at the apex (2-D measurements: 8.1% and 28.6%, respectively). Three-dimensionally calculated wall thickness in the healthy individuals was systematically and significantly smaller than corresponding 2-D wall thickness (by 11.2%, 8.7%, and 2.6% at the apical, low, and mid slices, respectively). CONCLUSIONS: Cardiac wall thickness measurements from short-axis MR studies can be obtained with a higher accuracy by the newly developed 3-D approach than with the conventional 2-D approach.

Adult↗
PubMed1997

Wall thickening at rest and contractile reserve early after myocardial infarction: correlation with myocardial perfusion and metabolism.

BACKGROUND: Abnormalities in wall thickening and their reaction to stimulation can be studied by magnetic resonance imaging. OBJECTIVE: To analyse the relationship between these abnormalities and changes in myocardial perfusion and fatty acid metabolism. METHODS: Fifteen patients with a myocardial infarction underwent low-dose dobutamine magnetic resonance imaging to assess their wall thickening and contractile reserve, and technetium-99m sestamibi (MIBI) and beta-methyl-iodophenyl-pentadecanoic acid (BMIPP) single-photon emission tomography to assess their myocardial perfusion and fatty acid uptake. For nine segments per patient, the wall thickening was scored as normal, hypokinetic or akinetic, and the myocardial perfusion as normal (> 65%), mildly to moderately reduced (35-65%) or severely reduced (< 35%). Abnormalities in fatty acid uptake were compared with the myocardial perfusion and defined as matched (difference < or = 10%) or mismatched (difference > 10%) reduction. RESULTS: Thirty-four segments had abnormal wall thickening (13 hypokinetic and 21 akinetic). The wall thickening at rest was significantly related to the uptake of MIBI (P < 0.001), but not to abnormalities in the uptake of BMIPP. All of the akinetic segments had an abnormal uptake of MIBI (15 severely and six mildly to moderately reduced), whereas 7 of 13 hypokinetic segments had a normal and five a midly to moderately reduced uptake. A significant relationship between abnormalities of fatty acid metabolism and the contractile reserve was also found (P < 0.002): 14 of 16 segments with and only six of 18 without contractile reserve had a mismatched reduction in uptakes of MIBI and BMIPP. CONCLUSION: This study confirms the relationship between the wall thickening at rest and the residual perfusion after infarction. On the other hand, the contractile reserve, which is an accepted indicator of the viability of the infarct region, is associated strongly with abnormalities of fatty acid metabolism.

Adult↗
PubMed1997

Absence of Epstein-Barr virus (EBV) in a gastrointestinal stromal cell tumour (GIST) in an adult human immunodeficiency virus-seropositive patient with past EBV infection.

Gastrointestinal stromal cell tumours (GIST) of the small intestine are rare malignancies. Recently, an association of Epstein-Barr virus (EBV) with malignant stromal cell tumour in young people with AIDS and past EBV infection has been described. We describe a 33-year-old heterosexual male with asymptomatic human immunodeficiency virus (HIV) infection who had had an EBV infection in the past and who presented with an EBV-negative GIST. The association between EBV and malignant stromal cell tumours in young people with AIDS could not be reconfirmed in our adult patient. The relationship between EBV and malignant stromal cell tumours in AIDS patients and the possible pathogenetic role of EBV remains to be established, at least in adults.

Adult↗
PubMed1997

Doppler sonography evaluation of superior mesenteric artery flow to assess Crohn's disease activity: correlation with clinical evaluation, Crohn's disease activity index, and alpha 1-antitrypsin clearance in feces.

OBJECTIVE: This study was undertaken to investigate the value of Doppler flow measurements of the superior mesenteric artery (SMA) as a marker for disease activity in patients with Crohn's disease. SUBJECTS AND METHODS: Duplex Doppler sonography measurements of SMA blood flow volume were obtained in 29 consecutive patients with suspected Crohn's disease. We prospectively sought a correlation between the independent assessment of Doppler flow measurements and markers for disease activity: Crohn's disease activity index and fecal alpha 1-antitrypsin clearance and our reference standard based on clinical history, physical examination, laboratory values, endoscopy, surgery, and follow-up. RESULTS: In 27 of 29 patients, adequate measurements of SMA blood flow were obtained. In 15 patients no disease activity was judged to be present or no Crohn's disease (n = 2) was found at follow-up (group 1). In 12 patients, activity of Crohn's disease was diagnosed (group 2) on the basis of the reference standard. In group 2 the Doppler SMA blood flow values were significantly higher (p < .05) than those for group 1 (826 +/- 407 ml/min versus 323 +/- 103 ml/min). Of the other parameters investigated, only the alpha 1-antitrypsin value correlated with the reference standard but to a lesser degree than the values for SMA blood flow measurement. CONCLUSION: This prospective study shows that SMA Doppler blood flow measurements can be used to assess disease activity in patients with Crohn's disease. This approach may be of value in the diagnosis and follow-up of patients with Crohn's disease, providing directly available, quantifiable, noninvasive information on disease activity.

Adult↗
PubMed1996

Reproducibility of human cardiac 31P-NMR spectroscopy.

The reproducibility of the phosphocreatine to adenosine triphosphate ratio (PCr/ATP) was assessed from cardiac phosphorus-31 (31P) NMR spectra of the human left ventricle acquired with three different localization techniques. Cardiac 31P-NMR spectra (n = 68) were obtained at rest from 16 healthy subjects with three-dimensional (3D) image selected in vivo spectroscopy (ISIS), 1D spectroscopic imaging (SI), or with a combination of 2D ISIS and the 1D SI technique (ISIS + SI). The average PCr/ATP ratios were 1.41 +/- 0.20 for ISIS + SI and 1.31 +/- 0.19 for ISIS and were in the lower range of values obtained in previous studies, mainly because of a lower saturation correction factor for the cardiac PCr/ATP ratio. The SI experiment yielded an average PCr/ATP value of 0.98 +/- 0.20, significantly lower as compared to the correct values obtained with ISIS + SI and ISIS (p < 0.001), underscoring the need for 3D localization to avoid contamination of the NMR signal by liver tissue. Intersubject standard deviations of the PCr/ATP ratio were comparable to values reported previously. For all three localization techniques the absolute intra-examination differences in PCr/ATP (0.06 for ISIS to 0.15 for ISIS + SI) were significantly smaller (p approximately 0.03) than inter-examination differences (0.24 for ISIS to 0.29 for ISIS + SI). Therefore, consecutive acquisition of cardiac 31P-NMR spectra from the same patient during a single examination, e.g. under various cardiac loading conditions, appears to be a reliable approach for metabolic evaluation of heart disease.

Adenosine Triphosphate↗
PubMed1996

Comparison of ultrafast dipyridamole magnetic resonance imaging with dipyridamole SestaMIBI SPECT for detection of perfusion abnormalities in patients with one-vessel coronary artery disease: assessment by quantitative model fitting.

The value of ultrafast MRI for detection of myocardial perfusion abnormalities in patients with coronary artery disease (CAD) was assessed in 10 patients with stable angina pectoris and angiographically proven one-vessel CAD using double-level short-axis ultrafast MRI with bolus injection of gadolinium-DTPA and tomographic technetium-99m SestaMIBI imaging (SPECT) during dipyridamole-induced coronary hyperemia. Abnormally perfused regions were assessed with SPECT and MRI in all (100%) patients. Agreement in localization between arteriography and SPECT was 80%; between arteriography and MR, 70%; and between SPECT and MR, 90%. The signal intensity increase after the bolus injection of gadolinium-DTPA using a linear fit, and the slope of gadolinium-DTPA wash-in using double exponential model fitting were significantly different between abnormally and normally perfused regions. These preliminary results demonstrate the potential of dipyridamole ultrafast MR to monitor stress-induced flow maldistribution in patients with single vessel CAD.

Aged↗
PubMed1996

Assessment of left ventricular volume and mass by cine magnetic resonance imaging in patients with anterior myocardial infarction intra-observer and inter-observer variability on contour detection.

Remodeling of the left ventricle after myocardial infarction can be documented by calculation of left ventricular volume and mass, using endocardial and epicardial tracings of multilevel multiphase short-axis cine magnetic resonance (MR) imaging series. We assessed left ventricular volume and mass from 8 slices and during 12 phases of the cardiac cycle in seven patients with an anterior wall myocardial infarction; one patient was studied twice, leaving eight MR examinations to be evaluated. Purpose of this study was to assess the intra-observer and inter-observer variability of epicardial volume, endocardial volume, and left ventricular mass from contours manually traced by two independent observers. For the eight MR examinations, epicardial volume was found to be 292 +/- 51 ml (mean +/- SD) at end-diastole, which decreased to 237 +/- 55 ml at end-systole. Endocardial volume was 141 +/- 31 ml at end-diastole, which decreased to 79 +/- 27 ml at end-systole. Left ventricular ejection fraction was 45 +/- 8%. Mean left ventricular mass, when averaged over all patient studies and all phases, was 159 +/- 30 g. Intra-observer and inter-observer variability were found to be 3.5% and 5.2% for endocardial volume, 2.0% and 2.5% for epicardial volume, and 3.6% and 3.6% for left ventricular mass, respectively. The contour analysis showed a statistically significant phase effect in the endocardial contour in the midventricular slices, which was resolved after establishing a more precise definition for the tracing of the endocardial border. In conclusion, left ventricular volume and mass in patients with an anterior wall myocardial infarction can be assessed with high reproducibility and reliability from manual contour tracings. A precise protocol for the definition of endocardial and epicardial contours is required to obtain reproducible and reliable results.

Humans↗
PubMed1996

Quantification of pulmonary and systemic blood flow by magnetic resonance velocity mapping in the assessment of atrial-level shunts.

The objective of this study was to asses the feasibility and accuracy of magnetic resonance (MR) velocity mapping to calculate pulmonary-to-systemic flow ratio (Qp:Qs) in patients with a suspected or diagnosed atrial-level shunt. During a one-year period, all patients referred to our department for further evaluation of an atrial-level shunt underwent the same imaging protocol. Multiphase-multisection gradient-echo MR image sets of the heart were acquired to measure left and right ventricular stroke volumes for validation. Ascending aorta and main pulmonary artery volume flow were measured with MR velocity mapping. Qp:Qs ratios were calculated from both stroke volume data and flow data. Twelve patients, including 6 children, were studied. Six patients had an established diagnosis of atrial septal defect, and the other 6 patients were suspected to have an atrial-level shunt. Measurements of left and right ventricular stroke corresponded closely with those of aortic (r = 0.98) and pulmonary flow (r = 0.99) respectively, and Qp:Qs flow ratios agreed with stroke volume ratios (r = 0.92). In 5 patients with a suspected shunt, the diagnosis could be rejected. Shunts were demonstrated in the other 7 patients. M(r) velocity mapping offers an accurate method to measure aortic and pulmonary artery volume flow that can be useful in the evaluation of atrial-level shunts, in order to establish a definite diagnosis and/or to quantify the Qp:Qs ratio.

Adolescent↗
PubMed1996

Assessment of acute myocardial infarction in man with magnetic resonance imaging and the use of a new paramagnetic contrast agent gadolinium-BOPTA.

To assess the feasibility of and characterize the new paramagnetic contrast agent gadolinium-BOPTA/dimeglumine (Gd-BOPTA) to detect acute myocardial infarctions with MR imaging, 24 patients (53.3 +/- 8.3 yr) were examined 9.3 +/- 3.6 days after a first myocardial infarction. Short-axis T1-weighted and T2-weighted MR imaging was performed at three slice levels. T1-weighted images were obtained before, immediately after, 15, 30, and 45 min after injection. Patients received either 0.05 or 0.1 mmol/kg body weight Gd-BOPTA. Images were qualitatively and quantitatively analyzed. Two patients showed no signs of infarction on T2-weighted images as opposed to contrast-enhanced T1-weighted images. Contrast-to-noise ratio was not affected by the dosage level. Signal intensity (SI) of normal to infarcted myocardium was significantly improved by both dosages (p < .0005) but a dosage of 0.05 mmol/kg produced significantly higher SI inf/norm (1.42 +/- 0.07 vs. 1.34 +/- 0.06, respectively, p = .015). SI of normal and infarcted myocardium enhanced immediately after administration of 0.05 mmol/kg (29.3 +/- 5.1% and 53.8 +/- 9.6% respectively), which decreased thereafter to 5.3 +/- 4.8% and 40.2 +/- 8.5% respectively, at 45 min (p < .002 for normal myocardium). SI enhancement immediately after 0.1 mmol/kg Gd-BOPTA showed no decrease within the first 45 min. Gd-BOPTA enables the detection of myocardial infarction. Optimal infarct delineation is achieved from 15 to 45 min after administration of 0.05 mmol/kg body weight Gd-BOPTA. Gd-BOPTA at 0.05 mmol/kg does improve image quality as measured by contrast-to-noise ratio and SI enhancement as compared to 0.10 mmol/kg.

Adult↗
PubMed1996

Magnetic resonance angiography of dialysis access shunts: initial results.

The objective of this study was the feasibility of imaging hemodialysis fistulae with magnetic resonance angiography (MRA). MRA was performed in eight Brescia-Cimino fistulae and seven goretex loop grafts, five of which were stenosed and 10 normal. We compared two MRA methods: a 2D magnetization prepared turbo field echo (MPTFE) and a 3D phase contrast (PC) sequence. Digital subtraction angiography served as the gold standard. MPTFE MRA provided satisfactory quality images of the entire fistula in 14 out of 15 cases, and PC MRA in 9 of 15 cases (p < .05). MPTFE MRA identified all eight stenoses with one false-positive result. PC MRA identified seven of eight stenoses with two false positives. It is feasible to obtain diagnostic images of dialysis fistulae with MRA.

Angiography, Digital Subtraction↗
PubMed1996

Right ventricular diastolic function in children with pulmonary regurgitation after repair of tetralogy of Fallot: volumetric evaluation by magnetic resonance velocity mapping.

OBJECTIVES: We sought to assess right ventricular diastolic function in young patients with corrected tetralogy of Fallot and pulmonary regurgitation. BACKGROUND: Pulmonary regurgitation is an important problem in repair of tetralogy of Fallot. Its effects on right ventricular diastolic function in children are unknown. METHODS: Nineteen children with repair of tetralogy of Fallot (mean age [+/- SD] 12 +/- 3 years, mean age at operation 1.5 +/- 1) and 12 healthy children were studied. Summation of magnetic resonance velocity mapping pulmonary and tricuspid volume flow curves provided right ventricular time-volume curves. Ventricular size was assessed with tomographic magnetic resonance imaging (MRI). Graded exercise testing was performed. RESULTS: Systematic and random differences (mean +/- SD) of velocity mapping and Doppler tricuspid time to peak velocities (peak E: 1 +/- 26 ms, r = 0.43; peak A: 2 +/- 11 ms, r = 0.76), E/A ratio (0.04 +/- 0.5, r = 0.63) and duration of pulmonary regurgitation (20 +/- 35 ms, r = 0.74) were satisfactory. In 6 patients (group I), late diastolic forward pulmonary artery flow was absent; in 13 patients (group II), this flow contributed 1% to 14% to right ventricular stroke volume. Significant differences were increased deceleration time (315 +/- 91 vs. 168 +/- 28 ms, p < 0.001), decreased filling fraction (44 +/- 11 vs. 55 +/- 16%, p = 0.02) and increased peak early filling rate (378 +/- 124 vs. 286 +/- 112 ml/s, p = 0.018) between control subjects and group I, and increased deceleration time (230 +/- 40, p = 0.03) between control subjects and group II. Pulmonary regurgitation, ventricular size and ejection fraction did not differ significantly between patient groups. Exercise function was diminished with restrictive right ventricular physiology (p < 0.001, group II vs. control subjects). CONCLUSIONS: Impaired relaxation and restriction to filling affect right ventricular function in children with repair of tetralogy of Fallot and pulmonary regurgitation. Restrictive right ventricular physiology is associated with decreased exercise function.

Adolescent↗
PubMed1996

Magnetic resonance techniques for assessment of myocardial viability.

In general, the following three standards for myocardial viability can be used: (a) preserved coronary flow (adequate perfusion); (b) preserved wall motion (systolic wall thickening); and (c) preserved metabolism (metabolic integrity). The current magnetic resonance (MR) techniques provide a great potential to measure all three standards of viability. Adequate perfusion can be assessed by spin-echo MR imaging and/or ultrafast MR imaging, systolic wall thickening by cine MR imaging, and the presence of metabolic integrity can be determined by MR spectroscopy. These noninvasive and versatile techniques have led to an increasing interest and research in recent years. Particular strengths of the MR techniques are: the inherent three-dimensional data acquisition without radiation exposure; the intrinsic soft-tissue contrast that allows tissue characterization; the excellent spatial resolution (in the 1- to 2-mm range), which permits the evaluation of regional abnormalities; multitomographic imaging capabilities that allow acquisition of cardiac images in any plane; the inherent sensitivity to blood and wall motion; and the potential for in vivo measurement of myocardial metabolism using MR spectroscopy. This review article demonstrates that MR techniques might play a growing role in the assessment of myocardial viability.

Cell Survival↗
PubMed1996

Cine gradient-echo MR imaging and MR velocity mapping in the evaluation of congenital heart disease.

Cine gradient-echo (GRE) magnetic resonance (MR) imaging and MR velocity mapping can be applied to assess cardiovascular function and to measure volumetric flow in patients with repaired and untreated congenital heart disease. GRE images, particularly when displayed in a cine loop, are very useful for visualizing surgical anastomoses and conduits and for detecting stenosis, regurgitation, and left-to-right shunts. Multisection cine GRE imaging is a suitable method for measuring global right ventricular function, an important issue in congenital heart disease. MR velocity mapping is used for quantitative assessment of hemodynamics. Pressure gradients can be estimated from peak blood flow velocities in stenotic pulmonary arteries or surgical conduits. Because flow volume can be measured with MR velocity mapping, main-, left-, and right pulmonary artery flow, valvular regurgitation, left-to-right shunts, and ventricular filling can all be quantified. The abilities to elucidate complex cardiac anatomy and to measure cardiac function and flow in one examination make MR imaging a useful comprehensive tool for follow-up of congenital heart disease.

Adult↗