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J Doornbos

Publications and source records attributed to J Doornbos.

At least 19 recordsLinked to original sources
PubMed2005

Measurement of the Michel parameter rho in muon decay.

The TWIST Collaboration has measured the Michel parameter rho in normal muon decay, mu(+)--> e(+)nu(e)nu (mu). In the standard model, rho = 3/4. Deviations from this value imply mixing of left- and right-handed muon and electron couplings. We find rho=0.750 80+/-0.000 32(stat) +/- 0.000 97(syst) +/- 0.000 23, where the last uncertainty represents the dependence of rho on the Michel parameter eta. This result sets new limits on the W(L)-W(R) mixing angle in left-right symmetric models.

Journal Article↗
PubMed2004

Multisequence magnetic resonance imaging study of neuropsychiatric systemic lupus erythematosus.

OBJECTIVE: To investigate the relationship between magnetization transfer imaging (MTI), diffusion-weighted imaging (DWI), proton magnetic resonance spectroscopy (H-MRS), and T2 relaxometry findings in patients with primary neuropsychiatric systemic lupus erythematosus (NPSLE). METHODS: The study group consisted of 24 female patients (mean age 36 years [range 23-65]) who had had a variety of neuropsychiatric symptoms that were judged to be due to NPSLE according to the criteria of the American College of Rheumatology. Patients with current active disease were excluded from participation. Quantitative MTI, DWI, H-MRS, and T2 relaxometry data were acquired in all patients, and the correlation coefficients were calculated. RESULTS: MTI results reflecting a decrease in homogeneity of cerebral parenchyma correlated significantly with H-MRS results representing axonal damage. MTI results also correlated significantly with DWI results reflecting increased diffusivity in the cerebral parenchyma. Finally, MTI results reflecting decreased cerebral homogeneity correlated significantly with increased T2 relaxation time, associated with either edema or gliosis. Increased T2 relaxation time correlated significantly with DWI results reflecting increased diffusivity. With the exception of the correlation between H-MRS and MTI findings, there was no significant correlation between H-MRS results and any other parameter. CONCLUSION: The selected study parameters represent different biologic features in the human brain and can be informative with regard to different pathologic processes in NPSLE. The demonstrated associations between MTI, DWI, H-MRS, and T2 data in patients with a history of NPSLE suggest that there is one pathogenesis and/or common neuropathologic outcome in NPSLE despite differences in clinical presentation.

Adult↗
PubMed2003

Three-dimensional navigator coronary MRA with the aid of a blood pool agent in pigs: improved image quality with inclusion of the contrast agent first-pass.

PURPOSE: To evaluate the effect of including the first-pass of a blood pool agent (BPA) on the image quality of three-dimensional navigator coronary MRA. MATERIALS AND METHODS: A pig model was used to perform: 1) T1 simulation of the BPA, based on actual blood samples, and 2) BPA-enhanced three-dimensional navigator coronary MRA, with or without inclusion of the first-pass of the BPA. The acquisitions with inclusion of the first-pass were timed with the use of a test bolus. The acquisitions without first-pass were started one minute after bolus injection (steady-state). A gradient echo acquisition technique with centric k-space sampling was applied. Comparison of both acquisitions was based on determination of contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and vessel length. RESULTS: T1 simulation shows a distinct T1 reduction during first-pass (to a level below 50 msec), increasing to 190 msec during steady-state. Images obtained with first-pass inclusion showed improved CNR (8.6 +/- 1.7 vs. 4.5 +/- 1.8), SNR (11.9 +/- 1.6 vs. 7.4 +/- 2.0), and vessel length (99.2 +/- 10.9 mm vs. 60.5 +/- 21.8 mm) as compared to the acquisitions during steady-state only (all: P< 0.05). CONCLUSION: The image quality of three-dimensional navigator coronary MRA combined with a gadolinium BPA in pigs is improved when starting the image acquisition during first-pass of the bolus.

Animals↗
PubMed2003

A neuroimaging follow up study of a patient with juvenile central nervous system systemic lupus erythematosus.

BACKGROUND: The course of central nervous system systemic lupus erythematosus (CNS-SLE) is largely unknown. New imaging techniques are available to assist in monitoring the disease course. OBJECTIVE: To report a case of juvenile CNS-SLE, in which magnetic resonance imaging (MRI) was used to assess disease activity. CASE REPORT: A 10-year-old female patient with SLE presented with convulsions; MRI and computed tomography (CT) of the cerebrum disclosed abnormalities. Despite adequate treatment, two years later she had a generalised convulsion, and MRI showed new lesions. MR spectroscopy (MRS) indicated neuronal loss, inflammation, and metabolically compromised tissue; magnetisation transfer imaging (MTI) showed an increase in whole brain lesion load. After exclusion of a malignancy, CNS-SLE was the most likely diagnosis, and cyclophosphamide pulses were administered. Initially, multiple sclerosis (MS)-like lesions regressed, but despite maximal immunosuppressive drugs, new lesions formed and disappeared. When immunosuppressive drugs had been stopped for six months MRI showed improved lesions and MTI histograms. DISCUSSION: In this case report, the anatomical substrate, metabolic aspect, neuroimaging, and clinical course of MS-like lesions in a child with CNS-SLE are described. The way in which radiological techniques can support clinical decision making in this young patient with progressive CNS-SLE is illustrated.

Child↗
PubMed1999

Diastolic dysfunction in hypertensive heart disease is associated with altered myocardial metabolism.

BACKGROUND: Hypertension is an important clinical problem and is often accompanied by left ventricular (LV) hypertrophy and dysfunction. Whether the myocardial high-energy phosphate (HEP) metabolism is altered in human hypertensive heart disease and whether this is associated with LV dysfunction is not known. METHODS AND RESULTS: Eleven patients with hypertension and 13 age-matched healthy subjects were studied with magnetic resonance imaging at rest and with phosphorus-31 magnetic resonance spectroscopy at rest and during high-dose atropine-dobutamine stress. Hypertensive patients showed higher LV mass (98+/-28 g/m2) than healthy control subjects (73+/-13 g/m2, P<0.01). LV filling was impaired in patients, reflected by a decreased peak rate of wall thinning (PRWThn), E/A ratio, early peak filling rate, and early deceleration peak (all P<0. 05), whereas systolic function was still normal. The myocardial phosphocreatine (PCr)/ATP ratio determined in patients at rest (1. 20+/-0.18) and during stress (0.95+/-0.25) was lower than corresponding values obtained from healthy control subjects at rest (1.39+/-0.17, P<0.05) and during stress (1.16+/-0.18, P<0.05). The PCr/ATP ratio correlated significantly with PRWThn (r=-0.55, P<0.01), early deceleration peak (r=-0.56, P<0.01), and with the rate-pressure product (r=-0.53, P<0.001). CONCLUSIONS: Myocardial HEP metabolism is altered in patients with hypertensive heart disease. In addition, there is an association between impaired LV diastolic function and altered myocardial HEP metabolism in humans. The level of myocardial PCr/ATP is most likely determined by the level of cardiac work load.

Adenosine Triphosphate↗
PubMed1999

Equilibrium phase MR angiography of the aortic arch and abdominal vasculature with the blood pool contrast agent CMD-A2-Gd-DOTA in pigs.

Meglumine-carboxymethyldextran-ethylenediamino-gadoterate (CMD-A2-Gd-DOTA) was evaluated as a blood pool contrast agent for magnetic resonance angiography (MRA). MRA of large body vasculature was performed in seven pigs using a gradient-echo sequence at 1.5 T before and after 0.05 mmol/kg CMD-A2-Gd-DOTA injection. The signal- and contrast-to-noise ratios (SNRs, CNRs) were measured, as well as the pharmacokinetic clearance pattern. CMD-A2-Gd-DOTA visualized the vasculature with a high SNR and CNR for over 110 minutes after injection, but for the renal arteries the CNR was only significant within 15 minutes. Image quality was maximum within 15 minutes, producing enhancement (mean +/- SD) as follows: aortic arch 738 +/- 272%, abdominal aorta 393 +/- 123%, left renal artery 202 +/- 95%, right renal artery 248 +/- 107%, inferior vena cava 371 +/- 129%, and portal vein 513 +/- 145%, all P values < or =0.001. The clearance pattern was triphasic. Due to the excellent enhancement of vasculature without background enhancement, CMD-A2-Gd-DOTA is potentially a useful MR blood pool contrast agent for equilibrium phase MRA.

Abdomen↗
PubMed1999

Blood pool contrast agent CMD-A2-Gd-DOTA-enhanced MR imaging of infarcted myocardium in pigs.

The purpose of this study was to assess the ability of the new blood pool contrast agent meglumine-carboxymethyldextran-ethylenediamino-gadoterate (CMD-A2-Gd-DOTA) to depict acute occlusive myocardial infarction (AMI). First-pass gradient-echo and delayed spin-echo magnetic resonance imaging (MRI) was performed 5 days after induction of AMI in a pig model. MRI was correlated with pathology. First-pass imaging with CMD-A2-Gd-DOTA allowed detection of infarcted myocardium in all pigs (n = 7). The infarction was recognized as a black spot on MRI as well as on a parametric image. The signal intensity (SI) amplitudes of normal versus infarcted myocardium were 80.55 +/- 18.61 versus 8.48 +/- 15.50 on MRI and 81.62 +/- 18.50 versus 1.61 +/- 3.73 on the parametric image (both P values < 0.001. The contrast ratio between normal and infarcted myocardium was not significantly improved on spin-echo MRI, suggesting largely intact vascular integrity outside the occluded area. CMD-A2-Gd-DOTA is useful for depicting occlusive myocardial infarction by first-pass MRI. Spin-echo imaging is promising in assessing vascular integrity. J. Magn. Reson. Imaging 1999;10:170-177.

Analysis of Variance↗
PubMed1999

Diagnosis and management of anomalous origin of the right coronary artery from the left coronary sinus.

The anomalous origin of the right coronary artery (RCA) from the left sinus of Valsalva coursing between the aorta and the pulmonary artery or right ventricular outflow tract, is considered a potentially fatal abnormality which may require surgery. However, diagnosing the correct course with coronary arteriography may be difficult. Fast gradient echo magnetic resonance (MR) imaging can be helpful to identify and confirm the course of aberrant coronary arteries and their relationship to the surrounding tissue. In this study, diagnostic procedures and management are described of four patients in whom the RCA originated from the left sinus of Valsalva. Although reported as investigational by the Task Force document on MR imaging by the European Society of Cardiology we are of the opinion that MR coronary angiography may have an important future role in the assessment of anomalous coronary arteries.

Adult↗
PubMed1999

Stenosis quantification from post-stenotic signal loss in phase-contrast MRA datasets of flow phantoms and renal arteries.

In this study a semi-automated and observer-independent algorithm for quantifying post-stenotic signal loss (PSL) in 3D phase-contrast (PC) magnetic resonance angiography (MRA) of patients with renal artery stenosis is presented. This algorithm was developed on MRA datasets of stenotic phantoms, which were included in a flow circuit with stationary flows. The length and the severity of the PSL (incorporating both length and degree of PSL) in the maximum intensity projections (MIPs) of MRA datasets were proposed for quantifying stenoses. The algorithm was tested in renal arteries of ten patients with renal artery stenosis and seven healthy volunteers. Digital subtraction angiography (DSA) was performed in the patients and served as the gold standard. Stenosis severity showed better correlation with the severity of the PSL than with the length, both for in vitro as in vivo. Spearman correlation coefficients (rS) showed statistically significant correlations between the severity of the PSL and parameters determined by DSA, i.e. percent diameter stenosis (rS = 0.90). The length of the PSL showed no correlation with the diameter stenosis (rS = 0.37).

Adult↗
PubMed1999

Magnetic resonance imaging of ischemic heart disease: why cardiac magnetic resonance imaging will play a significant role in the management of patients with coronary artery disease.

The role of magnetic resonance imaging in the diagnosis of ischemic heart disease has great potential impact on patient management, because a number of aspects of ischemic heart disease can be evaluated in one imaging session. High resolution coronary magnetic resonance angiography is currently available, although several technical improvements are awaited to make the technique routinely applicable. A major advance will probably include the availability of magnetic resonance blood pool contrast agents to improve vessel visualization. Contrast media, in combination with either first pass or delayed myocardial scanning, will also play an important role in myocardial perfusion imaging. Functional magnetic resonance assessment of regional and global ventricular function is currently a well-established technique and is considered a new gold standard, which may impact on routine cardiology practice. This review summarizes some of the recent magnetic resonance developments for evaluating various aspects of ischemic heart disease, including magnetic resonance coronary angiography, flow imaging, and imaging of myocardial perfusion and function.

Blood Flow Velocity↗
PubMed1999

Correlation of heart rate variability with cardiac functional and metabolic variables in cyclists with training induced left ventricular hypertrophy.

OBJECTIVE: To examine the correlation between heart rate variability and left ventricular mass in cyclists with an athlete's heart. METHODS: Left ventricular mass and diastolic function were determined at rest and myocardial high energy phosphates were quantified at rest and during atropine-dobutamine stress in 12 male cyclists and 10 control subjects, using magnetic resonance techniques. Ambulatory 24 hour ECG recordings were obtained, and time and frequency domain heart rate variability indices were computed. RESULTS: In the cyclists, the mean of all RR intervals between normal beats (meanNN), the SD of the RR intervals, and their coefficient of variation were significantly greater than in control subjects (p < 0.01, p < 0.01, and p < 0.05, respectively). For cyclists and control subjects, only meanNN correlated with left ventricular mass (r = 0.48, p = 0.038). The heart rate variability indices that correlated with functional or metabolic variables were: meanNN v E/A peak (the ratio of peak early and peak atrial filling rate) (r = 0.48, p = 0.039); the root mean square of successive differences in RR intervals among successive normal beats v E/A area (ratio of peak early and peak atrial filling volume) (r = 0.48, p = 0.040); percentage of successive RR intervals differing by more than 50 ms v the phosphocreatine to ATP ratio at rest (r = 0.54, p = 0. 017); and the SD of the average RR intervals during all five minute periods v the phosphocreatine to ATP ratio during stress (r = 0.60, p = 0.007). CONCLUSIONS: Highly trained cyclists have increased heart rate variability indices, reflecting increased cardiac vagal control compared with control subjects. Left ventricular mass has no major influence on heart rate variability, but heart rate variability is significantly correlated with high energy phosphate metabolism and diastolic function.

Adult↗
PubMed1999

Infarcted myocardium in pigs: MR imaging enhanced with slow-interstitial-diffusion gadolinium compound P760.

PURPOSE: To assess the value of P760, a gadolinium chelate with slow interstitial diffusion and high relaxivity, for magnetic resonance (MR) imaging of acute myocardial infarction in pigs. MATERIALS AND METHODS: First-pass gradient-echo MR imaging and spin-echo MR imaging were performed with P760 and then with gadoterate meglumine in eight pigs with occlusive acute myocardial infarction. P760 signal intensity enhancement and clearance were compared with those of gadoterate meglumine. RESULTS: The first-pass enhancement ratio of P760 in normal myocardium was higher than that in infarcted myocardium (1.37 +/- 0.06 [SEM] vs 1.05 +/- 0.03, P = .03). The myocardial first pass showed a blood pool-like curve for P760. The blood pool enhancement ratio 40 seconds after injection was higher for P760 than for gadoterate meglumine (left ventricular cavity, 1.75 +/- 0.06 vs 1.45 +/- 0.06, P = .009). Spin-echo MR imaging showed improved contrast between normal and infarcted myocardium after P760 administration: The ratio before contrast material administration was 0.21 +/- 0.03, that at 15 minutes was 0.48 +/- 0.05 (P = .002), and that at 25 minutes was 0.47 +/- 0.07 (P = .003). CONCLUSION: P760 is an MR imaging contrast agent characterized by low diffusion, a blood pool effect soon after low-dose administration, and fast elimination. This agent is useful for improved myocardial perfusion MR imaging of acute myocardial infarction.

Animals↗
PubMed1999

Changes in muscle volume, strength, and bioenergetics during recombinant human growth hormone (GH) therapy in adults with GH deficiency.

Adults with GH deficiency (GHD) suffer from muscle weakness, which can be caused by the frequently reported decrease in muscle mass. However, measurements of both muscle strength and mass of muscle tested are scarce in adults with GHD. The aim of the present study was, therefore, to investigate intrinsic muscle strength (strength expressed per muscle volume unit) in adults with GHD at baseline and after 52 weeks of recombinant human GH (rhGH) therapy given in low, more physiological doses. A second objective was to investigate the influence of GH on muscle bioenergetics in the resting muscle. Isometric and isokinetic quadriceps strengths were measured in 28 males with GHD and in healthy controls matched for age and height. Quadriceps mass, determined by magnetic resonance imaging, and muscle bioenergetics, determined by phosphorus nuclear magnetic resonance spectroscopy, were measured in 20 of 28 patients with GHD and in controls matched for age and height. All patients were treated with doses of rhGH ranging from 0.6-1.8 IU/day, given for 52 weeks. Measurements of muscle mass, strength, and bioenergetics were repeated after 52 weeks of treatment with rhGH. The mean GH dose at 52 weeks of rhGH treatment was 1.3 +/- 0.8 IU/day. The mean serum insulin-like growth factor I level at baseline was 9.4 +/- 0.7 nmol/L and significantly increased to 26.4 +/- 1.2 nmol/L after 52 weeks of rhGH treatment. Adults with GHD had significantly reduced quadriceps muscle mass (P = 0.034) and reduced isometric muscle strength (P = 0.002) and tended to have low isokinetic muscle strength (P = 0.06), which all improved after rhGH therapy. Intrinsic muscle strength was not significantly different in adults with GHD compared with that in healthy controls and did not change during rhGH therapy. No bioenergetic abnormalities at baseline or after rhGH therapy were found in males with GHD. In conclusion, quadriceps muscle mass is decreased in adults with GHD and increased with rhGH therapy. These changes in muscle mass account for the changes in muscle strength found in these patients, as no changes in intrinsic muscle strength were found.

Adult↗
PubMed1998

MR imaging of hyaline cartilage at 0.5 T: a quantitative and qualitative in vitro evaluation of three types of sequences.

OBJECTIVE: To identify an optimal pulse sequence for in vitro imaging of hyaline cartilage at 0.5 T. MATERIALS AND METHODS: Twelve holes of varying diameter and depth were drilled in the cartilage of two pig knees. These were submerged in saline and scanned with a 0.5-T MR system. Sixteen T1-weighted gradient echo (GE), two T2-weighted GE, and 16 fast spin echo sequences were used, by varying repetition time (TR), echo time (TE), flip angle (FA), echo train length, profile order, and by use of fat saturation. Contrast-to-noise ratios (CNR) of cartilage versus saline solution and cartilage versus subchondral bone were measured. Cartilaginous lesions were evaluated separately by three independent observers. Interobserver variability and correlation between the quantitative and qualitative analyses were calculated. RESULTS: The mean CNRs of two specimens of cartilage versus saline solution ranged from 6.3 (+/- 2.1) to 27.7 (+/- 2.5), and those of cartilage versus subchondral bone from 0.3 (+/- 0.2) to 22.5 (+/- 1.4). The highest CNR was obtained with a T1-weighted spoiled 3D-GE technique (TR 65 ms, TE 11.5 ms, FA 45 degrees). The number of lesions observed per sequence varied from 35 to 69. Observer agreement was fair to good. The T1-weighted spoiled GE sequences with a TR of 65 ms, TE of 11.5 ms and FA of 30 degrees and 45 degrees were significantly superior to the other 34 sequences in the qualitative analysis. CONCLUSION: T1-weighted spoiled 3D-GE sequences with a TR of 65 ms, a TE of 11.5 ms, and a FA of 30-45 degrees were found to be optimal for in vitro imaging of cartilage at 0.5T.

Animals↗
PubMed1998

Objective stenosis quantification from post-stenotic signal loss in phase-contrast magnetic resonance angiographic datasets of flow phantoms and renal arteries.

In this study a semi-automated and observer-independent algorithm for quantifying post-stenotic signal loss (PSL) in three-dimensional phase-contrast (PC) magnetic resonance angiography (MRA) of patients with renal artery stenosis is presented. This algorithm was developed on MRA datasets of stenotic phantoms, included in a flow circuit with stationary flows. The length and the severity of the PSL (incorporating both the length and the degree of PSL) in the MRA datasets were proposed for quantifying the stenoses. The algorithm was tested in renal arteries; ten patients with renal artery stenosis and seven healthy volunteers were investigated. Digital subtraction angiography was performed in the patients and served as the gold standard. Stenosis severity showed better correlation with the severity of the PSL than with the length, both for in vitro and in vivo measurements. Spearman correlation coefficients (rs) showed statistically significant correlations between the severity of the PSL and parameters determined by digital subtraction angiography, i.e., percent diameter stenosis (rs = 0.90). The length of the PSL showed no correlation with the diameter stenosis (rs = 0.37). In conclusion, this study presents a semi-automated and observer-independent way of quantifying signal loss, and the severity of the PSL is proposed for quantifying stenoses, rather than the length of PSL.

Aged↗
PubMed1998

Ultrasmall superparamagnetic particles of iron oxide (USPIO) MR imaging of infarcted myocardium in pigs.

The purpose of this study is to assess the potential value of ultrasmall superparamagnetic iron oxide (USPIO) for the detection of acute myocardial infarction by magnetic resonance (MR) imaging. Spin-echo magnetic resonance imaging of the heart was performed before, immediately after, and approximately 35 and 90 min after 30 micromol Fe/kg of USPIO administration in seven pigs with surgically induced myocardial infarction. Gradient-echo sequences were used to identify contraction abnormalities at the site of infarction. Myocardial signal intensities were measured using region-of-interest analysis in normal and infarcted myocardium. In addition, liver and lung signal intensities were measured. Pathologic correlation was performed after sacrificing the animals. The infarct area was located with wall-motion analysis. The site of infarction was confirmed at pathologic examination. The signal-intensity ratio between infarcted and normal myocardium was not significantly changed after USPIO administration at equilibrium stages (immediately after injection p = 0.64, at 35 min p = 0.32, at 90 min p = 0.73). The signal intensity of the liver decreased significantly after contrast administration (p < 0.05). For the lung, the change in signal intensity after USPIO administration was not significant. This pig model is well suited to study wall motion abnormalities after induction of acute myocardial infarction. USPIO-enhanced magnetic resonance imaging does not improve the visualization of acute myocardial infarction at equilibrium stage.

Animals↗
PubMed1998

Circadian rhythm of plasma leptin levels in upper and lower body obese women: influence of body fat distribution and weight loss.

Plasma leptin concentrations were measured every 20 min for 24 h in eight normal weight women and in eight upper body and eight lower body obese women matched for body mass index. The circadian rhythm of leptin, which could mathematically be described by a cosine, was characterized by an acrophase just after midnight in all subjects. The amplitude of a cosine fit as well as the average 24-h leptin concentration were increased by 280% and 420%, respectively, in obese compared to normal weight women. All characteristics of leptin concentration profiles were similar in upper body and lower body obese women, except for a significantly higher amplitude in the lower body obese group. Visceral and sc body fat depots were measured using magnetic resonance imaging in all three groups. Average 24-h leptin concentrations were strongly correlated with sc fat (r = 0.84), whereas visceral fat was not an independent predictor of the plasma leptin level. A loss of 50% of the overweight was associated with a 55% decrease in the average 24-h leptin concentrations in obese women (95% confidence interval, 12.3, 26.6), whereas the characteristics of the circadian rhythm of leptin remained unchanged. Finally, it was observed that a fasting plasma leptin concentration is not an acceptable indicator of the average leptin concentration over 24 h.

Adipose Tissue↗