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Biomedical subjects

J Valk

Publications and source records attributed to J Valk.

At least 73 records · Page 4Linked to original sources
PubMed1995

Semiquantitation of regional myocardial blood flow in normal human subjects by first-pass magnetic resonance imaging.

The purpose of this study was to investigate the feasibility of first-pass MR imaging for measurement of regional myocardial blood flow in human beings. The first pass of the contrast agent Gd-DTPA through the myocardium was imaged in 12 normal volunteers with an ECG-gated Turbo-Flash sequence. The MTT of the contrast agent through the myocardium after a bolus injection was derived from curves of SI versus time. The bolus was injected through an intravenous catheter, which was advanced to the central venous position (preferably the right atrium). To investigate myocardial input function, different bolus concentrations and catheter positions were compared. It is concluded that first-pass MR imaging is feasible in human subjects when a central injection of 0.03 mmol/kg of Gd-DTPA is applied. MTT values were similar throughout the myocardium of normal subjects at rest, reflecting normal perfusion. Absolute values of MTT were related to the myocardial input.

Adult↗
PubMed1995

Protocol for two-dimensional magnetic resonance coronary angiography studied in three-dimensional magnetic resonance data sets.

The purpose of this study was to develop a standardized method of 2D MRA of the proximal 50 mm of the major epicardial coronary arteries. Therefore the efficacy of fixed imaging planes (transverse, coronal, sagittal, 30-degree RAO equivalent, and 60-degree LAO equivalent) in imaging coronary arteries was compared to that of oblique planes defined by the operator on a previously obtained image. 3D data sets obtained by a respiratory-gated 3D MRA method in eight patients with a mean age of 57 years were studied by multiplanar reformatting. Efficacy of planes was expressed as an IOE. Fixed transverse imaging planes proved to be equally efficacious as operator-defined planes in imaging the left main (IOE 2.2 +/- 1.0 vs 2.2 +/- 0.9, p = NS) and LAD (IOE 6.0 +/- 1.9 vs 8.2 +/- 2.0, p = NS). Operator-defined planes were superior to fixed imaging planes in imaging the RCA (IOE 6.3 +/- 1.2 vs 3.5 +/- 1.2, p < 0.001) and the LCx (IOE 6.2 +/- 2.3 vs 4.8 < 2.3, p < 0.05). On the basis of these results, a standardized 2D MRA protocol for the proximal coronary arteries was proposed. Pitfalls in interpretation of coronary MRA images were discussed.

Aged↗
PubMed1995

Remote expert consultation for MRI procedures by means of teleradiology.

From April 1992 to January 1993, radiology expert opinion for MRI procedures was offered by means of teleradiology. The experiment was carried out in addition to an existing service of a mobile MRI unit. MRI images were sent by means of teleradiology via regular telephone lines from the mobile MRI unit to an academic hospital, which served as expert consultation centre. During this period, 43 requests for expert opinions were performed. This article describes the clinical effects of these expert opinions, and the technical and organisational requirements to perform teleradiology in daily clinical practice.

Humans↗
PubMed1995

Partially saturated fluid attenuated inversion recovery (FLAIR) sequences in multiple sclerosis: comparison with fully relaxed FLAIR and conventional spin-echo.

Fluid attenuated inversion recovery (FLAIR) sequences produce selective cerebrospinal fluid (CSF) suppression by employing a very long inversion time (TI). We used the FLAIR sequence to study patients with multiple sclerosis (MS) at 0.6 T. So far, a very long TR (and long acquisition time) has been used in a fully relaxed (FR-FLAIR) system. To speed up the FLAIR sequences, we used a shorter TR, and demonstrated that complete CSF suppression can be maintained with partial saturation (PS-FLAIR) by reducing TI at the same time. The introduction of partial saturation, however, reduced the contrast between lesions and normal appearing white matter (NAWM). Suboptimal CSF suppression therefore had to be accepted to maintain sufficient lesion to NAWM contrast. Using a TE of 60 ms, the PS-FLAIR and FR-FLAIR performed equally well in the detection of MS-lesions, although the former provided poorer CSF suppression. Both FLAIR sequences, however, provided poorer constrast between lesions and NAWM compared to conventional spin-echo sequences. Although the long acquisition time of the FLAIR sequence can be reduced by using partial saturation, complete CSF suppression and good lesion to NAWM contrast are incompatible at short TRs. Using a TE of 60 ms, conventional spin-echo sequences detect more lesions and provide better contrast between lesions and NAWM than FLAIR sequences in MS patients.

Brain↗
PubMed1995

The syndrome of autosomal recessive pontocerebellar hypoplasia, microcephaly, and extrapyramidal dyskinesia (pontocerebellar hypoplasia type 2): compiled data from 10 pedigrees.

The syndrome of autosomal recessive pontocerebellar hypoplasia, microcephaly, severely impaired mental and motor development, and extrapyramidal dyskinesia is a distinct system degeneration, previously designated pontocerebellar hypoplasia type 2 (PCH-2). To further characterize its clinical and neuroimaging features, we compiled data from 10 nonrelated pedigrees. Six pedigrees were Dutch, two Swedish, and two German. All 16 patients showed an identical profile of virtually absent developmental milestones, early-onset severe chorea, and microcephaly together with pontocerebellar hypoplasia. Family distribution supports autosomal recessive transmission. The present data support the PCH-2 phenotype as a distinct neurogenetic entity.

Adolescent↗
PubMed1995

Correlating MRI and clinical disease activity in multiple sclerosis: relevance of hypointense lesions on short-TR/short-TE (T1-weighted) spin-echo images.

Magnetic resonance imaging (MRI) is being used as an outcome criterion in therapeutic trials in multiple sclerosis (MS) on the assumption that it, as a sensitive marker of biologic disease activity, could serve as a surrogate marker of disability. We evaluated the relation between MRI findings and disability in a quantitative follow-up study of 48 MS patients. Median duration of follow-up was 24 months (range, 10 to 42 months). Computer-assisted volume measurements employing a seed-growing technique yielded a standard error of measurement of 0.275 cm2. The median total area of the hyperintense lesions on the initial T2-weighted images was 8.4 cm2. The median increase was 0.76 cm2/yr (9%). In a subgroup (n = 19) with short-TR/short-TE spin-echo (SE) images, we measured the hypointense lesion load. The median total area of the lesions at entry was 0.70 cm2, with a median increase of 0.28 cm2/yr (40%). The total area of the hyperintense lesions on the initial T2-weighted images showed a weak correlation with the Expanded Disability Status Scale score at entry (Spearman rank correlation coefficient [SRCC] = 0.30; 0.02 < p < 0.05). The increase in disability showed a positive correlation (SRCC = 0.19) with the increase in hyperintense lesion load on the T2-weighted SE images, but this correlation did not reach statistical significance (p = 0.09), probably because of lack of clinical progression.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

The effect of gadolinium on the sensitivity and specificity of MR in the initial diagnosis of multiple sclerosis.

PURPOSE: To determine whether gadolinium can improve the sensitivity and specificity of MR imaging for the initial diagnosis of multiple sclerosis. METHODS: Patients (n = 57) with neurologic symptoms suggesting multiple sclerosis were studied prospectively. MR imaging consisted of T2-weighted and gadolinium-enhanced T1-weighted spin-echo images. Lumbar puncture was performed for cerebrospinal fluid analysis in 34 patients. RESULTS: After imaging, 17 patients (35%) had clinically definite multiple sclerosis. Cerebrospinal fluid examination had a sensitivity of 69% and specificity of 38%. Using liberal criteria, the sensitivity of T2-weighted MR imaging was 94% and the specificity 55%; using more strict criteria, the specificity increased to 65% with a sensitivity of 88%. Gadopentetate dimeglumine enhancement increased the specificity further to 80% with a loss of sensitivity (59%). CONCLUSION: Gadolinium enhancement increases the specificity of MR imaging in the early diagnosis of multiple sclerosis.

Adult↗
PubMed1994

Limited duration of the effect of methylprednisolone on changes on MRI in multiple sclerosis.

Treatment with methylprednisolone reduces the duration and severity of clinical relapses in multiple sclerosis (MS), while reducing the number of gadolinium-enhancing lesions on T1-weighted MRI. We performed serial MRI imaging after methylprednisolone treatment to see whether suppression of enhancement persists and whether related abnormalities on T2-weighted images disappear at follow-up. Thirteen patients with definite MS received a total of 31 courses of methylprednisolone over an average period of 50 weeks. Gadolinium-enhanced MRI was obtained before and after treatment, then at monthly intervals, using a standardised repositioning and imaging protocol. Two experienced readers in conference defined the number of active (gadolinium-enhancing and new or enlarging nonenhancing) lesions. We detected 609 active lesions on 195 examinations. Directly after treatment the reduction in the number of enhancing lesions was 78%, indicating restoration of the BBB and suppression of inflammation. It was uncommon for a lesion which stopped enhancing to show enhancement on a subsequent examination. No beneficial effect was observed on the rate of disappearance of related abnormalities on T2-weighted images, indicating persistent change such as oedema, cellular infiltration or demyelination. Moreover, in 89% of cases, an increase in the number of active lesions was observed before new clinical activity, if any, was observed (on average 52% earlier). MRI enabled us to demonstrate that the duration of the effect of methylprednisolone treatment is temporary (on average 9.7 weeks).

Adult↗
PubMed1994

Radiotherapy response of cerebral metastases quantified by serial MR imaging.

A patient with cerebral metastases, treated with radiotherapy, underwent serial gadolinium-enhanced MR imaging. The MR images were quantified using home developed software to evaluate the changes in volumes of tumor mass and edema after radiotherapy (mean precision of the quantification technique less than 5%). The decrease in tumor volume and edema observed after radiotherapy preceded clinical improvement. The presented technique can be used to accurately assess, more directly than using clinical scales, the effect of putative therapies.

Brain Edema↗
PubMed1994

Computed tomography in evaluation of early secondary bone grafting.

Computed tomography (CT) was used to determine the fate of the bone graft in cleft lip and palate patients. Eight right-sided unilateral cleft lip and palate patients from the Free University Hospital in Amsterdam, treated with early, secondary bone grafting, were evaluated immediately after the operation and 1 year postoperatively. Approximately 70% of the volume of transplanted iliac crest bone was still present in the cleft area after 1 year.

Bone Resorption↗
PubMed1994

Magnetic resonance evaluation of disease activity during pregnancy in multiple sclerosis.

We followed two women with MS during pregnancy by means of serial unenhanced MR imaging. On each follow-up image, we assessed the number of new or enlarging lesions. Both women showed a decrease in MR disease activity during the second half of pregnancy and a return of MR disease activity to prepregnancy levels in the first months postpartum. These findings support the view that pregnancy reduces disease activity in MS.

Adult↗
PubMed1994

Temporal lobe epilepsy: the various MR appearances of histologically proven mesial temporal sclerosis.

PURPOSE: To determine the frequency of appearance of various MR signs in mesial temporal sclerosis, to determine the optimal scanning planes for their visualization, and to propose a histologic explanation for the diminished demarcation between gray and white matter in the temporal lobe, a frequent MR finding in patients with mesial temporal sclerosis. METHODS: MR scans of 14 surgically treated patients with epilepsy and histologically proven mesial temporal sclerosis were assessed for the presence of six features: feature 1, high signal intensity in the hippocampus; 2, reduced hippocampal size; 3, ipsilateral atrophy of the hippocampal collateral white matter; 4, enlarged temporal horn; 5, reduced gray-white matter demarcation in the temporal lobe; and 6, decreased temporal lobe size. RESULTS: Feature 1 was present in 14 patients and was best appreciated on the T2-weighted images in planes parallel to the long axes of the hippocampi. Feature 2, present in 12 patients, and feature 6, present in 9 patients, were optimally seen in the coronal planes and on the inversion-recovery sequences in particular. Feature 3, present in 12 patients, was optimally seen on the coronal T2-weighted images. Feature 4, seen in 11 patients, was equally well seen in all planes (transverse, coronal, and parallel to the long axes of the hippocampi). Feature 5, seen in 10 patients, was best appreciated on the T2-weighted images in the planes of the long axes of the hippocampi. Histologic investigation of the temporal lobe white matter in the 10 patients with feature 5 demonstrated on the MR scan showed abnormalities in 7 cases. Oligodendroglia cell clusters were found in 6, with concomitant corpora amylacea in 1 case and perivascular macrophages with pigment a sole finding in another case. CONCLUSION: Of the six features found in cases of mesial temporal sclerosis on MR, increased hippocampal signal intensity is the most consistent. A decreased gray-white matter demarcation in the temporal lobe parenchyma is also a frequent feature of this disease. A combination of multiple scanning planes results in an optimal demonstration of lesions.

Adolescent↗
PubMed1994

MR of the caudal regression syndrome: embryologic implications.

PURPOSE: To evaluate the spectrum of developmental anomalies observed in patients with the caudal regression syndrome and relate them to the pathogenesis of this syndrome. METHODS: Nineteen children with caudal regression were investigated with MR. RESULTS: The level of vertebral agenesis varied from T-11 to S-5. In 9 of the 19 children the characteristic high-ending wedge-shaped cord terminus was observed. A separation of the anterior and posterior spinal roots of the cauda equina was observed in 9 patients. Four patients had a tethered spinal cord, in 1 in combination with a wedge-shaped cord terminus. CONCLUSIONS: The pathogenesis of the caudal regression syndrome can be divided into two kinds: there is usually a disturbance of the primary neurulation process; in other cases there is a derailment of the process of degeneration and differentiation of an initially normally developed primary and secondary neural tube. MR aids understanding of the morphology and pathogenesis of congenital malformations involved (including the associated anomalies of the genitourinary and gastrointestinal systems), but other studies are still necessary to determine the exact mechanism of this syndrome.

Adolescent↗
PubMed1994

Toxic leukoencephalopathy after inhalation of poisoned heroin: MR findings.

Retrospective MR studies of four patients with neurologic symptoms after inhalation of contaminated heroin vapor revealed extensive, typically symmetrical lesions in the white matter of the cerebrum, cerebellum, and midbrain. Selective involvement of the corticospinal tract, the solitary tract, and the lemniscus medialis also has been found.

Administration, Inhalation↗
PubMed1994

Phase-contrast cine MR imaging of normal aqueductal CSF flow. Effect of aging and relation to CSF void on modulus MR.

Cine phase-contrast MR imaging was used to study pulsatile CSF flow in the aqueduct in 11 young controls (mean age 30 years) and 9 old controls (mean age 69 years). A high-resolution gradient echo technique and an oblique imaging plane, perpendicular to the aqueduct, was used to avoid volume averaging. Phantom studies confirmed that the technique was accurate. Aqueductal velocity and flux in old controls was higher than in young controls, but the differences were not significant. For all controls together, the averaged peak velocity was 4.2 +/- 1.5 cm/s in rostral and -7.8 +/- 4.9 cm/s in caudal direction; for the flux it was 0.16 +/- 0.10 cm3/s in rostral and -0.29 +/- 0.19 cm3/s in caudal direction. Phase-contrast measurements were significantly related to flow-void on modulus MR images, but not with ventricular size or cortical atrophy. The present technique avoids underestimation of aqueductal flow, and therefore reveals higher aqueductal velocity and flux values than previous studies. Factors other than age or atrophy seem to determine aqueductal CSF flow.

Adult↗
PubMed1993

[Pelizaeus-Merzbacher disease].

Two cases of Pelizaeus-Merzbacher disease are described, one with the classical and one with the connatal form, both in the same family. It is an X-linked disease affecting the myelinisation of the brain. Pelizaeus-Merzbacher manifests itself within a few months after birth and has a progressive character. The disease is caused by a point mutation in the PLP gene coding for the myelin-protein proteolipid protein. MRI imaging has improved the possibility for diagnosis especially in families with cases of Pelizaeus-Merzbacher disease and PLP gene detection has brought antenatal diagnosis in focus.

Adult↗