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Biomedical subjects

J Valk

Publications and source records attributed to J Valk.

At least 127 records · Page 7Linked to original sources
PubMed1991

White matter disorders.

Magnetic resonance imaging (MRI) has a leading role in the diagnosis of white matter disorders because of its superior sensitivity. It also allows a detailed analysis of white matter disorders, improving the specificity of the diagnoses. There is an increasing knowledge about MRI patterns, in particular in hereditary metabolic disorders. Although these patterns are not always pathognomonic, they often serve as a guide for further diagnostic steps. In the non-hereditary white matter disorders, MRI has an increasing role in the diagnoses, follow-up, and monitoring of clinical trials. In inflammatory disorders, gadolinium-diethylenetriamine-penta-acetic acid (Gd-DTPA) appears to be helpful in analyzing the 'natural' course of the disease. Magnetic resonance spectroscopy (MRS) is gradually also finding a niche in the diagnosis of white matter disorders, both as a marker of neuronal loss and as an indicator of the age and activity of a lesion. New magnetic resonance techniques, such as diffusion and magnetic transfer imaging, will probably provide more information about the involvement of myelin sheaths.

Central Nervous System Diseases↗
PubMed1990

Value of gadolinium-diethylene-triamine pentaacetic acid dynamics in magnetic resonance imaging of acute myocardial infarction with occluded and reperfused coronary arteries after thrombolysis.

The use of the paramagnetic contrast agent gadolinium-diethylene-triamine pentaacetic acid (DTPA) was evaluated in magnetic resonance imaging (MRI) of 18 patients with an acute myocardial infarction after thrombolysis. The patency of the infarct-related vessel was assessed by coronary angiography. At 58 +/- 9 hours after infarction MRI was performed before and after bolus injection of 0.1 mmol/kg gadolinium-DTPA. Myocardial signal intensities were measured using a circumferential profile. Normal and infarcted myocardium showed a maximum signal intensity enhancement of 35 and 66%, respectively. Signal intensity of infarcted relative to normal myocardium (I/N) increased from 1.06 +/- 0.16 before to a maximum of 1.39 +/- 0.13 after gadolinium-DTPA (p less than 0.001), whereas the contrast between normal myocardium and a pseudo-infarct region in 2 healthy volunteers did not change. Between patients with reperfused infarct-related vessels and occluded vessels without collaterals, maximum I/N did not differ. However, observing I/N as a function of time after injection of gadolinium-DTPA, the reperfusion group differed from the occlusion group on images acquired directly after injection (1.29 +/- 0.10 vs 1.14 +/- 0.05, p less than 0.02). Thus, gadolinium-DTPA enhanced the visualization of acute myocardial infarction on relatively longitudinal (T1)-weighted MR images and its dynamics seem of potential value for the noninvasive assessment of coronary artery reperfusion after thrombolysis.

Adult↗
PubMed1990

MR imaging of the various stages of normal myelination during the first year of life.

The normal process of myelination of the brain mainly occurs during the first year of life. This process as known from histology can be visualized by MRI. Because of the very long T1 and T2 of immature brain tissue it is necessary to use adjusted pulse sequences with a long TR in order to obtain sufficient tissue contrast. With long TR SE images five stages can be recognized in the process of normal myelination and brain maturation. During the first month of life long TR short TE SE images show what are believed to be myelinated structures by correlation with published histological studies with a high signal intensity, unmyelinated white matter with a low signal intensity and gray matter with an intermediate signal intensity. The signal intensity of unmyelinated and myelinated white matter is reversed on long TR long TE SE images. In the course of a few weeks the signal intensity of unmyelinated white matter becomes high and the signal intensity of myelinated white matter becomes low also on long TR short TE SE images. These changes are believed to be caused by a loss of water and a change in chemical composition of brain tissue just prior to the onset of a wave of myelination. With progression of myelination the signal intensity of white matter changes from high to intermediate to low. These changes result in stages of isointensity, first in the central parts of the brain, later in the peripheral parts. At the end of the first year the adult contrast pattern is reached in all parts of the brain. IR images are also able to depict the progress of myelination, but appear to be less sensitive to subtle changes in the degree of myelination. The precise normal values for the five stages depend on the magnetic field strength and the pulse sequences used.

Brain↗
PubMed1990

Computer-assisted estimation of lines of action of human masticatory muscles reconstructed in vivo by means of magnetic resonance imaging of parallel sections.

The orientation of these lines of action was estimated in 9 healthy subjects, by reconstructing the muscle shape from a series of parallel sections obtained by MRI. In order to gain insight into sources of error, the lines of action of the masseter and medial pterygoid were estimated from two mutually perpendicular series of sectional images. Average results were compared with anatomical data from the literature. The results indicated that the accuracy of the estimate was principally dependent on the reliability of the reconstructions; the average accuracy of the estimated orientations was about 5 degrees.

Adult↗
PubMed1990

A case of progressive aphasia without dementia: "temporal" Pick's disease?

We report a patient who suffered from progressive aphasia for nine years, before developing mild behavioural disturbances. Sequential computed tomography (CT) scanning and magnetic resonance (MRI) imaging showed progressive bilateral temporal atrophy. The case is thought to be a temporal form of Pick's disease, in which isolated progressive aphasia was the only symptom over many years.

Aphasia↗
PubMed1990

MR findings of cartilage invasion by laryngeal cancer: value in predicting outcome of radiation therapy.

Thirty-nine patients who underwent radiation therapy with curative intent for laryngeal cancer were examined before treatment with magnetic resonance (MR) imaging, between November 1985 and January 1987. MR findings of cartilage invasion were correlated with the effectiveness of radiation treatment. Adequate interpretation of the MR examinations was not possible in four cases (10%). Cartilage invasion was found in 16 of the 35 remaining patients and was found even in small glottic lesions, clinically staged as T1b and T2. Laryngeal cancer recurred in 10 of the 16 patients with cartilage invasion shown by MR imaging. The presence of even small foci of invasion of the thyroid cartilage by laryngeal cancer appeared to increase the subsequent risk of tumor recurrence. Cartilage invasion seen at MR imaging might therefore shift the preference to partial laryngectomy as the initial treatment for small glottic tumors. Alternatively, radiation therapy alone would appear to require stringent follow-up to detect possible recurrence.

Adult↗
PubMed1990

Age-dependent changes in localized proton and phosphorus MR spectroscopy of the brain.

After birth the human brain is subject to major maturational changes, which are associated with changes in the biochemical composition of the brain and brain metabolism. Magnetic resonance (MR) spectroscopy has special capabilities in the analysis of in vivo metabolism. Volume-selective proton and phosphorus MR spectroscopy of the brain was performed on a 1.5-T magnet in 41 healthy children aged 1 month to 16 years. With advancing age, phosphorus spectra revealed a decrease in the ratios of phosphomonoesters (PMEs) to beta-adenosine triphosphate (ATP) and PMEs to phosphocreatine (PCr) and an increase in the ratios of phosphodiesters to beta-ATP, PCr to beta-ATP, and PCr to inorganic phosphate (Pi). No significant changes were observed in Pi/beta-ATP and pH. No changes occurred after the age of 3 years. Proton spectroscopy revealed an increase in the ratios of N-acetylaspartate (NAA) to choline (Ch) and NAA to creatine (Cr) and a decrease in Ch/Cr with increasing age. The most rapid changes were noted during the first 3 years of life, but changes were still observed at the age of 16 years.

Adenosine Triphosphate↗
PubMed1990

Cervical lymph node metastasis: assessment of radiologic criteria.

To estimate the accuracy of different radiologic criteria used to detect cervical lymph node metastasis in patients with head and neck carcinoma, seven different characteristics of 2,719 lymph nodes in 71 neck dissection specimens from 55 patients were assessed. Three lymph node diameters, their location, their number, the presence of a tumor, and the amount of necrosis and fatty metaplasia were recorded. The minimal diameter in the axial plane was found to be the most accurate size criterion for predicting lymph node metastasis. A minimal axial diameter of 10 mm was determined to be the most effective size criterion. The size criterion for lymph nodes in the subdigastric region was 1 mm larger (11 mm). Groups of three or more borderline nodes were proved to increase the sensitivity but did not significantly decrease the specificity. Radiologically detectable necrosis (3 mm or larger) was found only in tumorous nodes and was present in 74% of the positive neck dissection specimens. Shape was not a valuable criterion for the radiologic assessment of the cervical lymph node status.

Carcinoma, Squamous Cell↗
PubMed1989

[Diagnosis of laryngeal carcinoma using proton spin resonance tomography].

Seventy-eight patients were investigated by magnetic resonance (MR) imaging using optimal scan parameters and a surface coil. Forty-two patients were also examined by computer tomography (CT). Sixteen patients underwent laryngectomy. MR imaging of cancerous tissue in the larynx, and particularly of non-invaded and invaded cartilages, was examined by comparing MR images with sliced surgical specimens. Pre-operative CT and MRI findings were evaluated by comparing them with postoperative histopathological findings. MR T1-weighted images demonstrate localisation and extent of cancerous tissue. With combined use of T1-weighted and proton-density images MR imaging is superior to CT for showing cartilage invasion. Unfortunately, gross movement artifacts, which resulted in non-diagnostic images, occurred in 16% of the examinations.

Aged↗
PubMed1989

Imaging of brain metastases. Comparison of computerized tomography (CT) and magnetic resonance imaging (MRI).

For the demonstration of brain metastases both CT and MRI are available as diagnostic modalities. To compare both imaging methods as to their sensitivity in detecting brain metastases CT scans and MR images of 60 patients with suspected brain metastases were evaluated. Comparing contrast-enhanced CT and plain MRI neither modality was found to be clearly superior in this respect.

Adolescent↗
PubMed1989

Magnetic resonance imaging of partial temporomandibular joint disc displacement.

Unilateral magnetic resonance imaging (MRI) of the symptomatic temporomandibular joint (TMJ) was performed on 55 patients. The position of the articular disc in relation to the condyle was established on sagittal images. Particular attention was paid to partial or complete anterior positioning of the disc. MRI was correlated with clinical and, in 33 cases, surgical findings. The concept of partial anterior displacement may be useful in relation to treatment planning.

Adolescent↗
PubMed1989

Anterolateral lumbar meningocele presenting as an ovarian cyst, in a patient with neurofibromatosis.

A case of an anterolateral lumbar meningocele in a patient with neurofibromatosis is presented. As anterolateral lumbar meningocele may present itself only by non-specific symptoms like low back pain or abdominal pain, such symptoms require prompt diagnostic work up in patients with neurofibromatosis. The significance of MR imaging in early recognition of this rare anomaly is emphasized.

Adult↗
PubMed1989

Imaging the bone marrow with magnetic resonance during a crisis and in chronic forms of sickle cell disease.

Five patients with sickle cell disease have been studied by magnetic resonance imaging (MRI) in three instances during a crisis. Attention was directed to the pelvis and lower extremities. Bone marrow pathology has been classified according to generalised or circumscribed alterations in signal intensity on T1 weighted spin-echo sequences. Both acute and chronic changes were observed.

Adult↗
PubMed1989

Schilder's diffuse sclerosis: case study with three years' follow-up and neuro-imaging.

Schilder's diffuse myelinoclastic sclerosis, a rarely described disease in childhood, was diagnosed in the case of a 6-year-old girl with subacute cerebral disease. CT-scanning showed asymmetric rim-enhancing lesions within the cerebral white matter. Spontaneous clinical improvement occurred prior to corticosteroid treatment. Follow-up by CT and MRI for three years showed the development of stable amyelinic lesions. Improvement in motor control and in electrophysiological recordings contrasted with an arrest in neuropsychological development. The differential diagnosis and the prognostic implications of this disease are stressed.

Child↗