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Biomedical subjects

J Valk

Publications and source records attributed to J Valk.

At least 109 records · Page 6Linked to original sources
PubMed1992

A comparison of jaw muscle cross-sections of long-face and normal adults.

Long-face subjects have smaller maximum molar bite forces than do normal individuals. This has been attributed both to differences in moment arms and size of the jaw muscles. In this study, a comparison was made between the mid-belly cross-sectional areas of the jaw muscles of 13 long-face and 35 normal adults by means of serial MRI scans. The subjects were selected on the basis of anterior lower face height as a percentage of anterior total face height. These and other cephalometric variables were measured from lateral radiographs. In the long-face group, the cross-sectional areas of the masseter, medial pterygoid, and anterior temporal muscles were, respectively, 30%, 22%, and 15% smaller than in the control group. By a discriminant analysis and a multivariate analysis of variance, these differences were found to be significant (p less than 0.001). The findings of this study hint that differences in the sizes of the jaw muscles of long-face and normal subjects might explain, in part, the observed differences in maximum molar bite force.

Adult↗
PubMed1992

A correlative triad of gadolinium-DTPA MRI, EDSS, and CSF-MBP in relapsing multiple sclerosis patients treated with high-dose intravenous methylprednisolone.

In a prospective study, we compared the number of gadolinium-DTPA (Gd-DTPA) enhancing lesions on MRI with the CSF and clinical findings before and after a total of 20 courses of high-dose intravenous methylprednisolone in relapsing multiple sclerosis patients. Before treatment, there was a significant correlation of Gd-DTPA enhancement (seen on 16 of 20 scans) and CSF myelin basic protein (MBP). If enhancement with Gd-DTPA represents inflammation and CSF-MBP indicates myelin breakdown, the amount of inflamed tissue should correlate with the amount of myelin being damaged. Clinical improvement occurred following 15 of 20 courses, and decrease of Gd-DTPA enhancement in 12 of 16 scans; the mean CSF-MBP level was the only CSF variable to return to reference values. There was a significant correlative triad of decrease in CSF-MBP, Gd-DTPA enhancement, and clinical disability. Thus, the clinical effect of methylprednisolone might be accompanied by a reduction of inflammation and myelin breakdown.

Adult↗
PubMed1992

Do metastases in vertebrae begin in the body or the pedicles? Imaging study in 45 patients.

We analyzed CT scans of the spine obtained in patients with vertebral metastases to determine what specific portion of the vertebra is initially involved by metastasis. The CT findings were then correlated with the abnormalities seen on plain films. Forty-five patients with histologically proved metastases in 95 vertebrae were included in the study. In all patients, CT scans and plain films of the spine were obtained within 1 week of each other. Analysis of the CT scans showed that the vertebral body was the portion of the vertebra that was most frequently destroyed by the metastases. Destruction of a pedicle was never identified in the absence of involvement of the body. The opposite was true on plain films, in which the most common finding was destruction of the pedicles. CT showed that the position of the metastases in the vertebra correlated with the sites of entry of the vertebral vessels. Our results show that the initial anatomic location of metastases within vertebrae is in the posterior portion of the body. Analysis of CT scans shows that the body is involved before the pedicles, although destruction of the pedicles is the most common finding on plain films. The pedicles are not the primary site of metastatic involvement. Destruction of the pedicles occurs only in combination with involvement of the vertebral body.

Adult↗
PubMed1992

Relapsing-remitting multiple sclerosis: sequential enhanced MR imaging vs clinical findings in determining disease activity.

OBJECTIVE: Sequential MR imaging frequently shows disease activity (clinically silent new brain lesions) in subgroups of patients with multiple sclerosis and therefore is valuable in monitoring the effects of treatment. Monitoring of disease activity in patients being treated for relapsing-remitting multiple sclerosis will increase in importance as new and safe therapies are developed. We studied sequential enhanced MR images of patients with early relapsing-remitting multiple sclerosis to define the MR features that indicate disease activity in this subgroup of patients and to compare MR imaging and clinical findings for this purpose. SUBJECTS AND METHODS: Seven patients with relapsing-remitting definite multiple sclerosis were examined monthly for 4-12 months. For each image, a standard repositioning protocol consisting of three images was used to ensure reproducibility of axial (double oblique) image planes, planned according to internal landmarks. A total of 58 unenhanced T2-weighted and enhanced T1-weighted MR images were obtained. RESULTS: MR images showed new enhancing lesions in six of the seven patients. On 25 (43%) of the 58 enhanced T1-weighted MR images, a total of 50 new enhancing lesions were observed, and on one image a reenhancing lesion was seen. The unenhanced T2-weighted images showed corresponding abnormalities for 92% of the new enhancing lesions. At follow-up, most lesions (86%) were enhanced on only one occasion: 4% were enhanced on more than two consecutive monthly MR examinations. Forty-nine percent of the lesions seen on T2-weighted images "disappeared" (beyond the resolution of the imaging system) after a mean follow-up of 3.5 months, especially lesions that were initially smaller than 5 mm. During the study, only five clinical relapses occurred in three patients (all at times when MR images showed contrast-enhancing lesions), and fixed disability did not increase. On 21 additional occasions, MR images showed new enhancing or reenhancing lesions in patients who were clinically stable at the time (4.2 times more clinically silent disease activity). CONCLUSION: Our results suggest that contrast-enhanced MR imaging is more sensitive than clinical monitoring for detecting new disease activity in patients with relapsing-remitting multiple sclerosis and that MR imaging might be useful in the evaluation of therapeutic regimens.

Adult↗
PubMed1991

Magnetic resonance imaging vs palpation of cervical lymph node metastasis.

In a series of 100 patients with head and neck carcinoma, the preoperative histopathologic findings of palpation and magnetic resonance imaging were compared with regard to both laterality and lymph node level (I through V). The overall error for palpation in detecting affected sides was 32%. Gadolinium-enhanced magnetic resonance images reliably upgraded 60% of the clinically negative necks, the overall error of magnetic resonance imaging being 16%. However, for both modalities, the sensitivity per level was too low to allow for selective neck dissections in case of only one positive level. These findings show that apart from primary tumor grading, magnetic resonance imaging can improve the preoperative grading of cervical lymph nodes. In selected cases, this may change the treatment plan to a "wait-and-see" policy or a more conservative type of neck dissection.

Aged↗
PubMed1991

Malformations of the spinal cord in 53 patients with spina bifida studied by magnetic resonance imaging.

The incidence of associated malformations of the hindbrain and spinal cord in patients with spina bifida was investigated by a clinical and magnetic resonance study. The incidence of these malformations in combination with spina bifida was 49/53 (92.5%). Fifty-tree children born with spina bifida aperta (40 patients) or spina bifida occulta (13 patients) formed the study group. The incidence of the various malformations were: Chiari malformations, type I, 10/53 (19%), and type II, 20/53 (38%); syringomyelia, 13/53 (24.5%); hydromyelia 4/53 (7.5%); tethered cord malformation, 35/53 (66%); diastematomyelia 2/53 (4%). Thirty-seven of the 49 patients with associated malformations had no clinical signs at the time of our study. The results point to the fact that in the pediatric age group, associated spinal defects often remain asymptomatic.

Abnormalities, Multiple↗
PubMed1991

Pattern recognition in magnetic resonance imaging of white matter disorders in children and young adults.

Magnetic resonance imaging (MRI) is considered to be a highly sensitive modality for visualizing white matter abnormalities. Estimations of its specificity are far less positive. However, diagnostic specificity depends upon both the inherent qualities of MRI and on the quality of image interpretation. Systematic and detailed analysis of many image elements, and substantial prior experience improve the quality of image interpretation and thus improve diagnostic specificity. The present study has been set up to develop a pattern recognition system which combines sensitivity and specificity, systematic analysis of image elements and prior experience. This pattern recognition is based on the data of 277 patients with white matter disorders referred for MRI. The information was stored in a data base and computer analyzed. Twenty-two MRI patterns were discerned in as many disease categories. The frequency of occurrence of each MRI abnormality was assessed per disease category to establish the pattern of abnormalities characteristic for each separate disease category. The pattern recognition program was also written so that: (a) when fed data about MRI abnormalities observed in a new case, the computer produces a differential diagnosis with probabilities and 95% confidence intervals for each differential diagnosis; (b) specific data on the MRI findings of new cases could be added to the data base to improve the experience and accuracy of the program. This program for pattern recognition of abnormalities in the MR images of white matter disorders enhances the specificity of image interpretation and provides a wonderful aid for teaching purposes.

Adolescent↗
PubMed1991

Neuroimaging in lissencephaly type I.

The CT scan's of 22 patients with lissencephaly type I, a severe developmental disorder of the cerebral cortex, were studied. In 6 patients a magnetic resonance (MR), scan was also performed. The CT and MR scans of the lissencephaly patients were compared to a control group consisting of 49 patients with a normal CT or MR scan. In lissencephaly the cortical thickness was always larger than 10 mm, as compared to less than 7 mm in the normal situation. In lissencephaly the WSF/DSF index (with/depth of the sylvian fissure) was always larger than 0.29, while in the normal situation less than 0.25.

Adolescent↗
PubMed1991

The MR spectrum of peroxisomal disorders.

In the last decade an increasing number of peroxisomal disorders has been recognized. Almost all peroxisomal disorders affect the central nervous system. Many of them lead to demyelination, some of them lead to migrational disturbances. The MR pattern of X-linked adrenoleukodystrophy is well known, but the pattern of the other peroxisomal disorders is less well known. We evaluated the gray and white matter abnormalities of 20 patients on 32 occasions. We compared the results with histological data and in this way came to the description of a number of characteristic MR patterns occurring in peroxisomal disorders: (1) Neuronal migrational disturbances in combination with hypomyelination, dysmyelination or demyelination. (2) Symmetrical demyelination of posterior limb of the internal capsule, cerebellar white matter and brain stem tracts with a variable affection of cerebral hemispheres. (3) Symmetrical demyelination, exhibiting two zones, starting in the occipital area and spreading outwards and forwards; affection of brain stem tracts. (4) Less characteristic patterns of demyelination. The patterns are illustrated and differentiation from other disorders is discussed.

Adolescent↗
PubMed1991

Serial quantitative MR assessment of optic neuritis in a case of neuromyelitis optica, using Gadolinium- "enhanced" STIR imaging.

A patient is presented with neuromyelitis optica. MR imaging, using a short inversion time inversion recovery (STIR) technique, clearly depicted the lesion in the left optic nerve. Subsequent serial STIR imaging, with and without Gadolinium-DTPA, allowed quantitative assessment of changes parallel to improved optic nerve function. STIR imaging is a sensitive technique to demonstrate optic nerve lesions, and enables quantitative assessment to be made of the effect of (steroid) medication.

Adult↗
PubMed1991

Relationships between jaw muscle cross-sections and craniofacial morphology in normal adults, studied with magnetic resonance imaging.

In 32 Caucasian adult males serial MRI scans of the jaw muscles were taken approximately perpendicular to the mean fibre direction of the jaw muscles to determine their cross-sectional areas. These areas are proportional to the maximal isometric strength of a muscle. To describe facial skeletal variation, nine angular and 21 linear cephalometric measurements were recorded, and statistically reduced by means of multiple regression and principal component analysis. Six components were extracted, rotated, and subsequently correlated with the maximal cross-sectional areas of the jaw elevators and anterior digastric muscle. Positive significant correlations were found between a linear combination of several transversal skull dimensions on the one hand, and the maximal temporalis and masseter cross-sections on the other. A negative significant correlation was found between the flexure of the cranial base and the temporalis cross-section. Surprisingly, no significant correlations were found between either anterior facial height or posterior facial height and any of the jaw muscles cross-sections. It was concluded that, in adult males with normal skull shape, relationships exist to a limited extent between craniofacial morphology and the cross-sectional areas of the jaw muscles.

Adult↗
PubMed1991

An in vivo validation of quantitative blood flow imaging in arteries and veins using magnetic resonance phase-shift techniques.

Magnetic resonance (MR) techniques have recently been introduced, allowing quantitative measurement of blood flow with high spatial and temporal resolutions. These techniques are based on the phase of the MR signal rather than on the amplitude, and are referred to as MR phase or velocity mapping. Clinical validation is still lacking. We therefore performed an in vivo validation of such a technique in 17 healthy volunteers. Velocity maps were acquired at 50 ms intervals over the cardiac cycle in the aorta, superior and inferior vena cava. Plots were made of flow velocity and volume flow vs time and used for calculation of left ventricular stroke volume (SV), cardiac output (CO) and venous return. Comparison with Doppler ultrasound (x) yielded y = -7.5 + 1.1x (r = 0.76) for SV measurements (ml), and y = 0.3 + 0.9x (r = 0.86) for CO calculations (1 min-1). Comparison between MR SV (x) and MR determination of venous return (y), obtained by summation of the flow volumes per cardiac cycle in the superior and inferior vena cava, was close to identity, y = 1.3 + 1.0x (r = 0.91). Also, preliminary applications are presented in patients with aortic diseases. The findings of this study show that magnetic resonance velocity imaging can be accurately applied in vivo as a non-invasive means of measuring flow.

Aortic Dissection↗
PubMed1991

Myelination as an expression of the functional maturity of the brain.

A prospective cross-sectional study was performed on hydrocephalic infants and children. MRI was used to assess the state of myelination and to quantify the intracranial cerebrospinal fluid (CSF) volume repeatedly in all children. At the same time, neurodevelopmental testing was performed. A positive correlation was found between the progress of myelination and psychomotor development, but there were no significant correlations between CSF volume and myelination or between CSF volume and psychomotor development. This study provides strong evidence in favour of Flechsig's thesis that myelination expresses the functional maturity of the brain. The interdependency of neuronal maturation and progress of myelination are discussed.

Brain↗
PubMed1991

Occult metastatic neck disease: detection with US and US-guided fine-needle aspiration cytology.

The authors performed a prospective study of the value of ultrasonography (US) and US-guided fine-needle aspiration cytology (FNAC) for assessment of N0 lesions in the neck. Preoperative US was performed in 107 patients with squamous cell carcinoma of the head and neck, who underwent 132 elective neck dissections. During the US examination of the last 54 patients, who underwent 70 elective neck dissections, US-guided FNAC was performed. US alone was found to be an unreliable method for detecting occult lymph node metastasis; the accuracy never exceeded 70% (93 of 132), with a sensitivity of 60% (32 of 53) and a specificity of 77% (61 of 79). In contrast, US-guided FNAC had an accuracy of 89% (62 of 70), a sensitivity of 76% (25 of 33), and a specificity of 100% (37 of 37). Because of the high sensitivity and specificity of US-guided FNAC for the assessment of the N0 neck, this modality may play an important role in directing treatment of these patients in the future.

Biopsy, Needle↗
PubMed1991

Quantitative MRI changes in gadolinium-DTPA enhancement after high-dose intravenous methylprednisolone in multiple sclerosis.

In 12 patients with definite multiple sclerosis who received a total of 21 courses of high-dose (1 gram daily for 10 consecutive days) intravenous methylprednisolone, we performed MRI of the brain with and without gadolinium-DTPA before and after treatment. On the initial MRI, there was a total of 98 enhancing lesions, 93 of which were also represented on the unenhanced images. After treatment, 13 patients improved clinically, and 78 of the lesions lost enhancement but remained visible on the unenhanced images. There were six new enhancing lesions on the second MRI. Thus, the blood-brain-barrier integrity improved after high-dose IV methylprednisolone, which correlated well with the clinical improvement. The lesions remaining visible on the unenhanced images indicate an incomplete histologic recovery at the time of the second scan, and also demonstrate that unenhanced MRI alone is not sufficient to monitor disease activity in the short term in multiple sclerosis.

Adult↗