Jaap Valk

Histopathologic correlate of hypointense lesions on T1-weighted spin-echo MRI in multiple sclerosis

Postmortem unfixed whole brains from five multiple sclerosis (MS) patients were examined by MRI using a T2- and T1-weighted spin-echo (SE) sequence and histology to investigate the histopathologic characteristics of hypointense lesions on T1-weighted SE MR images. The degree of hypointensity was scored semiquantitatively by two blinded observers in reference to normal-appearing white matter. Signal intensities of the lesions and the normal-appearing white matter were measured to obtain contrast ratios. Hematoxylin-eosin stain was used to assess degree of matrix destruction (decrease of density of the neuropil) and cellularity of a lesion, Klüver-Barrera stain for degree of demyelination, Bodian stain for axonal density, and immunostaining of glial fibrillary acid protein for reactive astrocytes and fibrillary gliosis. Nineteen lesions were selected for analysis. Nearly all lesions were compatible with the chronic MS plaque: hypocellularity, absence of myelinated axons, in the presence of reactive astrocytes. Contrast ratios of the lesions were highly correlated (R = -0.90; p < 0.01), with degree of hypointensity scored semiquantitatively. Degree of hypointensity on T1-weighted SE images did not correlate with degree of demyelination or number of reactive astrocytes, but was associated with axonal density (R =-0.71; p = 0.001). A trend was found with degree of matrix destruction (R = 0.45; p = 0.052). We conclude that, in our limited sample, hypointense lesions seen on T1-weighted SE MR images are associated histopathologically with severe tissue destruction, including axonal loss. Our results need to be substantiated in a larger study on more varied patient material to evaluate the use of hypointense lesions as a surrogate marker of persistent deficit in MS patients.

Evaluation of magnetic resonance imaging for determination of left ventricular ejection fraction and comparison with angiography.

Left ventricular ejection fraction was measured by magnetic resonance imaging (MRI) and compared with standard monoplane left ventriculography in 46 patients with various cardiac diseases. Two different MRI strategies were used. In 28 patients (group 1), ejection fraction was determined using a single slice comparable with the right anterior oblique projection of the ventriculogram. Comparison of left ventricular ejection fraction yielded a poor correlation between single slice MRI (y) and ventriculography (x) (y = 28.7 + 0.47 x, r = 0.65). In 18 patients (group 2), a multiple contiguous slice MRI technique was used to allow ejection fraction and stroke volume determination by summing up the volumes of ventricular cavity intersections. Regression analysis showed a high correlation between multiple slice MRI (y) and ventriculography (x) (y = 7.2 + 0.88 x, r = 0.98). Also, correlation between MRI right (y) and left (x) ventricular stroke volumes was satisfactory, (y = -12.8 + 1.09 x, r = 0.83). It is concluded that the multiple slice imaging technique in MRI provides an accurate noninvasive means for quantification of left ventricular ejection fraction that can be extended to the determination of left ventricular volume.

The functional basis of ocular dominance: functional MRI (fMRI) findings.

Changes in cortical metabolism and cerebral perfusion may be recorded non-invasively with functional magnetic resonance imaging (fMRI). In pilot experiments, using fMRI with photic stimulation, we found differences between activated areas when the left or the right eye was stimulated separately. In this study we investigated whether this could be explained by ocular dominance. We studied 26 healthy volunteers (mean age 23.3 +/- 3.5 years). Ocular dominance was determined by means of the near-far alignment test. fMRI-measurements consisted of a double-slice gradient echo sequence. Slices were acquired placed parallel on either side of the calcarine fissure. Visual stimulation was done with goggles with two LED matrices (red light, 8 Hz); each in front of one eye. In each subject, the left and right eye were stimulated separately and together, in a randomly alternating order. Twenty-two subjects showed activation, of whom eight subjects had a dominant left eye and 14 a dominant right eye. In general the size of the activated area was bigger upon stimulation of the dominant eye. The difference with the area upon stimulation of the non-dominant eye was statistically significant in the right eye dominant group. These results indicate that the dominant eye actually activates a larger area of the primary visual cortex than the non-dominant eye. This provides for the first time a functional basis for the concept of ocular dominance.

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.

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.

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.

Rapid spontaneous resolution of an acute subdural hematoma.

A patient is reported who had spontaneous resolution of an acute traumatic subdural hematoma within 6 hours. In this period, clinical signs improved and computed tomography suggested disappearance of the hematoma. Magnetic resonance imaging demonstrated no real disappearance, but rather a redistribution of the blood. A rapid resolution like this has not been observed previously in the natural history of acute subdural hematoma.

Parametric fMRI analysis of visual encoding in the human medial temporal lobe

A number of functional brain imaging studies indicate that the medial temporal lobe system is crucially involved in encoding new information into memory. However, most studies were based on differences in brain activity between encoding of familiar vs. novel stimuli. To further study the underlying cognitive processes, we applied a parametric design of encoding. Seven healthy subjects were instructed to encode complex color pictures into memory. Stimuli were presented in a parametric fashion at different rates, thus representing different loads of encoding. Functional magnetic resonance imaging (fMRI) was used to assess changes in brain activation. To determine the number of pictures successfully stored into memory, recognition scores were determined afterwards. During encoding, brain activation occurred in the medial temporal lobe, comparable to the results obtained by others. Increasing the encoding load resulted in an increase in the number of successfully stored items. This was reflected in a significant increase in brain activation in the left lingual gyrus, in the left and right parahippocampal gyrus, and in the right inferior frontal gyrus. This study shows that fMRI can detect changes in brain activation during variation of one aspect of higher cognitive tasks. Further, it strongly supports the notion that the human medial temporal lobe is involved in encoding novel visual information into memory. Hippocampus 1999;9:637–643.

MRI OF NORMAL OR CANCEROUS LARYNGEAL CARTILAGES: HISTOPATHOLOGIC CORRELATION

MRI appearances of laryngeal cartilages, normal or invaded by cancer, are still relatively unfamiliar to most clinicians. Twelve primary laryngeal tumors out of a series of 65 patients which have been investigated by MRI were examined postoperatively by macroscopic and microscopic sectioning of the surgical specimens. Images were obtained with a 0.6 Tesla superconductive system using a solenoid surface coil. The authors emphasize the value of a combined use of T1‐weighted and balanced (relatively T2‐weighted images with still T1‐characteristics) Spin Echo images. T1‐weighted images permit differentiation between pathological and normal bone marrow. Balanced images allow separation between nonossified cartilage and tumor tissue. MRI is an additional tool in the diagnostic workup of cartilage invasion by tumor.

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.