Stig Holtås

Assessment of regional cerebral blood flow by dynamic susceptibility contrast MRI using different deconvolution techniques

Regional cerebral blood flow (rCBF) was assessed using dynamic susceptibility‐contrast MRI at 1.5 T. A simultaneous dual FLASH pulse sequence and Gd‐DTPA‐BMA (0.3 mmol/kg b.w.) were used for examination of 43 volunteers, measuring rCBF in frontal white matter (WM) and in gray matter in the thalamus (GM). Arterial input functions (AIFs) were registered 1) in the carotid artery and 2) in an artery within the GM/WM slice. The measured concentration‐vs.‐time curve was deconvolved with the AIF using both Fourier Transform (FT) and Singular Value Decomposition (SVD). Relative rCBF was given by the height of the deconvolved response curve. For each volunteer, eight different rCBF maps were calculated, representing different combinations of deconvolution techniques, AIFs, and filters. The average GM–WM rCBF ratios ranged from 2.0–2.2, depending on methodology. Absolute rCBF was 68 ± 28 ml/(min 100 g) in GM and 35 ± 13 ml/(min 100g) in WM (mean ± SD, n = 39). GM–WM rCBF ratios obtained using SVD were 6–10% higher than corresponding ratios obtained using FT. Magn Reson Med 43:691–700, 2000.

Isolated acute vertigo in the elderly; vestibular or vascular disease?

Intruduction –‐ Elderly patients with isolated acute vertigo are commonly encountered in clinical practice, but little is known about the underlying cause of the symptoms. Material & methods –‐ We prospectively studied 24 patients aged 50–75 years with the acute onset of isolated vertigo lasting > 48 h and no abnormality on neurological examination other than nystagmus. The study protocol included neuro‐imaging (MRI 22 patients, CT 2 patients), Doppler sonography, and electro‐oculography. Results— MRI/CT showed the presence of an infarction of the caudal cerebellum in six patients (25%), 3 of whom had a potential cardioembolic source and normal Doppler sonography findings, whereas 3 patients had ipsilateral vertebral artery occlusion and normal cardiac findings. MRI of the posterior fossa was normal in 18 patients. On electro‐oculography, ataxic pursuit eye movements was a characteristic finding in patients with cerebellar infarction, whereas caloric test findings were not discriminative. Conclusion –‐ A caudal cerebellar infarction may easily be misdiagnosed clinically as a labyrinthine disorder, and was found to be the cause in one fourth of patients presenting with isolated acute vertigo.

Proton MR spectroscopy in clinical routine

In vivo magnetic resonance spectroscopy (MRS) addresses metabolic pathways and their steady states in different tissue types. The brain has by tradition, and due to technical limitations in other organs, been one of the tissues most studied by MRS, and both 1H‐ and 31P‐MRS have been used. Although 31P‐MRS is outstanding for the evaluation of sources of metabolic energy in the brain, 1H‐MRS has become the major clinically applied method in neurospectroscopy, as it provides information on markers of neuronal function, myelin, cell membranes, and metabolic active compounds. Furthermore, MR sensitivity is much greater for protons than it is for phosphorus and 1H‐MRS, therefore allowing better spatial resolution. This review focuses on neurospectroscopy and diagnostic insights into diverse neurological problems provided by 1H‐MRS applied as a clinical tool. J. Magn. Reson. Imaging 2001;13:560–567.

Perfusion-related parameters in intravoxel incoherent motion MR imaging compared with CBV and CBF measured by dynamic susceptibility-contrast MR technique

Objective: Perfusion-related parameters obtained by intravoxel incoherent motion (IVIM) MR imaging (MRI) were compared with cerebral blood volume and flow (CBV and CBF), retrieved by dynamic susceptibility-contrast (DSC) MRI. Material and Methods: Twenty-eight volunteers (average age 68.5 years) were investigated. Spin-echo echo-planar imaging with IVIM-encoding gradients was employed (36 different b values, 0-1200 s/mm2). The perfusion fraction and the pseudo-diffusion coefficient were calculated for regions in thalamus gray matter and frontal white matter, using asymptotic and full fitting. In DSC-MRI, a Gd-DTPA-BMA contrast-agent bolus was monitored using simultaneous-dual FLASH. Deconvolution of the measured tissue concentration-versus-time curve with an arterial input function from the carotid artery was applied, and maps of CBV and CBF were calculated. Results: The correlation between the perfusion fraction and CBV was r=0.56 (p<0.0000006) using asymptotic fitting, and r=0.35 (p<0.0004) when full fitting was applied. Average CBF was 41.5 ml/(min 100 g), to be compared with the IVIM-based value of 63.6 ml/(min 100 g), obtained from the median value of the pseudo-diffusion coefficient in combination with assumptions about capillary network structure. Conclusion: The IVIM concept provided results that agreed reasonably with conventional CBV and CBF. The non-linear fitting to noisy signal data was problematic, in accordance with previously presented simulations.

Disturbances of speech prosody following right hemisphere infarcts.

ABSTRACT The ability to perceive and express emotional, as well as number of linguistic prosodic qualities of speech was tested in 20 Swedish‐speaking patients with right‐sided cortical, as well as purely subcortical brain infarcts, and in 18 normal controls. The infarcts were assessed by clinical neurological examination, and by CT, EEG, and measurements of regional cerebral blod flow (rCBF). In the patients the identification of emotional messages was disturbed, as well as the identification and production of several linguistic prosodic qualities. The study supports the claim that prosodic impairment could be linguistic in nature, and not secondary to affective disorder. The total degree of anatomical and functional disturbance of the right hemisphere played a role for both the ability to identify emotional messages and for identification of two of the linguistic prosodic qualities tested. However, it was not possible to find support for the hypothesis that the organization of prosody in the right hemisphere mirrors that of propositional speech on the left side.

No relationship between epidural fibrosis and sciatica in the lumbar postdiscectomy syndrome : a study with contrast-enhanced magnetic resonance imaging in symptomatic and asymptomatic patients

Study Design. Symptomatic patients were retrospectively analyzed and compared with a control group from an ongoing prospective and consecutive study. Objectives. To determine the presence and extent of epidural fibrosis in patients with and without recurrent sciatic pain after previous lumbar discectomy, contrast-enhanced magnetic resonance images were evaluated and correlated with surgical findings in the symptomatic patients. Recurrent hemia and bony stenosis were ruled out as the probable causative agent, as well as any morphologic explanation other than fibrosis. Summary of Background Data. Repeat surgical results for patients with the lumbar postdiscectomy syndrome with epidural fibrosis alone are often unfavorable. The pathogenic role of epidural fibrosis, however, has not been established. Methods. The magnetic resonance images of eight patients with recurrent or persistent sciatic pain after lumbar discectomy were compared with those of eight asymptomatic patients constituting a control group. All were examined with magnetic resonance imaging on a 0.3 T unit before and after intravenous injection of gadolinium-DTPA, and clinically, 6 months to 4 years after surgery. The symptomatic patients subsequently underwent reoperation. Results. Fourteen patients had focal or diffuse epidural fibrosis around the nerve root and/or the thecal sac at the operated level, whereas the postoperative findings for two patients were “normal,” one in the operated and one in the control group. No difference between the groups regarding mass effect or affection of the nerve roots or thecal sac was noted. At reoperation of the eight symptomatic patients, fibrosis was the only pathologic finding in all cases except one, in which surgery confirmed the normal finding on magnetic resonance imaging. Six of the eight operated patients had recurrent or persistent symptoms within a year of the reoperation. Conclusion. No differences regarding the presence and extent of epidural fibrosis between the symptomatic and asymptomatic patients could be demonstrated with contrast-enhanced magnetic resonance imaging. The role of epidural fibrosis as the causative agent in the lumbar postdiscectomy syndrome is questioned.

A ring-enhancing metastasis with central high signal on diffusion-weighted imaging and low apparent diffusion coefficients

Abstract Diffusion-weighted imaging (DWI) has been reported to be useful in the differential diagnosis between abscesses and cystic or necrotic tumours. However, experience is still limited and the true sensitivity and specificity remain to be determined. Our purpose is to describe a ring-enhancing metastasis of adenocarcinoma with a DWI pattern similar to that reported for abscesses. The tumour had a diameter of 1.5 cm and give signal from its centre similar to that of normal brain on T1-weighted images, whereas it was increased on T2-weighted images, and surrounded by a low signal ring, suggesting a capsule. The signal was high on DWI and the apparent diffusion coefficient (ADC) was low (0.55 × 10–3 mm2/s). The findings were misinterpreted as representing an abscess in the early capsule-formation stage, but the signal pattern probably represented early tumour necrosis with intracellular oedema, but without liquefaction. Findings on DWI during the early capsule formation stage in abscesses and early tumour necrosis are probably similar and must be interpreted with caution.

Brain metastases--comparison of gadodiamide injection-enhanced MR imaging at standard and high dose, contrast-enhanced CT and non-contrast-enhanced MR imaging.

The aim was to compare the abilities of contrast-enhanced CT, non-contrast-enhanced MR imaging and contrast-enhanced MR imaging using standard (0.1 mmol/kg b.w.) and high (0.3 mmol/kg b.w.) doses of Gadodiamide injection to detect brain metastases (i.e. blood-brain barrier damage). Sixteen patients with at least 2 metastases found by CT were evaluated by MR imaging using non-contrast-enhanced spin-echo, T1-weighted, T2-weighted sequences, and contrast-enhanced spin-echo T1-weighted sequences at 2 dose levels. Gadodiamide injection was first given at the dose of 0.1 mmol/kg b.w. After imaging, another 0.2 mmol/kg b.w. was given, yielding a cumulative dose of 0.3 mmol/kg b.w. No contrast media-related adverse events were recorded. The images were evaluated openly by one and blindly by 2 investigators and the number of metastases, size, delineation (open study) and diagnostic certainty (blind study) of each individual metastasis noted. High-dose MR imaging showed significantly more and smaller metastases than any other examination, and gave a higher diagnostic certainty. All high-dose images were superior to those with the standard dose MR imaging when compared blindly in pairs. We conclude that spin-echo MR imaging with a high dose of Gadodiamide injection is an efficient way to improve the detection of brain metastases, in particular of small ones.

Proton magnetic resonance spectroscopy in brain tumours: clinical applications

Abstract Parallel to the rapid development of clinical MRI, MR spectroscopy (MRS) has, after starting as an analytical tool used in chemistry and physics, evolved to a noninvasive clinical examination. Most common neuroradiological diagnostic indications for MRS are functional inborn errors, neonatal hypoxia, ischaemia, metabolic diseases, white matter and degenerative diseases, epilepsy, inflammation, infections and intracranial neoplasm. Compared to CT and MRI, well-established morphological diagnostic tools, MRS provides information on the metabolic state of brain tissue. We review the clinical impact of MRS in diagnosis of tumours and their differentiation from non-neoplastic lesions.

Paragangliomas of the spinal canal

Abstract We report the clinical MRI and histopathological features of five consecutive cases of spinal paraganglioma. Three intradural tumours were found in the typical location (two at the L4, one at the S2 level); one intradural extramedullary tumour arose at an unusual level, from the ventral C2 root, and one extradural tumour growing along the L5 nerve root sheath had an aggressive growth pattern with early, local paraspinal recurrence and, eventually, intradural metastatic spread. This type of growth pattern has not been described previously. Paragangliomas of the spinal canal are more common than previously thought and can be located anywhere along the spine, although the lumbosacral level is the most common. Their appearance on MRI can not disinguish them from other tumours in the spinal canal. Even though paragangliomas in general are benign and slowly growing their growth pattern can vary and be more aggressive, to the point of metastatic spread.