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Biomedical subjects

R E Sepponen

Publications and source records attributed to R E Sepponen.

28 records · Page 2Linked to original sources
PubMed1984

Chronic subdural hematoma: demonstration by magnetic resonance.

The ability of magnetic resonance (MR) to identify intracranial hematomas was tested in five patients with clinical and computed tomographic signs of chronic subdural hematoma. The extracerebral collections were displayed as a zone of bright intensity using the T1-weighted inversion recovery (IR 1,500/400) sequence, reflecting the lesions' short T1 relaxation times. The collections also showed high intensity using the spin echo (SE) sequence, with a longer delay of 100 ms and 160 ms, reflecting the long T2 relaxation time. The spin echo sequence with a repetition time of 500 ms and an echo delay of 160 ms (SE 500/160) almost effaced other structures in the image, thus increasing the specificity of this pulse scheme for detection of chronic blood collections. Although in two of the five patients the subdural hematomas were in the isodense CT phase, all were easily visualized with MR.

Adult↗
PubMed1983

Nuclear magnetic resonance (NMR) imaging of intracerebral hemorrhage in the acute and resolving phases.

Nuclear magnetic resonance imaging of intracerebral hemorrhage revealed a considerable difference in the appearance of the bleedings in the acute and resolving phases. Attention is drawn to the shortening of the relaxation time T1 within the first 2 weeks after the acute onset of symptoms with the location of the change at the periphery of the lesion. The change was most evident with T1 dependent inversion recovery sequence (IR 1,500/400). With this pulse scheme the acute hemorrhage was visualized as a dark area during its early days. A bright zone, reflecting the shorter T1, was not seen until the resolving phase at the end of the 1st week. Although its pathophysiological aspects are so far unknown, this finding may offer an opportunity for dating intracerebral hemorrhages.

Acute Disease↗
PubMed1983

Serial nuclear magnetic resonance (NMR) imaging in patients with cerebral infarction.

Seven patients with supratentorial infarction were studied by means of serial nuclear magnetic resonance imaging using saturation recovery (SR) and proton density (PD) sequences. The earliest changes were visible in the more sensitive T1 dependent images (SR) and may reflect the cytotoxic component of ischemic brain edema. Further progress was also clearly discernible in the PD images and may mainly reflect the slower vasogenic component of ischemic brain edema. Nuclear magnetic resonance imaging seems to provide a new approach to early diagnosis of ischemic brain infarction. Furthermore, it may elucidate some aspects of the pathophysiology of ischemic stroke in man.

Adult↗
PubMedDate not supplied

T1 rho dispersion imaging of head and neck tumors: a comparison to spin lock and magnetization transfer techniques.

The potential of T1 rho dispersion, spin lock (SL), and magnetization transfer (MT) techniques to differentiate benign and malignant head and neck tumors was evaluated. Twenty-four patients with pathologically verified head and neck tumors were studied with a .1-T MR imager. T1 rho dispersion effect was defined as 1 -(intensity with lower locking field amplitude/intensity with higher locking field amplitude). T1 rho dispersion effects were higher for malignant than benign tumors (P = .001). With T1 rho dispersion effect .14 as the threshold, sensitivity for detecting a malignant tumor was 91%, specificity was 77%, and accuracy was 83%. A strong correlation between T1 rho dispersion effects and SL effects and between T1 rho dispersion effects and MT effects in the head and neck tumors was found (r = .87, P < .001 and r = .90, P < .001, respectively). High T1 rho dispersion effects are not specific indicators of malignancy, because chronic infections, some benign tumors, and malignancies may overlap. Low T1 rho dispersion effect values are characteristic of a benign tumor.

Diagnosis, Differential↗
PubMedDate not supplied

Low field (0.02 T) nuclear magnetic resonance imaging of the brain.

Many technical and instrumental alternatives are available to obtain good spatial and contrast resolution in magnetic resonance (MR) imaging. Optimum field strength remains a controversial question. In spite of its inherent low signal-to-noise ratio, low field imaging exhibits some advantages. It is well established that the relaxation times are dependent on the magnetic field strength. In low fields the relaxation times, especially T1, are shorter and the relative differences of T1 between different tissues are larger. Other benefits are the ease of installation of the device, its cost effectiveness, and the obvious avoidance of hazards caused by the magnetic field. In this report we describe six cases of cerebral lesions studied with an MR imager operating at a field strength of 0.02 T (200 G). This is the lowest field strength reported in clinical MR imaging. The information obtained was equal to that of the CT studies performed on the same patients.

Adult↗
PubMedDate not supplied

Intracranial hematomas studied by MR imaging at 0.17 and 0.02 T.

The contrast in magnetic resonance (MR) images relies mainly on the relaxation time differences between the tissues. The relative differences in relaxation times T1 are bigger at lower field strengths, although the absolute values of T1 are smaller. A shorter T1 is also advantageous for the contrast of the T2 and proton density weighted images because of the more complete recovery of the spin system during the repetition time TR. Scrutiny of the clinical results of MR shows some unsolved problems in the specificity of diagnosing fresh intracranial hematomas. Low field MR imaging at 0.02 T seems to offer new vistas in this sense. Fresh subdural hematoma was more easily detected and differentiated at 0.02 T than at 0.17 T. The T2 of fresh intracranial hematomas was rather short compared with cerebrospinal fluid and edema and, unlike T1, was not highly dependent on magnetic field strength. The different visualization of acute versus late intracerebral hematoma and the changes during the resorption were demonstrated in follow-up studies of two patients at 0.17 T and of one at 0.02 T. In one patient the same lesion was imaged successively at both field strengths, showing the divergent contrast in the inversion recovery images at 0.02 and 0.17 T.

Cerebral Hemorrhage↗
PubMedDate not supplied

A method for T1 rho imaging.

The spin lattice relaxation time (T1) is dependent on the strength of the polarizing magnetic field. The relaxation at low field strengths provides information from the processes at macromolecular level. However, the decrease of the polarizing magnetic field decreases the signal-to-noise ratio that determines the resolution of magnetic resonance images. In this report we describe a method for T1 rho imaging. The method possesses the relaxation time contrast of low field strengths with signal-to-noise ratio provided by the higher polarizing field. The relaxation time T1 rho is obtained under spin lock conditions. The spin system relaxes toward thermal equilibrium along the locking field. This process is analogous to the spin lattice relaxation at low field strength and characterized by the time constant T1 rho. T1 rho and T1 rho-dispersion may provide new imaging parameters for noninvasive tissue characterization.

Biophysical Phenomena↗
PubMedDate not supplied

Synergistic enhancement of MRI with Gd-DTPA and magnetization transfer.

Magnetization transfer (MT) between protons of macromolecules and protons of water molecules is a recently introduced mechanism for tissue contrast in MR imaging. The MT effect is strong in tissues where there is an efficient cross relaxation between macromolecular protons and water protons and where this interaction is the dominant source of relaxation. Paramagnetic ions shorten relaxation times and decrease the MT effect. These two facts led to the assumption that, in the case of contrast enhanced MRI, the combination of the T1-weighted imaging method and the MT technique may yield increased contrast, compared with standard methods. The synergistic effect is demonstrated in this work with studies of egg white samples and by imaging three patients with different brain pathologies. The lesion-to-white matter contrasts, with standard T1-weighted sequences with and without the MT effect, were compared before and after the introduction of Gd-DTPA. In each case the synergistic effect of T1 weighting and MT improved the contrast enhancement provided with Gd-diethylenetriamine pentaacetic acid.

Brain↗