Raimo Sepponen

A method for chemical shift imaging: demonstration of bone marrow involvement with proton chemical shift imaging

A new method for chemical shift imaging is described. In this method the spin-echo signals are collected with the field gradient switched on, which reduces the imaging time considerably. A human bone marrow pathology is demonstrated by proton chemical shift imaging.

Diagnosis apparatus and the determination of tissue structure and quality

The invention relates to a diagnosis apparatus for simultaneously collecting information on tissue structure and tissue quality from a target, e.g. human body to be examined. The apparatus of the invention comprises means (1) for emitting ultrasonic pulses and for detecting and registering reflections from the interfaces between tissues in target area (16) determined by said means, and means (10) for processing the information obtained from a target area by means of said ultrasonic pulses as well as means (8) for visualizing the information for finding and localizing tissue area to be characterized. The apparatus is further provided with elements (2, 3, 11, 12, 13) for collecting tissue identification information by means of a nuclear magnetic resonance or NMR-phenomenon from target to be examined in manner that the tissue identification area (19) sensitive to nuclear magnetic resonanse is arranged to be produced in said target area (16) localized and visualized by ultrasonic pulses for immediate analysis on said tissue area to be characterized.

A Method for Tlp Imaging

The spin lattice relaxation time (Tl) 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 Tip 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 Tip 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 Tip. Tip and Tip-dispersion may provide new imaging parameters for noninvasive tissue characterization.

Accurate prediction of high-frequency power-transformer losses and temperature rise

The high-frequency power-transformer design equations for winding and core losses and temperature rise were reviewed from literature and formulated for spreadsheet calculations using material (Steinmetz loss coefficients, ferrite resistivity, copper resistivity), geometry (core area, core length, winding area, winding length), winding (number of primary turns, copper fill factor, primary to secondary area ratio) and excitation (input voltage, switching frequency, duty cycle, current harmonic components) parameters. The accuracy of each design issue was first validated and quantified separately using regression analysis. Calculated core losses, winding AC-resistance equations and heat transfer capacity calculations were compared with the results from calibrated heat sink measurements, finite-element method (FEM) analysis and measurements using thermal test blocks, respectively. Finally three EFD20 type transformers (solid wire, noninterleaved foil and interleaved foil winding) were fitted into an active clamp forward converter (100-300 kHz switching frequency, 0-78 W throughput power) for comparison between the theory and experiments. Standard error of predicted core losses and heat transfer capacity were determined to be 0.0581 and 0.15 W, respectively. The results of the in circuit tests suggests that the transformer total losses can be predicted with the average standard error below 0.2 W with datasheet type information only. The most significant uncertainty was heat conduction through and losses generated in the interconnecting wires between the test transformer and other converter components.

Computer-based detection and analysis of heart sound and murmur.

To develop a digital algorithm that detects first and second heart sounds, defines the systole and diastole, and characterises the systolic murmur. Heart sounds were recorded in 300 children with a cardiac murmur, using an electronic stethoscope. A Digital algorithm was developed for detection of first and second heart sounds. R-waves and T-waves in the electrocardiography were used as references for detection. The sound signal analysis was carried out using the short-time Fourier transform. The first heart sound detection rate, with reference to the R-wave, was 100% within 0.05–0.2R-R interval. The second heart sound detection rate between the end of the T-wave and the 0.6R-R interval was 97%. The systolic and diastolic phases of the cardiac cycle could be identified. Because of the overlap between heart sounds and murmur a systolic segment between the first and second heart sounds (20–70%) was selected for murmur analysis. The maximum intensity of the systolic murmur, its average frequency, and the mean spectral power were quantified. The frequency at the point with the highest sound intensity in the spectrum and its time from the first heart sound, the highest frequency, and frequency range were also determined. This method will serve as the foundation for computer-based detection of heart sounds and the characterisation of cardiac murmurs.

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.

Detection of falls among the elderly by a floor sensor using the electric near field

We present a new fall-detection method using a floor sensor based on near-field imaging. The test floor had a resolution of 9×16. The shape, size, and magnitude of the patterns are used for classification. A test including 650 events and ten people yielded a sensitivity of 91% and a specificity of 91%.

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 (IR1,500/400). 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.

3D spin-lock imaging of human gliomas

We investigated whether the simultaneous use of paramagnetic contrast medium and 3D on-resonance spin lock (SL) imaging could improve the contrast of enhancing brain tumors at 0.1 T. A phantom containing serial concentrations of gadopentetate dimeglumine (Gd-DTPA) in cross-linked bovine serum albumin (BSA) was imaged. Eleven patients with histologically verified glioma were also studied. T1-weighted 3D gradient echo images with and without SL pulse were acquired before and after a Gd-DTPA injection. SL effect, contrast, and contrast-to-noise ratio (CNR) were calculated for each patient. In the glioma patients, the SL effect was significantly smaller in the tumor than in the white and gray matter both before (p = 0.001, p = 0.025, respectively), and after contrast medium injection (p < 0.001, p < 0.001, respectively). On post-contrast images, SL imaging significantly improved tumor contrast (p = 0.001) whereas tumor CNR decreased slightly (p = 0.024). The combined use of SL imaging and paramagnetic Gd-DTPA contrast agent offers a modality for improving tumor contrast in magnetic resonance imaging (MRI) of enhancing brain tumors. 3D gradient echo SL imaging has also shown potential to increase tissue characterization properties of MR imaging of human gliomas.

T1ρ dispersion imaging of diseased muscle tissue

Abstract T1ρ dispersion, or the frequency dependence of T1 relaxation in the rotating frame, was used for in vivo muscle tissue characterization in 13 patients with primary skeletal muscle disease and in eight normal subjects for comparison. T1ρ dispersion measurements represent a new approach to magnetic resonance tissue characterization, possibly reflecting the macromolecular constituents of tissue. A definite, statistically significant, difference was found between the relative T1ρ dispersion values of normal and diseased muscle tissue. T1ρ dispersion measurements and images may increase the accuracy of identification of diseased muscles. Early identification of affected muscles is important for accurate diagnosis by muscle biopsy.