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.

Contrast-to-noise ratio of multiple slice spin lock technique: prospects for liver imaging.

Spin lock (SL) MRI technique has been demonstrated to provide similar lesion/liver contrast to conventional MR technique. Multiple slice SL technique allows a large number of slices to be collected within a given repetition time due to the short echo time. In addition, the short echo time reduces movement and susceptibility artefacts. In the present study, the potential of the multiple slice SL technique in liver imaging was evaluated by using tissue nuclear magnetic resonance (NMR) information and tissue NMR parameters obtained at 0.1 T. 10 healthy volunteers were imaged at 0.1 T for the measurement of tissue T1rho, T1, and T2 relaxation times. Tissue radiofrequency-attenuation information was obtained from the literature, and included in the contrast-to-noise ratio (CNR) calculations. Our results demonstrated that by increasing the number of slices the acquired liver-to-spleen CNR decreases with all locking field durations (locking time, TL). However, with small TLs, the difference is small which is important for liver MRI where a wide coverage, i.e. large number of slices, is important. Long locking pulse durations are more favourable than short TLs if large flip angles are used. With an optimal combination of a moderate amount of slices, reasonably large flip angle, and TL of the order of 20 ms, high CNR is achieved in SL MRI.

Multiple-slice spin lock imaging of head and neck tumors at 0.1 Tesla: exploring appropriate imaging parameters with reference to T2-weighted spin-echo technique.

RATIONALE AND OBJECTIVES: Spin lock imaging has been shown to be useful in characterizing head and neck tumors. The purposes of this study were to explore and develop multiple-slice spin lock gradient-echo (SL-GRE) sequences for head and neck imaging and to compare the tumor contrast on SL images to spin-echo (SE) T2-weighted images at 0.1 T. METHODS: On the basis of measured relaxation times of tumors and head and neck tissues, the authors evaluated with signal equations the effect of imaging parameters on tissue contrast produced by the SL-GRE sequence. In the clinical study, 34 patients with pathologically verified head and neck tumors were imaged with multiple-slice SL-GRE (repetition time 1500 ms/echo time 30 ms) out-of-phase fat/water sequences and compared with T2-weighted SE (repetition time 1500 ms/echo time 120 ms) sequences. The conspicuity of tumors was evaluated by calculating the contrast-to-noise ratios (CNRs). RESULTS: The combination of a short echo time of 30 ms and the length of locking pulses in the range of 10 to 35 ms produced optimal CNRs for head and neck tumor imaging. The measured CNRs and subjective evaluation for tumor detection were satisfactory with both imaging sequences. However, the CNRs between tumors and salivary gland tissues were significantly greater with the SL sequence than with the T2-weighted sequence. CONCLUSIONS: The multiple-slice SL-GRE technique provides image contrast comparable to that of SE T2-weighted imaging for head and neck tumors at 0.1 T. With short locking pulse lengths and echo times, wide anatomic coverage and reduced motion and susceptibility artifacts can be achieved. The out-of-phase SL technique is useful in imaging salivary gland tumors.

A shielded Overhauser marker for MR tracking of interventional devices.

Improvements to an active MR tracking technique are described. Real-time position monitoring of interventional procedures can be realized by incorporating a small marker that emits an NMR signal into the tip of an interventional device, and the marker's emitted NMR signal is enhanced by use of the Overhauser phenomenon. A significant advance over prior designs has achieved by making the marker have a cylindrical shape and by confining the saturation energy to the marker's interior. The performance of the improved active marker was verified in the laboratory and in vitro. The experiments demonstrated that the marker was visible in MR images when inserted in different excised tissues, and even in air, with positive contrast and with various imaging sequences. The tissue magnetization was minimally perturbed, and the marker emitted a variable but enhanced signal in all orientations in the magnetic field. The marker can potentially be used to mark locations on the body for frameless stereotaxy or to identify inserted devices.

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.

High-accuracy MR tracking of interventional devices: the Overhauser marker enhancement (OMEN) technique.

A new technique for visualization of interventional devices in magnetic resonance imaging is presented. Determination of the position of an invasive device is made possible by incorporating into the device a small marker that emits the NMR signal. This signal is enhanced by the use of the Overhauser phenomenon. This technique differs from the earlier reported techniques for marking interventional instruments in the sense that the contrast between the marker and tissue is not based on different relaxation rates, but on NMR signal enhancement. A prototype marker was constructed and inserted into an inductively fed loop-gap resonator that couples saturation energy with the marker. Circuit analogies are presented that model the Overhauser phenomenon and the coupling circuit. In vitro experiments demonstrated that the marker is visible in MR images up to a slice thickness of 50 mm when inserted in excised animal liver and fat tissues.

Spin lock and magnetization transfer MR imaging of local liver lesions.

The present study was designed to evaluate tissue contrast characteristics obtained with the spin-lock (SL) technique by comparing the results with those generated with a magnetization transfer(MT)-weighted gradient echo [GRE, echo-time (TE)=40 ms] sequence. Twenty-eight patients with hepatic hemangiomas (n=14), or metastatic liver lesions (n=14) were imaged at 0.1 T by using identical imaging parameters. Gradient echo, single-slice off-resonance MT, and multiple-slice SL sequences were obtained. SL and MT-effects were measured from the focal liver lesions and from normal liver parenchyma. In addition, tissue contrast values for the liver lesions were determined. Statistically significant difference between the SL-effects of the hemangiomas and metastases, and also between the MT-effects of the lesions was observed (p < 0.02). Tissue contrast values for the lesions proved to be quite similar between the SL and MT techniques. Our results indicate that at 0.1 T multiple-slice SL imaging provides MT based tissue contrast characteristics in tissues rich in protein with good imaging efficiency and wide anatomical coverage, and with reduced motion and susceptibility artifacts.

Determination of T1rho values for head and neck tissues at 0.1 T: a comparison to T1 and T2 relaxation times.

In order to optimize head and neck magnetic resonance (MR) imaging with the spin-lock (SL) technique, the T1rho relaxation times for normal tissues were determined. Furthermore, T1rho was compared to T1 and T2 relaxation times. Ten healthy volunteers were studied with a 0.1 T clinical MR imager. T1rho values were determined by first measuring the tissue signal intensities with different locking pulse durations (TL), and then by fitting the signal intensity values to the equation with the least-squares method. The T1rho relaxation times were shortest for the muscle and tongue, intermediate for lymphatic and parotid gland tissue and longest for fat. T1rho demonstrated statistically significant differences (p < 0.05) between all tissues, except between muscle and tongue. T1rho values measured at locking field strength (B1L) of 35 microT were close to T2 values, the only exception being fat tissue, which showed T1rho values much longer than T2 values. Determination of tissue relaxation times may be utilized to optimize image contrast, and also to achieve better tissue discrimination potential, by choosing appropriate imaging parameters for the head and neck spin-lock sequences.

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.

Interventional MR imaging. Demonstration of the feasibility of the Overhauser marker enhancement (OMEN) technique.

PURPOSE: The poor localization facility of interventional instruments in MR imaging has been one of the major obstacles to the popularization of interventional MR imaging. It has been suggested that the Overhauser enhancement be used to generate markers of small size and high visibility. This article studies the feasibility of a localization marker based on this method. MATERIAL AND METHODS: A small Overhauser marker was constructed on the tip of a coaxial cable and comparative images were taken by a 0.23 T imager with and without electron spin irradiation. RESULTS: During irradiation an enhanced signal intensity from the marker was observed. The signal from the marker also exceeded the signal from a 0.25 mmol MnCl2 reference phantom. CONCLUSION: Its small size and high signal-to-noise ratio, together with immunity to most system nonlinearities and imaging errors, makes the Overhauser marker a promising localization method for the accurate positioning of interventional devices. The method may be applied at any field strength, and markers are visible in images obtained with any practical imaging sequence.

Spin lock and magnetization transfer imaging of head and neck tumors.

PURPOSE: To evaluate and compare the spin lock and magnetization transfer techniques in the differentiation of benign and malignant head and neck tumors at magnetic resonance (MR) imaging. MATERIALS AND METHODS: Forty consecutive patients with histologically verified head and neck tumors (20 malignant and 20 benign tumors, including five infections) were studied with a 0.1-T MR unit. The spin lock and magnetization transfer effects were defined as 1-(signal intensity with stronger preparation pulse/signal intensity with weaker preparation pulse). RESULTS: A strong correlation between the spin lock and magnetization transfer effects was found (r = 85, P < .001). With a spin lock effect of 0.48 and a magnetization transfer effect of 0.32 as the thresholds, sensitivity for detecting a malignant tumor was 95% and 94%, respectively, and specificity was 60% and 65%. CONCLUSION: Low spin lock and magnetization transfer effects are characteristic of benign tumors. High spin lock and magnetization transfer effects were associated with malignancy, but there were overlapping values for salivary gland infections, some benign tumors, and malignancies. The spin lock technique seems to be an effective method for generating magnetization transfer-based contrast in the head and neck tumors.

Low-field MR imaging--development in Finland.

The development project for application of MR imaging to diagnosis of internal hemorrhages was initiated by the Instrumentarium Corporation in 1978. The goal was to develop a diagnostic tool for emergency clinics. Due to the rapid development of imaging technology, the goal was changed to a cost-effective MR unit. During the past 16 years, several generations of low-field units have been introduced. Consequently, a vast amount of clinical and technical knowledge about low-field MR has been gained. The interest in low-field units is rapidly increasing. A part of this may be explained by the pressure to reduce the cost of health care. There are some features which make the low-field approach clinically interesting. These include the feasibility of open magnet configurations, and the availability of unique contrast parameters such as magnetization transfer and T1p. One important aspect is the inherent safety of a low-field MR unit. This article reviews the methods and devices introduced through the development of low-field technology in Finland.

Spin lock magnetic resonance imaging in the differentiation of hepatic haemangiomas and metastases.

Spin lock (SL) imaging technique, generating T1 rho-weighted images, was applied to the differentiation of hepatic haemangiomas from metastatic focal liver lesions. 17 haemangiomas and 16 metastases in 32 patients were imaged at the field-strength of 0.1 T using a multiple slice SL technique and a conventional gradient-echo (GRE) sequence with identical timing parametres. Spin lock effects of the hepatic lesions and different abdominal tissues were calculated. Images with adequate coverage of the liver and of good quality with few motion induced artefacts were acquired. A definite, statistically significant, difference was found between the SL-effects of hepatic haemangiomas and a liver metastases. Haemangiomas showed an SL effect of 46.6 +/- 3.4% and metastases of 56.2 +/- 5.8% (mean +/- SD, p < 0.0001). The multiple slice SL technique showed potential in distinguishing haemangiomas from metastatic liver lesions and should be considered as an alternative to the conventional T2 and magnetization transfer (MT) based methods.

Co-twin control study on cerebral manifestations of systemic lupus erythematosus.

All available twin pairs systemic lupus erythematosus (SLE) derived from the Finnish Twin Cohort were studied by clinical evaluation, magnetic resonance imaging (MRI), anticardiolipin (aCL), and antineurofilament (ANFA) antibodies. One of the five monozygotic and one of the eight dizygotic pairs were concordant for SLE. 10 of the 15 patients showed clinical neurological abnormalities, and 11 had abnormal MRI of the brain. Altogether, 12 patients were considered to have neuropsychiatric lupus (NPSLE). Seven of the 11 patients with long-term corticosteroid treatment had either central or cortical atrophy. High or moderate aCL level was found in eight patients and two co-twins. Of them, six patients had at least two manifestations of the antiphospholipid syndrome. ANFAs were found in five patients and four co-twins. Five co-twins fulfilled some of the SLE criteria. Of them, three MZ twins and one additional DZ co-twin with no ARA criteria had findings suggesting central nervous system (CNS) involvement. The results indicate that the majority of SLE patients has cerebral abnormalities either as a result of SLE, or concomitant risk factors. The co-twins without clinical SLE often have minor signs of SLE, and even they may have neurological and MRI abnormalities. However, their aCL and ANFA levels seem not to correlate with MRI abnormalities.

T1 rho dispersion imaging of diseased muscle tissue.

T1 rho 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. T1 rho 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 T1 rho dispersion values of normal and diseased muscle tissue. T1 rho 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.

Effects of recombinant alpha-2b-interferon therapy in patients with progressive MS.

The effects of systemic recombinant interferon-alpha-2b were studied in 6 carefully selected patients with progressive multiple sclerosis. 3.0 million IU were given as daily subcutaneous injections for 6 months, 5 patients showed worsening disability, and in 4 of them new or enlarged lesions were detected in MRI. In one patient no change in disability was found; his MRI showed regressed changes. The mean progression index during the treatment was significantly higher (p < 0.02) than during the previous 2 to 3 years' period of continuous progression. The frequency of peripheral blood natural killer (CD16+) cells declined significantly 3 months during the treatment, but returned to the pretreatment values after termination the treatment. An increase of intrathecal IgG synthesis and oligoclonal bands was demonstrated in 4 and 3 patients, respectively. Our experience suggests that long-term recombinant IFN-alpha-2b treatment may activate the immunological process of MS.

Cerebrospinal fluid and MRI findings in three patients with multiple sclerosis and systemic lupus erythematosus.

Three patients fulfilling the diagnostic criteria of both multiple sclerosis (MS) and systemic lupus erythematosus (SLE) were examined clinically, immunologically and by magnetic resonance imaging (MRI). In all three patients MRI showed several high-signal lesions compatible with MS and, additionally, non-specific small white matter lesions suggesting small vessel occlusion were seen. In CSF the cytoimmunological abnormalities were variable and showed only slight to moderate immunoactivation within the CNS at the time of sampling.

Magnetization transfer imaging of the abdomen at 0.1 T: detection of hepatic neoplasms.

Magnetization transfer (MT) techniques have been proposed as a method of increasing contrast in MR images. To evaluate the feasibility of MT imaging of the abdomen at 0.1 T and to assess the clinical utility of this technique, the authors studied tissue contrast with a gradient-echo pulse sequence and an MT sequence in four normal volunteers, and in 17 patients with known primary or secondary neoplasms of the liver. The MT technique increased contrast between the liver and other tissues such as spleen, skeletal muscle and subcutaneous fat. The technique also produced increased contrast between hepatic tumors and normal liver parenchyma in gradient-echo images.

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.