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M Komu

Publications and source records attributed to M Komu.

At least 37 records · Page 2Linked to original sources
PubMed1997

Effect of fasting and food intake on magnetization transfer of human liver tissue.

Magnetization transfer (MT) technique is a promising method in differential diagnosis of diseases in parenchymal tissues. Basic knowledge about circumstances and elementary factors that influence MT and its parameters is still insufficient, however. Having a meal before the magnetic resonance (MR) examination could change liver MT parameters compared to fasting state through alteration in liver perfusion, blood flow, and content of portal blood (proteins and other derivates from a meal). If MT parameters can be altered by a meal, then MR liver studies should always be performed after fasting. Before MRI examinations we examined three healthy volunteers after a high-fat meal with Doppler ultrasound technique to find out duration and magnitude of changes in portal blood flow. Duration of > or = 50% increased peak-flow value compared to fasting state in portal vein was > 90 min, which is enough for our MR examination. With a low-field 0.1-T MR imager we examined 10 healthy volunteers after a short (range from 3 h 45 min to 17 h 30 min) fast and also immediately after a high-fat meal. Magnetization transfer parameters, magnetization transfer ratio (MTR) and magnetization transfer rate Rwm of liver tissue were determined. MTR changed significantly (Student paired two-tailed t-test, p = .0044) after a meal, but Rwm did not (p = .0952). We recommend a 4 h fast before MR examination that aims to determine the MTR of liver tissue.

Adult↗
PubMed1996

Knee extension dynamometer: a new device for dynamic isokinetic magnetic resonance spectroscopy experiments.

In the present study we introduce a new device for exercise magnetic resonance spectroscopy (MRS). It operates in a standard whole-body scanner. Mechanical exertion unit allows maximal 10 degrees to 15 degrees short-arc knee extensions. The device operates hydraulically and is based on isokinetic movement. The force and work conducted are automatically controlled by the electronic control and computer unit. A small surface coil placed on the vastus medialis muscle allows the collection of spectra without interfering spectra from nearby resting muscles. The force used for the extensions can be followed simultaneously as a curve on the screen in the operator's room and the data is transferred to a personal computer for later analysis. Total work and fatigue percentage are also calculated by the device. It also allows the use of different isokinetic exercise protocols. The measurements of force proved reliable in repeat measurements using an isokinetic test device as a control. This device has been used clinically for over a year, is easy to operate, and offers reliable measurements. It is well suited to trials where muscle energy states versus time are followed since it allows noninvasive simultaneous quantification of muscle performance and collecting MRS spectra at rest, during exercise, and in the recovery phase.

Ergometry↗
PubMed1996

Determination of saturation transfer parameters of human tissues in vivo.

In order to study the applicability of magnetization transfer contrast (MTC) to tissue differentiation, the determination of the magnetization transfer (MT) parameters of normal tissues is necessary for the evaluation of pathological conditions. The time-dependent saturation transfer technique was used to investigate the observed magnetization transfer parameters in several human tissues in vivo at 0.1 T. The length of the off-resonance saturation pulse varied from 0 to 750 ms. The magnetization transfer contrast (MTC) was 0.71 in striated muscle, 0.49 in liver, 0.49 in renal cortex, and 0.50 in spleen. The observed magnetization transfer rates (Rwm) were 5.5 s-1 for muscle, 3.1 s-1 for liver, and 1.5 s-1 for both renal cortex and spleen. Our results indicate that measuring Rwm and possibly other relaxation parameters could be useful in tissue differentiation.

Adult↗
PubMed1996

Dynamic Gd-DTPA-enhanced MR imaging of the kidney: comparison between T1- and T2-weighted sequences.

OBJECTIVE: To determine whether T1- or T2-weighted sequences are more informative and practical in dynamic Gd-DTPA-enhanced MR imaging for the evaluation of renal blood flow and function. MATERIALS AND METHODS: Dynamic Gd-DTPA-enhanced MR imaging of the kidney was performed in 7 patients by either T1-weighted TurboFLASH (TR/TE/TI/FA = 9/4/27/8) or T2-weighted FLASH (TR/TE/FA = 32/22/10) sequences for comparison of the enhancement pattern. None of the subjects had a suspicion of renal dysfunction from laboratory data, and the absence of renal artery stenosis was confirmed by conventional angiography. RESULTS: During the early phase, the marked signal increase in T1-weighted imaging in the renal cortex corresponded to a similar marked decrease in signal intensity in T2-weighted imaging. During the middle and late phases, the medulla was dramatically decreased in intensity on the T2-weighted imaging resulting in a good contrast between the cortex and medulla. CONCLUSION: Both sequences may provide almost similar information about the renal cortical blood flow. However, T2-weighted dynamic MR imaging may be more informative than T1-weighted dynamic MR imaging about the concentrating ability in the renal medulla. A high concentration of Gd-DTPA in the tubular structure was suspected to cause a dramatic decrease in intensity in the medulla in T2-weighted imaging.

Adult↗
PubMed1996

MR imaging in the presence of small circular metallic implants. Assessment of thermal injuries.

PURPOSE: The thermal effects of MR imaging in the presence of circular nonferro-magnetic metallic implants were studied in 6 rabbits. MATERIAL AND METHODS: A sternotomy was performed and fixed with stainless steel wires, and small titanium rings (diameter 3 mm) were placed on the surface of the ascending aorta and subcutaneous tissue of the thigh. Four of the rabbits were exposed to an imaging procedure with a 1.5 T scanner applying a T1-weighted spin-echo sequence and a gradient echo sequence. Two of the animals served as unexposed controls. Thirty-six hours after the exposure, tissues adjacent to the implants were examined histologically and compared with corresponding samples of the control animals. RESULTS: In the area of the titanium rings, histologic analysis revealed slight inflammatory changes apparently caused by the operation. No evidence of thermal injury was found, suggesting that the presence of the rings does not contraindicate MR examinations. Necrosis was noted in all of the sternal specimens. This was probably post-operative, but it impaired the assessment of thermal injury in this area.

Animals↗
PubMed1995

Magnetic resonance imaging and magnetization transfer in experimental myonecrosis in the rat.

Experimental myonecrosis--induced by injection of notexin into rat tibialis anterior muscle--and subsequent regeneration were studied from 1 h to 20 days postinjury with magnetic resonance imaging using conventional and magnetization transfer sequences, and these findings were correlated with histopathology. MR images revealed necrosis within 1 h postinjection. Histopathologically, necrotized fibers enlarged and intercellular spaces widened, indicating intracellular and extracellular edema, which began to decrease after 48 h, whereafter the formation of new myofibers predominated. T2 increased progressively until 7.5 h, while T1 increased until 24 h. Magnetization transfer contrast (MTC) and magnetization transfer rate (Rwm) decreased rapidly postinjection; the decrease in Rwm lasted longer than in MTC (96 h versus 48 h, respectively). Spin echo, inversion recovery and magnetization transfer sequences revealed the lesions equally effectively. MR images and relaxation parameters reflect well the extent of histopathological injury and edema in the acute phase, whereas specific tissue changes in the regenerative phase were not detectable by MRI. MT imaging and especially magnetization transfer rate are as sensitive as conventional T2 contrast to alterations in water imbalance.

Animals↗
PubMed1995

Localized proton NMR spectroscopy in the striatum of patients with idiopathic Parkinson's disease: a multicenter pilot study.

Single voxel proton MRS was used to study brain metabolism in the striatum of patients diagnosed with idiopathic Parkinson's disease (PD). Peak metabolite ratios in long echo time spectra were evaluated in 151 patient spectra and 97 age-matched control spectra collected at four participating institutions using identical hardware and clinical protocols. Combining data from all ages (27-83 years old) showed no significant difference between patient and control ratios. However, in an elderly subset of patients (51-70 years old), a significant decrease in striatal N-acetylaspartate (NAA)/choline (Cho) was observed. Also, a significant decrease in the mean NAA/Cho ratio was observed in patients versus controls for patients not being treated with Sinemet (Du Pont Pharm, Wilmington, DE) (hereafter referred to as levodopa/carbidopa). This result is consistent with the hypothesis that NAA may provide a reversible spectroscopic marker for neuronal dysfunction, although a prospective follow-up study will be needed to confirm this. Quantitation of MRS would be useful to exclude the possibility that a change in Cho levels affected the NAA/Cho ratios.

Adult↗
PubMed1995

Spin-lattice relaxation and magnetization transfer in intracranial tumors in vivo: effects of Gd-DTPA on relaxation parameters.

Spin-lattice relaxation time T1 and relaxation parameters in magnetization transfer (MT) imaging were measured in 11 intracranial tumors before and after injection of Gd-DTPA at 0.1 T by using the inversion recovery method and the saturation transfer technique, respectively. Preinjection T1 relaxation times of the tumors were longer than those of white matter, but after Gd-enhancement the relaxation times of most tumors were in the same range as those of white matter. Gd-DTPA shortened the apparent relaxation time in the presence of off-resonance saturation pulse (T1a) due to marked shortening of the relaxation time of mobile water (T1w). Gd-DTPA decreased the magnetization transfer contrast (MTC) but did not influence on the magnetization transfer rate (Rwm). The parameters MTC and Rwm differed clearly between Gd-enhanced tumors and normal brain, whereas the relaxation time T1a was in many Gd-enhanced tumors in the same range as in normal brain.

Brain Neoplasms↗
PubMed1995

Magnetic resonance imaging of Achilles tendon xanthomas using a fat-water discrimination technique at 0.1 T.

RATIONALE AND OBJECTIVES: Tendon xanthomas are atherosclerotic plaque like collections of lipids that develop with age in the Achilles tendons of patients having familial hypercholesterolemia (FH). We tested a fat-water discrimination technique for imaging Achilles tendon xanthomatosis. METHODS: We used the spin-warp imaging technique optimized for low-field magnetic resonance (MR) imaging to obtain separate fat and water images of the Achilles tendon. Seven patients with FH, two patients with normal tendons, and three patients with other tendon pathology were studied. RESULTS: Normal tendons showed an intensity near or equal to that of the noisy background in all images. Compared with the background, the intensity of the FH tendons was approximately fivefold greater in magnitude images, fourfold in fat images, and 10-fold in water images. CONCLUSION: The method sensitively detected even subtle xanthomatosis in young patients, but differentiation of xanthomas from other pathologic lesions was possible with this method only when the tendons were significantly thickened.

Achilles Tendon↗
PubMed1995

Magnetization transfer in protein solutions at 0.1 T: dependence on concentration, molecular weight, and structure.

RATIONALE AND OBJECTIVES: We observed the magnetization transfer rates in a variety of protein solutions at 0.1-T magnetic field and compared our results with previous investigations at high magnetic fields (> 0.5 T). The effects of protein concentration, size, pH, denaturation, cross linking, and fiber formation were investigated. METHODS: We used the saturation transfer technique to determine the transfer of magnetization in gamma globulin, fibronectin, collagen, fibrinogen, and albumin solutions. RESULTS: The observed transfer rate increased with increasing concentration and size of the protein. Protein degradation decreased the transfer rate. Cross linking and fiber formation each increased the transfer rate, whereas buffer pH had no effect. CONCLUSION: Protein denaturation, aggregation, and fiber formation are important determinants of magnetization transfer in vitro. The size, concentration, and cross linking of the proteins contribute strongly to the transfer of magnetization at low fields, and the effect seems to be at least as important as at the higher fields.

Hydrogen-Ion Concentration↗
PubMed1995

Artifacts in MR imaging caused by small quantities of powdered iron.

The MR image artifacts caused by minute metallic particles were investigated by imaging small powdered iron quantities from 0.01 mg to 1.7 mg in water phantoms. Images with T1-weighted GRE 3-D and T2-weighted SE 2-D sequences were reconstructed with 5 MR imagers: at 0.04 T, 0.1 T (2 scanners), 1.0 T and 1.5 T. In GRE 3-D images the artifacts were round, clearly demarcated black areas, whereas in SE 2-D images artifact areas were elliptic and surrounded by a bright irregular rim with ghost veils in the direction of frequency encoding. The area of the artifact increased slightly up to 0.1 mg of iron, but grew clearly with larger samples. It appeared to behave independently on the MR imager system for all iron samples. This study shows that even microscopic magnetic particles cause a notable distortion in the MR image independently of the MR equipment used.

Artifacts↗
PubMed1994

Magnetization transfer imaging of lumbar disc degeneration. Correlation of relaxation parameters with biochemistry.

OBJECTIVES: The authors attempted to find out if magnetization transfer (MT) imaging with magnetic resonance imaging (MRI) provides new information of disc degeneration. SUMMARY OF BACKGROUND DATA: Magnetization transfer technique improves soft-tissue contrast and characterization. It measures the cross-relaxation and chemical exchange processes between free and macromolecule-bound water protons in tissues. METHODS: The lumbar MRI and MT of four living subjects and six cadaveric spines were performed at 0.1 T. Disc water, protein, proteoglycan, and collagen contents of cadaveric samples were correlated to MT parameters. RESULTS: The rate of magnetization transfer between free-water protons and the macromolecule-bound protons was elevated in degenerated discs. A positive correlation was found between disc collagen and total protein concentration and the rate of transfer. The contrast of normal and degenerated discs on MT images was not altered much. CONCLUSIONS: More studies are needed to fully establish the importance of MT processes in the disc.

Adult↗
PubMed1994

Diurnal fluid changes of lumbar discs measured indirectly by magnetic resonance imaging.

The feasibility of magnetic resonance imaging and the magnetization transfer technique for measurement of diurnal fluid changes in lumbar discs was studied with the use of 13 healthy subjects. The diurnal height loss of the subjects ranged from 13 to 21 mm. The disc signal in T2-weighted magnetic resonance imaging increased as much as 25% after overnight bed rest, presumably due to the enhanced influx of water. The change in magnetization transfer parameters also suggested increased hydration of the disc after bed rest. Magnetic resonance imaging techniques can be used for indirect measurement of the changes in fluid content and the interaction of water with macromolecules in the disc.

Adult↗
PubMed1994

Magnetic resonance imaging of the uterus in vivo and in vitro at an ultra low magnetic field (0.02 T): assessment of its normal structure and of leiomyomas.

The purpose of this investigation was to analyze the normal anatomy and leiomyomas of the uterus with an ultra low field (0.02 T) magnetic resonance imaging (MRI) device. MR imaging was performed on 18 uteri, 11 of which were imaged both preoperatively (in vivo) and as an operative specimen (in vitro), 6 only as an operative specimen, and 1 only preoperatively. All uteri were examined histologically after imaging. The junctional zone was much better delineated in vivo than in vitro, indicating that its appearance on MR is partly due to blood flow. No structures contributing to its visibility in vitro could be demonstrated histologically. Twenty leiomyomas (size range 7-79 mm) in 12 uteri were found with MRI. They were slightly better discerned in vivo than in vitro. The leiomyomas, having no degenerative changes, had a signal intensity which was the same or lower than that of the myometrium. On images obtained in vitro the signal intensity of these leiomyomas relative to that of myometrium correlated directly with their muscular content (R = 0.74, p = .002). The authors conclude that the junctional zone is a sum of physiological and structural factors, the latter being responsible for its in vitro delineation. MR imaging of the uterus in vitro did not give more information than MR imaging in vivo. All leiomyomas larger than 10 mm could be detected, indicating that MR imaging at 0.02 T is an accurate method for the imaging of the uterine leiomyomas.

Female↗
PubMed1994

Breast tumor imaging with ultra low field MRI.

Ultra low field MRI was evaluated for breast tumor imaging. Twenty-seven patients with a known or suspected breast malignancy were imaged preoperatively with a T2-weighted gradient-echo sequence. Additional IR- and gradient-echo sequences were used for measurements of T1 and T2 relaxation times. Seventeen resected specimens were also imaged within four hours after removal. Nineteen of 23 carcinomas detected at mammography were also detected with MRI (sensitivity 83%), and one of four benign cases was evaluated as pathologic (specificity 75%). Most of the tumors had T1 and T2 relaxation times longer than those of normal breast parenchyma. The T1 values of the tumors were significantly different from the T1 values of fat (p = .0002) and breast parenchyma (p = .0151). The tumor T2 values differed significantly from the T2 of breast parenchyma (p = .0223) but not from that of fat (p = .1475). In vitro tumor measurements were similar to the in vivo measurements. Despite these statistically significant findings, the calculated relaxation times were not considered sufficiently reliable for the clinical evaluation of breast tumors.

Adult↗
PubMed1994

Magnetization transfer in fatty and low-fat livers.

The magnetization transfer technique was applied to imaging of liver tissue at 0.1 T in order to examine the dependence of proton relaxation parameters on protein concentration. The effect of the fat signal on the values of these parameters was also evaluated by using the special fat/water separation method for low fields. The livers of pigs as a model for low-fat tissue and those of burbots as a model for fatty tissue were examined. For the low-fat liver tissue, the magnetization transfer rate Rwm correlated linearly with the total protein concentration very significantly (p = 0.0086). For the fatty liver, the relaxation parameters did not correlate well with the total protein concentration. After fat/water separation, the relaxation times T1 and T1w, the magnetization transfer rate Rwm and magnetization transfer contrast (MTC), measured from the water image, increased significantly. This indicates that the presence of fat in the liver will affect the measured values of magnetization transfer parameters.

Animals↗