Makoto Kawano

Dynamic state of water molecular displacement of the brain during the cardiac cycle in idiopathic normal pressure hydrocephalus

The predictive accuracy of iNPH diagnoses could be increased using a combination of supplemental tests for iNPH. To evaluate the dynamic state of water displacement during the cardiac cycle in idiopathic normal pressure hydrocephalus (iNPH), we determined the change in water displacement using q-space analysis of diffusion magnetic resonance image. ECG-triggered single-shot diffusion echo planar imaging was used. Water displacement was obtained from the displacement probability profile calculated by Fourier transform of the signal decay fitted as a function of the reciprocal spatial vector q. Then maximum minus minimum displacement (delta-displacement), of all cardiac phase images was calculated. We assessed the delta-displacement in white matter in patients with iNPH and atrophic ventricular dilation (atrophic VD), and in healthy volunteers (control group). Delta-displacement in iNPH was significantly higher than those in the atrophic VD and control. This shows that water molecules of the white matter in iNPH are easily fluctuated by volume loading of the cranium during the cardiac cycle, due to the decrease in intracranial compliance. There was no significant correlation between delta-displacement and displacement. The delta-displacement and the displacement do not necessarily yield the same kind of information. Delta-displacement demonstrated to obtain biophysical information about fluctuation. This analysis may be helpful in the understanding physiology and pathological condition in iNPH and the assisting in the diagnosis.

A method for assessing metabolic information on liver and bone marrow by use of double gradient-echo with spectral fat suppression

Abstract Our aim in this study was to create a noninvasive and practical method for evaluating metabolic information on the liver (iron content and lipid infiltration) and spine (bone mineral density and marrow fat degeneration) using double gradient-echo with and without the spectral fat suppression technique (double-GRE–FS). We arranged phantoms made of various concentrations of superparamagnetic iron oxide solution adjacent to neutral fat to obtain slice planes with various fat fractions using the partial volume effect. We obtained double-GRE–FS images and calculated the T2* values. The fat fraction was calculated from signal intensities of double-GRE–FS images after T2* decay, baseline, and slope corrections. We assessed the fat fraction and the relationship between R2* of the water component and the iron concentration. In addition, we evaluated those values in human bone marrow and liver, including a patient with liver steatosis. The actual fat fraction value was consistent with the fat fraction obtained with the double-GRE–FS method, and the calculated fat fraction was unaffected by the iron concentration. There was a strong positive correlation between R2* of the water component and the iron concentration. There was a negative correlation between the fat fraction and the bone mineral density, and the R2* was correlated with the bone mineral density. The calculated fat fraction in the liver steatosis patient was significantly higher than that in healthy volunteers. The double-GRE–FS makes it possible to assess the fat fraction and R2* simultaneously, and to obtain metabolic information on the liver and bone marrow.

Evaluation of perfusion-related and true diffusion in vertebral bone marrow: a preliminary study

Our aim in this study was to obtain noninvasively more detailed information on perfusion and diffusion in vertebral bone marrow. We analyzed two diffusion components using a biexponential function. Eleven healthy volunteers were examined. By a 1.5-T MRI, we performed single-shot diffusion magnetic resonance imaging to acquire diffusion-weighted images (DWIs) with multiple b values. We determined perfusion-related diffusion and true diffusion coefficients (D* and D), the fraction of the perfusion-related diffusion component (F), and the apparent diffusion coefficient (ADC) in the lumbar vertebral body. Then, we compared these diffusion parameters with the bone mineral density (BMD) obtained with dual-energy X-ray absorptiometry. Moreover, the fat fraction (FF) of the bone marrow was calculated by use of double gradient-echo images with and without spectral adiabatic inversion recovery in the same subject. The BMD showed a significant positive correlation with D*, whereas there was no significant correlation between the other diffusion parameters and BMD. There was a negative correlation between the D or ADC and FF, although no correlation was found between D* or F and FF. Diffusion analysis with a biexponential function made it possible to obtain detailed information on bone perfusion and diffusion in healthy young volunteers.

Prediction of back-scatter radiations to a beam monitor chamber of medical linear accelerators by use of the digitized target-current-pulse analysis method

In small-field irradiation, the back-scattered radiation (BSR) affects the counts measured with a beam monitor chamber (BMC). In general, the effect of the BSR depends on the opened-jaw size. The effect is significantly large in small-field irradiation. Our purpose in this study was to predict the effect of BSR on LINAC output accurately with an improved target-current-pulse (TCP) technique. The pulse signals were measured with a system consisting of a personal computer and a digitizer. The pulse signals were analyzed with in-house software. The measured parameters were the number of pulses, the change in the waveform and the integrated signal values of the TCPs. The TCPs were measured for various field sizes with four linear accelerators. For comparison, Yu’s method in which a universal counter was used was re-examined. The results showed that the variance of the measurements by the new method was reduced to approximately 1/10 of the variance by the previous method. There was no significant variation in the number of pulses due to a change in the field size in the Varian Clinac series. However, a change in the integrated signal value was observed. This tendency was different from the result of other investigations in the past. Our prediction method is able to define the cutoff voltage for the TCP acquired by digitizer. This functionality provides the capability of clearly classifying TCPs into signals and noise. In conclusion, our TCP analysis method can predict the effect of BSR on the BMC even for small-field irradiations.