[Improvement of Brain Contrast Using Spin Echo T1-weighted Image at 3 T MRI].

Brain T1-weighted images using spin echo (SE) sequence has poor contrast at 3.0 Tesla magnetic resonance imaging (3.0 T MRI) systems from the influence of crosstalk and magnetized transfer (MT) effect, and prolongation of the T1 value. Therefore, improving of scan parameters has been reported such as excitation flip angle (FA) and interleave data acquisition. The purpose of this study was to show the effects of alterations of presaturation pulse amplitude and chemical shift selective (CHESS) pulse amplitude. Gray-to-white matter contrast increased with decreasing amplitude of presaturation pulse in whole brain imaging. Presaturation and CHESS pulse consist of radio frequency pulse. Therefore, both pulses have a similar effect on MT pulse. Manual alteration of presaturation pulse amplitude for each scan lacks versatility on clinical use. However, decreasing amplitude of presaturation pulse is equal to decreasing thickness of presaturation pulse. About CHESS pulse, it requires no manual alteration for each scan. For example, switching fat suppression mode from strong to weak increase T1 contrast. Our study demonstrated that using not only low excitation FA and interleave date acquisition but also low amplitude of presaturation and CHESS pulse increase the contrast in T1 SE brain scans at 3.0 T MRI.

Image Evaluation of Free-breathing Navigator Echo and Triggered Cardiac-gated Delayed Myocardial Enhancement Magnetic Resonance Imaging in Sedated Infants.

We validated a navigator-echo-triggered sequence that drives magnetization before cardiac-gated inversion recovery T1 turbo field echo acquisition, in the sedated free-breathing pediatric population. Cardiac magnetic resonance imaging was performed on sedated infants with single ventricle. We calculated the signal-to-noise ratios and contrast-to-noise ratios of 2 groups of images obtained using respiratory triggering with and without navigator echo. All images were then visually assessed by 2 observers. The signal-to-noise ratio and the contrast-to-noise ratio were significantly higher with than without navigator echo (p<0.01; p<0.05). The visual assessment scores were also consistently better with than without navigator echo (p<0.01). Free-breathing navigator echo was found to have the advantage of decreasing the motion artifact caused by respiration. Cardiacgated inversion recovery T1 turbo field echo sequence for free-breathing navigator-echo-triggered respiration allows for the acquisition, in sedated infants, of diagnostic images whose quality exceeds that of the non-navigator-echo-triggered alternative.

A new phantom using polyethylene glycol as an apparent diffusion coefficient standard for MR imaging.

In recent years, magnetic resonance imaging (MRI) with diffusion-weighted imaging (DWI) has seen wide clinical use, such as for early detection of cerebrovascular diseases and whole body screening for tumors. The apparent diffusion coefficient (ADC) standard phantom, which mimics the ADC values of several lesions in the body, is indispensable for the development of new pulse sequences for DWI, such as diffusion-weighted whole-body imaging with background body-signal suppression (DWIBS). However, information on the ADC values of the previously reported ADC standard phantoms is limited, because these phantoms were made using only a few different materials at a limited range of concentrations, and the ADC values were measured only at certain temperatures. It has been considered difficult, if not impossible, to create a phantom that provides arbitrary ADC values, because it is difficult to calculate the concentrations of the materials and the temperature at ADC measurement. In this study, we used polyethylene glycol (PEG) as a phantom material, and developed an empirical formula to calculate the PEG concentration at any measurement temperature to obtain arbitrary ADC values of the phantom. DWI images of phantoms made using seven different PEG concentrations were taken under heating from 17 to 46 degrees C at 1 degrees C intervals. Using ADC values calculated from these DWI images, we developed two empirical formulas: i) an empirical formula to calculate the ADC values of phantoms made using any PEG concentration at any measurement temperature; and ii) an empirical formula to calculate PEG concentrations to obtain arbitrary ADC values at any measurement temperature. We inspected the accuracy of these empirical formulas by newly made PEG phantoms. A comparison between the ADC values calculated with the empirical formulas and the measured ADC values confirmed the high accuracy of these formulas. PEG phantoms are safe, inexpensive and easy to make, compared with the previously reported ADC standard phantoms. Our empirical formulas enable us to calculate PEG concentrations that provide arbitrary ADC values at any measurement temperature. The empirical formulas could be used within a range of ADC values from 0.37x10(-3) to 3.67x10(-3) mm(2)/s, PEG concentrations from 0 to 120 mM, and measurement temperatures from 18 to 45 degrees C. Using these formulas, it would be possible to make standard phantoms that mimic the ADC values of any clinical lesions. The PEG phantom might thus be an excellent new ADC standard phantom for MRI with DWI.

In vitro experimental study of the relationship between the apparent diffusion coefficient and changes in cellularity and cell morphology.

Diffusion-weighted magnetic resonance imaging (MRI) is frequently used clinically, and is available for the whole-body screening for tumors. The exact mechanism by which the apparent diffusion coefficient (ADC) value decreases in tumorous tissue remains unclear, although various theories have been proposed, including intracellular and extracellular factor theories. It is impossible to distinguish each factor in the intracellular and extracellular spaces as the source of MR signal generation by means of conventional comparison between MR images and pathological specimens. Other factors which have been reported to affect ADC include cellularity and cellular edema of human tissues, and temperature of phantoms at the time of measurement. We employed a new technique that enables cellular MR imaging using a newly developed bio-phantom containing a living culture tumor cell line, Jurkat-N1. We investigated possible reasons for observed decreases in ADC values for tumors, and we considered the contribution of both the intracellular and extracellular space to such a decrease. The ADC values of the bio-phantom increased with increasing heat exposure from 27 to 45 degrees C. ADC values also increased after the destruction by sonication of tumor cell membranes. ADC values decreased as cellularity increased in the bio-phantom. ADC values decreased due to cellular edema caused by a low salt concentration in the bio-phantom. Changes in pressure in the bio-phantom had no effect on the observed ADC values. We calculated both the intracellular ADC and extracellular ADC values using the ADC values, cellularity, and cellular volume of Jurkat-N1 cells in the bio-phantom. The extracellular ADC values in the bio-phantom were estimated to be lower than the ADC value of distilled water. These results indicate that not only intracellular ADC values, but also extracellular ADC values contribute to the determination of the ADC values of bio-phantoms. This is the first report to have examined the contribution of intracellular and extracellular space on the ADC values of bio-phantoms containing cultured tumor cells.

[Accuracy of measurement of radiochromic film density for high-energy X-rays].

Radiochromic film (RC-film) is of great interest as a film-type dosimeter for radiation oncology applications. We present a two-dimensional image-based evaluation of the measurement accuracy of a commercial RC-film product (Gafchromic MD-55-2 film, ISP TECHNOLOGIES, Inc.) by using a commercial Laser Densitometer (Model 1710, Computerized Medical Systems, Inc.) as an optical density imaging system. The coefficient of variation of the density (pixel-value) in one sample was approximately 3% to 11% at 3 Gy or less, and 3% or less at 4 to 60 Gy. Although the coefficient of variation between three samples at the same dose was about 14% at 1 Gy, it decreased as the dose increased, reaching several percent. In 1 to 6 Gy samples, geometric imaging artifacts [interference (moire) patterns] were observed, and it was found that scan-sampling pitch influenced the accuracy of measurement of the density of the sample. To improve the accuracy of density measurement, sufficient knowledge about characteristic features of the density measuring system is essential.