Biomedical subjects

J B Ra

Publications and source records attributed to J B Ra.

10 recordsLinked to original sources

PubMed1992

Radial scanning technique for volume selective 31P spectroscopy.

An interlaced radial scanning method that is ideally suited for 31P spectroscopy with short T2 components and a wide spectral range is presented. The proposed method, which uses an additional radial gradient and radial scans in the k-space, minimizes T2 decay during the selection time and also optimizes the volume selectivity in a given gradient field strength. Simulation and experimental results with a short selection time of 2 ms demonstrate that the proposed method is suitable for volume selective 31P spectroscopy.

Adenosine Triphosphate↗

PubMed1991

Application of single-shot spiral scanning for volume localization.

A new technique using a spiral scan single-shot RF pulse for localized volume selection has been developed and its experimental results are presented. This technique employs an additional radial-gradient coil in conjunction with the oscillating gradients for the spiral scan to localize the 3D volume. The short selection time in this technique minimizes both signal contamination from unwanted regions and signal attenuation due to T2 decay. We provide both the theoretical background of the technique and the experimental results obtained from a phantom as well as a human volunteer. The proposed method appears simple and accurate in localizing a volume which would be used as either fast imaging or localized spectroscopy.

Computer Simulation↗

PubMed1988

In vivo magnetic resonance imaging of sodium in the human body.

Sodium magnetic resonance imaging of the human body in vivo has been tried and its clinical application is considered. A short T2 imaging algorithm with total volume excitation and a specialized RF coil focused to the region of interest have been adopted to improve the signal-to-noise ratio. Using a 1.5-T human body imaging system, several important organs including heart, liver, gallbladder, kidney, and spine have been examined to demonstrate their sodium concentration in vivo.

Body Composition↗

PubMed1986

Quadrature-multiplexed rf excitation for information doubling in NMR imaging.

A quadrature multiplexed pulse sequence to double the data information in a given acquisition time is proposed for NMR tomography. This technique takes advantage of the Hermitian property of the Fourier transform operation in NMR imaging. The proposed technique uses two rf pulses with 90 degrees phase difference simultaneously applied for the excitation of the spins in two different slices. The method results in truly simultaneous data acquisition coming from two different anatomical slices which can be separated into the real and imaginary parts of the image domain. This technique, therefore, also allows us either to reduce the experiment time by half or double the number of slices in the same examination time, depending on the applied imaging scheme. As a preliminary study, simultaneous dual-slice imaging of a human head using a conventional single-slice imaging scheme was performed.

Fourier Analysis↗

PubMed1986

A method for in vivo MR imaging of the short T2 component of sodium-23.

A magnetic resonance imaging pulse sequence featuring a short echo time of 3.6 ms is described and used clinically for in vivo imaging of sodium-23 in the human head. In living tissues, sodium exhibits at least two transverse relaxation constants, namely, (a) a short component T2s = 0.7-3.0 ms and (b) a long component T2e = 16-30 ms. Since our first in vivo imaging of sodium, an echo time of 10-15 ms has been used by us and by other investigators. This echo time is adequate for the observation of the long T2 component of sodium. However, a substantial fraction of the sodium, namely, the short T2 component, representing about 40%, has remained undetected by the imaging method with this echo time and is now observable by the new pulse sequence. The proposed method is a hybrid technique combining both projection reconstruction and Fourier encoding schemes. The projection reconstruction is used for the xy plane imaging while the Fourier encoding is used for slice separation. Sodium MR images of the human head produced with a short and a long TE are presented and analyzed. There is an increase in the MR signal and improved visibility of intraparenchymal sodium with the new scheme of short TE.

Brain↗

PubMed1985

Chemical-shift artifact correction scheme using echo-time encoding technique.

An investigation has been undertaken to study the effects of chemical shift on NMR image obtained by the projection reconstruction technique. Mathematical simulation studies indicate that chemical shift causes blurring in NMR images regardless of the image reconstruction technique. A systematic study of such artifacts is presented and possible correction schemes are proposed. Exemplary results with and without correction of the chemical-shift artifact and pulse schemes employed for projection reconstruction are presented. The present chemical-shift correction scheme is basically the same as a spectroscopic imaging technique such as the existing 4-D NMR imaging method except that the encoding steps required can be reduced substantially in the case of modest spectroscopic resolution.

Magnetic Resonance Spectroscopy↗

PubMed1983

High-resolution circular ring positron tomograph with dichotomic sampling: Dichotom-I.

The circular ring transaxial positron camera developed earlier was refitted with a new dichotomic sampling scheme and aperture collimators on the detector array to improve the sampling and the overall system resolution. The z-axis slice thickness collimators were also limited to 1 cm, which corresponds to a slice thickness of 0.5 cm FWHM. Two different types of aperture collimators were adopted for high resolution (HR) and very high resolution (VHR) imaging, respectively. In HR mode a resolution of 6.5 mm FWHM was obtained without appreciable degradation of overall sensitivity, which represents a threefold improvement in resolution over the original system. In phantom studies with HR mode a sensitivity of 4500 counts s-1 muCi-1 cm-3 was obtained for a 20 cm diameter uniform phantom filled with water. A VHR mode experiment was also conducted to observe the ultimate resolution capability of the Dichotom-I system, and a resolution of 4.2 mm FWHM was obtained at the expense of sensitivity which was reduced by a factor of four from the HR mode experiment. The experience gained with Dichotom-I suggests a relatively simple and inexpensive modification of the existing NaI(T1) ring positron cameras, most of which suffer from low resolution due to poor sampling and poor intrinsic detector resolution.

Animals↗

PubMed1983

An analysis of the interpersonal perceptions of adolescents.

The main purpose of this study is to investigate the concerns, needs, and other characteristics of interpersonal relationships of adolescents as reflected in the stories they write in response to a stimulus provided in the instrument developed by the author. The second objective is to investigate the main sources of influence on the interpersonal perceptions of adolescents. The subjects are 655 adolescents in Virginia; 43% are public high school students attending grades 9 through 12; and 57% are residents of reformatory facilities, ages 15-18. A comparison of these two groups regarding the types and frequency of themes elicited is made. The themes also are analyzed by sex and race. Content analysis indicates that the predominant themes are affiliation (family and friendship), aggression, achievement (sports), and drugs. As to the sources of influence, "personal experience" ranked highest, followed by "from my mind and my imagination," while "TV" and "books" ranked third and fourth with similar percentages.

Adolescent↗

PubMedDate not supplied

In vivo NMR imaging of sodium-23 in the human head.

We report the first clinical nuclear magnetic resonance (NMR) images of cerebral sodium distribution in normal volunteers and in patients with a variety of pathological lesions. We have used a 1.5 T NMR magnet system. When compared with proton distribution, sodium shows a greater variation in its concentration from tissue to tissue and from normal to pathological conditions. Image contrast calculated on the basis of sodium concentration is 7 to 18 times greater than that of proton spin density. Normal images emphasize the extracellular compartments. In the clinical studies, areas of recent or old cerebral infarction and tumors show a pronounced increase of sodium content (300-400%). Actual measurements of image density values indicate that there is probably a further accentuation of the contrast by the increased "NMR visibility" of sodium in infarcted tissue. Sodium imaging may prove to be a more sensitive means for early detection of some brain disorders than other imaging methods.

Brain Neoplasms↗

PubMedDate not supplied

An algorithm for MR imaging of the short T2 fraction of sodium using the FID signal.

Multiecho magnetic resonance imaging of 23Na in the human body could provide valuable information regarding the distribution of the sodium in the intracellular and extracellular spaces in living tissues. Since it is known that more than half the intracellular sodium has a T2 value of less than 3 ms, the conventional spin-echo imaging technique is not appropriate for the quantitative study of sodium in living tissues. A pulse sequence using the three-dimensional planar-integral projection reconstruction algorithm was developed to provide images from the free induction decay (FID) signal and from the spin-echo. Using this imaging sequence, we are able to produce human head images with the FID signal immediately following the 90 degrees radiofrequency pulse thus preserving the signal from the very short T2 components. This technique with a multiple echo imaging scheme may open the possibility of discriminating between intracellular and extracellular sodium compartments in the human brain based on the T2 relaxation properties.

Algorithms↗