Biomedical subjects

C H Oh

Publications and source records attributed to C H Oh.

12 recordsLinked to original sources

PubMed1992

Extraordinarily potent antimalarial compounds: new, structurally simple, easily synthesized, tricyclic 1,2,4-trioxanes.

New, racemic, tricyclic trioxane alcohol 3 was designed and synthesized as a structurally simple analog of clinically useful, tetracyclic, antimalarial artemisinin. A series of 20 ester and ether derivatives of alcohol 3 were prepared easily, without destruction of the essential trioxane system. Chemical structure-antimalarial activity for each derivative was evaluated in vitro against chloroquine-resistant and chloroquine-sensitive Plasmodium falciparum parasites. Many of these derivatives were highly efficacious; carboxylate ester 9f, carbamate ester 10a, and sulfonate ester 12a had antimalarial potency similar to that of artemisinin, and carboxylate esters 9b and 9d, carbamate esters 10b and 10c, and phosphate esters 11a-c had antimalarial potency up to 7 times higher than that of artemisinin. Several of these most active analogs (e.g., carboxylate 9b and carbamates 10a and 10c) are stable crystalline solids, a feature of considerable practical value for any new drug candidate.

Animals↗

PubMed1992

Phase-scrambled RF excitation for 3D volume-selective multislice NMR imaging.

An RF excitation technique with which one can improve the effective dynamic range of the receiver and reduce the interference between slices for 3D volume-selective multislice MRI is described. The basic idea of the technique is to use phase scrambling in conjunction with slice encoding through the use of RF pulses. The spins in each slice are encoded by RF pulses which have the scrambled as well as slice-encoded phase components along the slice-selection direction. The scrambled, or randomly distributed, phase reduces the peak signal intensity, thereby reducing the dynamic range of the signal. Since the proposed technique utilizes RF slice encoding together with phase scrambling, interslice image interference is greatly reduced and the dynamic range is improved. In addition, the method has several advantages such as a reduction in the power requirement for the RF pulses and the elimination of the necessity for hardware such as nonlinear gradient coils.

Algorithms↗

PubMed1992

Histopathologic differences in the photoaging process in facial versus arm skin.

We used clinical criteria to study skin biopsy specimens with mild to moderate photoaging taken from the face and dorsal forearms of 74 Caucasian volunteers between the ages of 30 and 50. Facial skin had a greater number of granular cell layers, a higher degree of keratinocytic atypia, and more often showed a compact stratum corneum than arm skin. Furthermore, the dermis of facial skin had a more extensive perivascular and perifollicular lymphocytic infiltrate, more perifollicular fibrosis, a greater number of mast cells and melanophages, and thinner vascular walls than forearm skin. This study demonstrated that the photoaging process is different for face and arm skin. Appreciation of these differences should permit more refined studies of photoaging and the development of more efficient therapies.

Adult↗

PubMed1991

New spatial localization method using pulsed high-order field gradients (SHOT: Selection with High-Order gradienT).

A new spatial localization method using an additional set of high-order magnetic field gradients is described. The method uses a nonlinear part of high-order magnetic field gradient patterns which allows us to select a volume in conjunction with the selective radiofrequency (RF) pulse. Unlike the other existing volume selection methods such as ISIS or SPARS, the proposed selection method requires only one RF-gradient pulse pair to select a volume in two directions. The center of the selected volume can be moved to any arbitrary location within the body by the addition of precalculated lower order gradients which are simultaneously pulsed with the high-order gradient. The method also has the potential for localized spectroscopy from the FID signal which can be realized by using oscillating second- and first-order gradients for 3D selection with a single RF pulse. By using the proposed localization method, it is possible to design more flexible pulse sequences, e.g., the shorter echo-time spectroscopic pulse sequence. We have designed and constructed a six-loop r2 (or x2 + y2) gradient coil for initial application. By simultaneously applying this second-order gradient and proper x, y, and/or z gradients, 2D selections were achieved in arbitrarily selected positions in conjunction with a single selective RF pulse. Phantom and animal experiments have been performed and the results appear promising, especially in areas of NMR spectroscopic imaging applications where spatial localization is essential.

Animals↗

PubMed1991

An optimized multislice acquisition sequence for the inversion-recovery MR imaging.

An optimized multislice data acquisition scheme for inversion-recovery MR imaging is proposed and experimental results are presented. In this new scheme, instead of forming a set of multislice inversion-recovery sequences in series for a given phase encoding step, 180 degrees inversion pulses corresponding to different slices are interwoven with the spin echo data acquisition sequence in an optimal way depending on the desired inversion-recovery time. For example, between the 180 degrees inversion RF pulse and the spin-echo imaging sequence, a number of imaging and inversion sequences are inserted with different slice combinations, i.e., long inversion-recovery time is effectively utilized for the other slice pre-inversion and data acquisition. With the optimized sequence, imaging time has been reduced by as much as a factor of four compared with the existing methods.

Brain↗

PubMed1991

Treatment of steinstrasse with repeat extracorporeal shock wave lithotripsy: experience with piezoelectric lithotriptor.

Among 958 patients with renal stones who underwent extracorporeal shock wave lithotripsy (ESWL) monotherapy using an EDAP-LT01 piezoelectric lithotriptor steinstrasse developed in 55 (5.7%). Of these 55 cases stone fragments passed spontaneously in 35 (63.6%) and were treated successfully (no residual stone fragment in ureter) with repeat ESWL in 18 (32.8%). Only 2 patients (3.6%) required ureteroscopic management or open ureterolithotomy. Therefore, repeat ESWL is considered a good initial method to treat complicated steinstrasse.

Humans↗

PubMed1990

Radio frequency field intensity mapping using a composite spin-echo sequence.

A novel radio frequency (RF) field intensity mapping or imaging method using a composite NMR spin-echo sequence is proposed. A composite spin-echo RF pulse with 90 degrees y-180 degrees x-90 degrees y sequence makes phase change in the final image depending on the RF field intensity on the object. The resultant phase change or phase map can be used to obtain the actual RF flip-angle map for a given condition which includes the status of tuning and RF inhomogeneity, etc. Bloch equation has been solved numerically to obtain the effects of the RF field intensity as well as the main magnetic field inhomogeneity and the results are used for the mapping (imaging) of the RF field intensity. Phantom studies have been performed using a 1.5 Tesla whole body MRI system and the results are presented.

Humans↗

PubMed1990

Diagnostic value of the radioisotope erection penogram for vasculogenic impotence.

Radioisotope erection penography of 113 consecutive impotent patients (41 with psychogenic and 72 with vasculogenic impotence) and 15 normal potent men were obtained. Twenty minutes after intracavernous injection of 99mtechnetium-pertechnetate 40 mg. papaverine hydrochloride were administered into the corpus cavernosum to induce erection. A gamma camera with a pinhole collimator was used to monitor the radioactivity. Various penogram indexes were calculated from the time activity curve and their usefulness was evaluated. Index A1 was useful to differentiate vasculogenic and psychogenic importance. Indexes V1 and V2 were useful to differentiate arteriogenic and venogenic impotence. The radioisotope erection penogram is a simple, less invasive and valuable screening test in the identification of vasculogenic impotence, and is effective in differentiating arteriogenic and venogenic impotence.

Adult↗

PubMed1990

Prostacyclin-to-thromboxane A2 ratio in arteriogenic impotence.

It has been suggested that penile hypercoagulability predisposes to aging penile vascular changes and impotence, and that elevated thromboxane A2 during erection may contribute to hypercoagulability and atherosclerosis. Since the ratio of the prostacyclin concentration to the thromboxane A2 concentration is constantly maintained in normal hemostatic responses, an imbalance between thromboxane A2 and prostacyclin may be a factor to initiate vascular diseases and decrease blood flow. We assess the usefulness of the prostacyclin-to-thromboxane A2 ratio in penile blood during erection for diagnosis of arteriogenic impotence. The ratio in the arteriogenic impotence group was significantly lower (p less than 0.01) than in the psychogenic and venogenic impotence groups. Therefore, the prostacyclin-to-thromboxane A2 ratio seems to be useful to diagnose arteriogenic impotence.

Adult↗

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

Some results of high-flow-velocity NMR imaging using selection gradient.

A simple and new flow velocity measurement technique using conventional spin-echo sequence is proposed and its applications to a preclinical result are presented. This technique utilizes the phase velocity encoding effect due to 180 degrees rf and its corresponding selection gradient. This phase encoding and its phase velocity relations have been obtained by numerical solution of the Bloch equation. A flow velocity measurement obtained with a volunteer using this proposed technique indicates close agreement with other previously measured values.

Aorta↗

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↗