PubMed Health⌕ Search

Biomedical subjects

Y Higashida

Publications and source records attributed to Y Higashida.

34 records · Page 2Linked to original sources
PubMed1986

Evaluation of high resolution digital subtraction angiography in neuroradiology.

A digital subtraction angiography (DSA) system has been modified for capabilities of a 1024 x 1024 matrix with 10 bit depth. Spatial resolution was increased with expansion of the matrix, but contrast resolution was not increased as determined by phantom experiments. Smaller focal spots and magnification factors were also important for improvement of spatial resolution. Clinical evaluation using carotid, vertebral, and cervical DSA with intra-arterial contrast injections demonstrated that there was slight improvement in the image quality, but the final diagnosis and management of patients were not changed with the use of high resolution DSA. Further improvements in image quality of DSA will be accomplished by improvements of image intensifiers and use of smaller focal spots.

Angiography, Digital Subtraction↗
PubMed1985

Ultra-high-strip-density radiographic grids: a new antiscatter technique for mammography.

We conducted a comprehensive study on the application of ultra-high-strip-density (UHSD) grids to mammography for the improvement of image contrast. These UHSD grids have strip densities of 70 to 100 lines/cm. After investigating the performance of mammographic grids with various design parameters through Monte Carlo simulation studies, we made prototypes of UHSD grids having lead strip thicknesses of 20 to 37 micron, aluminum interspacer thicknesses of 80 to 120 micron, and grid ratios of 2 to 6. The UHSD grids can be placed inside the cassette without a Bucky tray and thus will not increase geometric unsharpness. The measured physical characteristics and the phantom images obtained confirmed our findings in the simulation studies. A 40 to 90% increase in contrast was achieved at Bucky factors of 2 to 3.5; these results are comparable with those from conventional antiscatter grid techniques in mammography. The potential usefulness of the UHSD grids was demonstrated in a preliminary clinical comparison of mammograms.

Equipment Design↗
PubMed1985

Stereoscopic technique in digital subtraction angiography.

Stereoscopic technique was applied to digital subtraction angiography (DSA) with alternate exposures from twin focus spots (6.5-cm separation) of an x-ray tube. Correct identification of two crossed aluminum wires was obtained more than 90% of the time when there was separation of more than 5 mm. Excellent clinical images of intravenous as well as intraarterial DSA have been obtained, and the clinical value of DSA was enhanced by application of the stereoscopic technique.

Angiography↗
PubMed1983

High-speed, single-screen/single-emulsion film systems: basic imaging properties and preliminary clinical applications.

We investigated the potential clinical use of single-screen/single-emulsion film systems by comparing their relative speeds, modulation transfer functions (MTFs), Wiener spectra, and H & D curves with those of conventional screen-film systems. The relative speeds of single screens with single-emulsion Kodak OM film (single systems) were 50-60% lower than those of the conventional double screens with double-emulsion Kodak OG film (double systems), but the single systems yielded a 75-110% increase in the MTF at 2 cycles/mm. The single system had a noise level comparable to or slightly greater than that of the double systems. Phantom images and preliminary clinical radiographs indicated that single systems can improve image resolution over that obtainable with double systems under the same exposure conditions. More importantly, the use of a single system provided an approximately 40% reduction in patient exposure while providing a comparable radiographic image quality.

Humans↗
PubMedDate not supplied

High resolution DSA: experimental and clinical evaluation.

The DSA system has been upgraded for capabilities of slow scan video technique and progressive T.V. read-out of 1024 X 1024 matrix with 10 bits of depth. A square wave test pattern made of lead bar demonstrated moderate improvement in spatial resolution, but imaging of a Burger-Rose phantom revealed no significant increase in contrast resolution. Clinical study of various angiograms with intraarterial injections showed that there was slight improvement in the visibility of the vessels, especially small arterial branches, while there was no increase in visibility of the veins. There were no cases in which diagnoses were altered by application of high resolution DSA. With future improvements of the image intensifiers, DSA with 1024 X 1024 matrix may reveal its potential advantage, especially when coupled to larger image intensifiers such as 12 or 14 in.

Angiography↗
PubMedDate not supplied

Hybrid digital subtraction angiography: initial clinical experience.

Hybrid digital subtraction angiography was performed after modification of a DSA system. Alternate high voltage (110-120 kV) and low voltage (65-70 kV) were obtained within short time intervals of 60-70 ms with a high voltage switching generator. Experimental phantom studies revealed the exposure dose per single image of hybrid subtraction was approximately 30% of that of conventional DSA. The SNR of hybrid subtraction was improved by increasing the exposure dose and application of postprocessing programs. Clinical application of intraarterial and intravenous DSA revealed that soft tissue artifacts were removed surprisingly well, but image quality decreased because of lowered SNR. Frame integration and matched filtering improved image quality of hybrid subtraction.

Angiography↗
PubMedDate not supplied

Computed radiography utilizing laser-stimulated luminescence: detectability of simulated low-contrast radiographic objects.

Threshold contrasts of low-contrast objects with computed radiography (CR) images were compared with those of blue and green emitting screen-film systems by employing the 18-alternative forced choice (18-AFC) procedure. The dependence of the threshold contrast on the incident X-ray exposure and also the object size was studied. The results indicated that the threshold contrasts of CR system were comparable to those of blue and green screen-film systems and decreased with increasing object size, and increased with decreasing incident X-ray exposure. The increase in threshold contrasts was small when the relative incident exposure decreased from 1 to 1/4, and was large when incident exposure was decreased further.

Lasers↗
PubMedDate not supplied

Dual-film cassette technique for studying the effect of radiographic image quality on diagnostic accuracy.

In order to investigate the relationship between diagnostic accuracy and radiographic image quality, we have developed a dual-film cassette which produces two radiographs simultaneously with a single exposure. One of these radiographs is of standard quality; the second is of lower quality because of degraded spatial resolution and a significantly lower exposure. We have studied the basic physical properties of the standard and low-dose screen-film systems which we use in the dual-film cassette by comparing their beam hardening, scatter fractions, contrasts, modulation transfer functions (MTFs), and Wiener spectra. The x-ray spectrum incident on the low-dose system contained more high-energy photons than that incident on the standard system, and the scatter fractions for the low-dose system were slightly less than or comparable to those for the standard system. While the radiographic contrast produced by the two systems were generally comparable, the standard system had a slightly higher contrast than the low-dose system in some cases. The MTF of the low-dose system was considerably lower than that of the standard system, and the low-dose system had a noise level considerably greater than did the standard system. Phantom images and clinical radiographs indicated that, for the low-dose system, the image quality degraded significantly.

Humans↗
PubMedDate not supplied

Performance of antiscatter grids in diagnostic radiology: experimental measurements and Monte Carlo simulation studies.

We have devised an experimental method with which one can accurately measure the transmission of primary radiation and the transmission of total radiation by an antiscatter grid in a setting similar to a practical radiographic examination. We measured the transmission values for 27 combinations of x-ray tube potentials, phantom thicknesses, screen-film systems, and grid parameters. The standard deviation of one measurement was estimated to be 2.9% and 1.5% for the total and primary transmissions, respectively. The measured grid transmission was compared with results predicted by our Monte Carlo calculations; 92% of the measured and calculated values agree within two standard deviations. This close agreement indicates that our Monte Carlo calculation can accurately predict the performance of antiscatter grids under diagnostic imaging conditions.

Biophysical Phenomena↗
PubMedDate not supplied

Digital TV tomography: description and physical assessment.

A digital TV tomography system, capable of retrospective reconstruction of multiple digital tomographic images, has been developed and its basic physical characteristics have been evaluated. The multiple tomographic images were formed through retrospective reconstruction of digital data acquired on a linear tomographic x-ray unit and an image intensifier-television system. Digital data were obtained with a series of 30 pulsed exposures during linear motion of the system. A distortion correction algorithm for the convex surface of the image intensifier was developed in order to reduce image distortion. A phantom study showed that the square-wave response at the fulcrum plane was slightly inferior to that in conventional tomography. There was also a slight decrease in the square-wave response away from the fulcrum plane and upon application of a correction algorithm, as compared with the response of the original reconstructed image at the fulcrum plane. The exposure dose for a single image was approximately half that in conventional tomography. Because of many advantages, including low exposure, short examination time, digital image manipulation, and applicability to picture archiving and communication systems, this is likely to become an important method in radiology when further technical refinements have been made.

Angiography, Digital Subtraction↗
PubMedDate not supplied

Quantitative measurement of high flow velocities by a spin echo MR technique.

A new method of flow measurement using a spin echo (SE) technique has been developed on the basis of the flow effect that at high velocities signal intensity decreases linearly with increasing flow velocity. Flow velocity is calculated from the signal intensity ratio of the flowing material in two images with the same imaging parameters but different echo times. The linear relationship between the signal intensity and flow velocity was examined with a steady flow phantom. When assessed with steady flows in the phantom, flow velocities calculated by this method were in good agreement with velocities measured by a flow meter. This method was used with ECG gating to measure the blood flow of the right common carotid artery of a healthy volunteer. The measured peak flow velocity and the pattern of flow velocities during systole correlated well with the results obtained by Doppler ultrasound.

Blood Flow Velocity↗
PubMedDate not supplied

Clinical evaluation of digital TV tomography.

A unit for digital TV tomography (DTT) was constructed on the basis of retrospective reconstruction of digital data acquired during a linear tomographic motion of an X-ray tube and an image intensifier with a television camera (I.I.-TV) assembly. Following descriptions of the basic principle and system, clinical results obtained with this unit are presented. Comparison with conventional tomography of the chest, skull, abdomen, and bones and joints showed equal diagnostic information in more than 50% of cases. Application to intra-arterial and intravenous DSA provided excellent images, but no new information was obtained. DTT has the advantages of technical simplicity, short examination time, low exposure dose, and compatibility with a PACS system. This technique will become an important part of a modern radiology department.

Aged↗