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Biomedical subjects

K Doi

Publications and source records attributed to K Doi.

At least 919 records · Page 51Linked to original sources
PubMedDate not supplied

A new microporous polyurethane vascular graft prepared by an excimer laser ablation technique.

Three types of polyurethane (PU) based tubes (internal diameter, 2 mm; wall thickness, 100 microns) with micropores of well controlled size and arrangement were fabricated using an excimer laser (KrF) ablation technique. The pore size (100 microns) and the longitudinal pore-to-pore distance (200 microns) were constant, and the circumferential pore-to-pore intervals were 60 degrees (type 1), 30 degrees (type 2), and 15 degrees (type 3). The surface of the fabricated tube was photochemically modified with photoreactive gelatin. Scanning electron microscopy showed that pore size and arrangement were precisely controlled as designed, and that a gelatinous layer thoroughly covered the luminal surface. The stiffness parameter (beta), inversely related to compliance, was determined from the change in external diameter against intraluminal pressure. An increase in the number of pores around the circumference decreased the beta value. The type 1 tubes implanted preliminarily in rats for 4 weeks showed good patency (80%). The combination of excimer laser-directed microporing and photochemical surface processing techniques enabled the development of a novel compliant small caliber vascular graft, which is expected to show enhanced transmural tissue ingrowth in vivo.

Animals↗
PubMedDate not supplied

Impregnation of basic fibroblast growth factor on a microporous small caliber graft enhances vascularization.

The incorporation of a cellular adhesive extracellular matrix and a growth factor into a designed concept for a vital, functioning artificial vascular graft may accelerate tissue regeneration, including endothelialization. Microporous polyurethane grafts (inner diameter, 1.5 mm; wall thickness, 100 microns; length, 20 mm; pore size, 100 microns), fabricated using an excimer laser ablation technique, were coated with a mixed solution of photoreactive gelatin, basic fibroblast growth factor (bFGF), and heparin, and were subsequently photocured by ultraviolet irradiation. Control grafts were treated only with photoreactive gelatin. Both bFGF/heparin impregnated grafts (n = 6) and control grafts (n = 9) were implanted in aortas of rats for 4 weeks. All the implanted grafts were patent when harvested. Endothelialization mainly proceeded from anastomotic sites for both groups. The endothelial coverage in the bFGF/heparin impregnated groups was greater than that in the control animals. At the midportion of the grafts, regenerated endothelial and subendothelial layers were seen for the bFGF/heparin groups, but only fibrin layers were seen for the controls. Thus, coimmobilization of bFGF and heparin significantly enhanced neoarterial wall regeneration through perianastomotic as well as transmural tissue ingrowth. The former was more extensive than the latter.

Animals↗
PubMedDate not supplied

Novel device to change left ventricular shape for heart failure treatment: device design and implantation procedure.

The Myocor Myosplint is designed to decrease left ventricular (LV) wall stress by changing LV shape, thus improving contractile function in dilated hearts. This shape change is accomplished by surgically placing three Myosplints perpendicular to the LV long axis, drawing the LV walls inward, and creating a symmetric, bilobular LV. Specially designed instruments aid in the precise delivery of these devices. The purpose of this study was to test the safety and feasibility of the procedure in dogs. Dilated cardiomyopathy was induced in 40 healthy dogs (26.3+/-1.7 kg) by ventricular pacing at 230 beats per minute for an average of 25+/-4 days. Using epicardial echocardiography, we placed the Myosplints across the LV chamber, avoiding the major coronary arteries, papillary muscles, and mitral valve. Once placed, the Myosplints were used to draw the LV walls inward to a prescribed distance. In all cases, we successfully implanted three Myosplints without using cardiopulmonary bypass. There were no complications related to the device or procedure. Myosplint implantation to change LV shape is safe and repeatable on a beating cardiomyopathic canine heart. Further study of the procedure will be needed in humans.

Animals↗
PubMedDate not supplied

Effect of film graininess and geometric unsharpness on image quality in fine-detail skeletal radiography.

Three direct x-ray films and three geometric conditions were used to study the effect of noise and sharpness on high resolution radiography of the hand. The Wiener spectrum of film graininess and the MTF of geometric unsharpness were measured. Radiographs of a wire mesh and a hand phantom, together with the Wiener spectra and MTFs, led to the following conclusions regarding fine-detail skeletal radiography, as currently employed: 1) bone structure detectable in vivo does not show minute structural detail; 2) the technique is primarily noise-limited; 3) the use of better geometry or finer grain film for improving resolution or noise is of limited practical value, whereas the use of poorer geometry or more noisy film results in appreciable degradation of skeletal images; and 4) the present standard technique for in vivo radiography of the hand, therefore, may be very nearly optimal for clinical applications.

Bone and Bones↗
PubMedDate not supplied

The effect of geometric and recording system unsharpness in mammography.

Modulation transfer functions (MTFs) and test object radiographs were used to study the effect of geometric and recording system unsharpness in mammography with the CGR Senographe x-ray unit. Results show that geometric unsharpness can be a significant factor in the detection of microcalcifications within the breast, depending on the size and shape of the focal spot, the focal spot-to-recording system distance, and the object-to-recording system distance (o.r.d.). A new recording system for mammography, the DuPont Lo-dose system, requires approximately 1/15th the exposure of a direct x-ray film, such as Kodak RP/M, to provide mammograms with comparable photographic density. With the Lo-dose system, geometric unsharpness can be reduced by use of a specially designed long cone with an increased focal spot-to-recording system distance. This cannot be accomplished with direct x-ray films because the x-ray unit is operating at near-maximum output conditions even when short cones are used. Although direct x-ray films have a higher resolution than the Lo-dose system, at certain o.r.d.s total resolution is found to be affected more significantly by geometric unsharpness than by the Lo-dose recording system. In several cases, clinical results show improved detection of microcalcifications at larger o.r.d.s by the Lo-dose system with a long one, combined with a reduction by a factor of 15 in patient exposure.

Breast Neoplasms↗
PubMedDate not supplied

Optical versus radiographic magnification for fine-detail skeletal radiography.

Fine-detail radiographic techniques for peripheral skeletal imaging have gained wide clinical acceptance. In this study, the imaging properties and clinical applications of the optical magnification technique, which employs fine-grain industrial film and a large focal spot, are compared quantitatively and qualitatively with those of three slow screen-film techniques, namely, contact exposure with a large focal spot, 2 times radiographic magnification with a 0.3 mm focal spot, and 4 times radiographic magnification with a 50 mu focal spot. The modulation transfer functions (MTF's) of the recording systems and focal spots are obtained and film sensitometry performed. Clinical comparisons are made for patients with metabolic, arthritic, and neoplastic skeletal disorders. The results illustrate the superiority of the optical magnification technique over contact or 2 times magnification techniques using slow screen-film systems. If a microfocus tube is used, however, direct radiographic magnification may provide images comparable in resolution, noise and contrast to those made with the optical magnification technique, and at lower radiation exposure to the patient.

Arthritis, Rheumatoid↗
PubMedDate not supplied

Comparison of non-screen techniques (medical vs. industrial film) for fine-detail skeletal radiography.

High resolution radiographic techniques for imaging the peripheral skeleton (hand and foot) have gained wide clinical acceptance. The two procedures receiving widest attention are non-screen techniques: one uses medical film (Kodak RP); and the other uses industrial film (Kodak Type M) combined with optical magnification. The imaging properties and clinical applications of these two techniques were examined. The modulation transfer functions (MTF's) of the recording systems, Wiener spectrum analyses of noise, and film sensitometry were obtained. Clinical comparisons were made from 200 consecutive patients radiographed with both techniques and the relative merits in metabolic, arthritic and traumatic afflictions were assessed. The results demonstrate the superiority of the industrial film compared to medical film technique in all parameters of image quality. However, the inconveniences of special processing and viewing necessitated by this technique, as well as the increased radiation exposure, limit its clinical application to small, selection groups of patients as determined from the clinical comparative study.

Arthritis↗
PubMedDate not supplied

Automatic bone segmentation technique for CT angiographic studies.

PURPOSE: The purpose of this work was to develop and evaluate an automatic bone segmentation technique for CT angiographic studies. METHOD: An automatic bone segmentation scheme was developed and applied to 40 CT examinations. The results of the segmentation were evaluated subjectively by two radiologists. RESULTS: The bone segmentation was, on average, rated between excellent and good. Automatic segmentation required approximately 25 s/case. CONCLUSION: With this high quality technique, bone can be segmented easily and accurately and subsequently can be removed from CT data sets for further 3D visualization and analysis of various organs.

Angiography↗
PubMedDate not supplied

Automated segmentation and visualization of the pulmonary vascular tree in spiral CT angiography: an anatomy-oriented approach based on three-dimensional image analysis.

A new method for automated segmentation of the pulmonary vascular tree in spiral CT angiography was developed based on 3D image analysis techniques and anatomic knowledge. For efficient and effective segmentation, an anatomy-oriented approach was introduced, in which several anatomic structures are segmented sequentially and the properties of each segmented structure are used for the next step of segmentation and for validation of intermediate results. By use of clinical data of 12 patients, parameters for segmentation were analyzed and optimized. The effectiveness of the segmentation method was evaluated through the visual assessment by comparison between images of the segmentation results by volume rendering and images of maximum intensity projection of the original volume data.

Angiography↗
PubMedDate not supplied

Significance of sublobular hepatic necrosis in the progression of chronic hepatitis C.

The clinical characteristics of hepatitis C virus associated chronic liver diseases (C-LD) in 17 patients were compared with hepatitis B virus associated diseases (B-LD) in 47 patients, by analysing the histological findings of the liver and the change in serum alanine aminotransferase (ALT) level. The persistence of the moderate abnormality in ALT (> 100 IU/L) for longer than 1 year was more frequently seen in the C-LD group (P < 0.01), although the severe exacerbation of the disease with ALT higher than 500 IU/L was more frequent in the B-LD group (P < 0.01). The patients with the histological finding of sublobular hepatic necrosis (SN) in the C-LD group progressed to advanced stages more frequently than those with SN in the B-LD group (P < 0.05). Furthermore, nine of 10 patients with SN in C-LD finally progressed to hepatocellular carcinoma (HCC) in 52 +/- 23 months, whereas three of 16 with SN in B-LD developed HCC in 81 +/- 34 months. Although the morphological features of SN in C-LD and B-LD were almost the same, SN in C-LD seemed to be a more significant diagnostic condition for the progression to liver cirrhosis or HCC. The patients with SN in the C-LD group should be closely followed for the early detection of HCC, although further study with a greater number of patients is necessary.

Adult↗
PubMedDate not supplied

New device for accurate measurement of the x-ray intensity distribution of x-ray tube focal spots.

A new device has been developed with which the focal spot distribution can be measured accurately. The alignment and localization of the focal spot relative to the device are accomplished by adjustment of three micrometer screws in three orthogonal directions and by comparison of red reference light spots with green fluorescent pinhole images at five locations. The standard deviations for evaluating the reproducibility of the adjustments in the horizontal and vertical directions were 0.2 and 0.5 mm, respectively. Measurements were made of the pinhole images as well as of the line-spread functions (LSFs) and modulation transfer functions (MTFs) for an x-ray tube with focal spots of 1-mm and 50-mum nominal size. The standard deviations for the LSF and MTF of the 1-mm focal spot were 0.017 and 0.010, respectively.

Radiographic Image Enhancement↗
PubMedDate not supplied

X-ray images of small blood vessels in angiography: question of isoplanatism.

The basic theory of x-ray image formation of blood vessels, which is related to isoplanatism, is discussed. The x-ray intensity distributions of the blood vessel images are derived first for the actual case, which gives "correct" x-ray images obtained by the ray-tracing method. Secondly, as an approximation of the actual case, the image distributions are derived by the convolution method, which corresponds to an isoplanatic case. It is concluded that, under practical conditions, x-ray images of blood vessels are given approximately by a convolution integral of the object distribution, that is, the input x-ray pattern of the vessel exposed with a parallel x-ray beam, with the line spread function of geometric unsharpness. Therefore, this theory provides support for the experimental procedure commonly used in obtaining blood vessel images, and for the validity of applying in angiography the concept of the line spread function and the modulation transfer function of geometric unsharpness.

Angiography↗
PubMedDate not supplied

Validity of computer simulation of blood vessel imaging in angiography.

The computer-simulation technique for imaging of vessels in angiography is being recognized as a useful tool for the study of the effect of physical parameters on the vessel image. We have examined the validity of this technique by comparing the computed image distribution directly with experimental results. The imput x-ray pattern of a blood vessel phantom, the LSF of the focal spot, and the LSF of a screen-film system were measured. From the data obtained, the final image distributions of the phantom were computed and compared with the experimentally determined distributions. A high-precision device for the alignment and positioning of the vessel phantom was employed in the experiments. Results indicate that computer simulation can correctly predict the image distribution of the blood vessel phantom.

Angiography↗
PubMedDate not supplied

A simple source of fluorescent x rays for the study of radiographic imaging systems.

The properties of a simple source of fluorescent x rays were investigated with regard to its suitability for the study of radiographic imaging systems. The source, consisting of a diagnostic x-ray tube, fluorescent targets, and filters, was found to yield highly monoenergetic x-ray fluxes with intensity sufficient to allow the speed of medium- and high-speed screen-film systems to be studied as a function of x-ray energy.

Spectrometry, X-Ray Emission↗
PubMedDate not supplied

Field characteristics of geometric unsharpness due to the x-ray tube focal spot.

The basic theory of field characteristics is discussed. It is shown that the point spread function and optical transfer function (OTF) of geometric unsharpness at any arbitrary field position can be derived from those at the central beam position. At all locations in the radiation field, the OTF in a direction parallel to the x-ray tube cathode-target axis does not depend on the field position X, which is perpendicular to the tube axis, whereas the OTF in a perpendicular direction does not depend on the field position Y, which is parallel to the tube axis. The theoretical result is used to demonstrate the field characteristic of the uniform, square focal spot.

Models, Theoretical↗
PubMedDate not supplied

Determination of radiographic screen-film system characteristic curve and its gradient by use of a curve-smoothing technique.

One of the important factors affecting radiographic image quality is the film contrast of the recording system, which may be expressed by the gradient of its H & D curve. Experimental determinations of H & D curves are subject to relatively small error, which can nevertheless cause large fluctuations and uncertainties in the calculated gradient. To reduce this fluctuation, we wrote a computer program for orthogonal-polynomial (discrete Legendre polynomials) curve fitting by means of least-squares estimation of parameters. This procedure facilitates curve smoothing and gradient computation following sensitometric measurements. The program was tested against a large number of measured characteristic curves. A brief description of the program is given, with examples which illustrate its applications.

Mathematics↗
PubMedDate not supplied

Monte Carlo simulation studies of detectors used in the measurement of diagnostic x-ray spectra.

Accurate determination of diagnostic x-ray spectra requires, among many other technical considerations, correction of the experimental data for the energy-dependent response of the x-ray detector. In this study, we investigated the energy response of three types of detectors (intrinsic germanium, lithium-drifted silicon, and sodium iodide) commonly used in the diagnostic energy range. We used a Monte Carlo simulation technique to compute photopeak efficiencies, escape peak losses, and Compton fractions as a function of incident x-ray energy for a variety of detector thicknesses and diameters. Calculated responses were compared with experimental results obtained for the Ge and Si(Li) detectors. The measurements, in which we used fluorescent x ray to simulate the monoenergetic beams assumed for the calculations, indicate good agreement between theoretical and experimental approaches. Techniques for correction of measured spectra for the known response of the detector were also evaluated.

Germanium↗