Medical progress through technology最新文献

Mammography instrumentation has evolved dramatically in recent years. New, more consistent and reliable X-ray generators have been introduced. X-ray tubes with sharper imaging capabilities, higher X-ray outputs, and photon spectra tailored for breasts of different compositions and thicknesses are available. High resolution image receptors which require lower patient dose are in routine use. Scatter reduction mechanisms allow images with higher contrast to be produced. The consistency of mammographic diagnosis has been improved by the introduction of stringent quality control programs which utilize simple phantoms for image evaluation and require that the patient dose be kept low. New developments in breast diagnosis include the use of digital image receptors and stereotactic needle positioning systems. In addition, computer aided diagnostic techniques are being developed. With currently available technology, high resolution, high contrast, and low dose images can be routinely acquired to aid in the early diagnosis of breast disease.

The cardiac response to a pacing pulse is potentially useful for rate adaptive pacemakers and threshold tracking systems. However, until now capture recognition of the ventricular-evoked response by the use of a single electrode for stimulation as well as detection was limited by the electrode polarization. Electronic measures against the stimulus polarization artifact have not been successful due to the variability of the after potential or the requirement of additional battery power. Following the idea of Lewin, Myers and Parsonnet, who introduced the idea of a non-polarizable porous electrode for physiological stimulation, titanium nitride (TiN) and iridium (Ir) coatings with fractal surface structure have been developed with high electro-chemical active surface areas and Helmholtz double-layer capacities of up to 50,000 microF/cm2, thus reducing the polarization artifact significantly. Two types of endocardial leads (10 with a fractal TiN coating and 5 with a fractal Ir coating) were implanted in the apex of the right ventricle and the polarization artifact, as well as the evoked response, was measured. Both types of pacing leads show a 90% reduction in the polarization artifact in comparison to conventional leads. If an autoshort of approximately 20 to 50 ms is applied after the pacing pulse, the polarization artifact of these leads is negligible, thus enabling reliable detection of at least the repolarization phase of the ventricular-evoked response, which is fully sufficient for capture recognition. Additionally, due to their low polarization losses, TiN- or Ir-coated electrodes with fractal surface structure have a unique stimulation and detection performance.

Bioelectrical impedance analysis (BIA) yields accurate, safe and non-invasive estimates of body composition in humans. Pharmacokinetic characterization of drugs represents the body as a series of non-physiologic compartments. We evaluated the utility of BIA in the pharmacokinetic characterization and dosing of water soluble drugs. Serial serum concentrations of gentamicin (G) in 30 hospitalized adults, and theophylline (T), in 15 normal adult males were obtained over a dosing interval after an 8h fast, and analyzed in duplicate by enzyme-mediated immunoassay technique. BIA was performed serially in duplicate during the same time period using a fixed frequency (50kHz, 800 microA) current-injection 4-electrode plethysmograph. Multiple regression techniques were used to develop descriptive models of pharmacokinetic parameters which yielded equations with p-values < 0.03 and coefficients of variation < 20% accounting for > 85% of the pharmacokinetic variability. The G models were then tested in 20 critically ill adults at steady state by serum concentration measurement (criterion standard) and BIA. BIA predictive equations yielded pharmacokinetic parameters not different (by paired t-tests) than those derived by serum concentration measurement. While BIA is an innovative approach to the non-invasive characterization water soluble drugs, further testing with variable frequency BIA under perturbed conditions is warranted.

Clinical gait laboratories have proliferated over the past two decades and an increasing number of research papers are reporting 'assessments' of pathological gait. Some criticisms have been levied at the value of most of these assessments, and some of their arguments are justified. Unfortunately, their review of the pathological gait literature was too superficial for them to justify their main conclusions. The purpose of this review is three fold. The first goal is to show that clinical gait assessments, properly done, do yield valuable diagnostic information to assist surgeons in planning orthopaedic procedures, in the planning of rehabilitation and in the assessment of prosthetic devices. The second goal is to present specific examples of pathological gait assessment to demonstrate the need to understand the fundamental goals and sub-tasks involved in walking, normal gait synergies and the value of a normalized data base. Finally, a generalized strategy will be demonstrated through the use of a diagnostic checklist that has been developed for all gait pathologies. This latter goal is logistically and financially important when we consider the high equipment and personnel costs of running a diagnostic gait service.

Electrical Impedance Tomography (EIT) is an imaging technique based on multiple impedance measurements using electronically multiplexed surface electrodes. The present study describes an EIT prototype tomograph which uses two frequencies of applied signal: 31.25 kHz (within the frequency range originally used in early EIT studies) and 250 kHz. The use of the latter frequency was made possible as a result of several technical innovations including the use of separate groups of electrodes for current injection and for differential voltage measurement and the use of parallel input channels distributed around the object. In vitro images were successfully obtained using the system at the above two frequencies. It is concluded from this study that Electrical Impedance Tomography can be used at sufficiently high frequencies to enable bio-electrical tissue characterisation.

Ventricular Assist Devices (VADs) are a support to the heart function and are used as bridge to transplantation for a brief period in patients awaiting a donor heart. They consist of two sacs with two artificial valves that allow blood flow, the whole connected to a specific electronic equipment. This study examines the performance of a segmented-polyurethane elastomer, namely Biomer, that has been extensively used to manufacture pneumatically actuated VAD blood sacs. Specimens obtained from three VAD blood sacs explanted from three human patients and specimens from one unimplanted blood sac were investigated for mechanical performance of the material and for the changes it undergoes as a result of mechanical stress and interaction with the surrounding biological environment. The application of tensile strength at break yielded no relevant differences between unimplanted and explanted specimens. Biomer exhibited a high elongation at break for both groups, with somewhat lower values for explanted specimens. SEM observations carried out on the inner surface--in contact with blood--of unstressed explanted specimens showed no thrombotic deposits, calcifications, microbial contamination or structural changes. The complementary broken surfaces of stressed specimens showed a distinctive fracture pattern.

The importance of scatter in mammography and the performance of conventional mammographic grids are reviewed. Without scatter control image contrast is significantly degraded. Conventional mammography grids improve the situation; however, their performance is limited. As a result for 5 to 8 cm thick breasts, a more ideal method of scatter control could result in a 25 to 45% improvement in contrast over that possible with conventional grids. One such approach is scanning slit mammography. The principles of this approach are presented along with the design and geometrical specifications of a prototype multiple scanning slit unit. The unit has a measured primary transmission of 91% and scatter transmission of 3%. Similarly measured performance values for a commonly used grid are 62% and 19%, respectively. Compared are images of a 6 cm breast phantom obtained with the scanning slit unit and a conventional grid. The scanning slit unit achieved noticeably greater image contrast with 30% less radiation. Also discussed are the limitations and engineering challenges of the technology.

A new design of Titanium dental implant, coated with Titanium oxide and with a Hydroxyapatite apex, was experimented in a Beagle dog's jaw for one year to evaluate the biocompatibility of the materials used and the biomechanical efficiency of the design. The explanted prosthesis and the surrounding bone were embedded in methylmethacrylate resin and the sections observed under Scanning Electron Microscopy (SEM), with an X-ray microprobe to check the interface with bone and the occurrence of ionic release. The results showed that the pin was well accepted by the bone. New bone grew on the metal surface developing a mechanical bond with the prosthesis. No ionic release of the metal was seen.

The electrical properties of tissues and cell suspensions are most unusual. They change with frequency in three distinct steps and their dielectric constants reach enormous values at low frequencies. We shall concentrate on the 'linear' properties as observed with applied fields less than 1 V/cm. The linear properties of interest include the dielectric constant epsilon and conductivity kappa. Extensive measurements have been carried out over a broad frequency range extending from less than 1 Hz to many GHz. Observed frequency changes of these properties obey causality, i.e., the Kramers-Kronig relationships which relate changes of dielectric constants with conductivity changes. A number of mechanisms have been identified which explain the observed data. These mechanisms reflect the various compartments of the biological material. These include membranes and their properties, biological macromolecules and fluid compartments inside and outside membranes. We summarize the mechanisms which contribute to the total frequency response.