Biomedical subjects

K Astrand

Publications and source records attributed to K Astrand.

10 recordsLinked to original sources

PubMed1991

The return of sensitivity to cold, warmth and pain from excessive heat in free microvascular flaps.

Recovery of sensitivity to cold, warmth and pain caused by excessive heat in various types of free microvascular flaps was studied psychophysically in 27 patients who had undergone such operations four months to four years earlier. A thermal stimulator based on the Peltier principle and controlled by a microprocessor was used to measure the sensitivity to temperature in the transplants. The results were compared with the measured thresholds in the opposite sites in corresponding normal body areas. The present study showed that sensitivity to cold, warmth, and pain caused by excessive heat did return to some free microvascular flaps. According to the measurements the sensation started to return after 6 months in some flaps, and all types of thermal stimuli were felt by one patient as early as 10 months after operation. The return was more pronounced in younger people and in smaller flaps. If the hands, feet, or head defects were reconstructed with a thin skin flap (posterior aspect of thigh, dorsum of foot, or subscapular) the recovery of sensitivity was verified. Sensation returned to the musculocutaneous and osteomusculocutaneous transfers if they were on the hands or the head, or if they were sutured to healthy tissue with normal sensation. The main advantage of the psychophysical sensory testing method that we used is that it gave exact numerical data that made it possible to compare results among the different patient groups and even those obtained at different clinics and laboratories.

Adolescent↗

PubMed1990

Osteoporosis and back pain in the elderly. A controlled epidemiologic and radiographic study.

The incidence of back pain was investigated in hip fracture patients, 50-99 years of age, and in 70-, 75-, and 81-year-old controls from the same population. The prevalence of vertebral fractures were evaluated from spinal radiographs. Eighty hip fracture patients and 103 controls, all between 70 and 75 years of age, were included in the radiographic study. The incidence of back pain of the controls was twice that of the hip fracture patients, 45-48% compared with 23-20%, respectively, for both female and male subjects. Conversely, vertebral fractures were radiographically shown in 43% of the hip fracture patients and in 22% of the controls. Thus, the major explanation for longstanding back pain in the elderly does not appear to be related to spinal osteoporosis.

Aged↗

PubMed1979

Influence of radiation dose on image quality.

When the speed of a recording medium is doubled the background quantum mottle is increased by a factor square root 2. However, the signal/noise ratio is changed not in proportion to the square root of the exposure, but in a linear fashion, i.e. by a factor 2. The change in the depiction of objects with a very high attenuation difference in relation to its surroundings appears not to be linear, but proportional to the square root of the exposure. Such objects (metal wire meshes, lead bar grids) should thus be avoided in routine evaluation of image quality since they give incomplete information as to image impairment when high-speed recording media are used.

Angiography↗

PubMed1979

Relevance of radiographic resolution capacity.

Resolution capacity is traditionally evaluated by radiography of metal objects (lead bar grids or fine slits). These objects yield high image contrast. Resolution, then, is limited by the sideways spread of information as expressed by the MTF. However, biologic objects of fine dimensions give rise to much less image contrast than the test objects of metal. Since the amplitude of the signals thus becomes reduced the signal/noise ratio in fact limits resolution capacity much more effectively than does the sideways spread of information. Thus, the MTF expresses a property of the radiographic system which appears only rarely to affect the information capacity of clinical radiographic images.

Contrast Media↗

PubMed1979

Optimised tomography for clinical use.

A technique elaborated by the present authors (1974) for the establishment of optimum tomographic movements was applied to ear tomography in order to design a movement that is not too complex, but yielding good tomographic depiction. Such a movement was found to consist of a spiral of 5 revolutions. Modern engineering appears to allow such complex movements to be carried out with satisfactory stability within a reasonable exposure time.

Ear, Inner↗

PubMed1979

Choice of screens in high-speed angiography.

In phantom experiments a number of intensifying screens were tested as regards their usefulness for angiography. Film speed was adjusted so as to make possible a constant radiographic exposure despite screen speeds varying by a factor of 3. Thus, screen unsharpness varied considerably. However, it was of no practical importance as long as the radiographic exposure was kept constant. This observation indicates that the modulation transfer function is of limited value in differentiating between screens for high-speed angiography. Likewise, film contrast was of little significance for image quality, as compared with radiographic exposure to the intensifying screens.

Angiography↗

PubMed1979

Quantity of tomographic blurring.

A spiral tomographic movement gives rise to a lower quantity of blurring than does a circular movement with the same tomographic angle since in the former the focus comes nearer to the central point. It has been demonstrated that the transfer function may be used to express the quantity of blurring for different tomographic movements. For the sake of convenience the blurring quantity for every type of spiral movement may be expressed in terms of the tomographic angle of a circular movement giving rise to the same transfer function.

Technology, Radiologic↗

PubMed1978

Testing of roentgen film quality.

Evaluation of film quality is often based upon the film's characteristic curve. A practical test method implying radiography of sandpaper sheets has been devised, yielding crucial information about the quality, which cannot be derived from the characteristic curve. Since this test appears to give more valid information about film quality than conventional sensitometry, it is suggested that the test procedure should be standardised and used by the manufacturers.

Absorptiometry, Photon↗

PubMed1977

Xerographic tomography.

Tomographic depiction using Xerox plates was compared with that of screen film tomography. The Xerox plates entail much higher demands as to the quality of tomographic blurring than screen film combinations. Circular or hypocycloid movements give rise to errors of depiction which are more disturbing in xerographic tomography due to the fact that the screen film combination has such properties as to be unable to record certain spurious signals present in the radiation relief, which appear in the higher-precision recording of the Xerox plates. This indicates that these plates are to be preferred if only the spurious signals can be eliminated. Suitable tomographic movements are described. To counteract the high radiation doses in xerotomography, it is suggested that specially constructed cassettes for simultaneous multisection tomography should be used.

Ear↗

PubMed1975

Soft tissue xeroradiography of the shoulder joint.

Soft tissue xeroradiography of the shoulder joint has been compared with a film technique arrived at previously. The xerox plates gave a lower radiation dose to the patient without loss of information. The film technique requires a tungsten target tube with an extra thin glass window (=0.5 mm Al), while the xerox technique may be used with standard tubes.

Humans↗