Soft tissue radiography.pptx

soft tissue radiography, high kvp technique

1. Soft tissue radiography

2. For low atomic number atoms, such as those found in soft tissue, the binding energy of even k-shell electrons is low (e.g. 0.3 KeV for carbon). Therefore, the photoelectron is released with kinetic energy nearly equal to the energy of the incident x-ray. For higher atomic number target atoms, electron binding energies are higher. Therefore , the kinetic energy of the photo-electron from proportionately lower. A photoelectric interaction cannot occur unless the incident x-ray has energy equal to or greater than the electron binding energy. A barium K-shell electron bound to the nucleus by 37 keV cannot be removed by a 36-keV x-ray.

3. As the relative vertical displacement between the graphs of soft tissue and bone demonstrates, a photoelectric interaction is much more likely to occur with high-Z atoms than with low-Z atoms (

4. Bone has an atomic number of 13.8, and soft tissue has an atomic number of 7.4 (see Table 9-3). Consequently, the probability that an x-ray will undergo a photoelectric interaction is approximately seven times greater in bone than in soft tissue. Question: How much more likely is an xCompton scattering is independent of the atomic number of tissue. The probability of Compton scattering for bone atoms and for soft tissue atoms is approximately equal and decreases with increasing x-ray energy. This decrease in Compton scattering, however, is not as rapid as the decrease in photoelectric effect with increasing x-ray energy. The probability of Compton

5. At 20 keV, the probability of photoelectric effect equals the probability of Compton scattering in soft tissue. Below this energy, most x-rays interact with soft tissue photoelectrically. Above this energy, the predominant interaction with soft tissue is Compton scattering. Low kVp resulting in increased differential absorption provides the basis for mammography, which is an example of soft tissue radiography.

6. Soft tissue radiography The density of different body structure varies due to its composition, the atomic number , and atomic weight. Soft tissue mainly comprises of fat and muscle which have low density and there is very less difference of contrast between these structure, so the contrast should be maximized to visualize the adjacent structures. Soft tissue is performed with same X-RAY machine as for hard tissue but less penetrating X ray should be used.

7. Soft tissue radiography technique uses the lowest kVp that will penetrate the structure adequately. For example , during mammography the kVp used is less 35. Due the decrease in kVp the radiation dose is greatly increased in soft tissue radiography, so proper lead shielding should be done during the examination.

8. Uses of soft tissue radiography In mammography To demonstrate the low density foreign bodies Calcification in tendons and arteries Cysticercosis Sub deltoid fat layer change in bursitis of shoulder

9. High kilovoltage technique

10. The kVp selected for high- kVp technique charts is usually greater than 100. This type of exposure technique also could be used for routine chest radiography to attain improved visualization of the various tissue mass densities present in the lung fields and the mediastinum. Lower or more conventional kVp settings provide increased subject contrast between bone and soft tissue. When 120 kVp is selected for chest radiography, however, all skeletal tissue is penetrated, and visualization of the different soft tissue mass densities present is enhanced. To prepare a high- kVp technique chart, the procedure is basically the same as for preparing the fixed- kVp technique chart. All exposures for a particular anatomical part would use the same kVp . Obviously, the mAs value would be much less.

11. High kilovoltage technique High kilovoltage technique is a radiographic technique which uses high kVp above 90 kVp to increase the range of tissues that can be visualized on the single radiograph. The difference in optical density between soft tissue and the bone is less at 120 kVp than 60 kVp as with increasing kVp , the attenuation in soft tissue increases and in bone it decreases.

12. The mAs can be decreased with the increase in the kilovoltage . Furthermore, with the increase in the kVp , scattered radiation also increase which can be compensated by the use of grid or air gap technique.

13. advantages The patient dose is reduced As lower mAs is used that ensures short exposure time with less patient motion during the examination Better penetration in lung tissue which is superimposed by the breast and dome of diaphragm. Greater exposure latitude

14. Wide range of tissues can be shown on a single radiograph. The patient dose is reduced

15. Disadvantages Special equipment is required Scattered radiation is increased Necessity of high ratio grid or air gap technique Soft tissue detail is lost Lower contrast

16. Macroradiography Macroradiography is a radiographic imaging technique used to increase the size of the image relative to that of the object. specialized equipment with fine focal spot is essential to perform macroradiography .

17. Principle Magnification depends on the ratio of the source to film distance to the source to object distance. magnification = image size/ object size = SID/SOD

18. Technique Depending upon the apparatus used like a platform between the source and the film , the part to be examined is placed on the radiolucent surface and the image receptor below the predetermined distance. Accurate centering and collimation of the beam is essential. The exposure required for the macroradiography are determined by the source to film distance. The use of the secondary grid is not required in macroradiography because the large air gap between the object and the film ensures the oblique scattered radiation not to fall on the film. Radiation dose is decreased in macroradiography , as no secondary grid is required to improve contrast.

19. Uses of macroradiography Sialography DCG Investigation of temporal bone Investigation of small renal vessels in angiography Investigation of the skeletal structure in detail.