The document discusses several radiographic techniques. It explains that high kilovoltage technique uses kVp above 90 kVp to improve visualization of different tissue densities on a single chest x-ray. Soft tissue radiography requires a low kVp, like in mammography, to maximize contrast between low density soft tissues through increased differential absorption. Macroradiography magnifies the image size relative to the object through a greater source-to-film distance compared to source-to-object distance.

3.  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.

4.  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 (

5.  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

6.  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.

7. 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.

8. 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.

9. 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

10. High kilovoltage technique

11.  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.

12. 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.

13. 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.

14. 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

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

16. 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

17. 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.

18. 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

19. 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.

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