1. PRINCIPLE OFTOMOGRAPHY& THEIR VARIOUS TYPES MODERATOR MR S. C. BANSAL LECTURER PRESENTED BY MANISH ANAND B. SC. MED. TECH. FINAL YEAR STUDENT POST GRADUATE INSTITUTE OF MEDICAL EDUCATION AND RESEARCH CHANDIGARH

3. Tomos (=slice) and

4. Graphia (=describing).

5. So the tomography is describing of slices by imaging it.

6. Tomography is a radiographic technique that selects a level in the body & blurs out structures below & above that plane leaving a clear image of this selected anatomy.

7. Tomography concerned with layer rather than plane.2

9. If we want to see the debris of potato we have to cut it into different slice, same in tomography if we want to see any underlying abnormality than we have to image the cut section . 3

11. There were no MRI , no ultrasound or CT.

12. Since the introduction of radiology in medicine, a need to see beyond the 2 dimensional image was gradually increasing, the first approach was to view orthogonal radiographs and make a mental 3D perception.

13. But real major break through was tomography which is also called planigraphy or body section radiography.4

15. His process was termed “Laminagraphy” by another American J. ROBERT ANDREWS who assisted KIEFFAR in the construction of this first tomographic device known as LAMINAGRAPH.5

16. Basic Principle of Tomography: If there is synchronous movement b/w either of two among the three that is the patient ,the x-ray tube or the image receptor, than there is blurring of image causes. While movement only one thing is constant that is the fulcrum point of the tomographic equipment and the plane which posses this point is well demonstrated. It also results blurring of image of that structure which lie above and below to that plane. 6

18. The x-ray tube remains Stationary while the film and the patient move.

20. Tomographic Angle: - It is the amplitude of tube travel expressed in degrees. Exposure Angle: - It is the angle through which the x-ray beam moves during the exposure. The exposure angle and tomographic angle are not always equal to each other, mostly T. angle is greater than the exposure angle this is due to equipment malfunction. 9

21. Section Thickness: - As we go apart from the focal plane the sharpness of image is decreases so the range of thickness that can be accepted by our eye is called the slice thickness. 10 Slice thickness inversely proportional to the tomographic angle

22. Pivot point/Fulcrum: - The only point of the system that remains stationary, we can also assume the axis around which the equipment move . Focal Plane:- The plane of maximal focus and represent the axis about which the x-ray tube and film rotate. 11

23. Tomography Blurring: C A Objects above or below fulcrum plane change position on film & thus blur A B C B B C C A A 12

24. 13 Tomographic Blurring Principle A' B’ C’ Distance travel by Film =X.

26. B’ = distance travel by image B

27. C’ = distance travel by image C

28. X = film travel distance

29. Here A’>B’ = X

30. To blur any image there should relative movement b/w the film and the object higher the relative motion more the blur.

31. Hence the image of A and c is being blur , there is no blurring of image B.14

33. Distance from focal plane αwidth of blur

34. Distance from filmαwidth of blur

35. Orientation of tube travel = maximum blurring when long axis of the part to be blurred is perpendicular to the direction of tube travel.15 contd…

36. 16 BLUR: Controlling Factors 1. Distance from objective plane:

37. 17 2. Exposure Angle: Increase in exposure angle, increase in movement, thinner focal plane and more blurring of above and below structures.

38. 18 3. Object Image Receptor Distance (OID): Greater OID, increased blurring

39. 19 4. Tube Trajectory: Maximum blurring occurs when object is perpendicular to tube travel. FIVE POSSIBLE TUBE TRAJECTORIES

40. 20 Five Possible Tube Trajectories: 1. LINEAR 2. ELLIPTICAL 3. CIRCULAR

41. Five Possible Tube Trajectories: contd. 4. SPIRAL 21

42. 22 Five Possible Tube Trajectories: contd. 5. HYPOCYCLOIDAL

43. Variable fulcrum: fulcrum level changes Fixed fulcrum: table and patient move, changing fulcrum level. 23

45. CONTRAST :- Because of thin layer is being recorded, inherent contrast is low, so the inherent contrast should high for tomographic structure for better contrast. e.g.- if there is bone with adjacent air cavity then the expectable contrast can be achieve by 1mm of thickness.

46. UNSHARPNESS:-

47. Geometric unsharpness: Increases with increase in size of focal spot and pivot to film distance. E.g.-in hypocycloidal movement the PFD is large so more than 0.6 mm focal spot is not allowed .

48. Movement unsharpness: Predominant in tomography due to extended exposure time. During tomography, linear grids must be used and the grid lines must be oriented in the same direction as the X-ray tube movement that results no grid cut-off with better image quality. NOTE: 24

49. X-RAY FOCUS PATH FULCRUM F F F F 25 CIRCULAR MOVEMENT AND POSITION OF GRID

51. This can be summarized as follows:Using fixed pivot equipment, all layers are recorded at the same magnification. Using a moving pivot system, magnification increases with increase in pivot height. In simultaneous multisection tomography the magnification is the same for all layers taken with a single exposure. 26 FFD __________________________ M= FOCUS-TO-PIVOT DISTANCE

53. 1st type of phantom image is produce in narrow angle tomography as shown in fig.

54. It is produce by the blurred margins of structures outside of the focal plane, and they are most likely to occur with circular tomography and narrow angle tomography.27

56. This type of phantom image most likely to occur when the shape of the part being examined is similar to that of the x-ray tube motion so it is common in skull tomography in circular motion.28 contd…

59. Curvilinear: The tube and I.R. is synchronized to perform movement in curve.

60. Circular Movement: The movement in circular fashion.

61. Figure of 8: The movement in figure of 8.

62. Hypocycloidal & Spiral Movement: As shown in figure.31

63. CIRCULAR HYPOCYCLOIDAL SPIRAL CURVILINEAR

64. Choice of Tomographic Movement: 33

65. 34 contd…

66. Equipment for Tomography: Tomography machines may be varied in appearance and function, but all have some basic requirements in common. They are: a linkage mechanism. a pivot unit. a mechanical drive. a drive control, usually a separate wall-mounted unit. tomographic table. 35

68. In linking them the rod must allow the x-ray tube and the bucky carriage to be further apart at the beginning and the end of their excursions.

69. To achieve this , the link rod may have a telescopic structure.

70. The physical dimensions of the link prevent completely free selection of the anode film distance.36

72. A scale mounted on an adjacent aspect of the tower is calibrated in cm or inch and position of the pivot is shown on the scale by means of a suitable indicator.37

74. The value of the exposure interval obtained is dependent upon the period of time required by the linkage arm to travel between these two stations and this in turn depends upon the speed and angle of the tube movement.38 contd…

76. It is an advantage of ceiling suspension that the tomographic drive is more direct and therefore more efficient when taken from such suspension than from a floor mounting.

77. It is customary for the speed of the motor to be variable by means of a remote control unit.

78. In some instances the exposure can be made during only one direction of tube travel.39

79. X-ray tube Linkage mechanism 40

81. selection of the angle of exposure

82. trial runs of the apparatus to be made without X-ray exposure. In some cases a warning lamp is included which indicates when the equipment is energized. 41

85. Group-II and

86. Group-III42

88. Many of the tables in this group provide only a linear tomographic trajectory.

89. A typical example of a tomographic table in this group possesses the following attributes:

90. Linear trajectory of the x-ray tube and the film .

91. A choice of three angle of tube swing ,40º, 20º, 8º.

92. A choice of two speed at each angle of exposure ,as follows

93. 40º at 1 s-3 s 20º with 0.5 s-1.5 s 8º with 2 s-0.6 s.43

95. These tables may allow conventional ‘on-table’ radiography.

96. Their characteristics, in respect of variable angles, variable speeds and motorized adjustments of layer-height are similar to the group first.44

98. The range of tomographic movements offered by this group of tables are:

99. Linear , circular, elliptical or both

100. Hypocycloidal, spiral or both.

101. In addition to the provision of multidirectional excursions of the X-ray tube, the table may have facilities

102. To tilt or rotate the patient or both

103. Television fluoroscopy.45

105. There is control on speed of movement.

106. Control on angle of exposure.

107. Control on time of exposure.

108. Adjust the fulcrum and the pivot point.46

110. Another factor in the time obtained is the angle of exposure, i.e. the angle of swing through which the tube moves.

111. When the tube describes a wide angle, exposure time will be also longer than when the angle is small.47

114. Zonography {narrow angle tomography}

115. Circular tomography

116. Pantomography

117. Multisection tomography

118. Trans axial tomography

119. Auto tomography

120. Skip tomography49

122. In this the exposure angle is wide and hence the slice thickness becomes thin.

123. The sharpness of all images is decreased by wide-angle techniques including those originating from the focal.50

126. Zonography is not efficient with linear tomography it needs multidirectional tube motion .

127. Zonography is specially useful for when the tissues being examined have little natural contrast.

128. The lungs offers ideal medium for this techniques where contrast is low and the interfering ribs are usually several centimeters from our plane of interest.52

130. 500 mA/150kVp

131. Automatic Exposure Control(AEC – Optional)

132. Anatomical Programs(APR – Optional)

133. 40°, 30°, 20° and 8° zonography

134. Fulcrum-height varies from 0-240mm with 1 mm increment. 53 Equipment For Zonography

136. 500mA/150kVp

137. Automatic Exposure Control(AEC – Optional)

138. Anatomical Programs(APR – Optional)

139. Exposure from knee to skull(16.5 sec to 64 sec)

140. + 135° to - 35° rotation54

141. Difference Between Zonography & The Wide Angle Tomography 55

142. 56 contd… PHANTOM HAVING LEAD LETTERS NARROW ANGLE TOMOGRAPHY WIDE ANGLE TOMOGRAPHY

144. As shown in fig. there is movement of grid also a/c to the movement of tube and always parallel to the base of image , if it is not than there is great grid cutoff.57

147. Because of long exposure time the chest tomography is not suitable.

148. Sharp cutoff of the blur patterns, which is conducive to phantom image formation.58

149. Difference b/w Circular Tomography & Linear Tomography 59

151. The X-ray film lies flat on a rotating horizontal table besides the patient.

152. Table is positioned, a little below the desired focal plane.

153. The X-ray direct obliquely through patient fall on to the film.

154. Tube remains stationary throughout the exposure.

155. The patient and the film both rotate in the same direction and at same velocity.60

157. Section thickness is determined by angle between X-ray tube and film.

158. More obliquely the central ray is directed towards the film, thinner is the tomo section.

159. All points are equally magnified and image is not distorted.

160. A patient sits on a special rotating chair in an upright position rotating table allows us to take image in coronal as well as in sagital plane.

161. When the patient is facing towards and opposite, there is coronal cut.

162. When patient turned sideways, there is sagital cut section. 61 contd…

163. 62 Trans Axial Tomographic Equipment:

165. Exposure skips during central portion of tomo when dense vertebral structure are superimposed over point of interest.

166. It is applicable to wide angle technique in which goal is to broaden the limits of visualization.

167. Usually 20º of time angle is skipped.

168. Technique works when there is fairly large distances between object if interest and object to be blurred.63

170. It used to show midline structure of brain stem, fourth ventricle.

171. The X-ray tube and film both remain stationary while head is rotated back and forth through an angle of approx 10º.

172. The only structures that remain in focus are those located along the axis of rotation. Other structures are blurred, including dense portion of temporal bone which tends to obscure delicate architecture of brainstem. 64

173. Auto Tomography: Breathing Technique 65 Tube and IR stationary, objects move

175. The patient remains stationary throughout examination.

176. An X-ray tube and film holder both rotate during exposure.

177. Film holder had protective pad and is considerably longer than the film.

178. Film is exposed through a narrow slit in its holder and moves across it as tube rotates and image is laid out as film passes the slit.66

180. The rounded configuration of teeth and mandible are taken and widely used in dentistry. Pantomography of jaw show TM joint on either side of film and teeth laid out between them.67 contd…

181. 68

182. 69 Air shadows N= nasal cavity NP= nasopharynx OP= oropharynx GP= glossopharynx E= external auditory canal Soft tissue shadows SP=soft palate T=dorsum of tongue E= Epiglotis PP= posterior pharyngeal wall

184. In this technique, several layers of the body section can be recorded using one exposure.

185. There is one mechanical fulcrum for the top film and a virtual axis for every other film.

186. In this technique top and bottom layers are equally magnified.70

188. The spacer may be 5 to 10 mm in thickness and made of radiolucent foam.

189. The section thickness depends upon the space b/w the spacer.71

191. Each of these radiographs is taken at exactly the same moment in the respiratory or other physiological phase.

193. Film quality is not so good.72

195. The tube film movement must be stable and exactly balanced and there must be synchronization of the travel time and exposure time at each of the exposure angles and tomographic movements . These are checked with a pinhole test device.

196. The pinhole test device is a lead plate with a very small beveled hole in the middle, which is positioned on the table top directly in line with the central tray.73

198. For a typical tomographic unit, the following standards are provided as a guide to evaluate acceptable performance:74 contd…

199. 1. Fulcrum Height Accuracy: - a. Section level: The agreement expected between the indicated and measured section levels varies somewhat, depending upon the type of tomographic unit. In all cases, however, agreement to within +/- 5 mm should be achieved. In measurements of this characteristic the level setting should always be approached from the same direction. b. Level Incrementation: In incrementing from one tomographic section to the next, level position should be reproducible to within +/-2 mm. In measurements of this characteristic, the level setting should always be approached from the same direction. 75 contd…

200. 2. Thickness of Cut: - a. Section Thickness: This characteristic varies with the type of tomographic motion and the exposure angle and uniformity. It is recommended that tolerance limits be established for each particular unit from images compared from one set of quality control measurements to the next. In measurements of this characteristic, the level setting should always be approached from the same direction. b. Exposure Angle: Indicated and measured exposure angles should agree to within +/-5 degrees. For units employing symmetric motion at wide angles, the symmetry of exposure angle should be within +/-5 degrees with respect to the midline. 76 contd…

201. 3. Mechanical Stability The density of the image pattern on the resultant film from the pinhole test should be nearly uniform and straight. The image should reveal no unexpected overlaps, inconsistencies of exposure, or asymmetries in motion. 4. Spatial Resolution Most tomographic units should depict a 40 mesh screen pattern, ie. 40 holes per inch. 5. Patient Entrance Exposure In making exposure measurements, care should be taken to ensure that the dosimeter is positioned in the x-ray beam during the entire exposure. Quantitative criteria are unavailable for the values of PEE expected for tomography. Facilities should set their own baseline standards. 77 contd…

203. One lead aperture plate, 4 x 4 x 1/8 inch with a 1/16 inch hole in the centre.

205. Place the lead aperture plate on top of the sponge and position on tabletop. Using the x-ray tube centering device, centre the x-ray tube over the plate. The hole in the lead aperture plate must coincide with the central ray of the x-ray field. 78 PINHOLE TEST: (Mechanical Stability and Tube Angle)

207. Select radiographic mode and expose the cassette using approximately 50 kVp and 5 mAs. Do not remove the cassette from the tray.

208. Select the most commonly used tomographic mode and cut thickness.

209. Select a cut level of 12 cm.

210. Expose the cassette in tomographic mode for the second time using approximately 50 kVp and 10 to 20 mAs.

211. Process the film.79 contd…

213. It shows us the symmetry of the exposure angle with a properly functioning unit, the exposed dotted will be equal in length on either side of center of tomographic arc.80

215. b = 5 cm.Hence, Tan θ=a/b Tan θ=1 Tube angle= θ =45

217. Wherever possible, the patient is positioned in such a way that the structure of interest is parallel to the film, so reducing the number of layer required for a complete record of structure.

218. In skull tomography, the patient is positioned prone whenever possible to reduce radiation dose to the eye lens.

219. A small field size is essential not only for radiation protection but also to improve radiographic contrast.82

220. Difference B/W Radiography And Tomography 83

222. Because of introduction of computer, newer imaging techniques and the advanced software, newer development of tomography occurs but the main principle of blurring is same.84

224. With the advent of computer, it has brought a great revolution in every fields. In radiology the conventional tomography get replaced by computer aided tomography called computed tomography.

225. Computed tomography is the process of creating a cross-sectional tomographic plane or slice of any part of body in which computer is used to make a mathematical reconstruction of a tomogram.85

227. CT was the end product of years of work by numerous scientists. Basis of CT were made by Austrian mathematician J. Radon, according to which 2-dimentional image would be reproduced from infinite set of projections of an object, by getting this idea G.N. Hounsfield along with Dr. Cormack made first prototype model of CT in 1972 named EMI scanner and was placed Atbinson morely hospital in England.86

229. These detectors do not form the image but information about attenuation is fed into computer where image is processed by several methods of mathematical reconstruction and displayed as visual image on TV monitor. 87

231. Dose level are low to patient as due to fine beam.

232. 2- or 3-dimentional image with axial cuts are possible in CT only.

233. Image manipulation can be done according to our choice so less risk of incorrect exposure.88 conventional tomogram CT image

235. References: 90 www.wikipedia.com Christensen’s Physics of Diagnostic Radiology X-ray Equipments for Student Radiographers: Chesney Clark’s Positioning in Radiography

236. 91 SKY IS LIMIT THANKS