Computed Tomography | CT Scanners | Biomedical Engineers TV | — Transcript

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1. 0:00[Music]
2. 0:05hi
3. 0:06welcome to another video of biomedical
4. 0:08engineers tv
5. 0:10in this video we will look into computer
6. 0:12tomography machines
7. 0:13which is also known as a ct scanner
8. 0:16let's look where it all began
9. 0:18godfrey hounsfield a biomedical engineer
10. 0:20contributed enormously towards the
11. 0:23diagnosis of neurological and other
12. 0:25disorders by virtue of his invention of
13. 0:27the computed axial tomography scan
14. 0:30for which he was awarded the nobel prize
15. 0:32in 1979
16. 0:34working for the electrical and musical
17. 0:36industry emi
18. 0:38limited and in collaboration with two
19. 0:40radiologists
20. 0:41james ambrose and lewis creel he
21. 0:43introduced the use of this machine in
22. 0:451971
23. 0:46at the atkinson-morley's hospital in
24. 0:48wimbledon he continued to improve the
25. 0:51quality of the device and the human head
26. 0:53was scanned for the first time in 1972
27. 0:56he continued his work on imaging of the
28. 0:58human body was later concentrated on the
29. 1:00next step in diagnostic radiology
30. 1:03namely magnetic resonance imaging
31. 1:07let's look into the principle of ct
32. 1:09scanners
33. 1:11ct is based on the fundamental principle
34. 1:13that the density of the tissue
35. 1:15passed by the x-ray beam can be measured
36. 1:17from the calculation of the attenuation
37. 1:19coefficient
38. 1:20using this principle ct allows the
39. 1:22reconstruction of the density of the
40. 1:24body
41. 1:25by two-dimensional section perpendicular
42. 1:27to the axis of the acquisition system
43. 1:30the ct x-ray tube typically with energy
44. 1:33levels between 20 and 150 kev
45. 1:36emits n photons monochromatic per unit
46. 1:39of time
47. 1:40the emitted x-rays form a beam which
48. 1:42passes through the layer of biological
49. 1:44material of thickness delta
50. 1:46x a detector placed at the exit of the
51. 1:49sample measures
52. 1:50n positive delta and photons delta n
53. 1:53smaller than 0 attenuation values of the
54. 1:56x-ray beam are recorded and data used to
55. 1:58build a 3d representation of the scanned
56. 2:01object or tissue
57. 2:03there are basically two processes of the
58. 2:05absorption the photoelectric effect
59. 2:07and the compton effect this phenomenon
60. 2:10is represented by a single coefficient
61. 2:12in the particular case of the ct the
62. 2:14emitter of x-rays rotates around the
63. 2:16patient and the detector
64. 2:18placed in diametrically opposite sides
65. 2:20pick up the images of a body section
66. 2:22beam and detector move in synchrony
67. 2:26unlike x-ray radiography the detectors
68. 2:28of the ct scanner do not produce an
69. 2:30image
70. 2:31they measure the transmission of a thin
71. 2:33beam one to ten millimeters of x-rays
72. 2:36through a full scan of the body
73. 2:37the image of that section is taken from
74. 2:39different angles and this allows to
75. 2:41retrieve the information on the depth
76. 2:43in the third dimension let's learn about
77. 2:46components of ct scanners
78. 2:49ct scanners are composed of three
79. 2:51important elements
80. 2:52an x-ray tube a jan tree with a ring of
81. 2:54x-ray sensitive detectors
82. 2:56and a computer first we will look into a
83. 2:59gentry
84. 3:00the jantry is the donut-like or
85. 3:02ring-shaped part of the ct scanner
86. 3:04it houses many of the components
87. 3:05necessary to produce and detect x-rays
88. 3:08these components are mounted on a
89. 3:09rotating scan frame
90. 3:11components of the gantry are mounted
91. 3:12onto a rotating scan frame
92. 3:14gentries vary in total size as well as
93. 3:17in the diameter
94. 3:18of the opening or aperture the range
95. 3:20size of aperture is typically 70 to 90
96. 3:22centimeters
97. 3:23the gentry is designed to be tilted
98. 3:25either forward or backward as needed to
99. 3:27accommodate a variety of patients and
100. 3:29examination protocols
101. 3:31the degree to which the gentry can be
102. 3:33tilted varies among systems
103. 3:35but more or less 15 degrees to 30
104. 3:37degrees as usual
105. 3:38the jantry also includes a laser light
106. 3:41that is used to position the patient
107. 3:42within the scanner
108. 3:44control panels located on either side of
109. 3:46the gentry opening
110. 3:47allow the radiologic technologist to
111. 3:49control the alignment lights
112. 3:51gentry tilt and movement of the table in
113. 3:53most scanners these functions may also
114. 3:55be controlled via the operator's console
115. 3:58a microphone is installed in the gentry
116. 4:00to allow communication between the
117. 4:01patient
118. 4:02and the radiologic technologist
119. 4:04throughout the scanning procedure
120. 4:06the second component is slip rings old
121. 4:09model design ct scanners used recoiling
122. 4:12system cables to rotate the gentry frame
123. 4:14this design limited the scan method to
124. 4:16the step and shoot move
125. 4:18and considerably limited the gentry
126. 4:20rotation times
127. 4:21newer systems use electromechanical
128. 4:23devices called slip rings
129. 4:25slip rings use a brush like apparatus to
130. 4:28provide continuous electrical power
131. 4:30and electronic communication across a
132. 4:32rotating surface
133. 4:33they permit the gentry frame to rotate
134. 4:35continuously eliminating the need to
135. 4:37straighten twisted system cables
136. 4:39slip rings allow the gentry frame to
137. 4:41rotate continuously
138. 4:43making helical scan modes possible
139. 4:46the third component is the generator
140. 4:48high frequency generator is usually used
141. 4:51in ct scanners
142. 4:52the generators are designed to be small
143. 4:54enough so that they can be located
144. 4:56within the gentry
145. 4:57highly stable three-phase generators
146. 4:59have also been used
147. 5:01but because these are standalone units
148. 5:03near the jantry and require cables
149. 5:05they have become obsolete generators
150. 5:07produce high voltage and transmit it to
151. 5:09the x-ray
152. 5:10tube the power capacity of the generator
153. 5:12is listed in kilowatts
154. 5:14the power capacity of the generator
155. 5:16determines the range of exposure
156. 5:17techniques like kilovolts and ma
157. 5:19settings
158. 5:20available on a particular system ct
159. 5:23generators produce
160. 5:24high kilovolts generally 120 to 140
161. 5:27kilovolts
162. 5:28to increase the intensity of the beam
163. 5:30and thereby reduce patient dose
164. 5:32in addition a higher kilovolt setting
165. 5:34will help to reduce the heat load on the
166. 5:36x-ray tube
167. 5:37by allowing a lower ma setting and
168. 5:39reducing the heat load on the x-ray tube
169. 5:41will extend the life
170. 5:42of the tube the fourth component is the
171. 5:46cooling system
172. 5:47cooling mechanisms are included in the
173. 5:49gentry they can take many different
174. 5:51forms such as blowers
175. 5:52filters or devices that perform oil to
176. 5:55air heat exchange
177. 5:56cooling mechanisms are important because
178. 5:58many components can be affected by
179. 6:00temperature fluctuations
180. 6:02the fifth component is the ct x-ray tube
181. 6:05x-ray tubes produce the x-ray photos
182. 6:07that create the ct image
183. 6:09their design is a modification of a
184. 6:11standard rotating anode tube
185. 6:13such as the type used in angiography
186. 6:15tungsten with an atomic number of 74
187. 6:18is often used for the anode target
188. 6:20material because it produces a higher
189. 6:22intensity x-ray beam
190. 6:23this is because the intensity of x-ray
191. 6:25production is approximately proportional
192. 6:27to the atomic number of the target
193. 6:29material
194. 6:30ct scan tubes often contain more than
195. 6:33one size of a focal spot
196. 6:340.5 and 1 millimeter are the common size
197. 6:37of a focal spot
198. 6:39just as in standard x-ray tubes because
199. 6:41of reduced penumbra
200. 6:43small focal spot and computed tomography
201. 6:45tubes produce
202. 6:46sharper images like better spatial
203. 6:48resolution but because they concentrate
204. 6:50heat on a smaller area of the anode
205. 6:53they cannot tolerate as much of the heat
206. 6:55a very large amount of stress
207. 6:57is placed on the ct scan tube scanning
208. 7:00protocols often require multiple long
209. 7:02exposures
210. 7:02performed on numerous patients per day a
211. 7:05ct
212. 7:06scan tube must be designed to handle
213. 7:08such stress
214. 7:10the sixth component is filtration
215. 7:13compensating filters are used to shape
216. 7:15the x-ray beam
217. 7:16they reduce the radiation dose to the
218. 7:18patient and help to minimize
219. 7:19image artifact as our teachers taught us
220. 7:22that radiation
221. 7:23emitted by a ct scan x-ray tube is
222. 7:25polychromatic
223. 7:26filtering the x-ray beam helps to reduce
224. 7:28the range of x-ray
225. 7:30energies that reach the patient by
226. 7:31removing the long wavelength or soft
227. 7:34x-rays these long wavelength x-rays are
228. 7:36readily absorbed by the patient
229. 7:38therefore they do not contribute to the
230. 7:40ct image but do contribute to the
231. 7:42radiation dose to the patient
232. 7:44in addition creating a more uniform beam
233. 7:46intensity
234. 7:47improves the ct image by reducing
235. 7:49artifacts that result from beam
236. 7:51hardening
237. 7:52filtering the x-ray beam helps to reduce
238. 7:54the radiation dose taken by the patient
239. 7:57and it also improves the image quality
240. 7:58of the ct scanners
241. 8:01the seventh component is collimators
242. 8:04collimation restricts the x-ray beam to
243. 8:06a specific area
244. 8:07as a result it helps reduce scatter
245. 8:09radiation the scatter radiation reduces
246. 8:12image quality and increases the
247. 8:13radiation dose to the patient
248. 8:15reducing the scatter radiation improves
249. 8:18contrast resolution
250. 8:19and decreases patient dose collimation
251. 8:21controls the slice thickness by
252. 8:23narrowing or widening the x-ray beam
253. 8:26the source collimator is located near
254. 8:28the x-ray source and limits the amount
255. 8:30of x-ray beam before it passes through
256. 8:32the patient
257. 8:33it is sometimes referred to as patient
258. 8:35dose and determines how the dose is
259. 8:37distributed across the slice thickness
260. 8:38like the dose profile
261. 8:40the source collimation resembles small
262. 8:42shutters with an opening that adjusts
263. 8:44dependent on the operator selection of
264. 8:46slice thickness in
265. 8:47mdct systems slice thickness is also
266. 8:50influenced by the detector element
267. 8:52configuration
268. 8:54scanners vary in the choices of slice
269. 8:56thickness available
270. 8:57choices range from 0.5 to 10 millimeters
271. 9:00and the last but not least component are
272. 9:02the detectors
273. 9:04the detectors are components of ct scan
274. 9:06machines which collect
275. 9:08information regarding the degree to
276. 9:10which each anatomic structure
277. 9:11attenuated the beam in conventional
278. 9:14radiography we use a film screen system
279. 9:16to record the attenuated information
280. 9:19in ct we use detectors to collect the
281. 9:21information
282. 9:22the term detector refers to a single
283. 9:24element or single type of detector used
284. 9:26in a ct system
285. 9:28the term detector array is used to
286. 9:29describe the entire collection of
287. 9:31detectors included in a ct scan system
288. 9:34specifically the detector array
289. 9:36compromises detector elements situated
290. 9:39in an arc or a ring
291. 9:40each of which measures the intensity of
292. 9:42transmitted x-ray radiation
293. 9:44along a beam projected from the x-ray
294. 9:46source to that particular detector
295. 9:48element
296. 9:50also included in the array are elements
297. 9:52referred to as reference detectors
298. 9:54that help calibrate data and reduce
299. 9:56artifacts
300. 9:57detectors can be made from different
301. 9:59substances each with their own advantage
302. 10:01and disadvantages in the next video we
303. 10:04will look into types of detectors in ct
304. 10:07scanners
305. 10:07types of ct scanners and their
306. 10:09application thanks for watching
307. 10:11biomedical engineers tv
308. 10:13see you guys in the next part of this
309. 10:16video
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313. 10:45you