Tomography.pptxTomography.pptxTomography.pptx

Tomography.pptx

1. PRINCIPLES OF TOMOGRAPHIC and EQUIPMENT By Mr. Dinesh Sekar M.Sc. Radiology Asst Professor/Clinical Supervisor Department Of Radiology

2. INTRODUCTION Tomography is a radiographic technique that select a level in the body and blurs out the structure below and above that plane leaving a clear image of a selected tomography TOMO: SLICE GRAPHY: DESCRIBING

3. Basic principles of tomography Synchronous movement of between either of two among the three Patient ,X ray tube , image receptor , than there is a blurring of images causes

4. Three methods The films remain stationary while the x-ray tube and the patient move The x-ray tube remains stationary while the patient and the film move The patien t remains stationary while the x-ray tube and film move

5. TERMINOLOGY TOMOGRAPHIC ANGLE EXPOSURE ANGLE FULCRUM PIVOT POINT FOCAL PLANE SECTION THICKNESS

6. TOMOGRAPHIC ANGLE It is the amplitude of the tube travel expressed in degrees EXPOSURE ANGLE it is the angle through which x ray beam moves during the exposure.the exposure angle and tomographic angle are not always equal to each other Mostly tomographic angle is greater than the exposure angle

7. 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 slice thickness

8. 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 xray tube and film rotate

9. BLURRING Blurring is the distortion of definition of objects out side the focal plane.

10. BLUR CONTROLING FACTORS Distance from objective plane

11. Exposure angle

12. Classification of TOMOGRAPHY according to the angle According to the tube movement Wide angle Narrow angle Linear tomography Circular tomography

13. Wide angle tomography The purpose of wide angle tomography is to extend , the limits of roentgen visibility to enable us to see object that are completely obscured by overlying shadow in general radiograph Exposure angle is wide and hence the slice thickness becomes thin Sharpness of all images is decreased including those originating from the focal

14. Most effective in studying tissues that have a great deal of image contrast because with wide angle tomography we have very thin section and no thickness difference between adjacent part of the image e.g : imaging of inner ear ossicles in which there is enough contrast in very thin section

15. Zonography (narrow-angle) Zonography is not efficient with linear tomography it needs multidirectional tube motion When the tissues being examined have little natural contrast The lungs offer ideal medium for this technique where contrast is low and the interfering ribs are usually several centimetres from our plane of interest

16. EQUIPMENT FOR ZONOGRAPHY

17. Circular tomography There is movement of grid also according to the movement of tube and always parallel to the base of image , if it is not than there is great grid cut off

18. Advantages Can produce a uniform section thickness All portion of phantom images are uniformly blurred , no matter how they orientation in space while as in linear motion only that images is being blurred that is perpendicular to the tube movement Disadvantages High cost Because of long exposure time the chest tomography is not suitable Sharp cutoff of the blur pattern , which is conductive to phantom image formation

19. Equipment for tomography A linkage mechanism A pivot unit A mechanical drive A drive control ( usually a separate wall mounted unit) Tomographic table

20. Tomography Equipment

21. Linkage mechanism It is long telescopic steel rod which couples together the x ray tube and bucky carriage by means of clamps and locking handle In linking them the rod must allow the x-ray tube and bucky carriage to be further at the beginning and the end of their excursion To achieve this the link rod may have telescopic structure the physical dimension of the link prevent completely free selection of the anode film distance

22. Pivot unit ( fulcrum tower) Turret like structure A pivot for the opposite movements of the x ray tube and the bucky tray A means to alter the height of the pivot point it is fitted to the edge of the x ray table which is nearer to the tube stand and linkage arm 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 suitable indicator

23. The mechanical drive Travels of the x-ray tube during the exposure can be achieved by a variety of means It is an advantage of ceiling suspension that the tomographic drive is more direct and therefore more efficient when taken from such suspension than a floor mounting It is customary for the speed of the motor to be variable by means of remote control unit In some instances the exposure can be made during only one direction of the tube

24. The drive control The control unit for the tube drive often in a separate wall mounted box This usually has switches which permit Selection of the tube’s speed of travel Selection of the angle of exposure 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

25. Tomographic tables Planned especially for tomography , although they may allow general radiography to be performed Three groups Group-1 Group-II Group-III

26. GROUP –I It is a simple table for radiography, having a floating top and the particular feature of an integrated tube stand suitable for tomography Many of the table in this group provides only a linear tomographic trajectory

27. GROUP ii Mainly in providing a circular or elliptical movement or both. in addition to a linear trajectory These tables may allow conventional on table radiograph

28. Group III Highly specialised The range of tomographic movement offerd by this group of tables are linear,circular,elliptical or both hypocycloidal,spiral or both In addition to the provision of multidirectional excursion of the x-ray tube , the table may have facilities To tilt or rotate the patient or both Television fluoroscopy

29. Peculiarities of tomographic table ABLE TO To produce the different types of movement There is control on speed of movement Control on angle of exposure Control on time of exposure adjust the fulcrum and pivot point

30. The speed of movement and length of trajectory Effect on exposure time The speed at which the tube moves during tomography controls radiographic exposure time, the faster the tube movement , the shorter is the interval of the exposure Another factor in the time obtained is the angle of exposure , i.e. the angle of swing through which the tube moves When the tube describes a wide angle, exposure time will be also longer than when the angle is small

31. conclusion Now a days the conventional tomography is being fully omitted because of high radiation dose and the long scanning time but the principle of tomographic blurring is still works in works in the form of computer aided tomography