Special X-ray Imaging.pptx of breast and imagn

basics of xrays

1. Special X-ray Imaging Dr. M. Yousuf Zaman

2. Contents Introduction Fluoroscopy & Mobile Radiography Dental Radiography DXA Tomosynthesis

3. WHAT IS DXA ? DXA is an X ray imaging technique primarily used to derive the mass of one material in the presence of another through knowledge of their unique X ray attenuation at different energies. Two images are made from the attenuation of low and high average X ray energy. DXA is a special imaging modality that is not typically available with general use X ray systems because of the need for special beam filtering and near perfect spatial registration of the two attenuations. Dedicated commercial DXA systems first became available in the late 1980s .

4. WHAT IS DXA ? DXA is one of the most accurate and precise methods for quantifying BMD and mass in vivo. Bone mineral mass, primarily consisting of hydroxyapatite , is the mineral component of bone that is left after a bone is defleshed , lipids extracted and ashed . The nature of the DXA system is that it creates a planar ( two dimensional ) image that is the combination of low and high energy attenuations. Although density is typically thought of as a mass per unit volume, DXA can only quantify the bone density as a mass per unit area, since it uses planar images and cannot measure the bone depth. In contrast, the measurement of bone density using a computed tomography (CT) system, called quantitative computed tomography (QCT), can measure the true volume and volumetric bone density. Bone size varies as a function of age.

5. WHAT IS DXA ? Thus, DXA bone density values increase from birth to adulthood, primarily because the bones become larger. Bone size is also influenced by ethnic differences and sex. One has to be careful to compare DXA bone density values to a similar population or results can be easily misinterpreted. Asians typically have lower DXA bone density values compared to sex and age matched Caucasians, partly due to bone size differences. The principle of operation for DXA involves two images that are made from the attenuation of a low and a high X ray energy beam, using special imaging equipment comprising special beam filtering and near perfect spatial registration of the two attenuation maps.

6. WHAT IS DXA ? DXA uses 2 levels of x-ray photon energy to measure the amount of minerals in bone. The difference in attenuation of the x-rays by bone generates 2-D measurements of bone mineral content in grams and areal BMD. DXA x-rays are produced with a fan beam or a pencil beam. Pencil-beam equipment uses small, angled x-ray beams that move across the patient in a linear direction. The fan-beam generators use a wider beam that reduces scan times but increases radiation dose to patients.

7. Fluoroscopy Used to visualize motion of internal fluid, structures Image intensifier or digital image plate gives a live image Coupled to display monitor Radiologist can watch the images “live” on TV-monitor; images can be recorded Fluoroscopy used to observe digestive tract Upper GI series, Barium Swallow Lower GI series Barium Enema

8. Definitions Fluoroscopy (radioscopy) Examination that allows real time continuous imaging using x-rays Can be used to demonstrate function or guide an interventional procedure where still images do not convey the required information Fluorography (acquisition or digital spot imaging) Method of acquiring a single still image using fluoroscopic equipment

9. Fluoroscopic and Fluorographic images Fluorographic image is of higher quality Fluorographic acquisition uses sufficient exposure to produce a clinically acceptable image s(higher dose) Fluoroscopic exposure uses the radiation available in one frame Two techniques are used together Fluoroscopy for patient positioning and the manipulation of instruments Fluorography only where image quality is essential to diagnosis or a decision as to the progression of the procedure 9

10. Features of the fluoroscopic and fluorographic images Still frame of fluoroscopic exposure Fluorographic image

11. LOW DOSE 10 mGy /min MEDIUM DOSE 20 mGy /min HIGH DOSE 40 mGy /min Patient entrance dose rates in fluoroscopy

12. Automatic Brightness Control Exposure factors varied according to image receptor signal level Automatic brightness control Signal used to control exposure factors: mA and kV Image intensifier: Photon output brightness gauge Flat panel: Signal to noise ratio assessment Signal feedback Generator

13. Other factors influencing patient dose Pulsing of X-ray beam Additional filtration Use of magnification with image intensifiers

14. Pulsed Fluoroscopy Continuous fluoroscopy : Any movements of the object during the frame (40 ms ) will be superimposed Pulsed fluoroscopy : Short pulses (e.g. 5 ms ) with higher mA gives less degradation of image due to movement

15. Additional Filters Equipment can place additional filtration in x-ray beam This cuts out lower energy x-rays that do not contribute towards image generation Reduces ESAK by 30-50%

16. Dental Radiography The tooth is a low attenuation static object that, when radiographed directly , places very limited demands on X ray generation. The image receptor is placed inside the mouth and irradiated externally. This universal low cost technique is known as an intraoral examination, with bitewing being the most common examination .

17. Dental Radiography When radiographs of the entire set of teeth are required, both the image receptor and the X ray source are external to the patient and the X ray beam is transmitted through the head, demanding significant X ray generation power and complex motion control for the X ray tube and image receptor. This procedure, known as an orthopantomograph (OPG), and the intraoral examination produce 2-D images that are captured most commonly on film but increasingly in electronic format.

18. Dental Radiography In special cases, when dental diagnosis requires 3-D information, CT units have been specially developed, most recently to include CBCT . The intraoral X ray tube is a small robust device with a stationary target operating with a tube current of only a few milliamperes . The X ray generator is typically very simple, often with a fixed tube voltage and tube current allowing output changes only by variations in exposure time.

19. Dental Radiography Major concerns with this device are the stability of the tube head and the collimation of the beam. International standards require that the focus to patient surface distance (FSD) be 200 mm. This is assured with the use of a collimating attachment that also restricts the beam to the region of the mouth being radiographed

20. Talk Outline What is breast tomosynthesis? Why do breast tomosynthesis? How does breast tomosynthesis work? How do we use it clinically? Clinical examples What is its clinical performance? Summary of advantages

21. What is Breast Tomosynthesis? A method of imaging the breast in three dimensions (3D) Image slices are 1 mm thick Image slices high resolution: like mammograms

22. Why do Breast Tomosynthesis? Because 2D images have tissue superposition 2D hides cancers 2D makes normal tissue look like pathology Clearer images

23. Conventional 2-D Imaging Incident X-rays Objects being imaged, at different heights 2-D image Images s up e ri m p o s e d on image

24. Potential Clinical Advantages of Tomosynthesis Better sensitivity Fewer recalls Potential for lower dose Potential for less compression

25. Better Sensitivity Removal of confusing overlying tissue makes for clearer imaging

26. ACR Phantom imaged with 4 cm cadaverous breast Phantom has low contrast fibers, masses, and calcifications Overlying breast tissue obscures object visibility

27. Digital Mammogram 1X dose Tomosynthesis 1X dose Slice at plane of phantom insert Tomosynthesis shows improved low contrast visibility over digital mammography Better Sensitivity

28. 2D Mammogram Tomosynthesis Better Sensitivity

29. Removal of confusing overlying tissue makes for clearer imaging

30. 2D Mammogram Tomosynthesis Fewer Recalls

31. FF D M TOMO slice 28 TOMO slice 43 TOMO slice 55 Superimposed Tissue from Different Levels in the Breast Resolved with TOMO

32. Potential for Lower Dose Reduced superimposed tissue reduces need for very low quantum noise Fewer recalls reduce additional diagnostic exposures O n l y on e v i e w n e ed e d ? U n f o r t u na t e l y , probably not.

33. Phantom studied as function of tomosynthesis dose Lower Dose

34. Digital Mammogram 4X dose Tomosynthesis 0.5X dose Slice at plane of phantom insert Tomosynthesis shows improved low contrast visibility over FFDM, even at much lower dose Lower Dose

35. Potential for Less Compression Compression not needed to minimize tissue overlap (structure noise) Still need compression to reduce patient motion

36. How does tomosynthesis work? Image the breast from several angles Use the multiple images to reconstruct the 3D dataset Process is very similar to CT imaging: view the body from different angles and reconstruct the volume

37. Tomosynthesis Acquisition Digital de t e c t or X-ray tube moves in an arc across the breast Series of low dose images are acquired at different angles Total dose similar to single view breast exam C o m press i o n plate B rea s t X-ray tube R econs t ru ct ed planes

38. Tomosynthesis Acquisition Incident X-rays Objects being imaged 2-D raw data images Image from multiple angles Exposure #1 Exposure #8 Exposure #15

39. Tomosynthesis Reconstruction Appropriate shifting and adding of raw data reinforces objects at specific height

40. Data Formats

41. THE END