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Digital APPLICATIONS C- Arm DSA Radiation Dose

2. MOBILE FLUOROSCOPY. C-ARM UNIT - Tube at one end - I.I. at other endTV Monitor control cart separate from unitUses Digital FluoroscopyLast Image Hold, Image EnhancementSave for hard copies from disk, Video Photographic Magnification, SubtractionStatic (pulsed) and continuous fluoroManeuverable and Versatile .

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Digital APPLICATIONS C- Arm DSA Radiation Dose

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    1. 1 Digital APPLICATIONS C- Arm & DSA & Radiation Dose July 2008 For RT 255 – SPRING

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    4. 4 RADIATION PROTECTION Remember the “Cardinal Rules” FLUOROSCOPIC Minimum source to skin distance = 12” Preferred SSD OF 18” ? Distance from tube and patient ? Distance from II to the patient 5 min Audible Alarm At least .25mm lead apron to be worn 5 R/min – 10 R/min BOOST – 20 R/min 2.2R/ma @ 80 kVp

    5. 5 RAD PROTECTION RULES OF GOOD PRACTICE -continued Never place your hand or other body part in primary beam Provide gonadal protection for the patient if possible FOR C-ARM – IF BEAM FROM BELOW – PLACE APRON ON TABLE BEFORE PATIENT IS ON TABLE Achieve maximum distance from the patient and tube (stand 90° from the patient- SEE Merrills – pg 212) Minimum 6 foot exposure cord for radiography Label and handle cassettes carefully

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    7. 7 fluoroscan

    8. 8 Digital Fluoroscopy and Digital Subtraction Angiography (DSA) DIGITAL FLUOROSCOPY Introduction Design and Equipments DIGITAL IMAGING CONCEPTS Binary Numbers Pixels Gray levels DIGITAL IMAGE DATA PROCESSNG IN DIGITAL FLUOROSCOPY Last Image Hold Gray-scale processing Temporal Frame Averaging Edge Enhancement

    9. 9 Digital Fluoroscopy A digital fluoroscopy system is commonly designed as a conventional one in which the analog video signal is converted to and stored as digital data by an analog to digital converter (ADC) (DAC to print image)

    10. 10 Last Image Hold reduces pt dose The last frame acquired before stopping x-ray acquisition is continuously displayed

    11. 11 LIH - stays on screen

    12. 12 DIGITAL Angiographic Equipment Single or biplane image intensification A C-arm or U-arm device is preferable to reduce the number of injections of contrast required Is the radiation does less? What are the other advantages?

    13. 13 Bi Plane Digital Angio Equipment Less Time for Procedure Less contrast for patient BUT - Not Less Radiation ALSO Can POST PROCESS And use DSA faster processing time than film No “jammed” films

    14. 14 Advantages of Digital Fluoro from Conventional Fluoro Post Processing results in ENHANCED Contrast Resolution SPEED OF ACQUISITION 1024 x 10 24 image matrix (1000 lines) System provides better spatial resolution than the 525 line system

    15. 15 Image digitizer (ADC) This turns the analog TV image into a digital image consisting of pixels the number of which depends on the lines per inch of the TV image The usual pixel numbers in an image are 512 x 512 conventional (SNR of about 200:1) Digital 1024 x 1024 (high resolution) SNR of 1000:1 is necessary for DF. Signal-to-Noise Ratio. All analog electronic devices are inherently noisy. Because of heated filaments and voltage differences, there is always a very small electric current flowing in any circuit. This is called background electronic noise. It is similar to the noise (fog) on a radiograph in that it conveys no information and serves only to obscure the electronic signal. Signal-to-Noise Ratio. All analog electronic devices are inherently noisy. Because of heated filaments and voltage differences, there is always a very small electric current flowing in any circuit. This is called background electronic noise. It is similar to the noise (fog) on a radiograph in that it conveys no information and serves only to obscure the electronic signal.

    16. 16 TV progressive scanning 30 images/sec acquired in the 512×512 matrix mode But higher spatial resolution image is required for 1024 × 1024 mode then only 8 images per second can be acquired. This limitation on data transfer is imposed by the time required to conduct the enormous quantities of data from one segment of memory to another. Interlaced Versus Progressive Mode. In Chapter 24, the method by which a conventional television camera tube reads its target assembly was described. That method was called an interlaced mode, where two fields of 262˝ lines each were read in 1/60 s (17 ms) to form a 525-line video frame in 1/30 s (33 ms). In DF, the camera tube reads in progressive mode. When reading the video signal in the progressive mode, the electron beam of the television camera tube sweeps the target assembly continuously from top to bottom in 33 ms (Figure 28-8). The video image is similarly formed on the television monitor. There is no interlace of one field with another. This produces a sharper image with less flicker. (Bushong, Stewart C.. Radiologic Science for Technologists: Physics, Biology, and Protection, 8th Edition. Mosby, 012004. 28.3.3.1). <vbk:0-323-02555-2#outline(28.3.3.1)>Interlaced Versus Progressive Mode. In Chapter 24, the method by which a conventional television camera tube reads its target assembly was described. That method was called an interlaced mode, where two fields of 262˝ lines each were read in 1/60 s (17 ms) to form a 525-line video frame in 1/30 s (33 ms). In DF, the camera tube reads in progressive mode. When reading the video signal in the progressive mode, the electron beam of the television camera tube sweeps the target assembly continuously from top to bottom in 33 ms (Figure 28-8). The video image is similarly formed on the television monitor. There is no interlace of one field with another. This produces a sharper image with less flicker. (Bushong, Stewart C.. Radiologic Science for Technologists: Physics, Biology, and Protection, 8th Edition. Mosby, 012004. 28.3.3.1). <vbk:0-323-02555-2#outline(28.3.3.1)>

    17. 17 DSA Equipment Digital subtraction angiography requires more complex equipment than digital radiography, specifically because it has to manipulate a number of pulsed images and at the same time create a subtracted image using the first pre contrast image as a mask DIGITAL FLUORO Range 100mA-200mA Patient Dose One potential advantage to DF is reduced patient dose. DF images appear to be continuous, but in fact they are discrete. Most DF x-ray beams are pulsed to fill one or more 33-ms video frames; therefore, the fluoroscopic dose rate is lower than that for continuous analog fluoroscopy even though the mA setting may be higher. Patient Dose One potential advantage to DF is reduced patient dose. DF images appear to be continuous, but in fact they are discrete. Most DF x-ray beams are pulsed to fill one or more 33-ms video frames; therefore, the fluoroscopic dose rate is lower than that for continuous analog fluoroscopy even though the mA setting may be higher.

    18. 18 Pulsed Fluoro & RP Some fluoroscopic equipment is designed for pulsed-mode operation it can be set to produce less than the conventional 25 or 30 images per second. This reduces the exposure rate. Collimation of the X ray beam to the smallest practical size and keeping the distance between the patient and image receptor as short as possible contribute to good exposure management.

    19. 19 Dose rate to patients

    20. 20 Digital Fluoroscopy ALTERNATE DIGITIZATION Digital video camera (Charge-couple device) Direct capture of x-ray (flat–panel detector)

    21. 21 DF Reduces Pt DOSE Uses High Voltage generator Tube operates in Radiographic Mode So PULSE programming keeps tube from overheating 1- 10 second image acquisition Generator can switch off/on rapidly = INTERROGATION TIME (ON TIME) Extinction time ( Switched OFF) Patient Dose One potential advantage to DF is reduced patient dose. DF images appear to be continuous, but in fact they are discrete. Most DF x-ray beams are pulsed to fill one or more 33-ms video frames; therefore, the fluoroscopic dose rate is lower than that for continuous analog fluoroscopy even though the mA setting may be higher. Patient Dose One potential advantage to DF is reduced patient dose. DF images appear to be continuous, but in fact they are discrete. Most DF x-ray beams are pulsed to fill one or more 33-ms video frames; therefore, the fluoroscopic dose rate is lower than that for continuous analog fluoroscopy even though the mA setting may be higher.

    22. 22 Digital Fluoroscopy and Digital Subtraction Angiography (DSA) DIGITAL IMAGE DATA PROCESSNG IN DIGITAL FLUOROSCOPY Last Image Hold Gray-scale processing Temporal Frame Averaging Edge Enhancement MORE LINEAR RESPONSE than F/S

    23. 23 Digital radiography principle

    24. 24 Digital Fluoroscopy- CCD Digital video camera (Charge-couple device) CCD is a solid state device that converts visible light photons to electrons layer of cyrstalline silicon – e’s The electron signal is read pixel by pixel and an image is formed Fast – very little lag time First used by Military Charge-Coupled Device The charge-coupled device (CCD) was developed in the 1970s for military applications, especially in night vision scopes. In the early 1980s, the CCD replaced the television camera tube in video systems. Today, CCDs are used in the home camcorder, commercial television, security surveillance, and astronomy (Figure 28-4). The demands of medical imaging are much more rigorous than in these other applications. That is why the first fluoroscopic CCD did not appear until 1983. The sensitive component of a CCD is a layer of crystalline silicon (Figure 28-5). When the silicon is illuminated, electrical charge is generated, which is then sampled, pixel by pixel, and manipulated to produce a digital image. The CCD is mounted on the output phosphor of the image intensifier tube and is coupled by fiber optics or a lens system (Figure 28-6). The principal advantage to CCDs in most applications, such as a camcorder, is their small size and ruggedness. Their principal advantages for medical imaging are listed in Box 28-1. The spatial resolution of a CCD is determined by its physical size and pixel count. Systems incorporating a 1024 matrix can produce images with 10 lp/mm. Television camera tubes can show spatial distortion in what is described as “pincushion” or “barrel artifact.” There is no such distortion with a CCD. The CCD has a higher sensitivity to light (DQE or detective quantum efficiency) and a lower level of electronic noise than a television camera. The result is higher signal-to-noise ratio (SNR) and better contrast resolution. These characteristics also result in substantially lower patient dose. The response of the CCD to light is very stable. Warm-up of the CCD is not required. There is neither image lag nor blooming. It has essentially an unlimited lifetime and requires no maintenance. Perhaps the single most important feature of CCD imaging is its linear response (Figure 28-7). Other image receptors have a sigmoid-shaped response, which makes it difficult to image either very dim or very bright objects. Information in the toe and shoulder region of such response is lost. This linear response feature is particularly helpful for subtraction imaging. The result is improved dynamic range and better contrast resolution. The next improvement in this type of imaging will probably be flat panel imagers composed of silicon pixel detectors (SPD). Such direct x-ray detectors exist in laboratories at this time. Perhaps at around the time all television camera tubes are replaced by CCDs, CCDs will begin to be replaced by SPDs! (Bushong, Stewart C.. Radiologic Science for Technologists: Physics, Biology, and Protection, 8th Edition. Mosby, 012004. 28.3.2). <vbk:0-323-02555-2#outline(28.3.2)>Charge-Coupled Device The charge-coupled device (CCD) was developed in the 1970s for military applications, especially in night vision scopes. In the early 1980s, the CCD replaced the television camera tube in video systems. Today, CCDs are used in the home camcorder, commercial television, security surveillance, and astronomy (Figure 28-4). The demands of medical imaging are much more rigorous than in these other applications. That is why the first fluoroscopic CCD did not appear until 1983. The sensitive component of a CCD is a layer of crystalline silicon (Figure 28-5). When the silicon is illuminated, electrical charge is generated, which is then sampled, pixel by pixel, and manipulated to produce a digital image. The CCD is mounted on the output phosphor of the image intensifier tube and is coupled by fiber optics or a lens system (Figure 28-6). The principal advantage to CCDs in most applications, such as a camcorder, is their small size and ruggedness. Their principal advantages for medical imaging are listed in Box 28-1. The spatial resolution of a CCD is determined by its physical size and pixel count. Systems incorporating a 1024 matrix can produce images with 10 lp/mm. Television camera tubes can show spatial distortion in what is described as “pincushion” or “barrel artifact.” There is no such distortion with a CCD. The CCD has a higher sensitivity to light (DQE or detective quantum efficiency) and a lower level of electronic noise than a television camera. The result is higher signal-to-noise ratio (SNR) and better contrast resolution. These characteristics also result in substantially lower patient dose. The response of the CCD to light is very stable. Warm-up of the CCD is not required. There is neither image lag nor blooming. It has essentially an unlimited lifetime and requires no maintenance. Perhaps the single most important feature of CCD imaging is its linear response (Figure 28-7). Other image receptors have a sigmoid-shaped response, which makes it difficult to image either very dim or very bright objects. Information in the toe and shoulder region of such response is lost. This linear response feature is particularly helpful for subtraction imaging. The result is improved dynamic range and better contrast resolution. The next improvement in this type of imaging will probably be flat panel imagers composed of silicon pixel detectors (SPD). Such direct x-ray detectors exist in laboratories at this time. Perhaps at around the time all television camera tubes are replaced by CCDs, CCDs will begin to be replaced by SPDs! (Bushong, Stewart C.. Radiologic Science for Technologists: Physics, Biology, and Protection, 8th Edition. Mosby, 012004. 28.3.2). <vbk:0-323-02555-2#outline(28.3.2)>

    25. 25 Digital Fluoroscopy Use CCD to generate electronic signal Signal is sent to ADC Allows for post processing and electronic storage and distribution BETTER RESOLUTION WITH DIGITAL UNITS

    26. 26 Video Camera Charged Coupled Devices (CCD) Operate at lower voltages than video tubes More durable than video tubes Semiconducting device Emits electrons in proportion to amount of light striking photoelectric cathode Fast discharge eliminates lag

    27. 27 CCD’s

    28. 28 Newer Digital Fluoroscopy Image intensifier output screen coupled to TFTs TFT photodiodes are connected to each pixel element Resolution limited in favor of radiation exposure concerns Direct capture of x-ray (flat–panel detector) a-silicon a-seleniumExit x-rays interact with CsI scintillation phosphor to produce light The light interact with the a-Si to produce a signal The TFT stores the signal until readout, one pixel at a time

    29. 29 CsI phosphor light detected by the AMA (active matrix array) of silicon photodiodes

    30. 30 Direct or Indirect Capture TFT IN -DIRECT – CsI phoshor coated on a-Si photodiode = light when exposed High DQE = lower dose DIRECT - a- Se (selenium) creates electron holes – no light spread = better spatial resolution

    31. 31 Modern Digital Fluoro System under & over table tubes

    32. 32 Digital Subtraction Angiography DSA uses an II/TV system combined with a high speed image processor in a digital angiographic system.

    33. 33 In traditional angiography, we acquire images of blood vessels on films by exposing the area of interest with time-controlled x-ray energy while injecting contrast medium into the blood vessels. The images thus obtained would also record other structure besides blood vessels as the x-ray beam passes through the body. In order to remove these distracting structures to see the vessels better, we need to acquire a mask images for subtraction. The mask image is simply an image of the same area without contrast administration. So, using manual darkroom technique, clear pictures of blood vessels are obtained by taking away the overlying background. In DSA, the images are acquired in digital format through the computer. With the help of the computer, all images would be recorded into the computer and subtracted automatically. As a result, we can have a near-instantaneous film show of the blood vessels alone after x-ray. In traditional angiography, we acquire images of blood vessels on films by exposing the area of interest with time-controlled x-ray energy while injecting contrast medium into the blood vessels. The images thus obtained would also record other structure besides blood vessels as the x-ray beam passes through the body. In order to remove these distracting structures to see the vessels better, we need to acquire a mask images for subtraction. The mask image is simply an image of the same area without contrast administration. So, using manual darkroom technique, clear pictures of blood vessels are obtained by taking away the overlying background. In DSA, the images are acquired in digital format through the computer. With the help of the computer, all images would be recorded into the computer and subtracted automatically. As a result, we can have a near-instantaneous film show of the blood vessels alone after x-ray.

    34. 34 Digital Subtraction Angiography DSA uses an II/TV system combined with a high speed image processor in a digital angiographic system.

    35. 35 Digital Subtraction Angiography (DSA) Performed for diagnostic and therapeutic purposes of vessel visualization in the body.

    36. 36 Digital Subtraction Angiography (DSA) DSA refers to a technique which compares two images of a region of the body before and after a contrast medium has been injected into the body for the purpose of studying blood vessels.

    37. 37

    38. 38 Digital Imaging Concepts FUNDAMENTALS Binary numbers Pixels Gray levels

    39. 39 Pixels and Matrix Pixel: The smallest element of a digital image Matrix: A two dimensional series of square boxes composed of pixels Digital fluoroscopy uses 512x512–1024x1024 pixels

    40. 40 Comparison of a clinical image at different matrix sizes 16x16 32x32 64x64 128x128 256x256 512x512

    41. 41 Gray Levels in Digital Fluoroscopy ADC samples the analog video signal exiting the video camera tube and converts the value of the video signal to a binary number for processing and storage ANALOG TO DIGITAL CONVERTER TAKE THE ANALOG ELECTRIC SIGNAL CHANGES IT TO A DIGITAL SIGNAL TO MONITOR –ANALOG TO DIGITAL CONVERTER TAKE THE ANALOG ELECTRIC SIGNAL CHANGES IT TO A DIGITAL SIGNAL TO MONITOR –

    42. 42   Comparison of a clinical image at different bit depths - gray levels 256 gray levels (8bits) 16 gray levels (4bits) 8 gray levels (3bits) 4 gray levels (2bits)

    43. 43

    44. 44

    45. 45   Use of Road Mapping with Clinical Images .

    46. 46 Digital Subtraction Angiography (DSA) Pre-contrast image Pos-contrast image Subtracted image

    47. 47 DIGITAL ADVANTAGE -Edge Enhancement Original Image Blurred Image Subtracted Image Edge-Enhanced image (Edge-enhanced image = [original image - blurred version] + original image.)

    48. 48 Mask Pixel Shift Subtracted image with the subtraction mask image is shifted several pixels

    49. 49 DSA MISREGISTRATION – CAUSED BY PATIENT MOTION – CAUSES BLURRING OF IMAGE RE-REGISTATION MAY BE ABLE TO FIX THIS MY SHIFTING PIXELS SEE PG 416 Bushong f patient motion occurs between the mask image and a subsequent image, the subtracted image will contain misregistration artifacts (Figure 28-14). The same anatomy is not registered in the same pixel of the image matrix. This type of artifact can frequently be eliminated by reregistration of the mask, that is, by shifting the mask by one or more pixels so that superimposition of images is again obtained. (Bushong, Stewart C.. Radiologic Science for Technologists: Physics, Biology, and Protection, 8th Edition. Mosby, 012004. 28.3.5.5). <vbk:0-323-02555-2#outline(28.3.5.5)>f patient motion occurs between the mask image and a subsequent image, the subtracted image will contain misregistration artifacts (Figure 28-14). The same anatomy is not registered in the same pixel of the image matrix. This type of artifact can frequently be eliminated by reregistration of the mask, that is, by shifting the mask by one or more pixels so that superimposition of images is again obtained. (Bushong, Stewart C.. Radiologic Science for Technologists: Physics, Biology, and Protection, 8th Edition. Mosby, 012004. 28.3.5.5). <vbk:0-323-02555-2#outline(28.3.5.5)>

    50. 50 CINE Equipment Cine radiography. Fluoroscopy unit with TV monitor: Single or biplane fluoroscopy units are available. Video equipment – DIGITAL RECORDING Other image recording devices: Images can be acquired and stored in a digital format (postprocessing). This is the fundamental principle of DSA.

    51. 51 Cinefluorgraphy aka CINE 35 or 16 mm roll film (movie film) 35 mm ? patient dose / 16 mm – higher quality images produced 30 f/sec in US – (60 frames / sec) THIS MODALITY = HIGHEST PATIENT DOSE (10X greater than fluoro) (VS SINGLE EX DOSE IS ?)

    52. 52 Cine Cinefluorography is used most often in cardiology and neuroradiology. The procedure uses a movie camera to record the image from the image intensifier. These units cause the greatest patient doses of all diagnostic radiographic procedures, although they provide very high image quality. The high patient dose results from the length of the procedure and relatively high inherent dose rate. For this reason special care must be taken to ensure that patients are exposed at minimum acceptable levels. Patient exposure can be minimized in a number of ways. The most obvious means of limiting exposure is to limit the time the beam is on. CINE - 2mR per frame (60f/sec) 400 mr per “look”

    53. 53

    54. 54 DR & GRID USE : QC

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