Fluoroscopy: Past and Present

Welcome to this web based training on Fluroscopy: Past & Present. Within this training we will explore fluroroscopy and how it has evolved over the years.     This concludes the web based training, Fluoroscopy:  Past and Present. You should now be able to: - Identify significant innovations related to fluoroscopy - Compare the components of image intensifier versus digital flat detectors - List the steps included in the imaging process - Identify methods to reduce dose - Identify and manipulate functions to improve image quality   Upon completion of this course you will be able to: - Identify significant innovations related to fluoroscopy - Compare the components of image intensifier versus digital flat detectors - List the steps included in the imaging process - Identify methods to reduce dose - Identify and manipulate functions to improve image quality   Fluoroscopy in the 1920s Physician looked directly at a fluoroscopic screen in front of the patient, who stood upright Image capture required extreme doses of radiation Patient and operator were exposed to scatter radiation Every time the conversion from analog to digital and digital to analog takes place, a little of the original data is lost.     X-Ray tubes for fluoroscopy are similar to those in radiography. Fluoroscopic tubes operate a lower mA.     Curvature of the components leads to image distortion at periphery. A phenomenon known as vignetting.                Line Art                                       Dithering                                  Gray Scale   Matrix Rows and Columns (1024 x 1024) Gray-scale Bit-depth (8 bit, 10 bit, 12 bit) Pixel Picture Element – 2 dimensional Spatial Resolution How well we can see detail. The spatial resolution of digital images is based on the pixel size of the detector Window Values The brightness and contrast of the image. Window width is the contrast, and window center is the brightness. Noise Used to be called graininess or quantum mottle but is now referred to as noise. Noise is detrimental to image quality and many of the steps we used to use to reduce quantum mottle on film we still use to reduce noise on digital images.   Detector Properties Include: Matrix and FOV (Field of View) Dose Rate Controls Dose Reduction     Digital Detector      Incident X-ray Photoelectric absorption in the scintillator Ionization and generation of light quanta Conversion of light into electric charge in the photodiode Amorphous silicon active readout matrix circuitry           Cesium Iodide (Csl)          Vignetting  No vignetting with a Flat Digital Detector Based on pixel size Smaller pixel size = better spatial resolution Fixed Value Based on Nyquist Limit Expressed in line pairs/mm 3.4 lp/mm   16” Image Intensifier – 200.96 sq. inches Digital Detectors – 282 sq. inches Greater coverage means improved workflow “Overhead views” can now be taken during fluoroscopy   Just like an image intensifier or radiography, AEC is used. Positioning over the correct dominant is critical for: - Image quality - Dose  Selection of the correct dominant is also important. ROI should have an average blackening in the image. ROI must cover the measurement field (dominant). Cannot collimate smaller than the size of the dominant. Contrast media (barium or iodine-based) should not completely cover the dominant.  Poor image quality may result. Dose reduction is a function of the Fluoro Organ Program. During a procedure, the system will automatically adjust the fluoro kV for the patient being imaged. If the kV goes too high, image contrast will be reduced. kV can be reduced to keep the contrast acceptable, but the dose can go down (increased noise). Contrast on the image vs. noise level. Every Fluoro Organ Program consists of 3 options of fluoro parameters: - Automatic 1 = Low dose fluoro - Automatic 2 = Standard fluoro - Automatic 3 = High dose fluoro 73 kV Plateau curve is standard for digital flat detector. System tries to stay at 73kV (keeps contrast constant) until tube limit is reached. If kV is allowed to increase, mAs will be reduced to get the desired dose (noise). Should the dose be increased? - Only after consulting with facility medical physicist - Can only be done by qualified Service Engineer Better solution……reduce the fluoro pulse frequency (15 pulses/sec. to 10 or 7.5 pulses/sec.) Pulse frequency rate can be set in the Fluoro Organ Program in the PEX Editor. Configurable Customizable Cover all possibilities Very simple to very complex Radiographic Fluoroscopic Adult and Peds Barium and Iodine Bones White/Bones Black By the 1950s, the patient lay on a table beneath a fluoroscope Mirror "optics" allowed operator to see fluoroscopic image without looking at it directly Operator's radiation exposure was reduced with lead apron Image intensification: increased workflow; decreased dose Fluoro system image intensifier under the table operated via remote control control room with remote control console x-ray tube over the patient Image intensifier over table; x-ray tube under table  Allows operators to stand next to patients   Required: protective radiation exposure measures Types of Pick-up Tubes Plumbicon Vidicon Orthicon Saticon CCD   Features Include: - Hundreds of thousands of photodiodes (pixels) - Virtually no image lag - Very low noise - Improved signal to noise ratio = better image quality X-ray radiation Driver electronics Photo diode Pixel Readout electronics Cesium iodide (Csl) Fluorescent input screen Photocathode Housing Focusing Electrodes Anode Output phosphor Introduced in 1948   Converts x-rays to visible light then to electrons then back to intensified visible light   Optics for viewing   Low light adaption required   Lower radiation dose than conventional radiographs Vacuum bottle K Factor displayed in a numerical value. K Factor is fluoro image integration – one or more of previous images integrated into the current image. Example: K Factor value of 2.0 Assumes half of the previous fluoro image is being integrated into the current fluoro image. Downside – movement in the imaging chain or the patient will produce noticeable image lag. Images from detector Images after k-factor processing With an image intensifier, going from full-field to zoom 3 would increase the dose by 5 times.   With a digital detector, going from full-field to zoom 3 increases the dose by just under 3 times.   This has to do with light output – less area for light output means more radiation to get adequate light. ZDF Format Full Format Zoom 1 Zoom 3 Zoom 2 Fluoro Programs: Characteristic Curves Characteristic Curve is similar in concept to filmH&D curve ​Based on water values (patient thickness) - helpsto set kV and mA values Required dose and selected fluoro curve deliverneeded kV and mAs Out of these values, the system calculates thewater value of the anatomy   Click the pop-up below to view additional information. Overview Fluoro Curves Checklist TitleChecklist TypeChecklist ContentFluoro & Acquisition Curves -- OverviewHTMLFluoro CurvesHTML Over 100 curves available Each has different parameters Some adult, some pediatric Some set for barium, some for iodine-based contrast media Fluoro curves part of the organ program Cardinal rule:  select the organ program based on patient size and what contrast media is  being used Fluoro Curves ChartHTMLPerforming a Fluoro ExamHTML  Automatic Dose Management Fluoro for just 1 second prior to making an acquisition image The fluoro system can then determine the water values and select the correct kV and mAs (based on fluoro curve used) These values are transferred to the acquisition side The resolution of a digital detector is based on what binning is used Binning takes information from adjacent pixels and combines them into one “super pixel” Binning required due to the number of pixels used  8.2 million x 15 pulses/sec.=120 million pixel readouts in 1 sec Based on this chart, fluoroscopy that is done at full field will use the highest levels of binning and will have the lowest levels of spatial resolution. The opposite will be true at fluoroscopy done at zoom 3.   Resolution & Binning -- DR Resolution & Binning -- DR Here is a table outlining binning in radiographic exposures and the resulting spatial resolution.   Maximum frame rate 8fps.