Fluoroscopic Imaging 2023 Pre-Lecture.pptx

Fluoroscopic Imaging Jack Pearse Session Aims Understand the underpinning physical principals of fluoroscopic imaging. Compare and contrast fixed and mobile fluoroscopic imaging. Consider radiation protection in fluoroscopic imaging. Explore image generation and optimisation feat...

Fluoroscopic Imaging Jack Pearse Session Aims Understand the underpinning physical principals of fluoroscopic imaging. Compare and contrast fixed and mobile fluoroscopic imaging. Consider radiation protection in fluoroscopic imaging. Explore image generation and optimisation features in fluoroscopic imaging. What is Fluoroscopy? “Fluoroscopy is a type of medical imaging that shows a continuous X-ray image on a monitor, much like an X-ray movie” (FDA, 2020) Why use fluoroscopy? Imparts anatomical and physiological information. Can be diagnostic or therapeutic. Allows for dynamic guidance of clinicians. Facilitates less invasive operative procedures. Can you think of any fluoroscopic procedures? MENTI Can you think of any fluoroscopic procedures? Common Applications: Orthopaedic – Arthrograms & theatre procedures. Angiography – Cardiac, cerebral, peripheral. GI Tract – Barium swallows, meals and enemas. Endoscopy – ERCP & OGD. Urology – Ureteroscopy, nephrostomy insertions, PCNL. Interventional Radiology – Line insertions, Embolisations, PTC. And many more!  Fixed Systems Fixed systems are installed in a specific room or suite. These are typically used for longer screening cases. Variety of styles including floor mounted, ceiling mounted and biplane. Mobile Systems Portable. Usually used to support theatre cases and shorter or less complex interventions.  Comparison of System Advantages Mobile Systems Fixed Systems Does not require custom More reliable x-ray generators. room design. Usually more features. Can be moved between theatres. Often better radiation protection. Room is designed to allow Can be replaced mid- uninhibited movement of c-arm. procedure without moving patient. X-ray Generation The mechanism for X-ray generation is similar in fluoroscopy to conventional x-ray systems. In fluoroscopy however there are a number of modes that are utilised for different methods of imaging: Continuous fluoroscopy Pulsed fluoroscopy High-Dose “Acquisitions” Single high-dose image Anode Heat Dissipation High-speed rotational anodes. Oil or water cooled systems. Range of focal spot sizes to balance detail with anode heating depending on application.  The Image Intensifier X-rays that pass through the patient reach the input phosphor. The input phosphor emits light. This light reaches the photo emissive layer which emits electrons towards the anode. These electrons reach the output phosphor which itself produces an amplified light signal. This light signal is recorded by a camera. Image Intensifier System (Seeram, 2019)  Flat Panel Detectors (FPDs) Similar to plain film direct digital receptors. The input x-rays that have passed through the patient are converted into electric via a Selenium photoconductor. This charge is transmitted to a thin-film transistor (TFT) array. This array is arranged in a matrix with each transistor mapped to a pixel. Comparison Advantages and Disadvantages of Flat Panel Detector Systems Advantages Disadvantages FPDs usage tends to Higher initial cost. utilise a lower dose. Size of receptor can There is a greater impact field of view with maneuverability FPDs. Higher image quality. Contrast Media Positive Media Negative Media Radiopaque Radiolucent Has a higher atomic Has a lower atomic number than surrounding number than surrounding tissues tissues Attenuates more x-rays Attenuates less x-rays Appears “Hyperdense” on Appears “Hypodense on image image” Contrast Media Contrast Media Double-Contrast Imaging Uses both positive and negative contrast together! Can be used in Barium meal and Barium Enema investigations. Double-contrast Image Digital Subtraction Angiography This is a process used in angiography to remove distracting detail and anatomical structures from the image. The operator begins acquiring the images before injecting contrast. The computer system uses the initial frames to create a “mask” demonstrating the background anatomy. For subsequent images (when the contrast is injected) the information from the “mask” is removed, leaving only the new information [contrast] visible on the screen. This creates a simpler image as anatomy not under scrutiny such as bones are not visible on the image to cause any distraction. This process can only work on anatomy that is not moving. Digital Subtraction Angiography (Fujihara, 2017) Visual Representation of Subtraction 0 0 100 0 0 0 0 100 0 0 0 0 0 0 0 0 0 100 0 0 0 0 100 0 0 0 0 0 0 0 100 100 100 100 100 Subtract 100 100 100 100 100 0 0 0 0 0 > = 0 0 100 0 0 0 0 100 0 0 0 0 0 0 0 0 0 100 0 0 0 0 100 0 0 0 0 0 0 0 Pre Mask Final Image Contrast 100 Image 0 100 0 0 0 0 100 0 0 100 0 0 0 0 0 100 100 0 0 0 0 100 0 0 0 100 0 0 0 100 100 200 100 100 100 100 100 100 100 0 0 100 0 0 Subtract = 0 0 100 100 0 0 0 100 0 0 0 0 0 100 0 > 0 0 100 0 100 0 0 100 0 0 0 0 0 0 100 Post Mask DSA Image Contrast Image Can you see why movement prevents this process? Roadmapping (Castro-Afonso et al., 2017) Biplane Systems Bi-plane systems are digital fluoroscopy systems that have multiple c-arms, allowing the clinician to take simultaneous images in multiple planes. With traditional systems, the radiographer must manoeuvre between the positions sequentially in order to gain an appreciation of A PA image of the the anatomy in 3 dimensions. heart A lateral image of the heart Radiation Protection The room in which the fluoroscopic imaging takes place is designated a “Controlled Area”. The controlled area should be demarked with warning signs. There should be local radiation rules associated with the room or system. Workers within the controlled area should wear lead PPE and undergo dose monitoring. Radiation Protection Some procedures such as cardiac angioplasties can incur a high dose, due to prologued screening time and high framerate. Therefore deterministic effects can be caused to the patient. Skin erythema can be induced following an exposure of over 2Gy cumulatively to an individual area of skin. Trusts will have follow-up procedures for patients whose “skin dose” reaches a certain level within a case. Methods of reducing dose. Using a “low dose fluoroscopy” setting Collimation. Reduce exposure factors. Reduce SID. Staff stand further from primary beam (Inverse-square law). Reduce pulse/frame rate. Using shallow angles. Lead shielding. Staging the procedure. Exposure Factor Control In fluoroscopy the exposure factors are adjusted automatically by the system by default, rather than the user setting specific exposure factors. There are various systems for how these factors are controlled. Two systems of note are Automatic Brightness Control (ABC) Automatic Dose Rate Control (ADRC) Automatic Brightness Control (ABC) Similarly in nature to the use of automatic exposure chambers (AECs) in conventional radiography, fluoroscopy automatically adjusts kVp and mAs via a system called Automatic Brightness Control (ABC). In image intensifier systems this is achieved by measuring the intensity of the output phosphor and adjusting the exposure factors to maintain a present brightness level.  Fluoroscopy Dose Settings Fluoroscopy systems will usually include a setting that refers to a general implication of dose imparted such as “Fluoro –” or “Low Fluoro”. These settings alter the method in which the ABC functions. Lower dose settings will skew the exposure factors in favour of higher kVp but lower mA, this results in lower image contrast but a lower dose. Where possible, the radiation used should be as low as reasonably practicable, however “higher dose” settings may be appropriate for large patients, if image quality is (Axelsson, Automatic Dose Rate Control (ADRC) Modern systems utilise a system called ADRC. With ADRC the exposure factors are algorithmically controlled. The system estimates anatomical thickness and applies initial setting based on the program selected. After each x-ray pulse, the system measures the pixel data against its parameters under the setting, adjusting accordingly for the next pulse to provide the programmed “optimal” exposure. After each run, the estimated patient thickness is updated based on the data and the starting exposure is updated. Changing programmes adjusts the algorithm applied. (Gislason- Lee et al., 2013) Image Quality – Further Considerations If your surgeon/radiologist/advanced practitioner is having trouble interpreting the images, before reaching for the Fluoro + button, consider: Screen Position Cleanliness of screens Lighting of the room Display settings Collimation Just as in conventional radiography, collimation is utilised to reduce irradiation of unnecessary anatomy and reduce scatter. There are a variety of collimation configurations that are found within fluoroscopy systems, such as independent side collimators, paired collimators and iris collimators. Collimation Linear Collimation Iris Collimation Depending on system, these Adjustments to collimation collimators may be paired or affect the full circumference of each side may move image. independently. Image “Flare” The less dense aspect of the Filtration has been applied to the upper image is too bright. (Ignore left lung. Resulting in more even Filtration Unlike conventional x-ray systems, fluoroscopy systems will usually have a filter or filters that can be positioned within the field of view to attenuate a section of the Reduces skin dose by filtering soft radiation from a section of the incidental beam. Reduces “flare” on the image. Improving visibility. Filtration Exposure Lock High density objects within the fluoroscopic field of view, such as metallic structures (commonly occurs with operating tables) can cause the ABC to attempt to compensate unnecessarily by increasing the x-ray exposure. Many systems will have a “technique lock” button that allows the exposure to be locked at a previously used level or override and set manual parameters.  Key 1. Height Control Panel Adjustment 2. Technique Lock + Exposure Adjustments 3. Subtraction 4. Roadmap 1 5. High Dose Image 6. Pulsed 2 15 Fluoroscopy 16 17 7. Continuous Fluoroscopy 18 8. Increased mA 9. Magnification 3 4 8 12 10.Mirror Image + Flip 5 9 11 13 Superior/Inferior 11.Reduce Motion 6 7 10 14 Blur 12.Iris Collimator Adjustment 13.Rotate Paired Filters Any Questions?