Digital FLUORO Summer 2008

DIGITAL FLUORO

Digital fluoroscopy is currently most commonly configured as a conventional fluoroscopy system in which the analog video signal is converted to a digital format with an analog-to-digital converter (ADC). An in-depth discussion of digital detector technologies (eg, flat-panel "direct" detection of x rays and charge-coupled device technology) is beyond the scope of this article. After a review of several fundamental digital imaging concepts including binary numbers, pixels, and gray levels, emphasis will be placed on discussions of the digital imaging tools specific to digital fluoroscopy and digital subtraction angiography (DSA).

Digital fluoroscopy is currently most commonly configured as a conventional fluoroscopy system in which the analog video signal is converted to a digital format with an analog-to-digital converter (ADC). With discussions of the digital imaging tools specific to digital fluoroscopy and digital subtraction angiography (DSA).

Early Fluoroscopy

CONVENTIONAL FLUOROSCOPY INVENTED BY THOMAS EDISON

Main source staff exposure is NOT the patient but direct beam Direct Fluoroscopy: obsolete In older fluoroscopic examinations radiologist stands behind screen and view the picture Radiologist receives high exposure; despite protective glass, lead shielding in stand, apron and perhaps goggles Main source staff exposure is NOT the patient but direct beam

pixels the smallest element of a digital image. A digital image is normally composed of a two-dimensional (square) matrix of pixels. The matrix size of an image is used to describe the number of pixels in each row and column of the image.

The size of a pixel determines the smallest detail visible in the image, the number of pixels (of a given size) determines the field of view of the image. pixel value is assigned to a certain color or gray level for visualization. The imaged object is more faithfully reproduced as matrix size increases and pixel size decreases.

63 K 1024

Digital fluoroscopy is most commonly configured as a conventional fluoroscopy system (tube, table, image intensifier, video system) in which the analog video signal has been digitized with an ADC. Alternatively, digitization may be accomplished with a digital video camera (eg, a charge-coupled device) or via direct capture of x rays with a flat-panel detector. For digital fluoroscopy systems in which the analog video signal is digitized with an ADC, the resolution is limited by the resolution of the video camera, which is typically 1–2 line pairs per millimeter.

Digital Image recording In newer fluoroscopic systems film recording replaced with digital image recording. Digital photospots acquired by recording a digitized video signal and storing it in computer memory. Operation fast, convenient. Image quality can be enhanced by application of various image processing techniques, including window-level, frame averaging, and edge enhancement. But, the spatial resolution of digital photospots is less than that of film images.

Digital radiography principle Clock Memory ADC I Iris t ANALOGUE SIGNAL DIGITAL See more in Lecture L20

Digital spot film images and photospot images may be acquired by using the same digital fluoroscopy system. Individual frames from a digital fluoroscopy sequence can be stored digitally and can be used instead of conventional spot film and photospot images. Digital photospot images will have the same characteristics (eg, resolution) as digital fluoroscopic images.

Digital format – print to film

Remote – over the table tube

Different fluoroscopy systems Remote control systems Not requiring the presence of medical specialists inside the X Ray room Mobile C-arms Mostly used in surgical theatres.

The digital image data from digital fluoroscopy may be processed by using many useful image processing techniques. These techniques may serve to decrease radiation exposure to the patient and medical imaging staff or improve visualization of anatomy. Processing options include last image hold, gray-scale processing, temporal frame averaging, and edge enhancement. Additional processing is available when digital fluoroscopy data are used to perform DSA.

STAT CH 7 & 8 DHS-RHB RAD PROT/FLUORO SYLLABUS RADIATION PROTECTION STAT CH 7 & 8 DHS-RHB RAD PROT/FLUORO SYLLABUS

Radiation Safety and Fluoroscopy Time Distance Shielding Also see Intro to Fluoro Lecture From RT 124 Spring 2007

Patient Protection Tabletop exposure rate Maximum 10 R/min Typically 1 – 3 R/min

Patient Protection Minimum source-to-skin distance 12” for mobile equipment 15” for stationary systems Audible alarm at 5 mins. Same rules for collimation

Patient Protection Typical exposure rates Cinefluorography Cassettes 7.2 R/min Cassettes 30 mR/exposure 105 mm film 10 mR/exposure

Protection of Radiographer and Radiologist Lead apron 0.25 mm Pb/eq Highest energy scatter 90o angle to the incident beam Same level as radiographer /radiologist’s gonads

The Patient & Scatter

WHATS WRONG?

Remote – over the table tube

Under table tube vs Over table tube (remote units) Need moving shield for Remote rooms

IsoExposure Curves Where is it SAFE??

ISOEXPOSURE CURVES

Patient entrance skin exposure (ESE) is higher when the fluoroscopic x-ray tube is too close to the tabletop.

KEEP I.I. CLOSE TO PATIENT

REDUCE DISTANCE OF IMAGE INTESIFIER PATIENT EXPOSURE REDUCE DISTANCE OF IMAGE INTESIFIER INCREASE DISTANCE FROM THE TUBE

PATIENT EXPOSURE REDUCE SIZE OF COLLIMATED BEAM WHEN POSSIBLE

ESE FOR FLUORO TLD PLACED AT SKIN ENTRACE POINT 1 – 5 R/MINUTE AVE IS 4 R/MIN INTERGRAL DOSE – 100 ERGS OF TISSUE = 1 RAD EXPOSURE OR 1 GM RAD = 100 ERGS

1 rad (of ionizing radiation) deposits 100 ergs of energy per gram 1 RAD -100 ERGS – 1 GRAM 1 rad (of ionizing radiation) deposits 100 ergs of energy per gram

DOSE REGULATIONS BEFORE 1974 - AT TABLETOP 5R/MIN (WITHOUT AEC) 5R/MIN (WITHOUT AEC) – BOOST MODE After 1974 with AEC 10 R/MIN 20R/MIN BOOST

SSD – TUBE TO SKIN DISTANCE FIXED UNITS 18” PREFERRED 15 “ MINIMUM MOBILE UNITS ( C-ARMS) 12’ MINIMUM

Conventional “FIXED” Fluoro

Mobile – C- arm fluoro

FLUOROSCOPY – ABOVE AND BELOW THE TABLE TUBE EXPOSURE TO TECH

Pulsed Fluoro Some fluoroscopic equipment is designed for pulsed-mode operation. With the pulsed mode, 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.

Dose rate to patients

Mini c-arm