Doses in Fluoroscopy factors influencing patient doses Colin Martin and David Sutton

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

Definitions Fluoroscopy (radioscopy) 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) Fluorography (acquisition or digital spot imaging)  Method of acquiring a single still image using fluoroscopic equipment

Fluoroscopic and Fluorographic images Fluorographic image is of higher quality 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 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 4

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

Example GE-CGR Advantix LCV (Fluoroscopy ) LOW DOSE 10 mGy/min MEDIUM DOSE 20 mGy/min HIGH DOSE 40 mGy/min Patient entrance dose rates in fluoroscopy

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

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

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

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

Patient dosimetry Irradiation geometry can vary throughout exam & between patients Irradiation geometry can vary throughout exam & between patients Patient exposure measured by air kerma- area product Patient exposure measured by air kerma- area product Measured with flat transmission ionization chamber (KAP meter) Measured with flat transmission ionization chamber (KAP meter)

Kerma-Area Product (KAP) or Dose-Area Product (DAP)  KAP is easily measured  KAP can be assessed for multiple projections, field sizes  KAP is a measure of the total amount of radiation incident on a patient Equal to: Dose in beam x Area of beam

Kerma-area product KAP meter X-ray focus Ave dose in beam = D Gy Area of beam = A cm 2 KAP = D x A Gycm 2 Dose x area is independent of distance from X-ray tube focus, because of inverse square law.

KAP is measured with large area ionisation chamber which intercepts entire X-ray beam

Patient selection for dose survey Select examination of interest Select examination of interest Define weight range (typically kg) Define weight range (typically kg) Make measurements / collect data for at least 20 patients – or more Make measurements / collect data for at least 20 patients – or more (more variability in dose data than for radiography)

Patient data to collect Tube voltage Tube voltage Tube current Tube current Screening time Screening time ABC mode ABC mode Dose rate setting Dose rate setting Image Intensifier field size used Image Intensifier field size used

Summary Uses both fluoroscopy and fluorography Uses both fluoroscopy and fluorography Different dose options Different dose options Factors such as pulsing, filters, etc. affect dose Factors such as pulsing, filters, etc. affect dose Use KAP to record all the radiation incident on the patient Use KAP to record all the radiation incident on the patient