COMPUTED TOMOGRAPHY FOR TECHNOLOGISTS 2ND EDITION EXAM 2024 CT technologists must understand both the of examinations and take steps to maximize the minimize the ANSWER risks benefits positive negative What are the two components regarding radiation dose to the patient ANSWER 1 appropriate patient selection 2 minumizing the dose to the pt w out compromising the diagnostic image quality CT scans provide one of the radiation doses in diagnostic radiology slide 3 ANSWER higher large w very thin slices X rays damage cells in ways how ANSWER 2 1 Direct interaction between an x ray photon and DNA bonds with the nucleus of the cell within the patient 2 X ray photon indirectly produces ion pairs in tissues as it passes through the body X rays damage cells in two ways ANSWER Direct interaction with DNA bonds Indirect effect caused by ionization of chemicals in the body Direct Interaction is also known as ANSWER Target Theory Gestating babies are radiosensitive ANSWER most Radiation effects may be but are more likely to be seen ANSWER immediate over a long period of time What are the effects of x ray radiation 4 ANSWER cancer genetic effects of future generations Long term effects 10 20 yrs effects of the embryo fetus first trimester maximum radiosensitivity The unit of x ray exposure in air ANSWER Roentgen R Units of absorbed dose ANSWER radiation absorbed dose rad SI unit Gray Gy 100 rad 1 Gy 1 rad 01 Gy or 1 cGy Convert the following 50 rad 200 Gy 1 rad ANSWER 5 Gy 20 000 rad 001 Gy or 1mGy Determine the total dose in Gy if an exam acquires 300 slices producing 2 rads per slice ANSWER 300 slices x 2 rad slice 600 rad x 01 6 Gy Accounts for different types of ionizing radiation ANSWER Quality factor Q In CT the quality factor is ANSWER 1 Attempts to account for the effects particular to the patient s tissue that has absorbed the radiation dose ANSWER Effective dose Effective dose attempts to quantify dose based upon the of certain tissues or organs ANSWER radiosensitivity The uniformity of the dose as the SFOV and patient thickness ANSWER decreases increase organ doses are higher for children or small adults compared with larger adults ANSWER Body scans are uniform than head scans ANSWER less The central dose of a body scan is approximately one third one half that of the peripheral dose ANSWER Z axis dose distribution profile describes variations that occur along the ANSWER length of the patient Total dose is from the radiation to the selected slice and from scatter radiation or tails from neighboring slices In general the tails will contribute approximately 25 to 40 to the total dose ANSWER Multiple scan average dose MSAD ANSWER Dose calculated from multiple scans Computed tomography dose index CTDI ANSWER Reported to FDA Slices must be contiguous CTDIw ANSWER Weighted average The weighted CTDI takes into account patient size and mAs used CTDIvol ANSWER Accounts for exposure variation in the z direction A measure of exposure per slice and is independent of scan length CTDIvol ANSWER The preferred expression of radiation dose in CT dosimetry Dose length product DLP ANSWER Accounts for the length of the scan CTDIvol is also known as ANSWER CTDIW pitch takes into account helical scan acquisition in relation ship of table movement to tube rotation DLP CTDI x mAs x total scan time pitch ANSWER DLP is considered to be a better indicator of patient exposurethan CTDI alone Radiation dose for CT examinations is substantially higher when compared with film or screen radiography ANSWER The higher dose is the price that is paid for the excellent low contrast resolution seen on CT images It is not unusual for the surface dose to be 10 times higher in CT and the average absorbed dose 100 times higher ANSWER It is estimated that for every CT examination a patient receives their chance of getting cancer in their lifetime increases by ANSWER 1 Some perspective ANSWER Average background radiation for Americans is about 3 mSv Exposure from a chest x ray is about 0 1 mSv Exposure from a chest abdomen or pelvis CT is about 10 mSV Factors effecting dose slide 15 ANSWER Radiation beam geometry Filtration bow tie Detector efficiency Slice width and spacing Pitch Scan field diameter Radiographic technique i e mAs and kVp Patient size and body part thickness Repeat scans Collimation The level of risk associated with a CT examination can be considered acceptable if ANSWER The individual is aware of the risk The individual receives some commensurate benefit Everything reasonable has been done to reduce the risk Ped CT General Principles ANSWER The patient or the parent should be told of the small risk involved The procedure should be restricted to cases in which it is specifically indicated and clinical information cannot be obtained by other means Every effort should be made to decrease the radiation dose by adjusting the kVp and mAs to a suitable level according to the size of the child being scanned Shielding should be used when possible all the way around special considerations peds CT ANSWER Increased sensitivity Higher effective dose Increasing use The radiosensitivity of a developing fetus is greatest from conception to 3 months gestation because this is the time of organ and neural crest development ANSWER Dose reducing strategies ANSWER Adjust mAs to suit the individual patient When available use automatic tube current modulation Avoid increasing kVp Increase pitch Limit the use of thin slices Limit repeat scans When available use iterative reconstruction methods Verify the CT is clinically indicated Customize the CT examination when possible Shield patient Interventional CT CT Fluoroscopy and Cone Beam CT ANSWER CT has proven useful for invasive interventional procedures that previously were performed using conventional fluoroscopic techniques CT Guidance of Percutaneous Procedures ADVANTAGES ANSWER Provides precise 3D localization of lesions Permits clinicians to plan an access route by showing the relationship of surrounding structures Because the tip of the needle can be seen interventions can be performed on small structures Information can be gathered on materials ranging from low to high density Contrast Media can be injected when needed Patients can be placed in a variety of positions CT Guidance of Percutaneous Procedures DISADVANTAGES ANSWER Disadvantages include a significantly higher dose to both patient and operator than normal fluoroscopy making ultrasound guided techniques a viable