CT Flashcards
In the American College of Radiology (ACR) CT Accreditation program, which examination is allowed to have the lowest contrast-to-noise (CNR) ratio and receive a passing score?
Pediatric Abdomen (CNR > 0.4)
** Note: Adult head and adult abdomen > 1.0 CNR, pediatric head > 0.7 CNR
In the American College of Radiology (ACR) CT Accreditation Program, what range of CT numbers in Hounsfield Units (HU) would be allowed (i.e. passing) for water?
-7 to 7
What is the correct order for arranging the CT numbers of the following tissues from lowest to highest values?
Kidney
Breast
Lung
Bone
Lung, Breast, Kidney, Bone
What is a reasonable estimate for the CTDI_vol of an abdomen scan for an average size adult?
20mGy
What is a reasonable approximation to calculate the fetal dose from an abdomen/pelvis CT scan?
CTDI_vol of the scan (better if using the SSDE)
How do you calculate pitch?
Table feed per rotation divided by detector size nT
How do you calculate CTDI_w?
= (1/3)CTDI_100_Center + (2/3)CTDI_100_Periphery
How do you calculate CTDI_vol?
= CTDI_w / pitch
What gating technique is used to minimize patient dose in cardiac CT?
Prospective gating
What are the six clinical protocols that need to be reviewed at least annually?
Adult abdomen
Adult head
Pediatric head (~ 1yr old)
Pediatric abdomen (40-50lb)
High resolution chest
Brain perfusion (if applicable)
What is the tolerance for the CT scout prescription accuracy test?
Within 2 mm
According to the ACR CT QC manual, what are the CNR limits?
Adult head = 1
Adult abdomen = 1
Pediatric head = 0.7
Pediatric abdomen = 0.4
According to the ACR CT QC manual, what are the spatial resolution limits?
Adult abdomen = 6lp/mm
High resolution chest = 8 lp/mm
How do you calculate CTDI_100?
= (f * CF * E * L) / (nT)
f = conversion factor for exposure to dose in air (=8.76 mGy/R)
CF = calibration correction factor
E = average measured exposure (in R)
L = active length of pencil ion chamber
n = number of detector elements
T = thickness of detector elements
