Term
| The ACR CT phantom has how many modules? |
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Definition
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Term
| What is the size of each module? |
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Definition
| 4 cm in depth and 20 cm in diameter |
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Term
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Definition
| Alignment, CT #, and slice thickness. |
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Term
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Definition
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Term
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Definition
| Uniformity, noise and in-plane distance accuracy. |
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Term
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Definition
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Term
| What is marked on the top of the phantom? |
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Definition
| Foot - at module 1 and Head and module 4. |
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Term
| The name of the ACR CT accreditation phantom is |
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Definition
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Term
| How does module 1 assess positioning and alignment? |
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Definition
| There are four BB's at the phantom surface at 3, 6, 9 and 12 o'clock. |
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Term
| What are the different materials and their CT#'s in Module 1. |
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Definition
| Bone +955 HU, Air -1000 HU, Acrylic +120 HU, Polyethylene -95 HU, and Water 0 HU. |
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Term
| How is slice thickness tested in Module 1? |
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Definition
| There are two ramps consisting of fine wires that are located 0.5 mm apart in the z-direction. Count the number of visible wires and multiple by 0.5 mm for the slice thickness. |
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Term
| In module 2, how many groups of cylinders are there? How many cylinders are in a group? |
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Definition
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Term
| What are the diameters of the different cylinders in Module 2. |
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Definition
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Term
| In the low contrast module, what is the CT # of the cylinder's and how different are they from background. |
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Definition
| The CT # is 90 HU and it is 6 HU different from background. |
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Term
| What is at the top of module 2? What is it used for? |
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Definition
| It is a 25 mm cylinder used to asses contrast-to-noise ratio. |
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Term
| What does Module 3 primarily consist of? |
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Definition
| A uniform tissue equivalent material. |
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Term
| What objects are in Module 3 and what are they used for? |
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Definition
| There are two small BB's located 100 mm apart to assess in-plane distance measurements. |
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Term
| What is the spacing of the bar patterns in module 4? |
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Definition
| 4, 5, 6, 7, 8, 9, 10, and 12 lp/cm |
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Term
| Besides bar patterns, what else is in Module 4. |
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Definition
| Four external BB's just like module 1. |
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Term
| What scans are done on the phantom? |
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Definition
| Adult head, adult abdomen, pediatric head, pediatric abdomen. |
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Term
| What display field of view should be used with the ACR phantom. |
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Definition
| As close to, but not smaller than 21 cm. |
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Term
| Proper alignment occurs when |
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Definition
| All 4 BB's are visible and the central wires in the slice thickness ramp are symmetrically located. |
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Term
| What size ROI should you use for the CT number calibration? |
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Definition
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Term
| What is the CT # calibration criteria for water? |
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Definition
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Term
| Which protocols do you have to measure all the CT #'s for? |
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Definition
| Just the adult abdomen protocol. |
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Term
| How large of an ROI should you use for the CNR measurement? |
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Definition
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Term
| Where do you place the two ROI's for the CNR measurement? |
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Definition
| One over the large (25 mm) cylinder and one between the large cylinder and the 6 mm cylinders. |
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Term
| What formula is used for CNR? |
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Definition
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Term
| What are the criteria for the CNR to pass? |
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Definition
| adult head and abdomen - CNR > 1; pediatric abdomen - CNR > 0.4, pediatric head - CNR > 0.7 |
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Term
| How large is the ROI for the uniformity test? |
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Definition
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Term
| How is uniformity measured? |
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Definition
| Place 5 ROI's; one in the center and four on the edges (top, bottom, left, and right), edge ROI's should be inward one ROI diameter. The CT #'s must be withing ±5 HU of the center ROI. |
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Term
What are the four pass/fail values for CTDIvol?
What are the diagnostic reference levels? |
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Definition
| Adult head - 80 mGy, Adult abdomen - 30 mGy, Pediatric head - 40 mGy, Pediatric abdomen - 20 Gy. Note - the DRL's are 5 mGy lower. |
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Term
| Where are the dosimetry phantoms to be placed. |
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Definition
| Adult head - in the head holder. The other 3 scans, the phantom goes on the table top. |
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Term
| What type of scan must be used to acquire dose information? |
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Definition
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Term
| What is the requirement for high contrast resolution. |
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Definition
>= 6 lp/cm for Adult Abdomen studies
>= 8 lp/cm for High Resolution Chest studies. |
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Term
| What is the requirement for low contrast resolution? |
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Definition
At least resolve the 6mm pins for Adult Abdomen & Head studies
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Term
| What document defines k-factors? |
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Definition
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Term
| What are k-factors. What are the units. |
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Definition
They are used to convert from DLP to effective dose.
Units are mSv per mGy·cm |
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Term
| How is effective dose calculated in CT? |
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Definition
| E (mSv) = k (mSv / mGy·cm) * DLP (mGy·cm) |
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Term
| K-factors are based on what? |
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Definition
| Adult (all) and pediatrics of various ages, and then by region of the body (head, neck, chest, abdomen/pelvis) |
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Term
| Effective dose represents radiation detriment averaged over ______ and _______. |
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Definition
gender and age.
(this seemed like an important point - effective dose is not age or gender specific) |
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Term
What does DLP stand for?
How is it calculated? |
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Definition
Dose Length Product
DLP (mGy·cm) = CTDIvol (mGy) × scan length (cm) |
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Term
| What is DLP a good reflection of? |
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Definition
| It reflects the total energy delivered for a given scan protocol. |
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Term
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Definition
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Term
| What does CTDIvol represent? |
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Definition
| The average absorbed phantom dose over they x, y, and z directions at the center of the scan length. It's averaged over the z-direction because it includes the effects of pitch. |
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Term
| What does CTDIW represent. |
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Definition
| The average absorbed dose over the x and y directions at the center of the scan where the scatter tails are negligible beyond the 100-mm integration limit. |
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Term
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Definition
| CTDIW = 1/3 CTDI100,center + 2/3 CTDI100,peripheral |
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Term
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Definition
Pitch = I / NT
I - table travel per rotation of the gantry
N - number of data slices
T - slice thickness (mm) |
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Term
| How is CTDI100 calculated? |
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Definition
CTDI100 = C × f × E × L / (NT)
f - 8.7 mGy/R
C - chamber factor (typically 1.0)
E - exposure measured with the pencil chamber
L - length of the chamber, 100 mm
N - number of data channels
T - thickness of a data channel (mm) |
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Term
| Define CTDI. What does it represent? |
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Definition
CTDI = Integrated Dose from ± infinity / NT
It represents the average absorbed dose along the z-axis from a series of continguous radiations. |
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Term
| What are the requirements for XR-29 compliance. |
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Definition
1. DICOM Structured Dose Reporting
2. Pediatric and Adult reference protocols
3. CT Dose Check
a. Dose notifications (user defined)
b. Dose alerts (CTDIVOL > 1000 mGy)
4. Automatic Exposure Control |
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Term
| What is another name for XR-29? |
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Definition
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Term
| What is the purpose of CTDIvol? |
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Definition
| To compare radiation output levels between different CT scanners and different protocols using a reference phantom. |
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Term
| Why doesn't CTDIvol estimate patient dose. |
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Definition
| Patient dose is a function of both patient size and scanner radiation output. CTDIvol is only a measure of scanner output. |
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Term
| What does the effective diameter of a patient represent? What is the formula for it? |
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Definition
It is the diameter of a circle that has the same cross sectional area as the patient.
Deff = √(AP×LAT) |
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Term
| What does SSDE stand for. How does it work? |
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Definition
SSDE - Size Specific Dose Estimate
CTDIvol is multiplied by a factor based on patient size (effective diameter) to get a size specific dose estimate.
SSDE (mGy) = fsize × CTDIvol
fsize depends on 16 or 32 cm phantom |
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Term
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Definition
| Because CTDIvol is not a measure of patient dose. |
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Term
| What does SSDE not account for? |
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Definition
| It only accounts for the actual patient dimension, it does not account for the actual patient attenuation which is what really determines absorbed dose. |
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Term
| What is DW. What does it represent? |
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Definition
Water equivalent diameter.
It's the diameter of a cylinder of water having the same attenuation as a patient. |
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Term
| Size Specific Dose Estimates (SSDE) are defined in what report. |
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Definition
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Term
| For the same CTDIvol how does the SSDE of a small patient compare to that of a large patient? |
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Definition
| SSDE small patient > SSDE large patient |
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Term
| How does kVp affect dose? |
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Definition
Lower kVp → lower dose
Higher kVp → higher dose |
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Term
| For identical CT settings, a child (smaller cross sectional area) will get _______ dose than an adult (larger cross sectional area). |
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Definition
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Term
| What are the fundamentral principles of radiation protection during imaging? |
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Definition
1. justification - the exam must be indicated
2. utilization - the correct modality must be used
3. optimization - appropriate balance between dose and image quality |
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Term
| What is the approximate HVL for tissue at 120 kVp? |
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Definition
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Term
| SSDE apply to what types of scans? |
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Definition
Torso (chest, abdomen, and/or pelvis)
Don't use SSDE for head scans. |
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