CT Imaging Instrumentation

Subgroup IV: Instrument Operations and Quality Control

CT performance characteristics

• slice thickness

• CT number accuracy

• uniformity

• noise

• contrast resolution

• spatial resolution

CT daily QC procedures

• tube warm-up

• tomographic uniformity

• accuracy of the CT number of water

• image noise

CT tube warm-up definition

monitoring of tube output and detector response

tomographic uniformity definition

variation in Hounsfield Units in ROIs within a uniform phantom

image noise definition

measured as std deviation of the CT numbers in an ROI

CT monthly or quarterly QC procedures

• laser light alignment

• slice thickness, measures in mm

• spatial resolution (high-contrast resolution)

• CT number accuracy

• contrast (low-contrast resolution)

How is spatial resolution measured?

line pairs/cm

CT semiannual QC procedures

linearity of Hounsfield Unit values

CT annual QC procedures

radiation dose

CT radiation dose procedure

• measure phantoms with pencil ion chambers in different locations

• calculate CT dose index (CTDI)

CT ring artifacts are due to

non0functioning detector (should also be seen on topogram)

most CT artifacts are related to ___

the patient, acquisition parameters, and/or reconstruction technique