CT Scan Parameters: Translation of Terms for Different Manufacturers

AAPM CT Lexicon version 1.1 08/31/2011

Table of Contents

Scan acquisition and user interface basics

Dose modulation and reduction tools

Multi-Slice Detector Geometry

Image Reconstruction and Display

Contrast Media Tools

Multi-planar formats and 3-D Processing

Service and Application Tools

Workflow

CT scan parameters: Translation of terms for different manufacturers

Introduction For the CT technologist who operates multiple scanner models, perhaps from multiple manufacturers, the variability in names for important scan acquisition and reconstruction parameters can lead to confusion, reduced comfort and an increased potential for error. The intent of this CT terminology lexicon is to allow users to translate important CT acquisition and reconstruction terms between different manufacturers' systems.

This represents a first step in the terminology standardization effort undertaken by this working group. Phase 2 of our work will:

1. Identify relevant terms from established standard lexicons (e.g. RadLex and DICOM) and other relevant literature and publish an expanded lexicon including these terms. 2. Form consensus recommendations on preferred terms.

This website will be updated as the terminology standardization work progresses.

The generic descriptions or terms in the first column are intended to orient the user to the relevant concepts; they are not consensus "preferred terms." The generic descriptions are not based on any single existing or pending terminology standard; however the references cited below were consulted in developing the generic descriptions. Future efforts of this Working Group include making recommendations for standardized terminology.

A number of individuals and groups have advocated for terminology standardization in CT, including at a March 30-31, 2010 FDA public meeting entitled "Device Improvements to Reduce Unnecessary Radiation Exposure from Medical Imaging" (transcripts available at: http://www.fda.gov/downloads/MedicalDevices/NewsEvents/WorkshopsConferences/UCM210149.pdf; see p. 153-155). Participants proposed a cooperative effort among professional organizations (AAPM, ASRT, ACR, etc.), industry, FDA, and standards organizations to accomplish this task, as is now being undertaken by this Working Group.

References IEC 60601-2-44 ed3.0 (2009-02) Medical electrical equipment – Part 2-44: Particular requirements for the basic safety and essential performance of X-ray equipment for computed tomography.

Kalra, M. K. and S. Saini. 2006. Standardized nomenclature and description of CT scanning techniques. Radiology 241, 657-660.

National Electrical Manufacturer's Organization. 2009. Digital Imaging and Communications in Medicine (DICOM). (Downloadable from: ftp://medical.nema.org/medical/dicom/2009/)

RadLex Tree Browser (http://radlex.org/)

Weber, N. M., C. L. Siegle, J. E. Miller, M. K. Hudson, J. M. Kofler, M. R. Bruesewitz, and C. H. McCollough. How to be a "multi-lingual" CT technologist: understanding scan parameters from different manufacturer's equipment. 2004 RSNA Annual Meeting poster (http://mayoresearch.mayo.edu/mayo/research/ctcic/upload/rsna2004-how-to-be-multilingual.pdf).

Weigold, W.G., et al. 2011. Standardized Medical Terminology for Cardiac Computed Tomography: A Report of the Society of Cardiovascular Computed Tomography. Journal of Cardiovascular Computed Tomography (downloadable from: http://www.scct.org/documents/JCCT427.pdf).

AAPM Working Group on Standardization of CT Nomenclature and Protocols

Members: Additional contributors:

AAPM: Cynthia McCollough (Chair) AAPM: Lifeng Yu Dianna Cody (Co-chair) Dustin Gress GE: Karen Procknow James Kofler Michael McNitt-Gray Hitachi: Catherine Neumann Robert Pizzutiello Neusoft: Keith Mildenberger ACR: Mark Armstrong Theresa Branham MITA: Stephen Vastagh Priscilla Butler RadLex: Daniel Rubin ASRT: Virginia Lester

DICOM: David Clunie Kevin O'Donnell

FDA: Thalia Mills

MITA: Gail Rodriguez

GE: John Jaeckle

Hitachi: Mark Silverman

Philips: Mark Olszewski

Siemens: Christianne Leidecker

Toshiba: Richard Mather

1. Scan acquisition and user interface basics Generic description GE PHILIPS SIEMENS TOSHIBA HITACHI NEUSOFT

The portion of the user interface where scans are Exam Rx Scan Procedure Examination eXam Plan Scan Scan Procedure (Neuviz 16); prescribed Protocol Main Scan Interface (Neuviz DUAL)

Other portions of the user interface, such as Desktop Active viewer Various “task cards”, Active display Image Image Display Area (Neuviz were reconstructed images are viewed such as “Viewing” Viewer 16); Viewer (Neuviz DUAL) CT localizer radiograph (i.e. the scanned Scout Surview Topogram Scanogram Scanogram Surview projection radiograph, often acquired by the CT system to allow the user to prescribe the start and end locations of the scan range)

Axial scan mode: Data acquisition while the Axial Axial Sequence Scan & View, Scan Normal Axial patient table remains stationary; the table position & Scan, Volume, may be incremented between x-ray exposures to Wide Volume collect data over a longer z axis range. (Aquilion One)

Helical or Spiral scan mode: Data acquisition Helical Helical Spiral Helical Volume Helical while the patient table is continuously moving along the z axis. Dynamic scan mode - single detector width: Cine or zero CCT Dynamic (continuous) Dynamic Dynamic CCT (Neuviz 16); Data acquisition at multiple time points over the interval Axial (Continuous CT) or Serio (intermittent); (Continuous or N/A (Neuviz DUAL) same anatomic location(s) while the patient table scan mode name: Intermittent) remains stationary; x-ray exposure can be DynMulti or DynSerio. continuous or intermittent

Dynamic scan mode - multiple detector Shuttle Jog Adaptive 4D Spiral; N/A N/A N/A widths: Data acquisition at multiple time points scan mode name: over the same anatomic location(s) while the DynMulti4D or patient table cycles back and forth between DynSerio4D (ECG designated start and end locations in order image triggered) a region wider than the detector

Interventional CT - Intermittent x-ray SmartStep Single CCT Model dependent: CT Fluoro (CTF) guideShot Single CCT (Neuviz 16); exposures Biopsy or Intervention N/A (Neuviz DUAL) (i-Sequence/i-Spiral) Interventional CT - Continuous x-ray SmartView Continuous CCT Model dependent: CT Fluoro (CTF) Not available Continuous CCT (Neuviz 16); exposures CARE Vision or N/A (Neuviz DUAL) Intervention (i-Fluoro)

Table increment (mm) per 360 degree rotation of Interval Increment (mm) Feed (mm) Couch movement Table Feed Increment (mm) the x-ray tube (axial scan mode) (mm) (mm)

Scan acquisition and user interface basics, continued Generic description GE PHILIPS SIEMENS TOSHIBA HITACHI NEUSOFT

Table feed per 360 degree rotation of the x-ray Speed Table speed Table Feed (mm/rot)* Couch speed Table Speed Table speed (mm/rot) tube (helical scan mode) (mm/rot) (mm/rot) (mm/Rot) (mm/rot)

Acquisition field of view: Diameter of the Scan Field of Not determined Not determined by CFOV (Calibrated Scan Field of FOV circular region within the scan plane over which View (SFOV, by tech; built into tech; built into Field of View) View (SFOV, projection data are collected. Nominally equal to cm) protocol protocol mm) the diameter of the primary beam at isocenter in the axial plane.

Tube current: Number of electrons accelerated mA mA* mA* mA mA mA* across an x-ray tube per unit time, expressed in units of milliampere (mA)

Tube current-time product: The product of tube Not used on mAs mAs mAs Not used on mAs current and exposure time per rotation, expressed this system this system in units of milliampere • seconds (mAs). In axial scan mode, this is equal to tube current × (scan angle ÷ 360) × rotation time. In helical scan mode, this is equal to tube current × rotation time.

Effective tube current-time product: In helical Not used on mAs per slice (= Effective mAs (= Effective mAs (= Not used on mAs per slice=(mAs/pitch) scan mode, this is the product of tube current and this system mAs/pitch) mAs/pitch) mAs/pitch) this system rotation time (expressed in units of milliampere • seconds (mAs) ÷ pitch)

Tube potential: The electric potential applied kV kVp kV kV kVp KV across an x-ray tube to accelerate electrons towards a target material, expressed in units of kilovolts (kV)

Pitch: Unitless parameter used to describe the Pitch Pitch Pitch CT Pitch Factor Pitch pitch table travel during helical CT; equal to table travel (mm) per gantry rotation ÷ total nominal beam width (mm)

Automated patient instructions AutoVoice Auto voice API (Automated Breath Control Auto Voice Auto voice Patient Instructions)

* Not able to be directly modified on the user interface. Value is calculated/determined by other settings.

2. Dose modulation and reduction tools Generic description GE PHILIPS SIEMENS TOSHIBA HITACHI NEUSOFT

Automatic exposure control Available in Available in Available in CARE Dose4D Available in SURE Available in DoseRight, ACS (AEC): A scanner feature that AutomA and DoseRight Exposure IntelliEC (automatic current automatically adapts the x-ray SmartmA Automatic Current selection) [Neuviz 16]; tube current to the overall Selection (ACS) DoseSave, ACS patient size to achieve a (automatic current specified level of image quality selection) [Neuviz DUAL]

Angular tube current SmartScan (CT/i D-DOM (Dose CARE Dose not available as a Adaptive mA D-DOM (Neuviz 16); modulation only) Modulation) separate item N/A (Neuviz DUAL)

Longitudinal tube current AutomA Z-DOM not available as a separate item SURE Exposure n/a Z-DOM (Neuviz 16); modulation N/A (Neuviz DUAL)

Angular and longitudinal tube SmartmA (x, y, Work in progress CARE Dose4D SURE Exposure IntelliEC ACS+DOM (Neuviz 16); current modulation z) 3D (X, Y and Z N/A (Neuviz DUAL) Modulation)

ECG-based tube current ECG Modulated DoseRight All features available in ECG Modulation ECG Dose N/A modulation mA Cardiac HeartView package (except (3), Modulation only available for SOMATOM Definition Flash) (1) Retrospective gated spiral mode: use “Pulsing” settings in Trigger card

(2) Prospective triggered sequence: use “Adaptive Cardio Seq.” and “Pulsing” settings in Trigger card.

(3) Prospectively triggered spiral (“Flash” mode)

Image quality reference Noise Index Reference image Quality reference mAs Standard Standard reference image parameter for AEC Deviation or Deviation (% ) or standard, low- standard, low- dose, or high- dose, or high- quality quality

3. Multi-Slice Detector Geometry

Generic description GE PHILIPS SIEMENS TOSHIBA HITACHI NEUSOFT

Fixed Model dependent: Model dependent: Fixed (32 row and Asymmetric-16 slice; Asymmetric (Neuviz Multi-slice detector array Fixed or Asymmetric Adaptive or Fixed above); Fixed-64 slice 16); design Adaptive (16 row and Fixed (Neuviz DUAL) below)

Detector Collimation N x T Detector Configuration Detector Detector Collimation N x T (mm) Detector configuration Configuration (mm) or Aqu (Acquisition) on Configuration Configuration Exam Card

4. Image Reconstruction and Display Generic description GE PHILIPS SIEMENS TOSHIBA HITACHI NEUSOFT

Window width: Range of CT numbers Window Width Window Width Window width Window width Window Width Window Width (Neuviz 16); (maximum - minimum) that are distributed WW Window Width (Neuviz over the viewable grey scale of the display DUAL) device or film

Window center: The CT number in the Window Level Window Center Window center Window level Window Level Window Center (Neuviz 16); center of the viewable grey scale WL Window Level (Neuviz DUAL)

Reconstruction field of view: Width of Display Field DFOV (mm) FoV (mm) DFOV (mm) DFOV (mm) FOV (mm) (Neuviz 16); the square region mapped to the of View Rec FOV (Neuviz DUAL) reconstructed image matrix (DFOV) (cm)

Prescribing the reconstruction parameters Prospective Recon and Recon Job Prospective Multi Recon Axial or helical reconstruction prior to scan acquisition recon Additional recon Recons

Prescribing the reconstruction parameters Retrospective Offline Recon Recon Job Retrospective Post Offline reconstruction (Neuviz after scan acquisition recon or Re-Recon or Raw data Reconstruction 16); recon Image Reconstruction (Neuviz DUAL) Reconstruction property that determines Algorithm Reconstruction Kernel Filter Image Filter Reconstruction filter (Neuviz sharpness or smoothness of image in the Filter convolution 16); axial plane (FC) Recon Filter (Neuviz DUAL)

Helical interpolation options to achieve a Full (narrower) Slice width Slice width Slice width Slice width Slice width independent of wider or narrower section sensitivity profile or Plus (wider) independent of independent of pitch independent independent of pitch (Neuviz 16); mode pitch of pitch pitch Thickness (Neuviz DUAL)

Nominal width of reconstructed image Thickness Thickness Slice (mm) Image Slice Thickness Thickness along the z axis (mm) (mm) thickness Distance between two consecutive Interval Increment Position increment Reconstructio Interval Increment reconstructed images n interval

Fast but lower-quality reconstructed QC Image Evolving RT (Real-time SUREScan Real Time Evolving mode (Neuviz 16); images for rapid review of entire exam Image Check reconstructions reconstruction) Reconstruction N/A (Neuviz DUAL)

Off-center reconstruction coordinates are RL Center; Center x, Center x, Center y Center Center x, y Center x, center y called AP Center center y Position; (Vari Area)

Image Reconstruction and Display, continued Generic description GE PHILIPS SIEMENS TOSHIBA HITACHI NEUSOFT

Flip or rotate the image orientation is Flip/rotate Flip/rotate Mirroring (Flip in Rotate/Mirror Flip/Rotate Flip/rotate called Viewing card); Rotate

Image modifications to alter sharpness or Image Filters Image Evaluation > Image Filter, QDS Filter IMAGE ENHANCE FILTER smoothness (done in image space without enhancement Manipulation (Viewing (Neuviz 16); reconstructing images) filter card) DISPLAY MODE (Neuviz DUAL)

5. Contrast Media Tools Generic description GE PHILIPS SIEMENS TOSHIBA HITACHI NEUSOFT

Bolus tracking: Scanner feature to automatically Smart Prep Bolus Tracking CARE Bolus SUREStart Predict Bolus Tracking initiate a prescribed axial, helical or dynamic scan (includes Test Scan when a threshold level of contrast enhancement is Bolus and Bolus reached at a specified region of interest Tracking)

Test Bolus: Scan mode used to measure the Take axial scans at Time Lapse Test Bolus Dynamic study Not TIBT (Neuviz 16); contrast transit time using a small injection of zero table feed and available Tracking layer contrast media process with MIROI (Neuviz DUAL)

Time-attenuation curve (TAC): Graph of the Smart Prep graph or Time Lapse graph Enhancement Time Density Curve Monitoring Time Lapse Graph contrast enhancement versus time MIROI graph Curve Graph

Threshold: CT number (HU) where bolus Transition ROI Threshold Level Threshold ROI (HU) Threshold Threshold tracking tool will trigger the system to begin the Threshold scan

Scanner feature used to quantitatively evaluate MIROI (multiple Tracker ROI Tools DynEva Real Time No special N/A the TAC image region of (dynamic Monitoring name interest) evaluation)

Monitoring delay: Time from injection to the start Monitoring Delay Post Injection Delay (on Delay (on Scan Delay (PIT) Post Injection of monitoring scans (Time 1 in figure below) Delay monitoring scan) SUREStart) Time

Monitoring interval: Time between consecutive Monitor ISD Cycle time Cycle time Real time monitoring Monitoring Cycle time (Neuviz monitoring scans to (Time 2 in figure below) (InterScan Delay) or pulsed monitoring Time 16); Bolus Timing (seconds) (Neuviz DUAL)

Scan delay: Time from when threshold is Diagnostic delay Post Threshold Delay (on scan) Delay (on helical) Scan Delay (PTD) Post reached and prescribed axial, helical or dynamic Delay Threshold Delay scan begins (Time 3 in figure below)

6. Multi-planar formats and 3-D Processing Generic description GE PHILIPS SIEMENS TOSHIBA HITACHI NEUSOFT

Reformatted image at an oblique Oblique reformat Oblique Oblique Oblique Oblique MPR oblique/curved plane (not an axial, coronal, or surface sagittal)

Saving images at various viewing Batch Loop Cine Radial Ranges Key Frame Movie Multi-Slice /Angle Cine angles about a volume or surface rendered object

Saving images at various planes Batch Reformat Batch MPR Parallel Ranges Batch MPR Multi planar reformat batch MPR through a volume

Surface-rendered object 3D SSD 3D (Shaded Shaded Surface ShadedVol Shaded Surface SSD (Shaded Surface Display – Display (SSD) (Shaded volume Display (SSD) surface display) 3D) rendering (SVR))

Volume-rendered object Volume Rendered Volume Rendering Volume Rendering Shaded Vol Volume Rendering Volume Rendering image (VR) Technique (VRT) (VR)

7. Service and Application Tools Generic description GE PHILIPS SIEMENS TOSHIBA HITACHI NEUSOFT

X-ray tube warm up Tube Warm-up Tube conditioning Check-up (calibrate and Warm up Warm up tube warm up (tube warm up) check values);

Calibrate (part of Check- up, can be performed separately)

Daily calibrations Fast Cals Not necessary to do Quality Daily Selectable air Air cals built into not required daily, (done in daily prep) daily calibrations calibrations can be Warm up recommend air scheduled after warm- calibration weekly up

Application information Learning Solutions On-line Help On-line Help; CT Life E-Learning Center Sentinel (Remote On-line Help or User Manual (task card) Service)

Application support Insite or Ilinq Customer Care Uptime In Touch Center CT Applications Applications Specialist assistance Solutions Center Helpline or Field Service Engineer

8. Workflow Generic description GE PHILIPS SIEMENS TOSHIBA HITACHI NEUSOFT

Scheduled (but not yet Patient Schedule Scheduled (HIS- Patient Browser – Modality Worklist MWM-modality Schedule scanned) patient list is called RIS) and Catalog- Scheduler Manager worklist (manual list) management

Already scanned patient list is List/Select Archive Manager Patient Browser – Directory Patient List Archive Manager (Neuviz 16); called Local Database Archive Management Interface (Neuviz DUAL)

User comments or text added User annotation Label (series) and Comment Annotation Comment N/A to an image is called Annotate (image)

Filming tools are called Auto/manual film Filming Film Sheet on Filming Filming Filming Filming composer task card

Data page summarizing scan Exam Text Page Image Parameters Patient Protocol Summary and Text Page Information Display Bar on the parameters, CTDIvol and or Series Text (series number 501) Exposure Record right hand side of the Main Scan DLP Page Interface & Dose Info series in Image Information List and Dose report at last series

Sorting patient list Sort Click on sort field In Patient Browser: Click on sort field Click on sort field Select field to sort by (name, (name, date, etc.) select “Sort” or “Filter” (name, date, etc.) (name, date, etc.) partient ID, etc.) and left click functions in menu bar with mouse to sort.