CT Acceptance Testing and Commissioning

CT acceptance testing and commissioning is the medical physicist's sign-off before a new scanner ever images a patient — the evaluation that confirms the delivered system meets its specifications and establishes the baselines the clinical program will run on. Acceptance answers one question: does the scanner meet the manufacturer's published performance and safety specifications? Commissioning answers a second: how should the scanner be used, and what reference values will routine quality control compare against?

A computed tomography (CT) scanner is a large capital purchase and a significant radiation source. Releasing one for clinical use without a documented acceptance evaluation leaves the facility unable to prove the system performs as specified, unable to establish defensible quality control baselines, and exposed at accreditation and inspection. This guide explains the governing standards in force, the phantom tests and tolerances a physicist checks, the CTDIvol dosimetry that anchors the dose side of the evaluation, and the documentation that makes the report defensible. DRPS performs this work as part of its CT physics testing and medical physicist consulting services.

Introduction

Acceptance testing and commissioning sit at the start of a scanner's clinical life, and the quality of that start propagates through every scan that follows. A protocol baseline set carelessly at commissioning becomes the reference every technologist trusts for years. A dose-display discrepancy missed at acceptance becomes a systematic error in every dose report. An image-quality baseline recorded without rigor leaves the routine quality control program with nothing meaningful to trend against.

The modern practice treats the installation as three distinct activities. Acceptance testing verifies the delivered unit against the vendor's specifications — the contractual question of whether the hospital received what it paid for. Commissioning determines how the system will actually be used: clinical protocol construction, image-quality and dose baselines, and the reference values for subsequent quality control. Routine quality control is the ongoing daily and periodic testing, performed mostly by technologists under physicist oversight, that watches for drift away from those baselines.¹

This arc is explicit in current professional guidance. AAPM Task Group 233 frames its methods so that CT performance can be approached "not only in terms of acceptance testing (i.e., verifying a device meets predefined specifications), but also system commissioning (i.e., determining how the system can be used most effectively in clinical practice)."¹²

Topic Explanation

What does a CT acceptance and commissioning evaluation cover?

A complete evaluation spans mechanical, safety, image-quality, and dose performance, each checked against a defined reference. The physicist does not simply run a phantom through the scanner; the evaluation is organized around the questions the facility must be able to answer later.

A typical scope includes:

Mechanical and geometric checks — table positioning and travel accuracy, localizer (scout) accuracy, gantry tilt, and alignment-light (laser) accuracy.
Radiation-beam checks — radiation beam width versus nominal, and beam/table increment accuracy.
Image-quality checks — CT number accuracy and linearity, image noise and uniformity, high-contrast (spatial) resolution, low-contrast detectability, and artifact evaluation.
Dose checks — CTDIvol measurement in standard phantoms, agreement with the console-displayed value, and verification of dose-reporting features.
Safety and functional checks — interlocks, dose-check notification and alert values, DICOM structured dose reporting, and reference-protocol availability.

The governing documents assign these to the qualified medical physicist. The ACR–AAPM Technical Standard for CT states that the performance of CT equipment must be evaluated on installation and monitored periodically.⁵ For background on the metrics that recur throughout this process, see our guides to CTDIvol and DLP dose metrics and CT image quality: MTF and low-contrast detectability.

Acceptance versus commissioning versus routine QC

The three activities use many of the same measurements but answer different questions, and conflating them is a common source of weak documentation.

Activity	Question it answers	Reference compared against	Who performs it
Acceptance testing	Does the scanner meet the vendor's specifications?	Manufacturer's published specifications	Qualified medical physicist
Commissioning	How will the scanner be used clinically?	Clinical needs; establishes the baselines	Qualified medical physicist
Routine QC	Has performance drifted from baseline?	Commissioning baselines and action limits	Technologist, under physicist oversight

The practical consequence is that the pass/fail criteria at acceptance come primarily from the manufacturer's specifications, supplemented by accreditation criteria and the test methods in IEC 61223-3-5. AAPM Report No. 233 deliberately provides no universal pass/fail table; it supplies the quantitative methods and leaves the limits to specifications and programs.¹²

Key Technical Principles

CT number accuracy, linearity, and uniformity

CT numbers are reported in Hounsfield units (HU), a scale defined so that water is 0 HU and air is −1000 HU. The scale is set by the linear attenuation coefficients of the material, water, and air:

HU = 1000 \times \frac{μ _{material} - μ _{water}}{μ _{water} - μ _{air}}

At acceptance, the physicist verifies that water reads close to 0 HU, that a set of known materials falls within expected HU windows (confirming linearity of the HU scale), and that the water value is uniform across the field of view. The ACR CT accreditation phantom program accepts a water CT number within approximately ±7 HU, requires each peripheral region of interest to fall within ±5 HU of the center value for uniformity, and specifies HU windows for reference materials such as acrylic, bone-equivalent material, polyethylene, and air.⁴ Many daily technologist checks use a tighter working action limit near 0 ± 5 HU, though the current ACR CT Quality Control Manual emphasizes trending the value over treating any single reading as pass/fail.³

High-contrast resolution, low-contrast detectability, and noise

Resolution and noise are the image-quality pair that defines whether the scanner can perform its clinical task.

High-contrast (spatial) resolution is characterized by the modulation transfer function (MTF) or, in accreditation practice, by resolving a line-pair or bar pattern. It is reconstruction-kernel dependent, so it is evaluated under defined conditions.
Low-contrast detectability describes the ability to distinguish a low-contrast object from its background; it is dose- and noise-dependent and is the harder of the two to specify.
Image noise is the standard deviation of CT numbers in a uniform region. At commissioning the physicist records the baseline noise for defined techniques; the ACR CT Quality Control Manual leaves the specific noise action limit to the qualified medical physicist rather than fixing a national number.³

AAPM Report No. 233 advances this further, describing task-transfer-function resolution, noise magnitude and texture, and task-based detectability measured under realistic reconstruction and automatic-exposure-control conditions — methods that are "more predictive of clinical performance than specification-based approaches."¹²

CTDIvol: the dose metric measured at acceptance

The computed tomography dose index (CTDI) is the foundation of CT dosimetry, and verifying it is a core part of acceptance. CTDI100 is measured with a 100 mm long pencil ionization chamber that integrates the dose profile from a single axial rotation, in standard polymethyl methacrylate (PMMA) phantoms: a 16 cm diameter "head" phantom and a 32 cm diameter "body" phantom.⁶

The weighted CTDI combines a central and a peripheral measurement to represent the average dose across the slice:

CTDI_{w} = \frac{1}{3} CTDI_{100, center} + \frac{2}{3} CTDI_{100, periphery}

Dividing by pitch gives the volume CTDI — the quantity displayed on the console and used in dose reports:

CTDI_{vol} = \frac{CTDI _{w}}{pitch}

and multiplying CTDIvol by the scan length gives the dose–length product:

DLP = CTDI_{vol} \times L (mGy cm)

Worked CTDIvol example

Suppose the physicist measures, with the 100 mm pencil chamber in the 32 cm body phantom, a central CTDI100 of 12 mGy and a peripheral CTDI100 of 24 mGy, for a scan performed at a pitch of 1.0.

The weighted CTDI is:

CTDI_{w} = \frac{1}{3} (12) + \frac{2}{3} (24) = 4 + 16 = 20 mGy

At a pitch of 1.0 the volume CTDI equals the weighted value:

CTDI_{vol} = \frac{20}{1.0} = 20 mGy

For a 25 cm scan length the dose–length product is:

DLP = 20 \times 25 = 500 mGy cm

The physicist then compares the measured 20 mGy against the CTDIvol the console reports for the same protocol. The displayed value is expected to agree with the measurement within the manufacturer's specified accuracy tolerance, commonly on the order of 20 percent, and IEC 60601-2-44 sets the dose-reporting accuracy requirements a modern scanner must meet.⁸ A persistent discrepancy larger than the specification is a finding: every downstream dose report inherits the console's value, so the display must be trustworthy. It is worth remembering that CTDI100 itself underestimates the equilibrium accumulated dose, particularly on the central axis of the body phantom, so CTDIvol is an index for comparison and management, not the patient's organ dose.⁶

Clinical Impact

The acceptance and commissioning evaluation shapes dose and image quality for the entire clinical life of the scanner, not just its first day. The protocols built at commissioning are the ones technologists use thousands of times. If the commissioning baselines are set with care — appropriate noise targets, correct reference CTDIvol values, verified automatic-exposure-control behavior — the routine quality control program has meaningful references to trend against and dose creep is caught early.

A disciplined commissioning also protects patients at the extremes. Pediatric protocols verified at commissioning prevent the single most consequential CT dose error, which is scanning a child on an adult technique. For the principles behind those protocols, see pediatric CT dose optimization and CT protocol optimization. Verifying the dose-check notification and alert values at acceptance, as described in our guide to CT dose check notifications and alerts, ensures the scanner warns the operator before an unusually high-dose scan rather than after.

The evaluation also matters at the facility level. Accreditation bodies require a physicist's evaluation, and payers increasingly tie reimbursement to accreditation. A scanner that fails its first accreditation phantom submission because acceptance was skipped costs the facility far more in delay and rework than the evaluation would have cost up front.

Practical Optimization Tips

A practical acceptance and commissioning project tends to follow the same sequence.

1. Review the purchase specification first

Before touching the scanner, obtain the manufacturer's performance specification for the exact configuration purchased. Acceptance is a comparison, and without the specification there is nothing to compare against. Confirm the tube, detector configuration, reconstruction options, and dose-management features match the contract.

2. Run mechanical and geometric checks before image quality

Table travel, localizer accuracy, and laser alignment are quick, and a problem found here explains downstream image-quality findings. Establish that geometry is correct before interpreting resolution or uniformity.

3. Measure dose in both standard phantoms

Measure CTDIvol in the 16 cm and 32 cm PMMA phantoms with a calibrated 100 mm pencil chamber, and compare against the console display for matched protocols. Document the chamber calibration traceability; see diagnostic dosimeter calibration and traceability.

4. Build and freeze commissioning baselines

Record noise, CT number, uniformity, and resolution baselines under the exact techniques routine quality control will repeat. These become the reference values the daily and annual program trends against — choose them deliberately.

5. Verify dose-management and safety functions

Confirm the dose-check notification and alert values, DICOM structured dose reporting, access controls, and reference protocols. These are standardized features under NEMA XR 29 and XR 25 and should be present and functional on a modern system.⁹¹⁰

Common pitfalls to avoid

Skipping the specification review and treating acceptance as generic QC — there is then no basis to accept or reject.
Setting commissioning baselines carelessly, leaving routine QC with meaningless references.
Measuring dose in only one phantom size and missing a discrepancy that appears only for head or only for body techniques.
Accepting the console CTDIvol without an independent measurement, so a systematic display error propagates to every dose report.
Treating a single CT-number reading as pass/fail rather than establishing a baseline and trending.
Leaving pediatric protocols for "later" instead of verifying them at commissioning.

Regulatory Considerations

CT equipment is regulated as a radiation-producing machine under state radiation-control programs, and its clinical use is governed by accreditation requirements — both of which expect a qualified medical physicist's evaluation. Unlike radioactive material, which falls under the U.S. Nuclear Regulatory Commission (NRC) or Agreement State programs, X-ray-producing equipment such as CT is regulated by the U.S. Food and Drug Administration at the manufacturing level and by state radiation-control authorities in use.

Key frameworks to reference at acceptance and commissioning:

ACR–AAPM Technical Standard for Diagnostic Medical Physics Performance Monitoring of CT Equipment — states that CT performance must be evaluated on installation and monitored periodically, and defines the qualified medical physicist's responsibilities.⁵
ACR CT Accreditation Program and ACR CT Quality Control Manual — provide the practical phantom tests, the continuous QC structure, and the tolerances many facilities adopt as their acceptance criteria.³⁴
AAPM Report No. 233 — the current performance-evaluation methodology for CT systems.¹²
IEC 61223-3-5 — the international standard for acceptance tests of CT imaging performance; IEC 60601-2-44 — basic safety and essential performance of CT, including dose-reporting accuracy.⁷⁸
NEMA XR 29 and XR 25 — standardized dose-management and dose-check features to be verified.⁹¹⁰

Across the states DRPS serves — Florida, Maryland, Virginia, Washington DC, California, Nevada, New York, Pennsylvania, New Jersey, and Delaware — the specific registration, inspection, and physicist-report requirements for CT equipment are set by each state's radiation-control program. A facility should confirm which rules and accreditation deadlines apply before scheduling acceptance. For the accreditation picture more broadly, see our guides to ACR accreditation physics requirements and the ACR CT accreditation phantom QC.

Frequently Asked Questions (FAQs)

What is CT acceptance testing?

CT acceptance testing is the formal evaluation a qualified medical physicist performs after a scanner is installed and before it is used on patients. It verifies that the delivered system meets the manufacturer's published performance and safety specifications, and it documents baseline values for image quality and dose that the routine quality control program will use going forward.

How is acceptance testing different from commissioning?

Acceptance testing asks whether the scanner meets the vendor's specifications. Commissioning asks how the scanner should be used in clinical practice: it establishes clinical protocols, image-quality and dose baselines, and the reference values against which daily and periodic quality control will be compared. Both happen before clinical use, and both are documented.

Who is qualified to perform CT acceptance testing?

A qualified medical physicist, typically a board-certified diagnostic medical physicist, performs or directly supervises CT acceptance testing. Many state regulations, accreditation programs, and equipment-purchase contracts require a physicist's acceptance report and certification before the scanner is released for clinical imaging.

What is the tolerance on the CT number of water?

The CT number of water is expected to be close to 0 HU. The ACR CT accreditation phantom program accepts a water CT number within approximately ±7 HU, and many daily technologist checks use a tighter working action limit near 0 ± 5 HU, with the current emphasis on trending the value rather than treating a single reading as pass or fail.

Does the console-displayed CTDIvol need to be verified at acceptance?

Yes. The physicist measures CTDIvol in standard 16 cm and 32 cm phantoms with a 100 mm pencil ionization chamber and compares the result against the value displayed on the console. The displayed dose is expected to agree with the measurement within the manufacturer's specified accuracy tolerance, commonly on the order of 20 percent, consistent with the dose-reporting accuracy requirements of IEC 60601-2-44.

What standards govern CT acceptance and commissioning?

The main U.S. references are AAPM Report No. 233 for performance-evaluation methods, the ACR CT Quality Control Manual and ACR CT Accreditation Program for practical tests and tolerances, and the ACR–AAPM Technical Standard for CT for the physicist's obligations. Internationally, IEC 61223-3-5 covers acceptance tests of CT imaging performance and IEC 60601-2-44 covers CT safety and dose reporting.

When should a scanner be re-evaluated after acceptance?

A full physicist evaluation is repeated at least annually and after any major service, tube replacement, software upgrade, or calibration change that could affect image quality or dose. Routine daily and periodic quality control, performed mostly by technologists against the commissioning baselines, runs continuously in between.

Key Takeaways

Acceptance and commissioning are distinct. Acceptance verifies the scanner against the manufacturer's specifications; commissioning establishes how it will be used and the baselines for routine quality control.
The physicist's sign-off comes before clinical use. A qualified medical physicist performs the evaluation and documents a report, which accreditation and many state programs require.
Pass/fail at acceptance comes from specifications. AAPM Report No. 233 provides methods, not a universal pass/fail table; limits come from manufacturer specifications, accreditation criteria, and IEC 61223-3-5 methods.
Verify the dose display. Measure CTDIvol in the 16 cm and 32 cm phantoms and confirm the console display agrees with the measurement within the manufacturer's specified tolerance, commonly about 20 percent.
Commissioning baselines are long-lived. Set them deliberately, because routine quality control trends against them for years.

Conclusion

CT acceptance testing and commissioning is not a formality to clear before the first patient — it is the moment that defines how a scanner will perform and how its dose will be managed for its entire clinical life. Acceptance establishes that the facility received a system meeting its specifications. Commissioning establishes how that system will be used and sets the references that routine quality control depends on. Done rigorously, with the manufacturer's specifications in hand, dose measured in both standard phantoms, and baselines chosen deliberately, the evaluation produces a defensible report, a scanner ready for accreditation, and a clinical program built on solid ground.

How DRPS Can Help

Diagnostic Radiation Physics Services performs CT acceptance testing and commissioning for hospitals and imaging centers, including full image-quality and dose evaluation, console-display verification, protocol and baseline commissioning, and the physicist certification report required before clinical use. Our board-certified medical physicists also support CT physics testing, accreditation preparation, and ongoing medical physicist consulting.

DRPS serves facilities across our service locations, including Florida, Maryland, Virginia, Washington DC, California, Nevada, New York, Pennsylvania, New Jersey, and Delaware. A strong acceptance program is not about passing one phantom test — it is about starting the scanner's clinical life with trustworthy dose and image quality.

Related Resources

References

Samei E, Bakalyar D, Boedeker KL, et al. Performance evaluation of computed tomography systems: Summary of AAPM Task Group 233. Medical Physics. 2019;46(11):e735-e756. doi:10.1002/mp.13763. PubMed
American Association of Physicists in Medicine. Performance Evaluation of Computed Tomography Systems. AAPM Report No. 233 (Task Group 233); 2019. aapm.org
American College of Radiology. ACR Computed Tomography Quality Control Manual. 2017. acr.org
American College of Radiology. CT Accreditation Program: Phantom Testing Instructions. Revised 2022. accreditationsupport.acr.org
American College of Radiology and American Association of Physicists in Medicine. ACR–AAPM Technical Standard for Diagnostic Medical Physics Performance Monitoring of Computed Tomography (CT) Equipment. Revised 2022. acr.org
American Association of Physicists in Medicine. The Measurement, Reporting, and Management of Radiation Dose in CT. AAPM Report No. 96 (Task Group 23); 2008. aapm.org
International Electrotechnical Commission. Evaluation and routine testing in medical imaging departments – Part 3-5: Acceptance and constancy tests – Imaging performance of computed tomography X-ray equipment. IEC 61223-3-5:2019. iec.ch
International Electrotechnical Commission. Medical electrical equipment – Part 2-44: Particular requirements for the basic safety and essential performance of X-ray equipment for computed tomography. IEC 60601-2-44:2009 (with Amendments 1 and 2). iec.ch
National Electrical Manufacturers Association. Standard Attributes on CT Equipment Related to Dose Optimization and Management. NEMA XR 29-2013. nema.org
National Electrical Manufacturers Association. Computed Tomography Dose Check. NEMA XR 25-2019. nema.org