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CT – CT Phantom

Object with known densities and structures

Checks image quality, contrast, resolution, slice thickness, and uniformity

MRI – ACR MRI Phantom

Gel phantom with defined structures

Tests image uniformity, signal-to-noise ratio (SNR), and geometric distortion

Ultrasound – Tissue-mimicking Phantom

Gel phantom with embedded features

Evaluates depth penetration, resolution, and image accuracy

Nuclear Medicine – Uniformity/Line Source Phantom

Phantom with radioactive solution or line source

Assesses gamma camera uniformity, spatial resolution, and energy calibration

Mammography – Mammography Phantom

Phantom with simulated microcalcifications, fibers, and masses

Tests low-contrast detectability, spatial resolution, and image quality

DXA – Spine Phantom

Phantom simulating bone density

Checks accuracy and precision of bone mineral density measurements

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Ultrasound

It is said that most problems in US can be identified by the simple daily QC tasks of visually inspecting the equipment. This includes the transducers, console, cables and screen etc.

The transducers are checked each time they are used for crystal drop out and if any is suspected then they will perform a more detailed test (using a paperclip).

The air filter is cleaned weekly as well. In my department I feel invested in this because as a HCA, I took it upon myself to clean it every week and felt the responsibility of helping to keep the machine in working order.

MRI QC

In MRI they run a PIQT on each scanner once a week. This is a specific Philips model phantom. It is used to check for signal to noise ratio, uniformity, image distortion. Much of the rest of MRI's QC is undertaken by the physicists because results get put into graphs that the radiographers have not been trained to interpret. It is hoped that this will change in the future.

Daily QC checks include checking the call bell and visual inspection of the coils for any damage or signal loss.

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Ultrasound- drop out test is used to check out for a failing probe. looking for areas where signal may be distorted or missing. performed by putting some ultrasound gel on the transducer and running a paperclip down the longitudinal surface keeping it perpendicular. a drop out will appear as an well defined vertical line or an part of the image where the signal is lost.

CT- every morning a QA is done with a phantom to check the quality of the hounsfield units. this phantom is made of air, water, calcium cartbonate, metal components, iodine, polymethacrylate and polyethylene or other alternatives to represent different densities found within the body.

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CT Phantom: A specialised device, often made of materials mimicking human tissue, used to test image quality, contrast resolution, and alignment. It helps assess the scanner’s accuracy and consistency.

Linearity Phantom: Tests the CT scanner’s ability to accurately display different densities, ensuring proper calibration and reliable diagnostic results.

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Mammo QA (daily): Check 2-D and 3-D standard bucky. Use 50mm Perspex  between the detector and the paddle to check the machine is measuring the compression as 50mm. Check the kV given (should be 29kV in our case for this test), check the mA (40-90 limit), and check signal to noise ratio (SNR) (50 minimum). Also check the filter that is automatically put on (should be rhodium).

DEXA QA: Every morning a QA test is undertaken on the machine with a spine phantom. This checks that the bone mineral density readings are accurate, tests the movement of the machine, and tests the consistency of radiation dose given out by the machine. These tests help prevent the need for repeat scanning on patients due to Machine faults. There is very little other QA undertaken by the operator.

Ultrasound QA:

Multi-daily:

-       Clean gel/body fluids off scanner, transducers, and cables after each patient

-       Ensure safe storage of probes not in use

-       Ensure transducer cables are properly stowed with no risk of being run over by scanner wheels

Daily:

-       Clean monitors of dust, gel, etc.

-       Check correct operation of main scanner controls

-       Inspect transducers during the session for damage

-       Check that video monitor brightness and contrast controls have been appropriately adjusted

-       Check the greyscale bar is fully displayed

-       Check grey levels on the ultrasound system monitor is matched by the grey level on PACS

Weekly:

-       Inspect switches, knobs and other controls for damage

-       Inspect all cables for damage

-       Inspect ultrasound system for damage such as cracks and dents

-       Test of brakes and wheel function

-       Element/crystal dropout test

-       Check/clean air filters of dust and fluff

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CT Geometric Accuracy test:

Tests the alignment and accuracy of the CT scanner in terms of patient positioning. For example, it checks whether the scanner can accurately represent the dimensions of the phantom’s internal structures (e.g., for size and shape).The phantom has markers known as reference points that are used to check the alignment of the scanner’s axis. Misalignment could lead to errors in measurements of internal structures, affecting the reliability of scans for clinical use, especially in procedures like radiation therapy planning.

US probe, drop out test:

used to evaluate the performance and integrity of the ultrasound transducer and its associated equipment. This test specifically looks for areas of signal loss or inconsistent data during the scanning process, which could indicate a malfunction or degradation of the transducer element. A “drop-out” refers to areas where the image fails to produce a clear, continuous signal, resulting in gaps or dark spots in the ultrasound image.

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U/S - Daily visual checks of transducer, cables and monitors are performed to ensure that equipment is functioning correctly, the transducer is also checked by the sonographer with gel by running a finger across the transducer to ensure there is no dropout of the crystals.

Nuclear Medicine - Daily QA testing of the gamma camera is performed using a cobalt 57 flood source, the flood is placed between the two detectors and the QA program runs to check for uniformity across the detectors  to ensure that image quality is maintained and there is not an issue with one of the photomultipliers.

CT - QA testing using a water phantom is performed on a weekly basis, the program checks for cross-field uniformity and accuracy of hounsfield units of the various regions of interest which would be seen on patients anatomy, i.e air, water, bone, fat and soft tissue.

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Everyday a QA is done in CT to check the quality and contrast of the Hounsfield units. This is done to ensure the quality of the image is maintained. A phantom has different densities that relate to the different Hounsfield units that must be in the range of the contrast scale. If this fails an engineer must be called before further use to rectify the problem.

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Daily QA check: Hounsfield units are measured to check that they are within a certain range. Each circle that appears on the CT console represents a different number related to the Hounsfield unit. Each circle on the QA image must be within each of the tolerance levels otherwise it will automatically fail.

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This is performed monthly with usually the same radiographers.
A phantom is used with various materials of different densities - measuring plastic, water etc. These numbers are measured against the baseline.
Contrast SCALE
Measuring contrast resolution - baseline of 108-132Hu
Recording the mean for plastic and water and the standard deviation for the water.
High contrast resolution
Measuring the standard deviation of line pairs - contrast resolution with a baseline between 33-41
Low contrast detectability (LCD)
Measuring average contrast Hounsfield units
Noise test
Measuring uniformity, the mean and standard deviation for noise. This is to look at the image, uniformity, same densities displayed and no ring artefacts (usually if present they are on the outer edges)

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Daily QC involves checking penetration by placing two blocks of perspex one on top of another, with one containing aluminium. The compression paddle is brought down to a pressure of 50 Newtons.
There are also daily monitor checks in the control room and in the reporting room as well as daily detector temperature checks.
The biopsy equipment is also checked daily for the accuracy of the machine in positioning the biopsy needle.
All these tests are recorded in a spreadsheet designed by medical physics to flag up any problems.
There are more QC checks performed weekly, monthly and quarterly by medical physics.

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Radiographer QA - With Radiographer QA, there are two parts to it. These are system check-up and quality check.

System check is when we check the detector, and this warms the x – ray tube. This is done every 24 hours if the system is in constant use. If the system is idle for more than 2 hours, then we have to do this before we start scanning. This is because the x – ray tube would have got cold, and this impacts the image quality. If we do not do this, then and still use the scanner then it can stress the x – ray tube out.

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Major MRI vendors offer software packages that perform automated daily quality assurance measurements using their own phantoms. Usually phantoms are filled up with the water in order to check radiofrequency. Also, there are daily visual checks involved, like helium, water or temperature checks and recorded on checklist.

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CT: - Daily checks are conducted on the equipment to ensure the safety of both patient and operator is maintained. They also ensure that image quality is maintained to a satisfactory standard for diagnostic reporting.
Tube warmups: - Performed daily by radiographers to ensure the longevity and efficiency of the equipment.
Air calibration: - Performed daily and weekly to ensure uniformity and ensure no mechanical artefacts are present.
Consistency Checks: - Performed weekly by department engineers using the phantom, this ensures the CT number/Hounsfield units are within limits set out by IPEM.

Ultrasound: - Daily checks such as visual inspections of wires and transducers are performed by the sonographers. These ensure the equipment is in safe and satisfactory working order before the list starts. The transducer is also checked using a little gel and the sonographer’s finger to ensure no crystal dropout has occurred causing artefact on an image. The rollerball on the console is also checked and cleaned to ensure a smooth working list and workflow.

MRI: - Daily visual checks are performed to ensure helium levels, water pressure, temperature and cleanliness is maintained within the scanner and plant rooms. Checks to ensure signal, signal to noise ratio, and uniformity are conducted using a phantom with these ensuring no artefacts are present and they are within the manufacturers safe working limits.

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In RNI, they perform a daily QA using cobalt 57. The flood used in our department is 3 years old and took about 50 minutes to complete.  It is placed between the gamma cameras. The half life of colbalt 57 is around 5-6 years. The QA looks for uniformity. The software can detect a gap which may suggest their could be a problem with the photo-multipliers. If a problem was detected, no scanning would happen until the problem had been repaired.

I also observed a weekly QA on the sentinel node probes which are used in theatre,s. A sealed sourced was used and referred to as 'the spot'. This sealed source was used in thyroid scans. Background noise is checked first and followed by 5 tests and readings are recorded. These are recorded in Excel and the probes are returned back to theaters.
All sealed sources are locked away and logged in and out to keep track of where they are.

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CT do a daily QA which uses a phantom made up of different densities inside. The materials are made up of different numbers that are related to the hounsfield unit numbers. The numbers detected are measured against the baseline numbers set. If any fail then our engineers are called to rectify the problem.

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US QA - Daily visual checks on the machine and cables. Ensure no damage to the transducers and the tracker ball. A check on a blank image can be done to check there are no pixel drop outs.

RNI QA - Using a cobalt 57, propped up in-between the gamma cameras, an image quality test can be carried out to check uniformity. if a 'gap' was noticed, this would suggest there was a problem with one of the photomultipliers. This test is done at the start of the day to detect any problems which could affect image quality.

CT QA - CT number uniformity and noise is tested using a phantom containing properties which have different HU (Hounsfield units) mimicking patients anatomy e.g. bone, soft tissues and air. The phantom is place on the table and centred vertically and horizontally. Once a scout image has been performed, on the reconstructed images, the ROIs (range of interest) can be selected in the centre of the different properties in the phantom and the standard deviation is recorded. the purpose of this test is to check uniformity of CT image.

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CT QC has a number of different tests carried out to ensure that the equipment is working correctly, and image quality and safety is maintained.

The tests carried out are:

Short Tube Conditioning (warm up) – carried out daily.

·        CT Number (housefield units)

·        Uniformity

·        Noise

·        Low contrast

Long Tube Conditioning (warm up) – N/A for general checks. Carried out by engineers for advance QC checks.

Air Calibration – carried out once weekly.

·        Scanning air (no phantoms used)

·        Calibrating machine to air

·        Checking uniformity (artefact)

Consistency test – carried out once weekly. (Head and body phantoms used)

·        Checks slice width

·        Checks spatial resolution

IQ Check – carried out every two weeks. (Head and body phantoms used)

·        Measures image quality

All QC checks are automated by the system, providing measurements and also tells the user if the system has passed or failed. This information should be noted on weekly checklists which are located in the CT control rooms.

If a system has measurements outside the reference values, or the system tells you that it has failed then the QC must be repeated. The positioning of the phantom has to be correct and is very sensitive to errors of positioning, and protocol choice is correct before proceeding for a second time.

If on repeating the scan the measurements have failed again this must be reported to the manufacturers and seek advice. All relevant information must be documented in the fault record folder and passed onto all staff members. Engineers can dial into the system remotely to assist with the faults.

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In our department, the QA is performed on a monthly basis.
The checks include:
- Visual inspection of the equipment; to check for any cracks, obstructions (of filters), frayed electrical cables etc. (this is also performed on a daily basis when using the equipment)
- Crystal Dropout; to check for any loss of elements which would indicate element drop out, which is likely to be clinically significant. This is performed by running a paperclip over the transducer and looking for any drop out
- Air Reverberation Test; Which tests for the uniformity and sensitivity
- Electric Noise Assessment; this assesses the noise on the images produced.

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In US there are daily QAs performed to check that equipment is working properlly. Visual checks are done on machines and transducer to check for damage. Also the transducer is checked by using a small amount of gel, for any damage to piezoelectric crystals layer, which will mean a drop in sound, innadequate penetration.
In RNI QAs are done daily as well. Calibrators are checked by using Radium 226 for accurate dose measure. This is checked against a criteria which includes accuracy, linearity, repeatability, background. Isolator room pressure in radiopharmacy checks are done daily to make sure there is a sterile environment.

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Monthly QA is performed and involves basic image evaluation. 3 tests are performed, the first is a visual assessment of the image on the screen using a small amount of gel looking for loss of contact etc, the second is a measurement of reverberation, and the third involves running a paperclip across the transducer again to check for drop-out. The actual equipment is also assessed for defects such as damage to the cables etc.

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Use of an image quality phantom to perform QA tasks on a daily/weekly basis depending on the scanner. Results must be uploaded onto a QA data record sheet. QA is performed to assess the following : Contrast scale, high contrast resolution, low contrast detectability, noise and uniformity, alignment light accuracy and includes a radiation protection checklist for CT.

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Daily flood test - a panel of radioactive source (in this instance cobalt -Co57) is used to flood the camera with radiation to check crystal efficiency. The radioactive panel is stored in the department for around 2 years and the longer you have it, the longer the QA test takes as the radioactive source decays over time and therefore gets weaker (producing less counts).

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a daily check is that there is no drop out of pixels when scanning, as this would indicate a damaged transducer.

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they use standardised settings and check a blank image for drop out. this would show as a black line cutting through the white horizontal lines. this can show an issue with the probes. Our department do this weekly

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They do daily tests checking AEC exposures and image quality e.g. dead pixels or artefacts, SNR and CNR. they do this using Perspex blocks and an aluminium square as a ROI. Also daily SMPTE test patterns for the quality of the viewing screens.
Weekly - calibration of the detectors and detector uniformity. Again a large clear perspex block is used for this checking for dead pixels, ghost image or incorrect calibration, artefacts. They also have a TORMAM phantom which checks image contrast and spatial resolution.
Monthly - safety checks e.g. that emergency stop buttons work, compression paddles are safe and not damaged, the foot pedals all work, automatic compression release works. Then monthly tests checking AEC function at alternative compression thicknesses. checking that the exposures are appropriate and filters alter for thicker breast tissues.
they also do daily and monthly checks on the stereotactic biopsy equipment checking that the needles used for biopsy are calibrated correctly for accurate biopsies. They have a special needle holding tool that allows them to do this.
They also calibrate the faxitron (small xray machine for imaging breast biopsy samples) on a monthly basis.

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Visual checks of cables, ports, transducers, buttons and tracker balls for damage and/or weakening.

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Water phantoms are used to check the radiofrequency coils in the MR scanners.
Programme selected on the console, phantom and coil set up as per the image and sent to the isocentre whilst the QC scan is ran. Pass/fail.

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CT - Numbers values (completed daily)
A phantom is used that has materials of different densities inside it. It has a material with a CT number of 0 (like water) and one material with a CT number of 800-1000HU. The CT numbers detected are measured against baseline numbers set. Suspension levels are water: baseline +/- 20 HU and other materials: baseline +/- 30 HU.

RNI - Uniformity (completed daily)
Uses a Cobalt 57 flood source. You flood the image of 5-15million counts each day of use, before imaging begins. The local remedial level is set at 3%. The Cobalt flood source is used to measure uniformity across the gamma camera head to reduce the amount of false positives or negatives.

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Cobalt 57 flood source
Used to check image uniformity because if it isn't, this would indicate an issue with one of the photomulipliers or cracks in the crystal. Has to be performed daily and the machine will not work until it has been done.