Quality assurance and quality control in Computed tomography.

Quality assurance and quality control in Computed tomography
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Introduction

Computer tomography – CT refers to the imaging modality which uses aspects of
X-ray photons of image production with regards to the reconstruction of digital
images. The CT scanner has x-ray tube and detectors producing X-rays beams
which pass on to the patient body. The beam is captured by the detectors and is
reconstructed into two or three-dimensional images. Analog data is captured by
the scanners which are digitally converted into various algorithms and
reconstructed into dimensional images. The images represent cross-sectional
slices which cut across the patient level. The image is acquired from a different
angle using different results from the different algorithm. The volumes displayed
to make up the images displayed on the two-dimensional pixels which carry the
identity designation which represents Hounsfield Unit. Further, contrast media
can be employed during the study, this help in distinguishing the different
structures from the same density body. The commonly used aspects in CT
studies are the intravenous and oral contrast agents. Constants perfusion often
has abnormalities such as extravasation and bleeding. Oral contrasts have been
employed in giving opacity of cavities linked to gastrointestinal organs thus
allowing greater differentiation process (Mansour et al., 2016).
Quality control aspects in CT are periodic tests performances on the scanners
which make comparison with some standards. If there is the sub-optimal
performance, steps to correct the defect are undertaken. High-quality output
levels of images offer maximum information improving the diagnosis and thus
improving overall patient quality. Quality assurance entails an assessment of CT
scanners performance levels. In this case, quality control takes critical steps and
initiates correction plan when the quality is lacking (Pina et al., 2009).
Quality control initiatives ensure that there are high-performance standards for
patients. Wear and drift out on the optimal adjustment can lead to low yield of
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the scanner to offer same image quality compared to its former image output,
this comparison of quality control data is essential to assess the performances of
the scanners. Fundamental principles of quality control entail periodic
performances, this promotes the interpretation of the assessment needs to be
done and further effective bookkeeping is crucial to ensure proper aspects of
quality control (Tsapaki, 2016).
Average CT number of water
Relevance: The average CT number of water is measured using phantom. It is a
water-filled cylinder of 20 cm in diameter. Procedure: Its assessment is
undertaken using scanning through the water phantom. Expected results: The
ROI is enlarged to about 2-3 cm, near the image center; the expected result is
the average CT number of water which is near 0. Acceptable levels: The
accepted levels are + or – 3. Failure Tests: The possible failure causes are the
miscalibration of the general algorithm which generates the CT number.
Frequency: the frequency being undertaken daily.
Assessment standard deviation of CT water number
Relevance: The assessment standard deviation of CT water number is assessed
using phantom. Procedure: Water is filled to a cylinder of about 20 cm in
diameter. The measurement used entails same images positioning the ROI on
the center and measuring the standard deviation on the CT number. Expected
results: The expected result entails a range of 2-7 CT numbers. Acceptable
levels: The acceptable levels entail small variation with standard deviation
increased leads to increase in noise image production. Failure Tests: Possible
causes of failures entails decreased levels of outputs in the tube or increased
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levels of electronic noise caused by the detectors, amplifiers. Frequency: This
needs to be done daily (Kitagawa et al., 2010).
High contrasts resolution assessment
Relevance: High contrasts resolution assessment is undertaken using high
contrast resolution phantom. Procedure: Measurement is undertaken on the
axial image which assesses entails the smallest row of holes which can be
observed clearly. Expected results: Expected result of this control entails
complete holes set in the same holes ranging from 0.75-1.0 mm. Acceptable
levels: The acceptable limits are assessed on the time of acceptance of testing.
Failure Tests: Possible causes of failure entail enlarged focal spot, excess
mechanical wear on the gantry motion, tube misalignment, and failures linked to
vibrations, detectors, and its related failures. Frequency: Done daily.
Low contrasts resolution
Relevance: Low contrasts resolution aspects are assessed using low contrast
resolution patterns on the imaging phantom. Procedure: Assessing the CT
image is undertaken using small holes which need to be observed clearly.
Expected results: The expected results entail 4-5 mm in diameter.
Acceptable levels: The overall acceptable limits are determined by the
baseline scan. Failure Tests: The key possible causes of failure entail high noise
levels. Frequency: The frequency of assessment is biannual.
Accuracy assessment distance
Relevance: Accuracy Assesment of distances is critical and is measured using
phantom object having two or more small objects which have a precise spatial
relationship which is known. Procedure: The assessment is undertaken using
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