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In multislice helical CT, the slice acquisition rate (SAR) is a measure of the imaging speed.
False
Beam hardening artefacts are commonly seen in the posterior fossa on a CT head scan due to the dense petrous bones.
True
In computed tomography, the term artefact is applied to any random discrepancy between the CT numbers in the reconstructed image and the true attenuation coefficients of the object.
False
Multislice helical CT allows for the imaging of a smaller volume of tissue in a single breath-hold.
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The principal advantage of multislice helical CT is its high imaging speed.
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Rings are a type of artefact that occur due to an inconsistency in a single measurement.
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The Data Acquisition Rate in multislice helical CT can be as low as 80 ms.
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Distortion artefacts in CT scans are caused by patient properties.
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Multislice helical CT imaging systems use a single detector array.
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A beam pitch of 2.0:1 means the x-ray beam width is equal to the patient couch movement.
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Wider slice imaging results in better spatial resolution at the same mA setting.
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Multislice helical CT has progressed from 4 to 16 slices in a very short time.
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A dual source multislice CT imaging system has a single x-ray tube and a single detector array.
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Image artifacts are a major limitation of Computed Tomography (CT) scans.
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The data acquisition rate of a CT scan is directly proportional to the number of slices it can image.
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Multislice helical CT imaging systems can produce slices of varying widths.
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Patient motion during a CT scan can cause a beam-hardening artefact.
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Increasing the scan time can reduce motion artefacts in CT scans.
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Multislice scanners are prone to cone beam artefacts.
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A faulty detector can cause a ring artefact in CT scans.
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High attenuation objects outside the field of view can cause streak artefacts in CT scans.
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Spiral scanning can reduce artefacts caused by patient motion.
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Reconstruction algorithms can minimize cone beam artefacts in CT scans.
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IV contrast can cause a beam-hardening artefact in CT scans.
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Study Notes
Multislice Helical CT Imaging
- Multislice helical CT imaging has a principal advantage of fast imaging speed, with a possibility of 80 ms imaging.
- It allows for acquisition of multiple slices in the same time required for a single slice.
- The slice acquisition rate (SAR) measures the efficiency of the multislice helical CT imaging system.
Advantages of Multislice Helical CT
- It enables imaging of a larger volume of tissue.
- It is possible to image the entire body, from head to toe, in a single breath-hold.
Artefacts in CT Imaging
- Artefacts are systematic discrepancies between CT numbers in the reconstructed image and the true attenuation coefficients of the object.
- Types of artefacts include:
- Streaking artefacts, caused by inconsistencies in a single measurement.
- Shading artefacts, caused by gradual deviations in a group of channels or views from the true measurement.
- Ring artefacts, caused by errors in individual detector calibration.
- Distortion artefacts, caused by helical reconstruction.
Causes of Image Artefacts
- Physics-based artefacts, such as beam hardening.
- Patient properties, such as metallic artefacts.
- Scanner-based artefacts, such as ring artefacts and cone beam artefacts.
- Helical and multislice artefacts.
Beam Hardening Artefact
- Beam hardening occurs when the mean beam energy increases as the x-ray beam passes through a dense area, absorbing lower energy photons and leaving higher energy photons.
- This artefact is common in the posterior fossa on a CT head scan due to dense petrous bones.
Multislice Detector Array
- Multislice helical CT imaging systems use multiple parallel detector arrays with thousands of individual detectors.
- A simple approach to multislice helical CT imaging is to use four detector arrays, each of equal width.
- The width of each detector array is 0.5 mm, resulting in four slices, each of 0.5-mm width.
Image Acquisition and Reconstruction
- Wider slice imaging results in better contrast resolution at the same mA setting because the detected signal is higher.
- This improvement in contrast resolution is accompanied by a slight reduction in spatial resolution due to increased voxel size.
- A larger tissue volume can be imaged with original contrast resolution at a reduced mA setting.
Solutions to Artefacts
- Scan parameters: shorten scan time, use spiral scanning.
- Patient parameters: breath hold, ensure comfortable patient position, and give clear instructions to the patient.
- Reconstruction algorithm minimizes cone beam artefacts.
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Description
This quiz covers the benefits of multislice helical CT imaging, including its speed, efficiency, and ability to image a larger volume of tissue.
