Questions-- Image production (CTB) -- Image Quality

Define each of the following terms :A. Spatial Resolution B. Contrast Resolution C. Temporal Resolution

Spatial resolution is the sharpness of structures within the image. Contrast resolution is the ability of the CT scanner to create visible contrast between tissues with similar attenuation properties. Temporal resolution is the ability of the CT scanner to create still images of moving parts.

Motion artifact in the heart can be minimized by using: A. Thicker reconstruction slices B. Thinner detector rows C. EKG Gating D. Decreased pitch

c

What quality control test evaluates the ability of the CT scanner to produce the same CT number for the same material regardless of where the ROI is placed? A. Accuracy B. Linearity C. Uniformity D. Contrast resolution E. Spatial resolution

c

After performing a CT of the chest, an ROI placed in the air outside of the patient yields of an average CT number of -1,223. This error represents a problem with: A. Accuracy B. Linearity C. Uniformity D. Contrast resolution E. Spatial resolution

A

After performing a CT of the chest, an ROI placed in the air outside of the patient yields of an average CT number of -1,223. This error represents a problem with: A.Accuracy B.Linearity C.Uniformity D.Contrast resolution E.Spatial resolution

A

Of the following options, what reconstruction slice thickness will display images with the highest level of spatial resolution? A. 0.625 mm B. 1.25 mm C. 5.0 mm D. 3.75 mm

A

What combination of variables will result in the least amount of image noise? A.Pitch = 0.9, Reconstruction Thickness = 5.0, Voltage = 140 B.Pitch = 1.0, Reconstruction Thickness = 3.5, Voltage = 130 C.Pitch = 1.1, Reconstruction Thickness = 2.0, Voltage = 120 D.Pitch = 1.2, Reconstruction Thickness = 1.0, Voltage = 110

A

Which of the following describes the ability of CT scanners to produce detailed images of small parts? A. Spatial Resolution B. Contrast Resolution C. Temporal Resolution D. Linearity E. Uniformity

A

Which of the following is measured in line-pairs per centimeter? A. Spatial Resolution B. Contrast Resolution C. Temporal Resolution D. Linearity E. Uniformity

A

Which of these acquisition thicknesses will result in the highest spatial resolution? A.0.625 mm B.1.25 mm C.2.5 mm D.3.75 mm

A

Which of these scans will have the best spatial resolution? A.600 mA, 1.0 sec.rotation, 1.0 mm slices, bone algorithm B.500 mA, 1.0 sec.rotation, 2.0 mm slices, standard algorithm C.400 mA, 0.5 sec.rotation, 3.0 mm slices, bone algorithm

A

Which of these variable changes is most likely to improve the contrast resolution of the resulting images? A. Decreased patient size B. Decreased reconstruction slice thickness C. Decreased acquisition thickness D. Decreased milli-amperage

A

Which of these variable changes is expected to improve the contrast resolution of CT scan? Choose two. A.Increase mA B.Increase kVp C.Increase matrix size D.Increase display field-of-view

A and B due to a decrease in image noise

Which of these scans will have the best spatial resolution? A. 600 mA, 1.0 second rotation time, 1.0 mm slices, bone algorithm B. 500 mA, 1.0 second rotation time, 2.0 mm slices, standard algorithm C. 400 mA, 0.5 second rotation time, 3.0 mm slices, bone algorithm D. 300 mA, 0.5 second rotation time, 4.0 mm slices, standard algorithm

A. 600 mA, 1.0 second rotation time, 1.0 mm slices, bone algorithm Just about every factor of a CT scan potentially affects the spatial resolution. In this question, the largest mA is desirable because this is expected to reduce the amount of image noise and increase the clarity of spatial resolution in the image. The longest rotation time is preferred because longer rotation times result in more projections through the patient and better spatial resolution. Thinner slices improve spatial resolution since small slices can visualize smaller parts. The bone algorithm, like other edge enhancing algorithms, increase spatial resolution by adding more sharpness to the image.

Which of these variable changes will increase temporal resolution? A. Increased pitch B. Increased rotation time C. Increased reconstruction thickness D. Increased kilovoltage potential

A. Increased pitch Increasing the pitch increases the temporal resolution. This is because increased pitch results in a faster overall scan, which helps to reduce motion artifact. Any variable change that makes the scan faster results in less motion artifact and better temporal resolution.

What combination of variables will result in the least amount of image noise? A. Pitch = 0.9, Reconstruction Thickness = 5.0, Tube voltage = 140, Matrix Size = 512 x 12 B. Pitch = 1.0, Reconstruction Thickness = 3.5, Tube voltage = 130, Matrix Size = 512 x 12 C. Pitch = 1.1, Reconstruction Thickness = 2.0, Tube voltage = 120, Matrix Size = 1024 x 1024 D. Pitch = 1.2, Reconstruction Thickness = 1.0, Tube voltage = 110, Matrix Size = 1024 x 1024

A. Pitch = 0.9, Reconstruction Thickness = 5.0, Tube voltage = 140, Matrix Size = 512 x 12 Of the options listed here, the tube voltage (kVp) is the primary factor influencing the image noise. Using a large to voltage, such as 140 kVp, will increase the amount of photons getting to the receptors and therefore decrease the image noise.

Several QC tests were performed on four different scanners. Based on the results of these tests, which scanner has the best CT number accuracy? A. Water phantom average = - 0.5 HU Water phantom standard deviation = 1.2 Line pairs = 12 lp/cm B. Water phantom average = 1.0 HU Water phantom standard deviation = 3.1 Line pairs = 14 lp/cm C. Water phantom average = -11 HU Water phantom standard deviation = 0.2 Line pairs = 13 lp/cm D. Water phantom average = 2.0 HU Water phantom standard deviation = 2.0 Line pairs = 10 lp/cm

A. Water phantom average = - 0.5 HU Water phantom standard deviation = 1.2 Line pairs = 12 lp/cm CT number accuracy refers to the ability of the scanner to produce a HU reading that is very similar to the expected reading. A water phantom should produce an average HU very close to zero. In this question, 0.5 hounsfield units is the closest number to zero.

The ability of the scanner visually discriminate between objects with similar physical density is called: A. Spatial Resolution B. Contrast Resolution C. Temporal Resolution D. Linearity E. Uniformity

B

When an ROI is placed over a homogenous structure, which of these values represent the image noise? A.HU Average B.HU Standard deviation C.Total area D.Circumference

B

When reviewing a CT of the lumbar spine, you notice the trabecular bone is not very sharp. This is a quality control issue related to: A.Contrast Resolution B.Spatial Resolution C.CT Number Accuracy D.Linearity E.Uniformity

B

Consider a CT scan used to evaluate the brain for metastatic disease. If the average CT number of the tumors differs only slightly from the surrounding brain matter, what characteristic of the scanner might cause limited visibility of the tumors? A. Spatial Resolution B. Contrast Resolution C. Temporal Resolution D. Linearity

B. Contrast Resolution Since the tumors have CT numbers very similar to the surrounding brain matter, it would be very important for this scan to have very high contrast resolution. If the contrast resolution is not high enough, these tumors would be impossible to visualize. Contrast resolution is by definition the ability to see the difference between objects that have very similar physical densities.

A CT of the cranium may call for 2.0 mm slices in the posterior fossa and 5.0 mm slices through the vertex. The 5.0 mm slices will display: A. Increased noise B. Decreased noise C. Increase spatial resolution

B. Decreased noise Compared to 2.0 mm slices, 5.0 mm slices will demonstrate decreased image noise. The major side effect of using these thicker slices is a decrease in spatial resolution.

When an ROI is placed over a homogenous structure, which of these values represent the image noise? A. HU Average B. HU Standard deviation C. Total area D. Circumference

B. HU Standard deviation The standard deviation represents the image noise in a homogeneous structure. Standard deviation is basically the average difference from the average. A large standard deviation means that the HU varies significantly from the average which results in a large amount of image noise. A small standard deviation means that the HU varies only a little from the average, which results in a small amount of image noise

Which of these variable changes may decrease the spatial resolution of the resulting CT images? A. Increased rotation time B. Increased reconstruction thickness C. Increased edge-enhancement D. Increased matrix size

B. Increased reconstruction thickness Increasing the reconstruction slice thickness results in a decrease in spatial resolution. Sometimes in increase in size thickness is preferred to decrease the image noise, but this does result in a decrease in spatial resolution.

Which of these scenarios will result in images with the best contrast resolution? A. Soft tissue algorithm with 1.0 mm slices B. Soft tissue algorithm with 2.0 mm slices C. Bone algorithm with 1.0 mm slices D. Bone algorithm with 2.0 mm slices

B. Soft tissue algorithm with 2.0 mm slices The main issue affecting contrast resolution is image noise. Image noise is reduced by using softening algorithms and thicker reconstruction slices. In this question, the soft tissue algorithm in 2.0 mm slices results in the least amount of image noise and therefore the best contrast resolution. The side effect of this option is a decrease in spatial resolution.

Half-scan algorithms improve which image quality variable in CT? A.Spatial Resolution B.Contrast Resolution C.Temporal Resolution D.CT Number Accuracy

C

When scanning a water phantom for quality control, you notice that an ROI in the center of the phantom reads 0 HU but an ROI on the edge of the phantom reads 4 HU. This is a problem with: A. Accuracy B. Linearity C. Uniformity D. Contrast resolution E. Spatial resolution

C

Of the following options, what reconstruction slice thickness will display images with the highest level of contrast resolution? A. 0.625 mm B. 1.25 mm C. 5.0 mm D. 3.75 mm

C. 5.0 mm For contrast resolution, thicker slices are better. In this particular question, 5.0 mm is the thickest slice, therefore it will result in the bests contrast resolution. The main side effect of using thicker slices is a reduction in spatial resolution. In other words, the image will have less noise and a smoother appearance, but the amount of detail will be reduced.

Which of the following is NOT caused by excessive image noise? A. Decreased spatial resolution B. Decreased contrast resolution C. Decreased temporal resolution

C. Decreased temporal resolution Image noise has the potential to affect both spatial resolution and contrast resolution in a negative way. Noise or mottle in the image decreases the ability to see detail in the images, which is the same as decreased spatial resolution. Noise also makes it difficult to see the difference between structures that have similar physical densities. This is the same as a decrease in contrast resolution. Temporal resolution is not correct because it is affected only by the speed of the scanned, not by the appearance of noise in the image.

Consider the following scenario. Several QC tests were performed on four different scanners. Based on the results of these tests, which scanner has the least amount of image noise? A. Water phantom average = - 0.5 HU Water phantom standard deviation = 1.2 Line pairs = 12 lp/cm B. Water phantom average = 1.0 HU Water phantom standard deviation = 3.1 Line pairs = 14 lp/cm C. Water phantom average = -11 HU Water phantom standard deviation = 0.2 Line pairs = 13 lp/cm D. Water phantom average = 2.0 HU Water phantom standard deviation = 2.0 Line pairs = 10 lp/cm

CWater phantom average = -11 HU Water phantom standard deviation = 0.2 Line pairs = 13 lp/cm Image noise is based on the standard deviation. The lowest standard deviation represents the least amount of image noise. In this question, the lowest standard deviation is 0.2.

Identify multiple ways the contrast resolution of the image data can be improved retrospectively.

Contrast resolution cannot be changed retrospectively, except when observing very small objects that may be completely lost in the presence of significant image noise. For that reason, increasing the reconstruction slice thickness and using a smoothing algorithm can reduce image noise and increase contrast resolution for small objects.

Which of these reconstruction algorithms are likely to produce the best spatial resolution? A. Standard algorithm B. Soft tissue algorithm C. Brain algorithm D. Bone algorithm

D

Which of these scans will have the best contrast resolution? A. 600 mA, 0.3 second rotation time, 1.0 mm slices, bone algorithm B. 500 mA, 0.4 second rotation time, 2.0 mm slices, standard algorithm C. 400 mA, 0.5 second rotation time, 3.0 mm slices, bone algorithm D. 300 mA, 1.0 second rotation time, 4.0 mm slices, standard algorithm

D. 300 mA, 1.0 second rotation time, 4.0 mm slices, standard algorithm Contrast resolution is affected by all variables listed here. The mA and rotation time should be considered together, since mA x rotation time results in the total mAs. The highest total mAs will increase contrast resolution. Contrast resolution is also increased by thicker slices and smoothing algorithms, such as the standard algorithm. This is because all these characteristics will reduce the amount of image noise.

Identify multiple ways the spatial resolution of the image data can be improved retrospectively, that is, without rescanning the patient.

Decrease reconstruction thickness, reconstruct into edge-enhancing algorithm, decrease DFOV