chicken

In a test for the averaging CT number of water, the largest acceptable variation would be

+ or - 4

The average CT value for blood is approximately

+25 hounsfield units

What is the dimension of each pixel in an image with a 512x512mm matrix and a DFOV equaling 25.6cm?

0.5mm

A CT scanner capable of producing an image that is a perfect reproduction of the actual anatomic section is said to have an MTF of

1

Which of the following quality control tests are performed daily on a CT scanner? 1) The CT number calibration 2) The noise levels (standard deviation) of a water phantom 3) The accuracy of the table movement

1 and 2 only

Which of the following would increase spatial resolution of a CT examination using the following parameters: 1) Change to small focal spot size 2) Perform 5mm sections 3) Reconstruct images in a 320x320mm matrix

1 and 2 only

Which of the following technical adjustments would decrease the quantum noise of a CT image? 1) Increased mAs 2) Decreased slice thickness 3) Increased slice thickness

1 and 3 only

A triphasic exam can be performed on which organ(s)? 1) Kidney 2) Lung 3) Brain 4) Liver

1 and 4

Oral barium contrast solutions used for CT scans of the abdomen and pelvis should contain approximately ________ barium.

1%-3%

The primary factors to reduce radiation exposure are: 1) Time 2) Distance 3) Shielding 4) Focal spot size

1, 2 and 3

which of the following statements about stochastic effects of radiation are true? 1) Risk increase with dose 2) There are no threshold doses 3) Probability of the effects depends on the dose

1, 2, and 3

Abnormalities of the middle and inner ear may be best demonstrated using CT sections of

1-2mm

With a CT exam, a 1% difference in tissue contrast corresponds with how my HU or CT numbers?

10

Which of the following structure normally calcifies? 1) Basal ganglia 2) Choroid plexus 3) Pineal gland

2 and 3

Which of the following terms are commonly used to describe the ability of a CT scanner to differentiate objects with similar linear attenuation coefficients? 1) Spatial resolution 2) Sensitivity 3) Contrast resolution

2 and 3 only

a typical range for skin dose to the patient during a CT study of the head is

2-4 cGy

What is the MSAD if the CTDI is 3 rads with a slice thickness (aperture width) of 5 and atable incremation of 5?

3

On the scout view, the patient measures 38cm across. An appropriate DFOV to best display the enture anatomy would be

40cm

What will be the dose length product (DLP) of a CT exam with a CTDI of a 2.5, a slice thickness of 5mm with 40 slices at 120kVp?

500 mGy/cm

During a CT study of the chest, IV contrast would most likely be required to demonstrate:

A dissecting aortic aneurysm

The measured density of an area is approximately +5 hounsfield units. This most likely represents

A renal cyst

During which of the following CT examinations is a misregistration artifact most likely to occur?

Abdomen

Of the following ranges, which would be the most suited for a scout (localizer) image of the abdomen?

Above the diaphragm to the iliac crest

A pheochromocytoma affects what organ?

Adrenals

What can be said of an ROI measurement with a standard deviation of 0?

All of the pixels in the ROI have the same value

Which of the following statement is usually true about radiation dose and image quality?

As dose increases quality increases

A high resolution CT of the chest would be needed to demonstrate which of these abnormality of the chest?

Asbestosis

Which of the following is capable of causing on edge gradient artifact?

Barium and air interface

Cupping artifacts most commonly occur in the

Brain

Narrow "window width" settings should be used to display small differences in tissue density of the:

Brain

The arteriovenous iodine differences (AVID) is calculated by:

Comparing the HU measurement of the aorta to the inferior vena cava

Which of the following conditions would not require the injection of iodinated contrast for proper visualization during a CT examination of the brain?

Concussion 2 days prior; R/O subdural hematoma

During a spiral or helical CT examination, the scanner acquires data

Continuously as the patient travels through the gantry and In the form of a complete volumetric data set

The term ______ describes the ability of a CT scanner to differentiate objects with minimal differences in attenuation coefficients.

Contrast resolution

What quality assurance test uses ROI's placed at the center and edges of a water phantom?

Cross-field uniformity

Quality control measurements to test the uniformity of the field of view should be performed:

Daily

Which of the following would magnify the CT image on the display monitor?

Decreased DFOV

which factor does NOT reduce patient dose?

Decreased DFOV

Partial volume averaging on the CT image may be decreased by

Decreasing slice thickness

The dimensions of a voxel may be decreased by which of the following?

Decreasing the section width

In which of the following cranial nerves would an acoustic neuroma be found?

Eighth

Which of the following hemorrhages can cross midline to go to both hemispheres of the brain?

Epidural

Which of the following abnormal findings reduces the density of the liver?

Fatty infiltrate

Pulmonary emboli are seen as:

Filling defects in the pulmonary arteries

An axial CT image should be viewed on the monitor in which of the following orientations?

From the feet toward the head with the patient's left on the viewer's right

a ______ is a benign, highly vascular mass commonly in the liver.

Hemangioma

Which of the following types of algorithms is best suited to demonstrate the bony detail?

High pass filter

Which of the following terms describes the appearance of an acute subdural hematoma on a CT image of the brain?

Hyperdense

As the pitch increases:

Image quality decreases

The lowest occupational radiation exposure during a CT exam is:

In the gantry plane outside the aperture

Which of the following will happen with a decrease in slice thickness?

Increase image detail

which of the following decreases patient dose during a spiral CT examination?

Increased pitch

After the intravenous administration of iodinated contrast media, a hepatic hemangioma may become _______ and no longer appear on the CT image.

Isodense

Which of the following factors does not affect the dimensions of a voxel?

Kernel

disc herniation is most common at what level?

L4-L5

Which of the following is the best scout or localizer projection for CT scan of the neck?

Lateral

On a CT scan, hydrocephalus show an affect on which part of the brain?

Lateral ventricles

On an unenhanced scan, how will a fatty liver appear as compared to the spleen?

Less attenuating

All of the following conditions are examples of deterministic effects EXCEPT:

Leukemia

When reviewing a CT of the abdomen, to best visualize most of the abdominal organs what combination of window width and level would be needed?

Level 50, width of 350-500

the spatial resolution of a CT scanner is usually expressed as

Line pair/cm

A CT test phantom with a variety of known densities is used to test for what?

Linearity

The term used to describe the relation between the linear attenuation coefficients of an object and the calculated CT number is

Linearity

The average density of a mass within the kidney measures (-85) Hounsfield units. This mass is most likely a

Lipoma

Which of the following QC tests is not done with a water phantom?

Low contrast resolution

High-resolution CT is most commonly used for the evaluation of the

Lungs

During CT angiography, images may be reconstructed using only the greatest density encountered along each ray. This type of specialized CT image is called a(n):

MIP image

The quantity of radiation dose received by the patient from a series of CT scans is referred to as the:

MSAD

Coronal images would be most useful for which area of the body?

Middle ear

The spatial resolution of a CT scanner is often measured using the MTF, which is an acronym for

Modulation transfer function

A voxel whose attenuation coefficient is less than that of water is assigned a pixel value with a(n) __________ CT number.

Negative

The grainy appearance of an image is commonly referred to as

Noise

Beta-Blockers are used as part of a cardiac CT protocol when the:

Patient has tachycardia

The CTDI is measured with a phantom and a:

Pencil ionization chamber

which of the following techniques will produce the smallest MSAD?

Pitch of 2

Which of the following formulas may be used to calculate the dimensions of a pixel?

Pixel size = DFOV/matrix size

The dimensions of a voxel may be calculated as the product of which of the following?

Pixel size and slice thickness

The liver enhancement that occurs 60 to 70 seconds after an IV bolus contrast injection is called the:

Portal venous phase

Pixels representing tissues with averaging attenuation coefficient's greater than that of water which of the following types of values?

Positive

Which of the following is not one of the basic principles of quality control?

Prompt repair of the equipment by the technologist

A pulmonary embolus will appear as a filling defect of the:

Pulmonary artery

Which of the following types of image noise can be most easily reduced by the CT technologist?

Quantum noise

What quality control test must be performed by a medical physicist?

Radiation dose measurements

Which of the following scanning protocols does NOT require IV contrast?

Renal stone

An image that is reconstructed a second time with some changes in technical factors is termed a:

Retrospective

Which of the following artifacts is not affected by the CT technologist?

Ring

The drip infusion technique of contrast media can be most effective used for which of the following

Routine head study

If the flow rate of a contrast injection is reduced from 4ml/second to 2ml/second, what other adjustment may be needed?

Scan delay is increased

A patient with brain metastasis is most likely to suffer which of the following after the injection of iodinated contrast?

Seizures

Another name for surface rending is:

Shaded surface display

The ability of a CT scanner to image a small high-density object is controlled by the _________ of the scanner.

Spatial resolution

An intrathecal injection of iodinated contrast material would be for which of the following CT examinations?

Spinal canal

Which of the following correctly describes the patient positon relative to the gantry for a CT study of the brain?

Supine, head first

Pitch may be defined as:

Table travel in one 360 tube rotation divided by slice thickness

Which of the following techniques assists in visualizing the vagina during a CT study of the pelvis?

Tampon insertion

Increasing the window width in a CT image increases:

The gray scale

The term "beam hardening" describes which of the following physical phenomena?

The increase in average photon energy of a heterogeneous x-ray beam

All of the following statements about retrospective image reconstruction are TRUE except:

The slice thickness and SFOV may be changed

Which of the following statements about MPRs is true?

They can be done in more than one plane

For a CT shoulder scan, why is the unaffected arm raised above the head?

To reduce streak artifacts

Complete CT examination of the chest for investigation of lung carcinoma should include sections from the

Top of the apices through the adrenals

What is another name for the non-equilibrium phase?

Venous phase

A region of interest measurement has an average density of +1.9 hounsfield units. This material is most likely

Water

Cupping and peaking artifacts can be observed by the use of which type of phantom?

Water

the average photon energy of the CT x-ray beam can be increased by

increasing filtration

which of the following factors has no measurable effect on spatial resolution?

kVp

which of the following technical factors exhibits a direct effect on a patient dose?

mAs

axial CT sections of the lumbar spine for intervertebral disk evaluation should be acquired with the plane of imaging

parallel to the plane of the intervertebral disk spaces

During CT scanning of the head, the gantry should be angled:

parallel to the supraorbitalmeatal line

a pencil ionization chamber phantom is used to measure

radiation dose

What two main features are assessed to measure image quality?

spatial and contrast resolution

during CT examinations, patients should be shielded above and below because of:

the rotational nature of the x-ray tube