CT Physics Comprehensive Exam

High dose of radiation

Cost

What are the disadvantages of Computed Tomography?

electrical

The detectors convert the attenuation data into _______________ signals.

conventional radiography

Sectional images are obtained from all of the following except:

gamma

The radiation used in Hounsfield's first experiments was:

scanning

Which of the following terms describes the systematic motion of the x-ray tube as it rotates around the patient to collect x-ray transmission readings?

MRI Imaging

CT Imaging

X-Ray Imaging

Rank the following imaging modalities from most to least effective in differentiating soft tissues in the body.

collecting x-ray transmission readings from the patient

Data acquisition refers to:

thickness

atomic number

density

The number of photons that interact with the tissues of the patient depends on the tissues:

Godfrey Hounsfield

Who is considered the "Father of Computed Tomography"?

1, 2, and 3

The main goal(s) in CT is to:

1. Minimize superimposition

2. Improve contrast resolution

3. Provide a large amount of clinical information in a short amount of time

hounsfield

Computed tomography is able to quantify the beam attenuation of a given structure. The measurements are expressed in ___________ units.

linear attenuation co-efficient

The amount of the x-ray beam that is scattered or absorbed per unit thickness of the absorber is expressed by the ______________.

Data acquisition

________________ is the collection of the x-ray transmission measurements from the patient.

+1000 HU

Bone

0 HU

Water

-1000 HU

AIR

image

Raw data that has been segmented and averaged so that each pixel has an associated Hounsfield Unit (HU) is ___________ data.

Hounsfield

Who developed the first clinically useful computed tomography scanner?

data acquisition geometry

The way the x-ray tube and detectors are arranged to collect transmission measurements describes:

Conventional slice by slice CT or Sequential CT

In which of the following data acquisition methods are slices taken at a specific location of the patient?

Used a pencil beam and a single detector, took 5 minutes to produce an image

First Generation Scanner.

Used a fan beam and 1 to 2 detectors, took approximately 20 seconds to produce an image.

Second Generation Scanner

Used a fan beam and an arc of multiple detectors, took about 1 second to produce an image.

Third Generation Scanner

Used a fan beam and a complete circle of detectors, took about 1 second to produce an image.

Fourth Generation Scanner

Utilized slip ring technology to have continuous gantry travel.

Continuous Rotation Scanner

Fusion of two modalities into a single image that offers anatomical and metabolic information.

PET/CT Scanner

The energy of the radiation beam

Which of the following influences the value of the Hounsfield unit?

Window width

The range of CT numbers is defined as the:

The x-ray tube and detectors

Which of the following is part of the image system?

1, 2, and 3

The purpose of the data acquisition or  imaging system is to:

1. produce x rays

2. shape and filter the x ray

3. detect and measure the radiation passing through the cross-section

The reconstruction circle

The field of view is:

protect the patient

The main purpose of a filter used in computed tomography is to:

electrical

The detectors convert the attenuation data into ___________ signals.

Detector efficiency

Ability to capture, absorb and convert x-ray photons to electric signals

Detector response time

Speed with which the detector can detect an x-ray event and recovers to detect another event

Detector dynamic range

The ratio of largest signal to be measured to the precision of hte smallest signal to be discriminated

High reproducibility

Ability to reproduce the same response with each x-ray absorbed

Afterglow

Persistence of the image even after the radiation has been turned off

Window level

The center of a range of CT numbers is called the

Preprocessor

Data from the CT detectors are first sent to the:

1, 2, and 3

The purpose of the data acquisition or imaging system is to:
1. produce x-rays
2. shape and filter the x-rays
3. detect and measure the radiation passing through the cross section

Grayscale manipulation using CT numbers

Windowing refers to:

1, 2, and 3

The purpose of collimation in computed tomography is:

1. to protect the patient

2. to ensure a constant beam width at the detector

3. to reduce scatter radiation

Homogeneous beam

All of the following are radiation beams produced by an x-ray tube designed for CT except:

Superimposition of structures

Which of the following is a limitation of radiography?

radiation energy

patient size

Attenuation depends on:

The beam becomes harder.

When a heterogeneous beam of radiation is attenuated by the patient:

90% efficient

Scintillation detectors are:

I = I₀e ^–µx

Which of the following represents the correct expression of Lambert Beer’s law?

x-ray tube

high frequency generator

detector electronics

collimators

The computed tomography gantry houses all of the following:

Detector configuration

What term is used to describe the number of data collection channels and the effective section thickness determined by the data acquisition system settings?

Decreases

As pitch increases, the image quality _______________.

Interpolation

___________________ is the mathematical process whereby data from tube rotations just above and just below a given slice position are used for image reconstruction.  This process allows for the reconstruction of a thin, motion free image form a volumetric data set acquired from a moving patient.

1, 2, and 3

Limitations of slice-by-slice sequential computed tomography scanning include:

1. longer examination time

2. inaccurate generation of three-dimensional images          

3. possible omitted anatomy because of patient respiration

Ray

The part of the x-ray beam that falls on one detector

View

A collection of rays for one translation across an object

Projection Profile

CT detectors generate a signal that represents the attenuation as the ray moves across the slice

Profile

Each transmission measurement obtained as part of a signal profile by each detector

Patient size

All the following are typical scan parameters for spiral/helical computed tomography scanners except:

Sequential/Axial Scanning

Scan method in which the CT table moves to the desired location and remains stationary or stops while the x-ray tube rotates within the gantry, collecting data.

Single Slice/Helical Scanning

Scan method that includes continuous rotating of the x-ray tube, constant x-ray tube output and uninterrupted table movement.

Multi-Slice Scanning

A scan design in which there are many parallel rows of detectors.  A single rotation can produce multiple slices.

Isotropic

When the slice thickness is equal to the pixel size, the data acquired are said to be:

Pitch

What is defined as the distance (in millimeters) that the computed tomography table moves during one revolution of the x-ray tube?

1, 2, and 3

Which of the following is/are types of detectors used in multislice computed tomography scanners?

1. hybrid detectors

2. nonuniform detectors

3. uniform detectors

1,2, and 3

In multislice computed tomography, the slice thickness is determined by the:

1. beam width in the z-axis

2. pitch

3. shape and width of the reconstruction filter

Creates overlapping slices without increasing radiation dose to the patient

Reduces partial volume effect

Helical data allows for the slice incrementation to be changed retrospectively.  The benefit(s) are the following:

Cone beam

Multislice utilizes which type of beam geometry?

Distance the table travels during 360 degrees/slice thickness; 1

The pitch ratio is expressed as____________________ and the ideal pitch is _______________. 

P = distance the table travels per rotation (d)/total collimation (W)

The definition of pitch in a multislice scanner, as defined by the International Electrotechnical Commission, states:

1, 2, and 3

The purpose of the data acquisition or  imaging system is to:

1. produce x rays

2. shape and filter the x ray

3. detect and measure the radiation passing through the cross-section

reduces partial volume effect.

creates overlapping slices without increasing radiation dose to the patient.

Helical data allows for the slice incrementation to be changed retrospectively.  The benefits are the following:

isotrophic

When the slice thickness is equal to the pixel size, the data acquired are said to be:

decreases

As pitch increases, the image quality _______________.

3D picture element

What does a voxel represent?

collecting x-ray transmission readings from the patient

Data acquisition refers to:

high frequency unit

The x-ray generator for computed tomography scanners is usually a:

The beam becomes harder.

When a heterogeneous beam of radiation is attenuated by the patient

the energy of the radiation beam

Which of the following influences the value of the Hounsfield unit?

spiral/helical scanner

Which scanner is based on slip-ring technology?

1 and 3 only

Attenuation depends on:

1. patient size

2. table speed

3. radiation energy

4. technologist skill

The type of detector material used.

Which of the following does not affect the quantity of x-rays that completely penetrates the patient:

helical

Which of the following would acquire data in a volume.

1.11 mm

If the field of view for an examination is 58 cm and the matrix size is 512 x 512, what is the approximate pixel size?

digitizers

Data from the computed tomography detectors are first sent to the _________ before going to the computer.

beam geometry

Which of the following refers to the size, shape, motion, and path traced by the x-ray beam as it scans the patient?

1, 2, and 3

Compared with conventional computed tomography scanners, slip-ring scanners offer the following advantage(s):

1. removal of cable wraparound

2. elimination of start-stop action

3. continuous rotation of x-ray tube and minimal interscan delays

protect the patient

The main purpose of a filter used in computed tomography is to:

1, 2, and 3

The purpose of collimation in computed tomography is:

1. to protect the patient

2. to ensure a constant beam width at the detector

3. to reduce scatter radiation

electrical

The detectors convert the attenuation data into _______________ signals.

number of detector rows is increased

What is the major difference between single slice helical scanning and mutlislice scanning?

cone beam

Multislice utilizes which type of beam geometry?

1, 2, and 3

Limitations of slice-by-slice sequential computed tomography scanning include:

1. longer examination time

2. inaccurate generation of three-dimensional images          

3. possible omitted anatomy because of patient respiration

slip rings

What allows the x-ray tube to continuously rotate so that a volume of the patient can be acquired?

pitch

What is defined as the distance (in millimeters) that the computed tomography table moves during one revolution of the x-ray tube?

distance the table travels during 360 degrees/slice thickness

The pitch ratio is expressed as____________________.

collimator width

The slice thickness in computed tomography is determined by the:

P = distance the table travels per rotation (d)/total collimation (W)

The definition of pitch in a multislice scanner, as defined by the International Electrotechnical Commission, states: