MId term #1 for CT

Cortical bone

+1,000 or high

Blood

+30-45

Air

-1,000

The range of CT numbers or Hounsfield Units varies from

-1,000 to 3,000

Modern pulsed CT scanners operate at

-120 kVp. -1 to 5 msec. pulses. -up to 1,000 mA.

The basic ingredients that define a helical scan process are:

-a continually rotating x-ray tube -constant x-ray output -uninterrupted table movement

The CT radiation beam is collimated

-at the tube exit. -at the detector entrance. -pre-patient and post-patient.

The smaller the scan field size, the

-better resolution -faster scan time -less the risk of motion

MSCT scanners have evolved greatly over the last few years, particularly with regard to slice combinations, scanning speed, and clinical utility. As these scanners gather more slices of data per rotation, a major technological challenge is

-the amount of data handled by the computer. -the number of images to be analyzed by the clinician. -developing technologies to minimize dose.

The CT console provides the radiographer access to

-the software program -data acquisition -data display

Water

0

Calculate pitch for the following parameters: couch movement of 10 mm/second and slice thickness per 360-degree rotation of 20 mm.

0.5:1

Factors that affect image quality in CT consist of: 1.) spatial resolution 2.) noise 3.) contrast media

1 and 2

In order for a CT x-ray photon to be measured, it must: 1. enter the detector 2. be absorbed by the detector material 3. transmit through the detector to be back-projected 4. have sufficient energy to undergo a Compton interaction 5. be converted to light and then electrical energy as a signal

1,2, and 5

High-resolution CT studies of the chest often require slice thickness to be reduced to:

2 to 3 mm

Which generation of CT scanner first used a fixed ring of detectors?

4th

What is the major advantage of volume CT over standard CT imaging?

Allows a volume of tissue to be examined rather than individual slices only

Which of the following modality was the first to use the principle of digital imaging?

Computed tomography (CT)

Which of the following statements is not an advantage of CT over conventional imaging?

Exposes the patient to much less radiation

Who was the first to incorporate digital imaging with the CT scanner?

Godfrey Hounsfield

A series of tissue density values that evolved for CT measurements is called ____ units.

Hounsfield

This is a mathematical method of estimating the value of an unknown functionusing the the known value on either side of the function.

Interpolation

Which of the following is not an advantage of multislice CT scanners?

Involves a total lower cost system to purchase and maintain

The CT radiographer usually varies the ____ to control the primary beam.

MA

Computerized storage and transmission systems for digitized images of all types are called

PACS

What controls the actual thickness of the CT slices?

Postpatient collimator

This determines the area within the gantry from which raw data are acquired.

SFOV

Any image that must be performed more than once because of human or mechanical error during the production of the initial image is known as repeat image. What effect does repeat images have on the radiation dose received by the patient?

The patient's skin and possibly the gonads receive a double radiation dose.

What is the purpose of radiographic beam filtration used in CT?

To increase beam hardness, thereby reducing patient skin dose and the dose to superficial tissues

In the event a CT patient needs emotional support for a procedure, during the acquisition

a patient family member should be allowed to attend to the patient.

The ____ is how well the detectors convert incoming photons.

absorption efficency

CT scan pitch uses all of the following technical parameters EXCEPT

acquisition mAs .

This contains finite set of steps performed in a prescribed sequence to solve a problem.

algorithm

An undesired feature or density in the CT image not representative of anatomy is a(a):

artifact

Digital radiography CT images can be accessed:

at several workstations at the same time, making image viewing very convenient for physicians providing patient care

What specifically do the CT detectors measure?

attenuation

The calculation of CT numbers is based upon the calculation of

attenuation coefficients.

A ____ artifact is caused by attenuation of the beam as it passes through the patient.

beam-hardening

The process of combining detector elements into various combinations in order set slice thickness is called detector

binning

The ____ is how well the detectors receive photons from the patient.

capture efficiency

The ____ is determined by how well the detector converts the absorbed photon information to a digital signal for the computer.

conversion efficiency

Computed tomography sections are available as

coronal, transverse, sagittal

Contrast is adjusted by windowing, changing window width and window level. Window level determines the:

determines the midpoint of the gray range

Which of the following is used to reduce the range of x-ray energies that reach the patient, reduce patient dose, and improves a CT image by creating a more uniform beam intensity?

filter

The primary mathematical method used in the creation of computerized medical images is the ____ transformation.

fourier

First-generation CT scanners scanned the ____ only.

head

The first commercial CT scanners could image the:

head only

The most recent generation of CT scanners use a ____ motion.

helical

CT is able to differentiate between tissues with similar densities compared with conventional radiography due to:

improved contrast resolution

In CT scanning, the total amount of energy directed at matter is expressed as

integral Dose.

An array of numbers arranged in a grid of rows and columns is called a:

matrix

Contrast is adjusted by windowing, changing window width and window level. Window width determines the:

number of gray levels displays

Fourth-generation CT scanners use the following configuration:

only rotating tube

The ratio between patient table speed and x-ray beam collimation or slice thickness defines:

pitch

The resolution of the CT image depends on the

pixel. voxel. matrix size.

A predetermined procedure or technique used in CT imaging is the definition for:

protocol

Contemporary CT scanners use solid state detectors. These detectors utilize

rare earth ceramic scintillators.

To achieve coronal or sagittal sections,

reconfiguration software is implemented

A ____ artifact is caused by detector error and are more common in CT systems with a third-generation design because the same detectors are being used repeatedly.

ring

Another term for topogram or localizer is:

scanogram

The localization image produced by the CT scanner is technically called a/an

scanogram

These devices are also called scintillation detectors because they use a crystal that fluoresces when struck by an x-ray photon.

solid-state detectors

A ____ artifact is caused by the presence of metal in the patient.

star

A ____ artifact is caused by motion.

streak

CT image data is acquired in the

transverse plane and reconstructed in any plane

An entire volume of tissue in a slice is called a voxel. true or false

true

The gantry houses the x-ray tube and the detector array. true or false

true

The number and shades of gray assigned to a CT image can be controlled by the technologist. true or false

true

Window width (WW) in CT controls displayed image contrast. true or false

true

Which medium serves as the baseline for CT numbers?

water

The reference material for CT is ____ and is related to the ____ of the tissue.

water, linear attenuation coefficient

____ controls the brightness of an image within a certain range.

window level

The gantry of the CT unit contains the

x-ray tube

This axis is defined by slice thickness, has a significant effect on the degree of volume avaerging that is present on the image.

z axis