COMPUTED TOMOGRAPHY

Question 1

PATIENT PREPARATION

Answer 1

*Scheduling the examination,
*Selecting the appropriate examination protocol
*Obtaining pertinent medical history
*Preparing the CT examination room

Question 2

In outpatient settings, the order is often written by the __ in his or her private office, and the clerical staff will then phone the scheduling division of the imaging facility to arrange an appointment.

Answer 2

clinician

Question 3

All CT examinations must be initiated by a clinician with appropriate credentials. In addition to physicians, clinicians who may order diagnostic tests include ___

Answer 3

nurse practitioners (NP) and physician assistants (PA).

Question 4

an often aide the radiologist in narrowing down, or pinpointing exactly, the disease or condition from which the patient suffers.

Answer 4

medical history

Question 5

The laboratory values most frequently reviewed before routine CT examinations are __

Answer 5

blood urea nitrogen (BUN) and serum creatinine.

Question 6

*Normal BUN levels:
*Normal serum creatinine levels:

Answer 6

7 and 25 mg/dL; 0.6 to 1.7 mg/dL

Question 7

The laboratory values for ___ and provide information about the blood’s coagulation ability.

Answer 7

prothrombin time (PT)

Question 8

*Normal PT range:
*Normal PTT range:

Answer 8

11 to 14 seconds; 25 to 35 seconds

Question 9

POSITIONING IN THORACIC PROCEDURES

Answer 9

*Most thoracic protocols are performed while the patient lies in a supine position on the scan table with the arms elevated above the head.
* In a few instances, primarily high-resolution CT protocols of the lungs, additional scans are obtained with the patient in the prone position.
*Using the shortest scan time possible helps to reduce artifacts created by respiratory motion

Question 10

POSITIONING IN NEUROANATOMY PROCEDURES

Answer 10

*The patient’s head is positioned in the head holder for most protocols of the head. Depending on the design of the head holder, it can sometimes also be used for neck protocols. When the head holder is not used, a molded sponge is placed directly on the scan table and the patient’s head is positioned within the sponge.

Question 11

SCOUT SCAN or also called as

Answer 11

localizer scans

Question 12

Why scout films are necessary

Answer 12

1.Identify correct technique factors to be used
2.Assess if the patient is prepared
3.Allow the technologist to prescribe the location of cross-sectional slices
4.Help the technologist select the optimal display field of view (DFOV) and the correct image center

Question 13

*The length of the localizer lines demonstrates the __
*The center of the line indicates the __

Answer 13

DFOV; image center

Question 14

The CT table moves to the desired location and remains stationary while the x-ray tube rotates within the gantry, collecting data

Answer 14

STEP AND SHOOT SCANNING

Question 15

The CT process can be broken down into three general segments:

Answer 15

data acquisition, image reconstruction, and image display.

Question 16

STEP AND SHOOT SCANNING
* Also referred to as __

Answer 16

axial scanning, conventional scanning, serial scanning, or sequence scanning

Question 17

When using this method there is a slight pause in scanning between data acquisitions, referred to as the interscan delay, as the table moves to the next location

Answer 17

STEP AND SHOOT SCANNING

Question 18

• Advantage: highest image quality when imaging phantoms who do not move or breathe
• Disadvantage: long examination time; data is limited in how they can be reconstructed

Answer 18

STEP AND SHOOT SCANNING

Question 19

___ scanners have many detectors situated in an arc (third- generation) or a ring (fourth-generation).
* In these systems the largest allowable slice thickness is less than the detector width, typically __
* The radiation emitted from the collimated x-ray source in these systems is commonly referred to as a __.
* Each gantry rotation produces data for a __.

Answer 19

SINGLE DETECTOR ROW; 10 mm; fan beam; single slice

Question 20

___ scanners a single rotation can produce multiple slices. Therefore, MDCT provides longer and faster z axis coverage per gantry rotation.

Answer 20

MULTIDETECTOR ROW;

Question 21

HELICAL scanning is Also called __
* Improved scanning speed by eliminating the__
* There are three basic ingredients that define a helical scan process:
__

Answer 21

spiral, continuous acquisition, volumetric scanning; interscan delay; 1) a continually rotating x-ray tube,
2) constant x-ray output, and
3) uninterrupted table movement.

Question 22

• Advantages: the ability to optimize iodinated contrast agent administration, the reduction of respiratory misregistration, and the reduction of motion artifacts from organs such as the heart.

Answer 22

HELICAL SCANNING

Question 23

are the components necessary for data acquisition.

Answer 23

The mechanisms housed within the gantry and the patient table

Question 24

The area of the anode where the electrons strike and the x-ray beam is produced.

Answer 24

FOCAL SPOT

Question 25

provide the electrons that create x-ray photons. This is accomplished by heating the filament until electrons start to boil off, hovering around the filament in what is known as a ___

Answer 25

FILAMENT; space cloud

Question 26

Where the x-ray photons that pass through the patient strike

Answer 26

DETECTORS

Question 27

the energy of the x-ray photons detected is converted to light

Answer 27

SOLID-STATE SCINTILLATOR:

Question 28

convert the light levels into an electric current

Answer 28

Photodiode

Question 29

the striking photon ionizes the __. These ions are accelerated by the high voltage on the detector plates

Answer 29

xenon gas

Question 30

shaped in order to compensate for the attenuations within the head and body; effectively hardens the beam and equalizes the amount of radiation reaching the image receptor

Answer 30

BOW-TIE FILTERS

Question 31

restrict the x-ray beam to a specific area, thereby reducing scatter radiation.

Answer 31

Collimators

Question 32

located near the x-ray source and limits the amount of x-ray emerging to thin ribbons.
This collimator limits the area of the patient that interceptsthe useful beam and thereby determines the patient radiation dose.  Prepatient collimation determines the radiation dose profile and patient radiation dose.

Answer 32

PRE-PATIENT COLLIMATOR

Question 33

ensure the beam is the proper width as it enters the detector and to prevent scatter radiation from reaching the detector
 reduces scatter radiation that reaches the detector array, thereby improving image contrast. It is mounted on the detector or adjacent to it.
The __determines the sensitivity profile and slice thickness

Answer 33

PRE-DETECTOR COLLIMATOR

Question 34

Converts the analog signal to a digital format

Answer 34

ADC (Analog to digital converter)

Question 35

The path that the x-ray beam takes from the tube to the detector
The DAS reads each arriving ray and measures how much of the beam is attenuated. This measurement is
called a __.

Answer 35

RAY; ray sum

Question 36

A complete set of ray sums.

Answer 36

VIEW

Question 37

the system accounts for the attenuation properties of each ray sum and correlates it to the position of the ray.

Answer 37

Attenuation Profile:

Question 38

The process of converting the data from the attenuation profile to a matrix is known as __

Answer 38

back projection

Question 39

This density number, in __, is the average of all attenuation measurements for that pixel.

Answer 39

Hounsfield units

Question 40

• The data that form the CT slice are sectioned into elements: __ is indicated by X, while __ is indicated by Y). Each one of these two-dimensional squares is a pixel (picture element).
• If the Z axis is taken into account, the result is a cube, rather than a square. This cube is referred to as a __.

Answer 40

width; height; voxel (volume element)

Question 41

• A __ is the grid formed from the rows and columns of pixels.
• In CT, the most common _ size is ___. This size translates to __ rows of pixels down and__ columns of pixels across.
• The total number of pixels in a matrix is the product of the number of rows and the number of columns

Answer 41

matrix; 512

Question 42

• The degree to which an x-ray beam is reduced by an object is referred to as attenuation.

Answer 42

BEAM ATTENUATION

Question 43

The amount of the x-ray beam that is scattered or absorbed per unit thickness of the absorber is expressed by the __ and is represented by the greek letter __

Answer 43

linear attenuation coefficient, represented by the Greek letter μ.

Question 44

HU Units are also referred to as __

Answer 44

CT numbers, or density values.