CT Test 2

State the range of kV that is commonly used in computed tomography

120-140 kVp

Why are scintillation-type solid state detectors coupled with a photodiode more common in new CT scanners as opposed to the xenon gas detectors

99% efficient, but slight afterglow

In order to create a CT image, the process can be described or subdivided into three main processes or phases; data acquisition, image reconstruction and image display. During these three main processes or phases involved in creating a CT image, what happens to the "data" during each phase?

Date Acquisition- acquiring data that results from the attenuation of the x-ray beam as it passes through the patient to strike the detector, the mechanisms housed within the gantry and the patient table are the components necessary for data acquisition -Image Reconstruction-refers to the process whereby a computer manipulates data collected from the detectors to create a CT image, raw data include all attenuation measurements obtained from the detector array, some raw data used in creation of the image, computer manipulates the raw data throughput the image reconstruction process -Image Display-final step in creating the CT image, analog monitors display the CT image

Why is it important for a detector to be efficient during the data acquisition process in CT

because that is what collects the information

Why is the Image Display so important for CT imaging

because the image is created to get a report

Location of pre-detector(post) collimators

below the patient and above the detector array, right before detectors

Disadvantage of small focal spot size

cannot tolerate as much heat

Advantage of Helical scanning

continually rotating X-ray tube, constant x-ray output, and uninterrupted table movement, decreased respiratory and cardiac motion artifact

Incorporating high kV affects patient dose by(if reducing mA)

decreasing patient dose

Purpose of pre-patient(source) collimator

dose profile, limits the amount of x-ray emerging to thin ribbons, acts on the beam before entering the patient

During what part of a CT exam procedure would the helical or spiral scanning occur

dynamic motion, contrast studies

During what part of a CT exam procedure would the conventional step and shoot or axial scanning occur

head, patient moves can stop and fix

Identify the scanning mode the advancement of the slip ring technology has allowed to be performed in computed tomography

helical

Why is Tungsten commonly used for the X-ray tubes used in computed tomography

high atomic number, high melting point

Identify an advantage of using Conventional or Step - and Shoot Scanning

highest image quality, CT table moves to desired location and remains stationary while the X-ray tube rotates within the gantry

Incorporating high kV affects intensity of the beam by

increasing intensity

Incorporating high kV affects penetrating ability by

increasing penetration

Why is it important for detectors in a detector array to be positioned so close together

information will get lost if there is space in between, allows the beam to be highly collimated

Explain the importance of not over working the computed tomography table or couch

it will wear out faster and need to be replaced more often

The detector array serves what purpose in CT

measures the intensity of transmitted x-ray radiation along a beam projected from the x-ray source to that particular detector element

Components housed within the gantry

microphone, speakers, laser light to position patient

Does raw data or image data require more computer space for archiving and storage

raw dara

Raw data for image reconstruction process

raw data- data sitting in the computer waiting to be made into an image, may be used to generate a new image, requires more space

Incorporating high kV affects heat load by

reducing load

Location of pre-patient(source) collimators

right before patient, near x-ray source

During what part of a CT exam procedure would the localizer, scanogram, or preliminary scanning occur

scout image, to get approx dose report

Disadvantage of Conventional or Step - and Shoot Scanning

slight pause in scanning between data acquisitions, only a single scan can be made each time patient holds breath

Why are high frequency generators used in computed tomography to create images

small enough so that they can be located within the gantry, CT needs high voltage for high energy

What are the common focal spot sizes used in computed tomography

small focal spot, 0.5 and 1.0mm most used

Advantage of small focal spot size

smaller size creates sharper image because of reduced penumbra

Image Data for image reconstruction process

the data averaged so that each pixel has an associated number, so an image can be formed, requires 1/5 of the storage raw data needs

Purpose of post-patient collimator

this detector shapes the beam after it has passed through the patient

What is the purpose of beam filtration

uniform intensity, patient has to be isocenter, reduce radiation dose and minimize image artifact