Computer Tomography

What type of generator is used in a CT scanner?

high frequency generator

What are some of the drawbacks to using C.T.?

high radiation dose especially in children.

How many detectors are in the curved array of a 3rd generation CT scanner?

hundreds

What was the main disadvantage of 2nd generation scanners?

increase beam scatter

If the tissue attenuates less x-ray photons than water, it has a positive or negative Hounsfield number.

negative

In first generation CT, the pencil x-ray beam used _____________ beam technology.

parallel

In CT, part of the beam that falls on one part of the detector is called...

ray

What is are the 2 main advantages of 3rd generation CT scanners?

reduced scanning time and reduced scatter radiation

What is the main advantage to 2nd generation CT scanners?

reduction of scanning time

What were the major developments in the newer generations of C.T?

x-ray beam and detector geometry

Which generation of CT scanners are common? Why?

3rd generation because 4th generation are more expensive

What is the difference in detectors between 3rd and 4th generation scanners?

3rd generation: detector array moves with the tube. 4th generation: detectors are fixed and does not move with tube

Multislice CT uses ____-____ rows of detector arrays

4 to 64+

What are 7 ways to limit radiation dose?

1. Proper centering. 2. Positioning to protect sensitive areas. 3. Use routine pediatric protocols. 4. Protect those in the room. 5. Immobilzation devices. 6. Use correct protocols and set best technique.

The CT technologist ensures that the patient is receiveing an appropriate exam by doing what 3 things?

1. Taking a thorough history. 2. Reviewing medical records. 3. Interceding on patient's behalf, as needed.

What are the 3 steps of CT?

1. data acquisition. 2. data reconstruction. 3. final image display which includes manipulation, recording and communication of that image.

What are the 5 parts of the CT gantry?

1. generator. 2. filter. 3. collimators. 4. detectors. 5. data acquistion system (DAS).

What are the 3 common features of all generations of C.T. scanners?

1. have an x-ray tube 2. have radiation detectors 3. have a gantry that holds the x-ray tube and detectors

C.T. is also used in what 3 ways?

1. positron emission tompgraphy or P.E.T. 2. single photon emission computed tomography or S.P.E.C.T. studies. 3. To plan and treat radiation therapy patients.

A CT scanning system includes what 3 things?

1. scanning unit or gantry. 2. operators console. 3. computer.

What are 4 advantages of multislice over single slice scanners?

1. shorter acqusistion time. 2. Decreased amounts of contrast media. 3. Improves spatial resolution. 4. Improved image quality.

What is the difference in beam and detector from 1st and 2nd generation to the 3rd generation?

A curved detector and wider beam that moved together.

What is the Hounsfield scale?

A scale of 2000 with bone at +1,000, Water at 0, and air at -1,000.

What is the key radiation protection principle that ensures that patient doses are kept low?

ALARA

What was the movement of the x-ray tube and single detector in the first generation C.T.?

Across the patient in a straight line, rotating 1 degree at a time to go around the patient 180 degrees total to produce one "slice". Patient would then advance in the tube and process would start all over again.

Each pixel is assigned a ......

CT number or a Hounsfield unit

What does the postpatient or predetector do in a single slice detector array? Where is it located

Controls slice thickness (single slice) and how many detector rows are exposed to limit scatter reaching the detectors (multislice) Located between patient and detector array.

Who demonstrated the first CT scanner in the early 1970s?

Godfrey Hounsfield

What does the prepatient collimator do? Where is it located?

Limits patient exposure and scatter production. Located between the patient and x-ray tube.

________ CT uses 4 to 64+ rows of detectors and collects data for mulitple slices in each revolution

Multislice

How long did one "slice" of data take in first generation C.T. scanners? How long for the enitire exam?

One slice took 4 to 5 minutes. Entire exam could take 1 hour or more

Which generation of CT scanners used linear detector array?

Second generation

What is the main difference between the 1st and 2nd generation CT scanners?

The 1st only had a single beam and detector where the 2nd had multiple beams and detectors.

What changes in the movement of a 2nd generation CT scanner compared to the 1st generation?

The tube could rotate more than a single degree before going over the patient

In the reconstuction of a image, the numbers in the matrix for each pixel represents ...

a gray value

How many detectors were used in the 2nd generation CT scanner?

about 30

The CT numbers or Hounsfield numbers are based on ...

attentuation of x-rays in water

Image data from C.T. are based on ______________ characteristics of anatomy being image.

attenuation

What does a pixel represent?

attenuation characteristics of the anatomy from a voxel

Where is the location of the data acquisition system (DAS)

between the detector array and computer

Using a ______ _______ results in a more consistent energy level of photons reaching detectors.

bowtie filter

Combines a tightly collimated x-ray beam and detectors that rotate around the patient; values of x-ray are transmitted and measured multiple times

computed tomography (CT)

Developments in C.T. scanners did not advance until _______ got better.

computers

How do 3rd generation scanners scan?

continuous rotating fan beam scan in a full 360 degrees

What views can we reconstruct a C.T. image?

coronal and sagittal planes and 3D images

Following a large number of calculations, a _______-________ _________ image is reconstructed and displayed.

cross-sectional axial

The 3rd generation scanners have a ___________ array of detectors.

curved

This amplifies electrical signal from detector and converts the signal to logarithmic data; it converts the raw data from analog to digital.

data acquisition system or D.A.S.

A physical component, consisting of multiple detectors, that efficiently absorbs the transmitted radiation and acurately converts it to an electrical signal

detector array

The beams in a 2nd generation CT scanner are parallel or divergent?

divergent

Second generation C.T. scanners has a small _____ beam and _______ array.

fan; detector

2nd generation CT scanners used ______ beam ________ technology.

fan; geometry

What is the most common reconstruction algorithm used for CT?

filtered back projection or F.B.P.

Which generation of CT scanners used pencil or parallel beam technology?

first generation

CT examinations account for approximately ______ of the U.S. population's radiation exposure resulting from medical procedures.

half

Continous rotation of the tube coupled with continuous movement of table allows for ______ scanning.

helical

________ CT allows the patient and table to move continuously and collects data for volume of tissue.

helical (spiral)

The principal drawback of the first generation CT scanners was the ...

long scanning time

What are the 4 image characteristics of a CT image to be reconstructed?

matrix, pixel, vowel, voxel volume

First generation C.T. scanners had a ___________ thick x-ray beam and a single __________

pencil; detector

If the tissue attenuates more x-ray photons than water, it has a positive or negative Hounsfield number.

positive

What are the 2 collimators present in a CT scanner?

pre-patient and post patient or predetector

In CT, transmission measurements for an individual detector in the electrical signal is called ...

profile

What is the main disadvantage to 3rd generation scanners?

ring artifacts

What determines the voxel volume?

size of pixel and thickness of the tissue

A technologic advancement that allows the tube to rotated continously without the need to rewind is called....

slip ring technology

What is an advancement made to 3rd and 4th generation scanners?

slip ring technology

What are the 2 major components of the CT scanning unit?

the gantry and CT table or couch

What is eliminated in 3rd and 4th generation CT scanners?

the need to translate

4th generation scanners have _______ of fixed detectors in a ________ inside the gantry.

thousands; ring

The first and second generations of C.T. scanners are considered "______________-_______" types.

translate-rotate

The sweep of the source and detectors around the body is called _________.

translation

In CT, this is composed of rays and is a snapshot of the measuresments from a certain location.

view