COMPUTED TOMOGRAPHY (CT)

Question 1

Computed tomography (CT) uses ____ power supplies , capable of providing stable tube currents and voltages.

Answer 1

High-fequency power

Question 2

Modern CT scanners make use of _____ in which high voltage is supplied to the tube through contact rings in the gantry.

Answer 2

slip ring technology

Question 3

is a circular contact with sliding brushes that allows the gantry to rotate continually, untethered by wires.

Answer 3

slip ring technology

Question 4

The use of slip-ring technology eliminated the _____

Answer 4

inertial limitations

Question 5

The CT x-ray tube can be energized up to ___ continuously.

Answer 5

60s

Question 6

Tube voltages range from ____

Answer 6

80 to 140 kV.

Question 7

Tube currents can range up to ____

Answer 7

1,000 mA.

Question 8

Time for a 360-degree rotation of the x-ray tube currently ranges between ____

Answer 8

0.3 and 2 seconds.

Question 9

Power loading on CT x-ray tubes can be as high as ___

Answer 9

∼100 kW.

Question 10

anode heat storage capacities are high

how much

Answer 10

exceed 4 MJ or 8 MHU or more.

Question 11

Anode heat dissipation rates are ___

Answer 11

∼10 kW

Question 12

is a principal cause of CT imaging system malfunction and is the principal limitation on sequential imaging frequency.
The anode-cooling rates of approximately 1

Answer 12

X-ray tube failure

Question 13

anode-cooling rates of approximately ___

how long

Answer 13

1 MHU per minute

Question 14

CT x-ray tubes are expected to last for at least _____

Answer 14

50,000 exposures

Question 15

_______ that separate the individual xenon detectors can also be made quite thin, and this improves the geometric efficiency by reducing dead space between detectors.

Answer 15

Metal septa

Question 16

is the fraction of primary x-rays exiting the patient that strike active detector elements.

Answer 16

geometric efficiency

Question 17

was the crystal used in the earliest CT imaging systems

Answer 17

Sodium iodide (NaI)

Question 18

Nal was quickly replaced by ___ and ___

Answer 18

bismuth germanate (Bi4Ge3O12 or BGO) and cesiumiodide(CsI), and calcium fluoride. Cadmium tungstate (CdWO4) and special ceramics are the current crystals of choice. 

Question 19

Detectors are separated from each other by a dead space of____, which reduces the geometric efficiency.

how thick

Answer 19

∼0.1 mm

Question 20

Scintillator Detector common light detectors are ____ and ___

Answer 20

photomultiplier tubes and photodiodes.

Question 21

Scintillators convert ___ of the absorbed x-ray energy into light energy (conversion efficiency).

Answer 21

∼10%

Question 22

CT was first demonstrated successfully in (year) and place

Answer 22

1970; England

Question 23

at the Central Research Laboratory of EMI, Ltd. _____, an engineer for EMI, and ______, Tufts University medical physicist from Johannesburg, South Africa,

Answer 23

Godfrey Hounsfield, Allan Macleod Cormack

Question 24

After CT was shown to be a useful clinical imaging modality, the first full- scale commercial unit, referred to as a ______, was installed in_____ in 1971

what type of scanner/ place

Answer 24

brain tissue scanner; Atkin on Morley’ Hospital

Question 25

The first CT scanners in the United States were installed in ____ at the Mayo Clinic, Rochester, Minn.

what month and year

Answer 25

June 1973

Question 26

In 1974, Dr. ______of Georgetown University Medical Center, Washington, D.C., developed the first whole-body scanner,

Answer 26

Robert S. Ledley

Question 27

first CT scanner, an ____, produced images with 80 X 80-pixel resolution (3-mm pixels), and each pair of slices required approximately 4.5 minutes of scan time and 1.5 minutes of reconstruction time

Answer 27

EMI Mark 1

Question 28

first CT scanners were capable of producing only ___ and thus were called ________

Answer 28

axial images ; CAT (computed axial tomography)

Question 29

first CT scanner used clinically was the ____ offered in ___(year)

mode/year

Answer 29

EMI Mark 1; 1972

Question 30

This first scanner was a ___ only

Answer 30

head scanner

Question 31

The system rotated __ degree, and then the x-ray tube/detector assembly translated in the other direction (Fig. 10-70). This scanning pattern continued until 180 degrees of data were acquired. This ____ geometry using the ____ is referred to as the first-generation CT. The scan required over____ and image reconstruction ran overnight.

Answer 31

1 ; rotate-translate ; pencil beam; 4 minutes

Question 32

used the same rotate-translate motion as before; however, more detectors were added and so the initial pencil beam geometry became a ___. A detector array using ____ meant that more data could be acquired in a given, and so this led to a shorter scan time and a larger, 160 x 160 matrix, reconstructed image.

Answer 32

narrow fan beam; 30 detectors;

Question 33

Third-generation scanners use a ____ technology and wide rotating ___ coupled with a large array of detectors (more than ___detectors).

Answer 33

rotate-rotate; fan beam; 800 detectors

Question 34

The third-generation CT geometry leads to the potential for _____ production

Answer 34

ring artifact

Question 35

Fourth-generation scanners used a ______ technology- use rotating tube and fixed ring of detectors (up to 4,800) in the gantry (rotate-fixed system).

Answer 35

rotate-stationary technology;

Question 36

Fifth Generation scanners- used a Stationary/Stationary technology- ______ CT (EBCT) or ultrafast CT. CT scanner has been developed specifically for cardiac tomographic imaging. They are capable of ____scan times and can produce fast-frame-rate CT movies of the beating heart.

how long is the scan

Answer 36

Electron beam; 50-msec scan

Question 37

Sixth Generation scanners- use _____ (also inaccurately called spiral CT) scanners acquire data while the table is moving; as a result, the x-ray source moves in a ____ pattern around the patient being scanned

Answer 37

Helical CT; helical pattern

Question 38

Recent innovations in x-ray tube design include a rotating envelope vacuum vessel called ___. heat dissipation rate about >60kW

Answer 38

Straton tube

Question 39

The Gantry includes:

Answer 39

xray tube, the detector array, high-voltage generator, patient support couch, and mechanical support

Question 40

2 types of CT Dectectors include:

Answer 40

Scintillator Detectors/Solid State Detectors and Gas-filled Detectors

Question 41

Detectors have high quantum efficiency, which is the percentage of incident x-ray photons that are absorbed.
- CT detectors have a quantum efficiency of ___ %.

Answer 41

> 90%

Question 42

CT imaging, two collimators are used include:

Answer 42

Prepatient collimator and Predector collimator (postpatient collimator)

Question 43

This collimator limits the area of the patient that interceptsthe useful beam and thereby determines the patient radiation dose.

Answer 43

Prepatient Collimator

Question 44

This collimator restricts the x-ray beam viewed by the detector array. This collimator reduces the scatter radiation incident on the detector array and, when properly coupled with the prepatient collimator, defines the slice thickness, also called the_____.

Answer 44

Predectector collimator (postpatient collimator); sensitivity profile

Question 45

 The mathematical principles of CT were first developed by ___ in 1917. ___’s study proved that an image of an unknown object could be produced if one had an infinite number of projections through the object.

Answer 45

Johann Radon

Question 46

The computer is a unique subsystem of the CT imaging system. At the heart of the computer used in CT are the ___ and ____

Answer 46

microprocessor and the primary memory.

Question 47

The time between the end of imaging and the appearance of an image—.

Answer 47

the reconstruction time

Question 48

Projection radiographs or CT radiographs are also known as ____

Answer 48

topographic or scout images.

Question 49

CT is expressed in terms of ______ in image quality

Answer 49

spatial resolution, contrast resolution, noise, linearity, and uniformity.

Question 50

For scan control: kVp is about ____ . maximum mA is usually ___The thickness of the tissue slice to be imaged also can be adjusted. Nominal thicknesses are ___ mm.

Answer 50

120 kVp; 400mA ; 0.5 to 5 mm.

Question 51

The degree of blurring is a measure of the _____ of the system and is controlled by a number of factors.
______ is a function of pixel size: The smaller the pixel size, the better is the _____.
______ for a CT image is limited to the size of the pixel.

Answer 51

spatial resolution

Question 52

The ability of the CT imaging system to reproduce with accuracy a high-contrast edge is expressed mathematically called as ___

Answer 52

edge response function (ERF).

Question 53

The measured ERF can be transformed into another mathematical expression called the

Answer 53

modulation transfer function(MTF).

Question 54

The spatial frequency for CT imaging systems is expressed often as

Answer 54

line pairs per centimeter (lp/cm)

Question 55

is the ratio of output to input modulation (signal amplitude) in an imaging system at each spatial frequency.

Answer 55

MTF

Question 56

The ability to distinguish one soft tissue from another without regard for size or shape is called

Answer 56

Contrast Resolution

Question 57

The ability to image low-contrast objects with CT is limited by the __ and ___ of the object and by the noise of the system.

Answer 57

size and uniformity

Question 58

Noise appears on the image as ___

Answer 58

graininess.