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1

Couch aka table

▪️movements
-vertical and horizontal
▪️carbon fiber properties
⬇️ absorption
⬆️strength
⬇️vibration

2

Mechanical injection systems include:

-consistency
-programming
-precise flow rates and volumes

3

Gantry

Houses the imaging components of the scanner

4

Data acquisition system (DAS)

Measures the number of photons that strike the detector, converts the information to a digital signal, and sends the signal to the computer 💻

5

X-ray tube

▪️Considerations for heat dissipation
-high anode rotation speeds
-larger and thicker anodes
-metal envelops
-dual focal spots
-power supplied by high frequency generator which enables ⬇️ heat loading

6

Detectors cooperate more consistently with a ____ beam

Homogenous

7

What does beam filtration do?

-beam uniformity
-filters out lower energy photons

8

Added/inherent filtration

-shape matches the beam divergence and the patient shape
-bow tie
-using a filter makes it easier for the detector to figure out what's going on

9

True or false: scanners require beam filtration

True

10

What are the two types of source collimation?

1. Pre
2. Post

11

What does collimation affect?

⬇️patient dose
⬇️scatter

12

What does collimation control?

-slice thickness by shaping the x-ray beam
-voxel length

13

Detectors

-measure exit radiation
-ultimately converts the measurements into an electrical signal proportional to the radiation intensity

14

True or false: detector spacing affects scatter radiation

True!
-spacing bars: arc
-distance measurements: middle to middle
-size: spatial resolution
▪️want small spacing bars
▪️want detectors to be as close as possible

15

want smaller sized detectors for better _____

Spatial resolution

16

Smaller detector = ⬆️ what?

Patient dose
-because it collects less data so need to ⬆️ dose

17

Detector characteristics

1.high efficiency (QDE)- photons must be captured, absorbed, and converted
-influenced by detector: size, spacing and material
-material: want high atomic #, high density, and increased thickness, if thickness is increased it is more likely to absorb
2. High stability- detector response to radiation must be consistent
-determined by: calibration requirements
3. Fast response time- no lag
4. Wide dynamic range- the variety of signals that can be measured by the detector

18

QDE

Detector efficiency

19

The wider the detector surface area the ____ the efficiency

⬆️ efficiency

20

Spacing contributes ____ to the image, x-rays hit it and nothing happens, so want spacing ____

Nothing to the image, want spacing closer together

21

Types of detectors

-ionization (xenon gas) ionization chamber
-solid state/scintillation

22

Ionization (xenon gas) ionization chamber

-not used in MDCT, MSCT
-1 step energy conversion
-converts directly to electrical energy
-used only in older models
Advantages:
-cheaper
-stable
-response time
Disadvantages:
-needs to be under pressure
-needs alot of space
-aluminum casing (causes a loss of photons)

23

Solid state/scintillation

-used in MDCT/MSCT
-2 step energy conversion
-x-ray energy converts to light energy converts to electrical energy
Advantages:
-⬆️absorption efficiency (94-100%)
-⬆️response time
Disadvantages:
-afterglow
-temperature and moisture sensitive
-spectral matching

24

Detector arrays

▪️Single detector row systems
-wide "Z" axis
-collimation controls slice thickness (largest allowable is less then the detector width)
-360 degree rotation = a single slice
▪️Multidetector row systems (better)
-collimation and number of detectors determine: number of slices and slice thickness, ⬇️slice thickness
-2 configurations

25

MSCT detector configurations

1. Matrix array
-aka fixed array, or uniform array
-isotopic (dimensions are the same)
-goal is to improve spatial resolution
-slice thickness is symmetrical
2. Adaptive array
-aka non-uniform array, or hybrid array
-anisotropic (dimensions are not the same, different shapes and sizes)
-slice thickness is variable
-thinner in the center, wider at the periphery

26

Multislice detector advantages

-more slices are obtained in a single 360 degree rotation
-increased volume coverage speed
-decreased time for data collection
-4 -> 320 slices per rotation
- ⬆️anatomical coverage (less chance of motion)
-design enables slice thickness manipulation
-partial volume effect
-retrospective slice thickness
-⬇️ breath holds

27

Other technical applications of CT

All about the heart rate
▪️cardiac imaging
-beta blockers: used to help reduce heart rate
-ECG: monitors heart rate
-Patients not allowed to have caffeine prior to exams because heart would be moving too much
▪️CT fluoro
-drainages and biopsies
▪️CT angiography
-contrast: PE's and stroke
▪️screening
-virtual colonoscopies
▪️CT simulation vs conventional CT scanners

28

5th generation

-fan beam geometry
-stationary-stationary
-millisecond scan time
-used for cardiac imaging in the 1980s
-⬇️ spatial resolution

29

6th generation (where CT scanners are heading to or becoming)

-dual source CT
-two tubes, detectors and DAS
-fan beam geometry
-short scan times designed for cardiac imaging
-⬆️ spatial resolution
-can use two kVp techniques

30

1st generation

▪️Motion of system: translate-rotate (180 degree rotation)
-(translate means move in a straight line)
▪️Shape or geometry of the beam: narrow pencil beam
▪️Path of tube travel: 180 degree rotation
▪️Detectors: no array (1-2 max)
▪️Scan time: 4.5-5.5 min total