Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Ct Physics Module 4 > Powerpoint > Flashcards

Powerpoint Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

Beam geometry

A

Refers to the size and shape of the X-ray beam emanating from the X-ray tube and passing through the patient to strike a set of detectors that collect radiation Atlanta attenuation data

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Beam geometry controls two?

A

Spatial resolution and dose

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Longitudinal axis ( z axis)

A

Cranial- caudal. Intensity of beam along the z axis would have equal intensity everywhere inside the beam and no intensity either side( rectangular shaped on graph)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Z- y axis

A

Side to side of the patient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Beam intensity is higher at _____ and less ____.

A

Middle

On edges

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

1 scan when talking about dose means?

A

One slice

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Dose measuring done by?

A

Physicists

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Z axis is bell shaped

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Smaller slice =

A

Increased dose to patient / better spatial resolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

D(z)

A

Dose distribution in a patient given by the function , which describes an arbitrary shaped dose intensity along patient axis

Dose distribution that is being measured

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Ct dosimetry

A

Instrumentation and methods used to measure patient dose from a Ct scanner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Ionization chamber

A

Small air filled container with thin walls that allow radiationto pass through. At high energy. Photons collides with air molecules some molecules are ionized. These free electrons can be collected on a conducting wire or plate and measured as electric charge . Amount of electric charge is proportional to the amount of ionization and to the radiation that passes through the chamber

Easiest and probably most accurate and is used almost exclusively useda

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Ct phantom

A

Ionization chamber is inserted in one of two cylindrical phantoms used to measure. Ensures standardization of measurements

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Small phantom simulate patients head at ___cm

A

16

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Largest phantom simulates patient body at ___cm

A

32

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Ct dose index (ctdi )

A

Dose descriptor developed by FDA. The ctdi represents the mean absorbed dose in scanned object ( irradiated slice) and therefore the unit for ctdi is grey. The absorbed dose can be increased by increasing the intensity of radiation or opening the collimators near X-ray tube

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Ctdi up the technique

A

Up

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Ctdi up when beam is

A

Higher

19
Q

Ctdi what is most used?

A

Ctdi volume

20
Q

Ctdi weighted

A

Account for average dose in x-y axis of patient instead of z axis . This can be done by placing the ionizing chamber in the center ctdi and at periphery , ctdi periphery of the phantom . In this case ctdi weighted can be calculated

21
Q

Ctdi volume

A

Dose descriptor which considers dose at z-axis

22
Q

Multiple scan average dose( msad)

A

First Ct dose descriptor to be identified and was standard for determining radiation dos in Ct.

It is the average dose , at a particular level from the surface , resulting from a large series of Ct slices. Formula is msad = ctdi x sw/bi

Bi is bed index distance and sw is slice width in millimeters

Not used anymore

23
Q

Factors controlled by tech

A

Slice thickness
Length of scan
Technique
Rotation time( faster less dose, decreased image quality)

24
Q

Dose length product

A

Takes both the intensity represented by ctdi volume and the extension ( represented by scan length ) of an irradiation into account. So the dose length product increases with the number of slices( correctly with the length of the irradiated body section) while the dose remains the same regardless of the number of slices or length r spectively

25
Q

Identification of organ dose

A

Takes into account the radiation type and the sensitivity of various tissue types. This is done by adding the absorbed dose to the tissue weighting factor plus the radiation weighting factor . These can be obtained from previously calculated tables

26
Q

Millisievert( msv) unit for effective dose

A

unit for effective dose

27
Q

Grays( gy)

A

Unit for absorbed dose

28
Q

Roentgen (r)

A

Exposure dose

29
Q

Optimization

A

Radiation protection

Minimizing radiation risk to patient while maintaining optimal image quality

Dose efficient equipment

Acceptance testing and quality control

Correct use of equipment

30
Q

Methods to reduce radiation dose

A

Increased screening techniques

Alternative diagnostic imaging

Reduction in multiphasic examination

Technical factor selection( ma, kvp)

31
Q

How collimation effects dose?

A

Beam width. Wider the collimation the lower the dose. In msct the measured radiation dose is inversely proportional to detector rows

32
Q

Pitch value selection

A

Pitch is increased by 2 then dose reduced in half

33
Q

Scanning geometry ( partial rotation)

A

Z axis filtering
Scanning mode
Scanning dosimetry survey
Filtration

34
Q

Bizmuth shield

A

When used with aec or tube current modulation , can cause increase a dose

35
Q

Improper centering by ___ to ____ can increase patient dose by 18% to 41% which causes noise

A

3 to 6

36
Q

Most used algorithmn in Ct?

A

Filter back projection

37
Q

Adaptive filtration

A

Used to reduce both the effects of partial volume averaging by resampling the data to a lattice with higher sample density and to reduce the image noise level

38
Q

Filtration

A

Bow tie filters intended to shape beam intensity within the sfov and to produce more uniform beam at detectors

39
Q

Pediatric patient

A

Image gently

Weight categories ( thorax and abdomen)

Age categories ( skull and brain)

40
Q

Out of field artificat

A

Due to suboptimal reconstruction algorithm

Images can be acquired using a field of view that is much smaller than object being scan thus reducing radiation

Higher resolution scanners will likely require iterative reconstruction or limited field of view scans to reduce the radiation dose required to achieve an acceptable level of noise

41
Q

Metal artifact

A

Streak artifacts are caused by multiple mechanisms including beam hardening , scatter, poisson noise, motion and edge effects.

42
Q

Metal deletion technique ( mdt)

A

Iterative technique that reduces artifacts due to all these mechanisms. Improved image quality can change diagnosis

43
Q

Kernel

A

Filter or algorithmn that effects image quality

44
Q

Detector pitch

A

Defined as table distance traveled in 360 degrees gantry rotation divided by beam collimation

Ct Physics Module 4 (1 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions