ct midterm

Shanks Redhaired · 7問 · 1年前

通報

問題一覧

generator used in ct scan

high frequency

where is ct generator located

inside the gantry/mounted on frame/in corner of the gantry

3 types of disks

conventional all metal, brazed graphite, cvd graphite anode

ct filtratiin purpose

removes long wavelength, shape the energy distribution

first filter size

3 mm aluminum equivalent thickness

flat filters materials

copper/aluminum

flat filters materials location

between xray tube and pt

cross section of patient

mostly oval shaped

shape for oval patient

bow tie

these filters have an increased thickness from center to periphery allowing them to attenuate radiation hardly at all in the center but strongly in the periphery

bow tie

they modifiy the xray spectrum uniformly across the entire field of view

flat

bow tie filters materials

low Z, high density, teflon

in some machines comb - it is close to the detector array are used to decrease the effective detector element width and thus increase the achievable geometrical resolution.

shaped collimator

where are xray tube filter located

mounted close to xray tube

it support the pt comfortably

pt couch

pt couch material

low Z (carbon fibre)

maximum table load

200-330 kg

types of collimation

pre pt, post pt

where is pre pr collimation located

xray tube housing

requires a scout radiograph for anatomical orientation and scan region (slice) selection and scan performed in sequential or helical mode.

routine scan

similar to a conventional radiograph, is very useful for selection of single slices or complete scan regions.

scout radiograph, survey radiograph, scanogram, topogram, scout view

This radiograph is taken with a low dose and low spatial resolution by transporting the patient slowly through the field of measurement with the X - ray tube in a fixed position with radiation emitted continuously or in pulsed mode.

scout radiograph, survey radiograph, scanogram, topogram, scout view

are particularly useful to select the gantry tilt according to anatomy.

lateral scanogram

For a long time, CT examinations consisted of scanning single slices sequentially.

sequential scanning, axial scanning, single slice scanning

is scanned, then the patient is transported for a scan increment, mostly equal to the chosen slice thickness. Then, a second scan is taken and the procedure is repeated

sequential scanning, axial scanning, single slice scanning

This examination mode is relatively time - consuming and has been largely replaced by the faster helical CT. One fundamental disadvantage is that overlapping images for 3D image reconstruction are generally not available

sequential scanning, axial scanning, single slice scanning

offer automated and therefore fast modes for scanning single slices sequentially. Cardiac scanning may be a future indication.

modern scanner

is used to record temporal changes in the density characteristics of an object. Typically, dynamic scanning is used to assess contrast medium dynamics

dynamic scanning, serial scanning

A representative selected slice is scanned repeatedly or multiphase examination of a complete organ is performed before, during and/or after administration of contrast medium

dynamic scanning, serial scanning

The observed changes may represent

physiological process, pathological process

Physiological process

heart motion, breathing

Pathological process

portosystemic shunts

is a minimally invasive technique, which provides an excellent 3D representation of portal and hepatic vascular anatomy.

dual phase ct angiography

methods serve to obtain information about the material composition in the tissues examined.

material selective scanning, dual energy ct

To achieve this, a selected slice is scanned with two different spectra, i.e. with different high - voltage values and possibly with different filtration.

material selective scanning, dual energy ct

This can be done in two successive scans or by switching the high voltage rapidly from projection to projection.

material selective scanning, dual energy ct

Several factors influences the external dimensions of the CT Gantry:

sad, scan fov, fan angle

The distance between the x-ray tube and the patient at the isocenter is shorter than long geometry.

short geometry

Improve image blur and decrease radiation dose.

long geometry

Electromechanical device consisting of circular electrical conductive rings and brushes that transmit electrical energy across a rotating interface.

slip ring technology

2 slip ring technologies

low voltage, high voltage slip ring

Convert alternating current to direct current

full wave rectifier

Device that has ability to store energy momentarily

capacitor

Assure a flownpf electricity within the x-ray generator

inverter circuit

Assure the high amount of voltage that is circulating or flowing in the x-ray generator to sustain the other part of the scanner

high voltage transformer

Maintain the consistent current or direct current

full wave rectifier

Housing that protects the xray tube

tube envelope

Negative side of the x ray tube

cathode assembly

When the cathode is activated there will be intense heating of the filament which lead to the release of electron

thermionic emission

Element added to filament

thorium

Focuses the electron emitted by the filament into one direction

focusing cup

It produces electron

filament

It contain what we call focal spot

target

Area of the focal target that is impacted

actual focal spot

Actual size or the area of the focalled spot that is projected out of the tube towards the object being radiograph

effective focal spot

Anode assembly

target, rotor stud, hub, rotor, bearing assembly

Cathode assembly

filament, focusing cup

Rotating part of the anode assembly

bearing assembly

2 types of bearing

ball, liquid

Bearing that requires lubrication

ball bearing

Bearing the continuous supply of gallium liquid used to lubricate

liquid bearing

Anode disk that is connected to tmz, circuit of all metal disc

conventional all metal disk

Anode disk that makes the anode lighter

brazed graphite disk

It is the lightest and more efficient in producing x-ray graphite

chemical vapor deposition graphite anode disk

Power capacity of anode disk

must be high

Power capacity Ma, kVp

>120kvp, 400ma

High speed rotors purpose

for heat dissipation

Anode heat capacity

7 mhu

Heat storage capacity

8 mhu

Anode focal spot size

must be small, robust, heat dissipation

X-ray tube life

approximately 5000 exposures

Inherent filtration of the xray tube typically

3mm aluminum

Filter that is made up of copper in aluminum

flat

Filter that displays between the x-ray source and the patient

flat

Filter that modify the x-ray spectrum uniformly across the entire fov

flat

Flat filter is made of

copper/aluminum

Filter decreases inhomogeneity to become homogenity

bow tie

Bow tie filter is made up of what

teflon

Filter that is being used to create gradient in the intensity of the x-ray theme

beam shaping

Filter that reduce the dynamic range of the signal recorded by the cy detector

beam shaping

Filter attempt to normalize thebeam hardening pf the beam to aid beam calibration

beam shaping

In attempt to normalize thebeam hardening pf the beam to what

aid calibration

Constructed by low Z material (Carbon fibre) so it will not interfere with x-ray beam transmission and patient imaging

patient couch

Should be smoothly and accurate motor driven so accurate positioning is possible.

patient couch

Capable of automatic indexing.

patient couch

Collimator Depends on the focal spot size

pre pt

Collimator Mounted on the x-ray tube housing

pre pt

Collimator Creates more parallel beam

pre pt

Collimator Reduces patient dose

pre pt

Collimator restricts the field of view of the detector

post pt

Collimator Reduces the scatter radiation on the detector

post pt

Collimator Determines the slice thickness

post pt

Group of detectors

ct detector technology

The image receptor in CT

detector

absorbs radiation and converts it to electrical signal

detector

Types of detectors

gas filled, scintillation, solid state

Refers to the efficiency with which the detectors can obtains photons transmitted from the patient.

capture efficiency

Capture efficiency other term

geometric efficiency

Refers to the number of photons absorbed by the detector and depends on the atomic number, physical density, size and thickness of the detector face.

absorption efficiency

100

Absorption efficiency other term

quantum efficiency

projection

projection

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