Please what do you know about CT?
it is an imaging technology that produces sliced images of an organ being examined
@Blaise this is a good attempt
I appreciate your usual participation
However MRI can still produce slice images
I appreciate your usual participation
However MRI can still produce slice images
CT like Blaise said is an x-ray imaging modality which produces the images of the body parts in slices
Remember that plain radiography produces a 3D structure on a 2D plane
Thats an object that has length, width and depth are produced as image having length and width only
This therefore means there is always a superimposition of structures
because of this most plain radiography exams are done in Ap and Lateral
Thats an object that has length, width and depth are produced as image having length and width only
This therefore means there is always a superimposition of structures
because of this most plain radiography exams are done in Ap and Lateral
To overcome this challenge of superimposition a conventional tomography unit was invented whose technology you have learnt
The relative motion between the tube and the patient leads to bluring of structures at some depth depending of how the fulcrum is set
The relative motion between the tube and the patient leads to bluring of structures at some depth depending of how the fulcrum is set
Thereafter, this was computerized or computer aided to have computerized axial tomography or computed tomography
The computed tomography - CT scan or computerized axial tomography -CAT Scan
has undergone several innovations like other technologies and that follows an improvement in the earlier stages to enhance efficiency by reducing scan time, better image quality
has undergone several innovations like other technologies and that follows an improvement in the earlier stages to enhance efficiency by reducing scan time, better image quality
Because of the fast image acquisition with less time it is preferred in trauma than MRI image which takes more time
Also it is less expensive when compared to MRI
Also it is less expensive when compared to MRI
The various innovations is what we call CT generations
1st, 2nd, 3rd, 4th etc generations
Moving from a pencil beam to a fan like beam
and from a single detector to an arc of detectors and later to rounded detector where only the x-ray tube moves and the detector stationary
read up the genrations and the differences
1st, 2nd, 3rd, 4th etc generations
Moving from a pencil beam to a fan like beam
and from a single detector to an arc of detectors and later to rounded detector where only the x-ray tube moves and the detector stationary
read up the genrations and the differences
we seem to have 1st to 4th generation CTs but further innovations has continued and they are now classified into another set of generations meaning we didnt stop at 4th
example of that is the electron beam CT which is now referred as the 5th generation CT and doesnt have a conventional xray tube like others but electron from the electron gun when it sweeps off the tungsten target it produces x-ray
It is then the x-ray passess through the body
This can be used for cardiac imaging, however for economy with newer innovations with small scan time and some even having floroscopy facility i wont advice we h
just have a dedicated cardiac units since other CTs can efficiently do all exams with right protocol
This can be used for cardiac imaging, however for economy with newer innovations with small scan time and some even having floroscopy facility i wont advice we h
just have a dedicated cardiac units since other CTs can efficiently do all exams with right protocol
we continued to further generations where we have spiral CT where the slip ring technology do not have need for cables again but by electromechanical induction the tube is moving without cable
we have a next generation called multislice or multi detectors= it means the detectors outside beig round the gantry are also wider so the beam dond have to be thin but cone like while multiple images are taken per rotation and the projection data are collected and analysed
later we have cone beam, dual source and even hybrid systems like PET-CT (POSITRON EMISSION TOMOGRAPHY-CT)SPECT -CT (single photon emission computed tomography CT)
Each of this has their perculiarity.
Each of this has their perculiarity.
A later generation yet to be in the market is the flat panel detector CT= The detector is expected to be flat like the image plate used in digital radiography
WHAT ABOUT THE ROOM DESIGN OF THE CT ROOM?
While we hope to continue to look inot this but working with x-ray the room must be leadlined with appropriate lead equivalence considering the beam energy
Spacious room and good lead glass
this facility should be evaluated with a meter before satisfying it to operate
While we hope to continue to look inot this but working with x-ray the room must be leadlined with appropriate lead equivalence considering the beam energy
Spacious room and good lead glass
this facility should be evaluated with a meter before satisfying it to operate
WHAT ARE THE COMPONENTS OF THE CT?
In a normal CT room you will see a big standing unit with a bore= this is called the gantry
it is in the gantry we have the xray tube , detectors and detector electronics
the other thing you see is the bed called couch which is made of carbon fibre for its light weight and radiolucency
In a normal CT room you will see a big standing unit with a bore= this is called the gantry
it is in the gantry we have the xray tube , detectors and detector electronics
the other thing you see is the bed called couch which is made of carbon fibre for its light weight and radiolucency
Look aroung within the same room you will see the generator which works in same principle as the one discussed in x-ray machines
you can see a shelve for storage whic is not linked to the machine pe say
you can see a shelve for storage whic is not linked to the machine pe say
recal the quantity of heat production in x-ray machine and compare to that of CT
This implies a means of efficient heat dissipation, similar processes are employed as xray machine but to improve efficience the unit can either be water coolant or air coolant
if is water coolant it has a connection of water pump which may have its circuitary in one of the shelves in the x-ray room
This implies a means of efficient heat dissipation, similar processes are employed as xray machine but to improve efficience the unit can either be water coolant or air coolant
if is water coolant it has a connection of water pump which may have its circuitary in one of the shelves in the x-ray room
What about radiation protection in CT ?
@MC
this has two aspects
protection to patient where we look at justification, optimization and dose limitation
Protection of personel where we look at shielding, time you are exposed and the distance you are from the source
this has two aspects
protection to patient where we look at justification, optimization and dose limitation
Protection of personel where we look at shielding, time you are exposed and the distance you are from the source
What are the differences between cone beam and fan beam?
CT have different generations which are deference according to the time used to take any image and array detectors used
@MC yes, all the innovations are to improve time of scan and that affected the detector configurations
First generation has pencil beam with single director while 2, 3, 4,5, have fan beam with many array detectors and also first generation use minutes/slise while second generation use 10-30seconds/slice ather generation use lower time compare to first and second generation respectively
@MC apt
you are on point
Amata meza for you.
you are on point
Amata meza for you.
In the CT unit we also have the control console where we have the controlling computer and a microphone to communicate with our patient
The patient is being observed through the lead glass window
In slice 38 you will see the block diagram of the CT data acquisition system. It doenst actaully follow a logical pathway but tried to show some process that can operate for image acquisition
while we will discuss image acquisition mdes lets briefly look at the diagram
How is imges acquired in CT
First the xray tube produce xray
this xray passes through the body and differential attenuation occurs as usual
the attenuated xray passes to the detectors which then send the photon to the sample hold unit tat begins to assign gray scale to the photons relative to the information they carry
How is imges acquired in CT
First the xray tube produce xray
this xray passes through the body and differential attenuation occurs as usual
the attenuated xray passes to the detectors which then send the photon to the sample hold unit tat begins to assign gray scale to the photons relative to the information they carry
Thes data are now passed to ADC which converts this intoa digital (DIGIT) imageby use of numbering to assign locations according to spatial and sampling frequency
These digital images are now proceesed and transferred to the DAC which now converts it into what the naked eyes will appreciate and displayed on the monitor
These digital images are now proceesed and transferred to the DAC which now converts it into what the naked eyes will appreciate and displayed on the monitor
WHAT ARE THE COMPONENTS WE CAN SEE IN CT
we said gantry
couch
computers
we said gantry
couch
computers
The couch has a weight limit beyong which the system will fail
The gantry too has a normal bore diameter which if samller for very obese patients they my get hung inside
normal bore is about 70 cm wide but currently wehave some about 85 cm to help in navigation during biopsy
The gantry too has a normal bore diameter which if samller for very obese patients they my get hung inside
normal bore is about 70 cm wide but currently wehave some about 85 cm to help in navigation during biopsy
The generator being a low vltage design means it needs small energy as input voltage and able to function well and give the multiplier effect via its HT transformers
Outside the xrt, and detectors the collimators and the filters are also within the gantry
the gantry can be angulated forward or backward in a range of 60 degrees thats 30 degrees on each side
The filters do the normal role as in xray units to reduce weak energies
the collimators are two pre patient and post patient, the first controls slice thickness and the later reduces scatter leaving the patient
the collimators are two pre patient and post patient, the first controls slice thickness and the later reduces scatter leaving the patient
Filtration will reduce the quantity (intensity ) of the beam but wll increase the quality (energy ) of the beam
another important component is the detectors which absorb the xray photons and convert them to electrical signals
each manufatuer has their make just as we say direct and indirect modes of image acquisition in digital radiography
each manufatuer has their make just as we say direct and indirect modes of image acquisition in digital radiography
WHAT PROPERTY WILL A GOOD DETECTOR POSSESS?
High overall efficiency to minimize the patient radiation dose.
Be very stable with time.
Insensitive to temperature variations within the gantry
High overall efficiency to minimize the patient radiation dose.
Be very stable with time.
Insensitive to temperature variations within the gantry
In terms of efficiency
The following are considered:
Quantum detection efficiency (their responsiveness to photons) what percentage of the emited energy is detected
Quantum conversion efficiency (degree of converting the photon to electrical signal= what percentage of the detected photon is converted?
Geometric efficiency (stability in design)
The sum of all the above gives total efficiency just as that of inherent and added filtration gives total filtration
The following are considered:
Quantum detection efficiency (their responsiveness to photons) what percentage of the emited energy is detected
Quantum conversion efficiency (degree of converting the photon to electrical signal= what percentage of the detected photon is converted?
Geometric efficiency (stability in design)
The sum of all the above gives total efficiency just as that of inherent and added filtration gives total filtration
the detectors can be solid state or gas ionization, the former is taking leads in most present day elecronics due to their relative advantage
There are three types of detector designs
They include
Adaptive array detector
Matrix detector
Hybrid detector
They include
Adaptive array detector
Matrix detector
Hybrid detector
there are possible detector noise which could be computational, electronic or quantum noise which will degrade image quality
The computer controls the entire process and storage and retrival systems
we will be drawing the curtain here
Your comments if any is welcomed dear
Your comments if any is welcomed dear
In the next class we look at the basic principles more
Thank you
@MC you are welcome