CT Technology at a glance

CT Technology at a glance

by Sunday Joshua Akochi -
Number of replies: 29

Please share your experience, comments or questions in our previous classes if any?

 

 

In brief how do you think image formation in CT is done?

 

Name one or two CT artefacts you know and how it can be reduced

Share your knowledge while we hope to begin our discussions in few minutes.

Thank you

In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by PLACIDE BIZIMANA -
Image formation in CT, for me . First there is exposure to patient, means x-ray passes into patient with different attenuation, then attenuated x-ray accepted by detectors, here x-ray if then ADS converts that electrical signal into digital signal, there after DAS converts that digital signal to visible data that can be displayed on monitor!!! The artifacts in CT are coefficients of object and systematic discrepancy btn CT number in reconstructed image and true attenuation..
In reply to PLACIDE BIZIMANA

Re: CT Technology at a glance

by Sunday Joshua Akochi -
@Placide this is indeed an amazing summary of the process of events that happens
In question 2 i wanted you to name any artefacts and how to minimize it, however that definition is awesome
Thank you
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by PLACIDE BIZIMANA -
For last session , I would like to ask, how position emission tomography differs from computerized Tomography..
In reply to PLACIDE BIZIMANA

Re: CT Technology at a glance

by Sunday Joshua Akochi -
@Placide Good question
In PET the source of radiation is the patient (administered radiopharmaceutical)while in CT the source is the machine (xray tube)
The positron interacts with electrons and cause annihilation process that then ove away from each other in 180 degrees. It is gamma ray from the annihilation interactions that are used in PET imaging.
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by PLACIDE BIZIMANA -
Also I would like to ask another question, To use DSCT means you get Two slice image at the same time?
In reply to PLACIDE BIZIMANA

Re: CT Technology at a glance

by Sunday Joshua Akochi -
@Placide
NO
It just tells you it has two sources of x-ray ganged with the detectors
Although it an contribute but doesnt mean two slices only
designs of most present day CTs are made to obtain more slices in one rotation that helps in reducing the time of scan
so if you hear 1, 4, 16, 32, 64, 1or 128 slice CT it means that in the CT 1, 4, 16, 64 or 128 slices are produced per revolution
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by PLACIDE BIZIMANA -
Again, what are the advantages of MDCT to conventional spiral CT. And how they differ in terms of division of X-ray beam.
In reply to PLACIDE BIZIMANA

Re: CT Technology at a glance

by Sunday Joshua Akochi -
MDCT has a wider design of the detector assembly giving room for wider acquisition per rotation and then reconstructed but in spiral CT the table movement is continuous all through the scanning process. This differentiates what we used to call step and shoot= a case the table moves and stops for an acquisition, then moves again and stops for another acquisition till the entire region is scanned but with spiral the table movement is continuous.
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
WHAT ARE THE PROCESS OF IMAGE FORMATION IN CT?

In line with Placide's overview we give this summary

X-ray beam passes through the body with the relative tube to patient movement preventing superimposition.
The beam is finely collimated to reduce scatter and give better contrast resolution
The collimated beam pass through the body and are differentially absorbed or attenuated
The beam exits the body and strike the detectors.
These detectors are quantitative and distinguish differences in tissue contrast.
Detectors converts photons to analogue signal
The ADC converts it to digital signal
Digital data is sent to CPU for reconstruction
The DAC converts the digital image into a visible image
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
Further overview on image formation
Scan data recieved from attenuation process is sent for preprocessing where these are sampled and assigned gray scales which forms the Raw data, these raw data are then passed to into digital images where Convolution/filtering takes place, convolution is like using two functions in a mathematics to generate a third function, and this is filtered just in a way we could refer to digital radiography in accessing exposure data recognition. Then the Filtered raw data is sent for back projection where the reconstructions occur either in backprojection, iterative or analytical methods which are mathematical processes or model and finally the Image data
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
WHAT IS CT NUMBER?
in conventional radiography we talk of about 5 densities but this seems to be different cos of the gray scales assigned to each data based on the information it carries
This is called ct number measured in HU =Hounsfield Unit.

It measure the mew (attenuation coefficient of tissue with respect to that of water)
It ranges from minus 1000 for air to plus 1000 for metalic components
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
It is give mathematically as attenuation coefficient of tissue minus that of water and divided by that of water
In CT there are ranges of CT numbers that helps you to know the composition of structure

To get a CT number of a structure in CT image you call up a cursor and draw a wider circle around the object and you have the value dispalyed
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
Pixel and Voxel in CT has similar meaning as in Digital radiography or any other digital images
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
WHAT ARE TERMS I CAN SEE IN CT AND WHAT DO THEY STAND FOR?

WIndow or windowing. you will hear bone window or soft tissue window during imaging
This is means in an image you will either decide to view the image in bone or in soft tissue window

This helps to display better image of one and compromising the other
example if i want to see brain CT in bone window i will appreciate the bony details but the brain or soft tissues would be poorly seen. This may reveal subtle fractures that are not readily seen on normal window and vice versa
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
So windowing is all about the adjustments and we have window width which is a range of values of ct numbers allowable in the particular instance and the window level as the median
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
Other terms
Pitch= table movement per revolution
Pitch ratio= pitch/slice thickness
field of view is the covered area it can be scan field of view which shows all the body parts to be covered same way you collimate all anatomy in chest x-ray
dispaly field of view is the range of image obtained

the scan field of view is usually bigger than the display field of view
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
resolutions is the ability of the ct to distinctly delineate closely related structures and can be spatial or temporal
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
Scout or scanogram is the first and preliminary image you get after positioning which is used for planning of the procedure

exposure factors are same as kv, mas....
You will be hearing protocols too which stands for all the techniques for a particilar exam

you will hear ct protocol of the head, spine, thorax= they imply techniques for each of the exams
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by MARIE CLAIRE NIYONIZEYE -
I know Ring artifact
In reply to MARIE CLAIRE NIYONIZEYE

Re: CT Technology at a glance

by Sunday Joshua Akochi -
@ MC thats nice
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
WHAT ARE POSSIBLE ARTEFACTS IN CT?

The students should be able to read up details in a text and appreciate the methods of reduction so as to be able to brain storm during such challenges in practice or advice a colleague having similar images
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
Artefacts can be due to the design of the system (physics based) like beam hardening so the use of filter and correction softeware is employed. worthy of note that the manufacture has correction software for different artefacts to help reduce incidence but that doesnt take the professionalism of the scientist

Patient based like things on the patient so reducing is proper changing and instructions
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
streak and or Ring artefcts could be due to metalic structure or commonly due to errors in the detectors. this can be minimized by caliberations and if it persists it means ifs damaged and should be replaced

Partial volume could be due to poor positioning so proper positioning is key to minimizing and because in some conditions this is not possible the use of thin slice thickness is a remedy

Beam hardening artefacts can happen when the body absorbd the beam differentially to reduce this filter helps to harmonize the energy of the beam so thats a remedy
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
WHAT CARE DO I TAKE OF THE CT MACHINE

Alway do daily tube warm up before start of work just as u do in xray
Periodic calibration with phantoms
These are basic and then cleaning and being sure nit to press thing you are not familiar with
care of electrical connections to avoid electrocutions
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
WHAT ABOUT CLINICAL APPLICATIONS?
CT is used for the various examinations and many more. You will study them in a practice class but is good you know what they stand for
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
Thank you so much for the time and attention and above all making the forum very interactive with your amazing contributions

You all rock for sure

really awesome workig with you
In reply to Sunday Joshua Akochi

Re: CT Technology at a glance

by Sunday Joshua Akochi -
We will continue on monday and if possible conclude our discussion

Have a blessed day