CT SCAN : GENERATIONS

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 Generations of CT scan :- 

Ct scan have gone many design changes since 1970.
A variety of CT geometries have been developed to acquire the x ray transmission data for image reconstruction.
 There are seven generations of ct scan...

(1) first generation -  translate rotate system



There are pencil x ray beam used in first generation. It is designed for brain imaging.
There are a total of 180×160= 28,800 rays are measured .
This combination of linear translation followed by incremental rotation is called translate - rotate motion.

Disadvantage:- 

→Water bath acted as a bolus
→Afterglow of Nal

(2) second generation- narrow fan beam



→Narrow fan beam & multiple detectors (linear array of 30 detectors).
→With 10° rotation increment only 18 translation would be required for 180° Image acquisition.
→Data 600 per projection and no. of projection.

(3) third generation - rotate/rotate



Third generation scanner uses increased number of detectors ( up to about 750 detectors) and rotate - rotate system.
There are fan beam of 50° - 55° is used.
Spatial resolution 5 to 10 lp/cm >1000 projection in 1 sec.

(4) fourth generation - rotate stationary



A large stationary 360° rings of detectors with the x-ray tube alone rotating round the patient fan beam.
There are 4800 detectors  are used which is not rotate around the patient.
The spatial resolution is 20 lp/cm.

 (5)fifth generation - electron beam ct scan



There are 50msec  time needed in cardiac imaging which is not possible with another generation ct scanners and it is done by fifth generation ct scan or electron beam CT scan.

It is used when fast imaging is required.
A CT scanner was developed specially for cardiac imaging which was capable of performing complete scan in a little as 10- 20 ms.



It doesn't use any conventional x ray tube.
It consist wave guide to accelerate an high energy electron beam.
These high energy electron strike on tungsten ring and produces a cone shaped x ray beam.

There is no moving part in the gantry.
Typical scan time is 30- 40 sec for 12 cm volume.

(6) sixth generation - spiral ct / helical ct



Although 3rd and 4th generation eliminate translation motion but there is problem, the scanning process stopped after per slice scan, so there is poor temporal resolution and long procedure time.

3rd/4th generation + slip ring technology + patient motion = 6th generation / helical CT
 
The development of helical or spiral ct was truly revolutionary advancement in CT scanning that finally allowed true 30 images acquisition within a single breath hold technique.

(7) seventh generation - MDST



It uses multiple detector array, the collimator spacing is wider and more x ray are used in producing image data.

Opening up the collimator in a single array scanner increase the slice thickness, but reduces spatial resolution in the slice thickness dimension hense, slice thickness is controlled by detector size not by the collimator.

A 4 contiguous 5mm detector array gives 20mm collimator spacing. 
The number of x rays, detected is 4 times higher than that of single array of 5mm.

It has better efficiency for patient imaging and detector pitch needs to be defined.

        

Can you answer my question? 

Which CT scan used in cardiac imaging ?
In which CT scan use narrow fan beam?
Who is the inventor of CT scan? 


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