Keywords:
Cardiac, CT-Angiography, Stents, Arteriosclerosis
Authors:
J. Hoe, R. K. Kwok; Singapore/SG
Methods and Materials
Subtraction ( using novel software) can be used to remove calcified plaques from the coronary arteries seen on CCTA scans.The calcium score scan can be used as the non-contrast data for subtraction.Subtraction is to remove blooming and beam hardening artifacts.The resultant images is a lumenogram,
only the contrast filled lumen is displayed
Software was developed to perform calcium subtraction of coronary arteries on 320MDCT.Calcium subtraction software has the potential to perform stent subtraction as–Stents are metallic and density may be higher or lower than calcium ,depending on type of stent–Stent material varies across vendors–Also–Position of stent may affect subtraction–E.g.
overlapping stents–Nature of native artery ,
calcified / not calcified plaque may also be present adjacent to wall of stent etc
Scans are performed on a 320 MDCT (Aquilion VISION ) scanner with gantry rotation time of 275 msec.Scanning parameters must be the same and are locked together e.g.
-kV,
-range,
-rotation speed,
reconstruction.Sophisticated algorithm is used for post processing using both rigid and deformable registration for calcium subtraction
Examinations can be performed in one or two breath-holds
.
19 patients were scanned using a 2 breathhold techniquen.
Pre contrast scan similar to coronary calcium scoring was used as the mask for subtraction,
followed immediately by CCTA study.In 5 patients tube voltage used was 120 kVp for both scans,
while in the rest 100kVp was used regardless of body weight.
CCTA was performed with phase window of 40-80% R-R cycle.
Most (18/19) cases were acquired using 1 heartbeat scan.1 case was acquired using 2 heartbeat scann.
All phases of both Non-Contrast and CTA
were reconstructed at 1% intervals and a single best phase for stent subtraction was selected for all vessels.
Stent subtraction from the CCTA images was performed using novel software.Quality of subtraction for contrast filled lumen visualisation and possible instent restenosis was assessed on a 4 point visual Likert Scale.