Cardiac CT With >64 Slices

Here is advantages and disadvantages of Cardiac CT With >64 Slices

256 Slice CT

1. Currenly the only commercially available 256 Slice CT Scanner(Philips) has a 128 detector configuration with double sample. Air bearings allow a rapid gantry location time of 0,027s, giving a temporal resolution of 135ms. The unit is larger that typical 64 slice scanner due to the wider detector array and the need with stand the high g-forces generated by rapid gantry rotation.
2. Z axis coverage is double(8 cm) that of a typical 64-slice scanner, but still short enough to require at least two gantry rotations to cover the heart completely, images may still be susceptible to step and misregistration artifacts. However , as fewer overlapping slices are required to cover the heart, scan acquisition time reduced.

320 Slice CT

1. The only commercially available 320 detector scanner (Toshiba) has ab ultrawide detector width of 16cm(320 x 0.5mm), which is wide enough to cover the entire heart in a single rotation without the need to move the patient through the gantry. The 350ms gantry rotation time gives a temporal resolution of 175ms using half scan reconstruction . The scanner has several technology advantages
2. Low radiation dose :single rotation cardiac acquisition allow complete data set to be obtained in a single prospective pulse. As there is no need for overlap between successive rotations, radiation dose is reduced(typically 1-3 mSv)
3. Arrthyhmia management :single rotation cardiac acquisition enables the scanner to wait for an appropriately long R-R interval before the acquisition ‘pulse’. This allows a static, isophasic datasheet in all patients providing ventricular rate is well controlled(heart rate <70 bpm)
4. Prospective single-beat functional : ultrawide detector array allows acquisition of functional data from all phases of cardiac cycle using only a single heartbeat

However , there also several disadvantages

1. The wide cone-beam angle (>14^o) requires substantial computer processing power to produce artifact -free  images, particularity to corrector scatter
2. Very wide detectors are substantially heavier than conventional detectors, resulting in higher centrifugal forces during rotation
3. As a result , temporal resolution is limited to 175 ms restricting single beat  prospective scanning to patient with heath rate<65bpm.