CT

Re-emergence of CT as Imaging Modality

As radiologists have to now read many more scans per day, Computer Aided Detection (CAD) programmes are likely to become the norm in huge turnover departments

"Over the last two decades, CT scanning took a backseat as MRI emerged as a relatively more powerful modality" - Dr Roshan Shetty Chief Consultant Radiologist BGS Global Hospitals Bangaluru

'Advanced medical imaging has advanced life expectancy'. This conclusion published in the November issue of the Journal of the American College of Radiology comes from a peer-reviewed study of more than a million patient outcomes gathered from more than 100 hospitals in the US. More relevant to today's healthcare debate is the point in the conclusion that this improvement in patient mortality was achieved with no impact on cost. I think this sums up the fact that advanced imaging is here to stay.

Over the last two decades, CT scanning took a backseat as MRI emerged as a relatively more powerful modality with it's high sensitivity to disease especially in the brain, spinal cord, joints, liver and the heart.

However, over the last decade CT scanning has evolved from axial to helical to Multi-Slice or Multi-Detector helical CT (MDCT/ MSCT) scanning and the resultant advanced applications have turned the modality into a truly robust volumetric imaging technique and the focus has once again returned to this powerful imaging modality.

MDCT isotropic voxel imaging with sub-millimeter resolution (same slice thickness in all planes) has made CT imaging a 'virtual reality' and also made it popular with clinicians as they can now see images in the way in which they are used to seeing it in the operating theatres (coronal sections by a surgeon during open surgery). This huge advancement has put tremendous pressure on radiologists to improve skill sets to deliver excellent reports. Resultant improvements in coverage and temporal resolution have opened the doors to challenging imaging tasks. The holy grail of early CT researchers was always the heart as with 8 and 16-slice CT scanners practically all other body applications had been covered. The beating heart however continued to pose a challenge as it moved faster than even the fastest scanners.

With 64 slice MDCT scanners, this last barrier was also breached as clinically significant and reproducible coronary angiograms could be performed.

On the flip side, there was a huge increase in the number of images available for perusal of radiologists. Fortunately giant leaps in computer technology in image storage and processing helped solve this problem. The emergence of PET-CT was another boost in the arm for the further growth of MDCT scanners.

Newer Advances

As the cardiac debate will end, in the coming two years CT will become a more reliable screening tool, future trends will be towards organ perfusion and drug delivery systems.

Perfusion imaging carries the potential to improve early detection of cancers due to the perfusion differences and also possibly to assess response to treatment. As radiologists have to now read many more scans per day, CAD (Computer Aided Detection) programmes are likely to become the norm in huge turnover departments and more applications than the current breast and lung modules are sure to come through.

Dual energy, dual source CT

scanners have now eliminated the need for breath holds and so will now be available to a host of people who were till now thought unfit to be scanned. Hybrid imaging is now the norm in most high end oncology centres with fusion CT/ MRI and PET images.

Research Trends

With all the hype surrounding the number game, each manufacturer was trying to upstage the other in terms of tube technology (trying to reduce their weight, increase their capacity, increase the number of tubes), detector technology (reduce after glow, using garnet- an actual gemstone), increase the number of slices (256, 320 and even higher).

Dual source dual energy CT which has two tubes with different photon energies and also a rotating gantry at the core of its advancement. Dual energy single source CT is also another advancement from another vendor. Some vendors have focused on increasing coverage (up to 48 cm in a single acquisition). Continuous dynamic imaging will soon enable one to visualise organs in motion- vocal chords during phonation, joints during movements.

Other vendors are designing scanners to accelerate research in the areas of cardiac disease and drug delivery systems. Their experimental studies on animal models have shown that the X-ray exposures are fast enough to capture the beating heart motion of the mouse.

CT Breast imaging is another dynamic area of research and perfusion as well as treatment options will be available on these scanners which will have the patient in the prone breast dependant position.

Spectral imaging is another certainty in newer systems. Here organs are colour coded according to their attenuation values (the human eye cannot for example differentiate 5,000 shades of grey). It utilises the detector's capability to capture data from different individual energies between 40 to 140kVp and look at the optimal energy of the individual organ. It thus allows for more accurate representation of organ and tissue and normal and diseased boundaries.

Concerns

On the flip side, there has been a huge increase in the number of images available for perusal of radiologists. Fortunately, giant leaps in computer technology in image storage and processing helped solve this problem. Newer scanners will make 3D technologists redundant as most of the reconstructions will be automated and available at the click of a button.

Radiation Hazard

MDCT quickly moved from poster boy to punching bag with rightly placed concerns about high patient and community radiation. The backlash has lead to many innovations in this direction by all CT vendors and all the recently released. MDCT scanners have significantly reduced radiation dosages to a fraction of what it is on previously available scanners.

Cost of Ownership

The initial high cost of ownership of these scanners is itself a huge hurdle in the way of exponential growth of these scanners. As individuals, hospitals and corporates struggle to invest in this costly high-end equipment which will become redundant in terms of technology in few years, manufacturers will be forced to keep upgrade paths for customers open for at least the initial few years after purchase of these new equipment.

Conclusion

One can safely conclude that the only thing that is permanent in this ever evolving field is 'change' and the next five years will see more tremendous innovations from the industry as CT scanning will move towards physiological and functional imaging.

roshanvshetty@gmail.com