What is spectral CT?
Spectral CT is a way to visualize tissue composition with CT. We can determine the atomic number of the tissues in the body; and if patient has received iodinated contrast, spectral CT can determine the amount of iodine in the tissues, and virtually subtract the iodine. The energy of the reconstructed image can be altered on a a sliding scale.
How does it work?
There are as many versions of spectral CT as there are manufacturers. At HCMC, we use Philips which has a dual layer detector set-up, and the spectral imaging occurs at the detector level. This means spectral is "always on", and the images are perfectly registered.
The data from the dual layer detector is undergoes "material decomposition" to generate the various reconstructions. You can read more about the physics of spectral CT here.
How can it be used?
Reduce radiation: By eliminating need for true non-contrast images, and reducing need for repeat exams
Amplify/remove iodine: Lower keV images can be used to salvage bad CT angiograms, do low-contrast dose CT exams, and increase conspicuity of lesions.
Iodine mapping: Iodine only images can be used to look at tissue perfusion, and determine if lesions such as cysts require further work-up (in general, no iodine = benign)
Characterize tissues: Determine composition of kidney stones and joint crystals. Spectral curves can be used as a CT "fingerprint" of tissues in question.
You can read more about the utility of spectral CT here and here. Neuroradiology applications can be seen here.
What does the future look like?
The future is wide open!
Every day, we discover new ways in which spectral CT can be used to help our colleagues and our patients. The technology is rapidly evolving; I am very excited about photon counting detectors in particular.
With its vast troves of data, I predict spectral CT will be at the exciting intersection of radiomics (and AI) with personalized medicine! Watch this space!