Advancements in computed tomography

Since the introduction of first computed tomography (CT) system in 1972 by GN Hounsefield and AM Cormick, which could scan only head, the scientists have successfully strived to bring about a vast number of advancements in CT technology, making it ultrafast with improved spatial as well as temporal resolution, lesser radiation, and faster reconstruction. There have been great improvements not only in workflow automation, patient comfort, and safety but also spectral CTs have made it possible to get the functional status as well in a number of conditions. All these advancements have helped in not only improving the diagnostic values of CT but also expanded the applications and the throughput multifold.

Although improvement in every component from patient table to the artificial intelligence has played a role in the advancements, the major impact came from improvements in detector technology, which has made it possible to reduce the detector collimation by more than 25 times, as compared to the detectors used in the first-generation scanners; from single-row detectors, now we have multi-row detectors.

Introduction of photon CT in 2021, which uses photon counting detector technology promises 100-percent geometric efficiency with higher spatial resolution and spectral information. The main advantages of photon CT are likely to be – highly dose efficient, with possibility to register or count every single photon with possibility to measure the energy of every individual photon and very-high spatial resolution

X-ray source remains the heart of any CT unit, and without improvements in the X-ray source systems any other major advancements in CT will be fruitless. The improved X-ray systems in the new CTs are capable of delivering high instantaneous power with high cooling rates of the X-ray tube, and yet being compact enough to be mounted inside the gantry. New tube technology with compact size and low weight makes the high rotation tubes, long scan ranges, and dual-source technology possible. And without this advancement the cardiac imaging would not have been what it is today.

One of the major drawbacks of CT has always been radiation exposure; lot has been done and is still being done to cut down the risk of radiation exposure to the patient and staff. The two techniques which have been introduced to cut the radiation dose are – implementation of the tin filter and iterative reconstruction techniques. The tin filter cuts out the lower energies to reduce dose and optimize image quality at the interface between two tissues with grossly different contrasts.

Another exciting development, which has further increased the modality’s potential is dual-energy CT (DECT), also known as spectral imaging. Although the concept was initiated in 1970 itself, the real practicality came only in the early part of this century. In dual-source energy CT, two energy levels are used to acquire images, which can generate a number of additional datasets. There are three different types of DECT platforms marketed by three different vendors – in one two X-ray tubes and two detectors are utilized to obtain simultaneous dual-energy acquisition and data processing, in the second which is basically a single-source DECT, a single X-ray tube that rapidly alternates between low and high energies and a single detector that quickly registers information from both energies are used, and in the third type, which is basically a detector-based spectral CT, a single X-ray tube with full dose modulation capabilities is paired with a detector made of two layers that simultaneously detect two energy levels. The major advantages of dual-energy CT lie in tissue characterization, liver lesion/renal mass characterization, material separation, renal stone characterization, and onco as well as vascular imaging.

Every day, improving artificial intelligence has created great potential to advance CT from reducing radiation exposure to ease-to-do scan, and finally to provide better images and diagnosis. The best of CT is yet to come and the day is not far when CT will be able to provide us not only the anatomopathological but also the functional information.