Recent advances in computed tomography – Current applications and future trends

From its humble beginnings as a single detector, with pencil beam geometry and a scan time of 5 minutes, CT has evolved into a technological marvel with a 640-slice capability, gantry rotation of an astonishing 0.275 seconds, covering 16 cm in a single rotation, and with ultra-high-resolution capability of 150 microns. Its isotropic voxels lend themselves to multi-planar capability with maximum and minimum intensity projection, multi- and curved-planar reformation, shaded surface display, volume rendering, 3D and 4D capability, and virtual endoscopy.

CT finds applications in virtually every organ system including the liver, lung tissue, and fat and those susceptible to patient motion and breathing like the thorax. CT has been the basis for interventional work like CT guided biopsy and minimally invasive therapy. CT images are also used as basis for planning radiotherapy treatment, and to assess the response to treatment and for oncoplastic and reconstructive surgery. CT is the method of choice for imaging trauma patients. The vascular system can be quickly imaged with CT angiography. Imaging of the liver is now possible in different contrast-enhancement phases. CT is also used as a screening tool for lung cancer. Coronary FFR-CT (fractional flow reserve) assesses the functional significance of a lesion.

Dual-energy CT systems. Potential applications of dual-energy CT systems are in oncology, detection of pulmonary embolism, renal calculi composition assessment, differentiating pancreatic parenchyma from acute hemorrhage, cardiac dual-energy perfusion, viability imaging, and cardiac iron detection.

Hybrid PET-CT. Integration of PET with CT scanners has allowed acquisition of noninvasive three-dimensional images of functional processes occurring in the human body by fusion of images, combining anatomy (CT) with function (PET). Since its advent, use of PET/CT for diagnostic and therapeutic purposes in oncology, neurology, and cardiovascular disease has been growing.

CT thermometry. Although thermometry based on MR imaging is the most widely employed technique for monitoring the effects of thermal procedures, CT thermometry in hyperthermal treatments is being explored. This technique is based on the dependency of the attenuation coefficient on temperature.

Therapeutic procedures. CT is extensively used to guide aspiration and drainage of collection and abscesses in the abdomen or pleural cavity and CT-guided tumor ablation.

Phase-contrast imaging. PCI is sensitive to the refraction of X-rays in matter. It records attenuation and phase changes of the transmitted X-ray beam and allows evaluation of planar or three-dimensional distribution of the scattering properties of the investigated object. Phase-contrast imaging of the breast and musculoskeletal field is now clinically validated.

Photon-counting technology for spectral CT. A new frontier in CT is photon-counting technology. When an X-ray passes though the body, its spectral distribution changes. Photon-counting detectors, used in photon-counting spectral CT, are able to measure the energy of a single photon and can be used to classify different materials.

Novel reconstruction algorithms. Iterative reconstruction algorithms produce higher-resolution and low-artifact images than back-projection reconstruction. 3D convolution back projection, Z-filter approach, 180/360-degree interpolation algo, and advanced single-slice rebinning are other advanced algorithms.

Hardware. CT tubes with greater heat capacities, dynamic collimation, ceramic scintillation crystals, and variable detectors are some of the CT hardware advances.

In conclusion, CT has more than exceeded the initial expectations it evoked when it was invented by Allan McCormick and Hounsfield in 1971. It has evolved into a versatile diagnostic and therapeutic tool and contributed greatly to the advancement of clinical medicine. The continual innovations in the field of CT technology have played, and will continue to play, a great role in the amelioration of suffering and betterment of human life.