CT scan technology has undergone remarkable progress, with focus on reduction of radiation dose and improved resolution, says Dr Sona Pungavkar, Consultant, MRI Centres, Global Hospitals, Mumbai
The original CT machines obtained scans in series, one after the other (2D images). The new generation CT scanners acquire continuous pictures in a helical/spiral pattern (3D images). The newest scanners, called multislice or multidetector CTs, allow more slices to be imaged in a shorter period of time. These scanners provide better resolution and can detect small abnormalities better.
CT scan technology has undergone remarkable progress, with focus on reduction of radiation dose and improved resolution. Some of the improved methods include:
Dose reduction techniques: Small amount of radiation passes through the body to create an image. Exposure to radiation must be limited, as it can cause several complications including cancer. Newly developed technology allows high quality images with reduction in dosage up to 40 per cent. The machine is optimized to minimize patient dose, limited to guidelines for recommended dose provided by American College of Radiology (ACR) according to the age of the patient.
Dual energy CT scanning: Also known as spectral imaging (SI) provides two data sets using low and high energy levels (kVp), which are acquired, simultaneously to freeze patient and gantry motion. It allows options for material analysis and tissue characterization. A large field of view, upto 50 cm can be obtained using SI.
Wider applications: The newer scanners, with multi-slice, multi-detector technology with helical scanning allow acquisition of 300 slices in 0.3 milliseconds. Because of reduced times, CT scan has replaced other high radiation techniques such as conventional Intravenous pyelography. A 30 second CT acquisition provides information about entire urinary tract, detecting small calculi, which could have been missed otherwise. Contrast excretion provides functional information.
Cardiac function and physiology: Entire heart can be covered in single heartbeat, allowing accurate assessment of myocardium and coronary arteries. Iodine-alone images of arteries can be obtained, by taking out the calcium. This allows better visualization of stenotic lesions. Deep vein thrombosis is a common occurrence, leading to morbid and fatal pulmonary embolism. These emboli can be lodged in small pulmonary arteries and are difficult to detect. Pulmonary angiography is now being performed using new technology with satisfactory delineation of the small arteries. Earlier more invasive techniques with cauterization were required.
Peripheral angiography: CT angiography is currently method of choice for evaluation of the peripheral arteries. This has been the result of multi-detector scanners. Previously, images were limited by calcification in the arteries of the leg. These limitations have largely been overcome by the new systems which have 64 detectors. The entire aorta and the lower limb arteries can be scanned in 15–20 seconds. Post processing involves stripping of bone and calcium.
Artifact reducing technology: Metal inserted in the body after intervention causes artifacts overlapping the area of interest. This allows sub optimal imaging with loss of information. With the new imaging techniques, the artifacts caused by these implants can be reduced considerably, increasing the accuracy of evaluation in the post-operative setting.
Post processing techniques: These have also advanced parallely. Earlier, long time was required to make a 3D image using C data on workstation. Currently, it takes few minutes to obtain superior quality images. 3D virtual patient modelling software is available, which enables preoperative assessment, navigation, and fusion with radiotherapy treatment plans and metabolic imaging such as PET.