Spiral CT Scan
Spiral CT Scan
CAT scan technology continues to evolve and promises better quality pictures and patients safety. Newer type of CT scans is known as Spiral or helical CT scan. It is called Spiral scan because the X-ray beam rotates around the patient during the scan in a spiral shape. This helps to give a continuous picture with no possible gaps between the 'slices' of the scan. The 'spiral' or 'helical' CAT scans provide more rapid and accurate visualization of the internal organs. They give more detailed pictures of the organs and tissues including blood vessels. The Spiral CT scans are faster than a normal CT scan. Many trauma centers have started using such scans for more rapid diagnose of internal injuries after serious body trauma.
A CAT scan or a CT scanner machine is a large machine in the shape of a doughnut. The patient is made to lie on a couch. The couch can slide backwards and forwards. The couch slips into the center of the doughnut shaped machine which takes the x-ray images around the body. The actual procedure takes anywhere from half an hour to one and half hours. During the CAT scan procedure, the patient's bodily movement has to be minimal and should remain as still and quiet as possible. This significantly helps to increase the clarity of the x ray images.
Some CAT scans need special preparations before hand. The preparation may vary according to the type of scan taken.
- For abdominal CT scans, the patient is asked not to eat or drink anything after midnight, the night before the scan. A 'contrast medium' has to be drunk or an injection of 'contrast medium' is administered to the patient. Some of this liquid can be taken at home but more of the liquid is taken in the x ray department before the scan. The contrast medium makes the digestive system show more clearly in the scan. This does not have any side effects.
- For CT scans of the head, the patient is given an injection of 'contrast medium' dye beforehand to make the scan clearer.
- For CT scans of the chest, the injection of 'contrast medium' dye is administered beforehand to show up the tissues in the area containing cancer or blood vessels more clearly.
- For pelvic CT scans, the patient is asked not to eat or drink after midnight of the night before the scan. An injection of 'contrast medium' is given before the scan. An injection of a drug to slow down the movement of the pelvis area is given so that there will be distortion during the time of the scan.
- For a rectal scan, the patient is given an enema occasionally. This makes the outline of the bowel stand out more during the scan.
- In certain detailed scans of the bowel called virtual colonoscopy, the patient is asked not to eat or drink for 36 hours before the study and two doses of a strong laxative the day before the scan is advised.
CBCT, also known as C-arm CT, Cone Beam Volume CT or flat panel CY is a medical imaging technique, like a conventional CT scan. It provides fast and accurate visualization of bony anatomical structures in three dimensions. It is essentially X-ray computed Tomography where the X rays are divergent, forming a cone. Unlike traditional dental x-rays that are flat images, CBCT scan can provide multiple images of the teeth, soft tissues, bone and nerve pathways. The image quality is better due to reduced scatter radiation. These images help compile exact 3D images of various angles of the face and jaw. It also allows the dentist to zoom into specific maxillofacial structures with alternate angles for clearer evaluation.
CBCT is important in planning and diagnosis in implant dentistry and interventional radiology among other things. In dentistry, it is used in oral surgery, endodontics and orthodontics.
CBCT is an important tool in image-guided radiation therapy for patient positioning and verification. Nearly 600 distinct images can be captured by rotating the CBCT scanner around the patient's head. In interventional radiology, a single 200 degree rotation over the region of interest provides volumetric data. The scanning software collects the data and reconstructs it, producing a digital volume composed of three dimensional voxels of anatomical data that can be manipulated and visualized with specialized software.
CBCT offers invaluable information in planning and assessment of surgical implants. A dental cone beam scan is the preferred method for pre surgical assessment of dental implant sites. Since CBCT is a 3D rendition, there are several structures that can be viewed with this facility, which are not available with conventional 2D radiology. CBCT offers an undistorted view of the dentition. That is why it is used for accurately visualizing both erupted and non erupted teeth. It is also used in tooth root orientation and anomalous structures.
Use of CBCT in Interventional Radiology (IR)
The scanner is mounted on a C arm in the IR suite offering real time imaging. Since this can be done on a stationary patient, it eliminates the time spent to transfer a patient from the Angiography suite to a conventional computed Tomography scanner. It also facilitates many applications of CBCT during IR procedures. Both primary and supplementary form of imaging can be done with CBCT. For fluoroscopy and soft tissues, it can be very helpful during complex procedures to reduce patient's radiation exposure.
Clinical applications of CBCT
In hepatocellular carcinoma, CBCT contrast confirms that the proper artery is selected to deliver the therapy. For benign prostatic hypertrophy BPH, CBCT provides soft tissue details needed to visualize prostatic enhancement, identify duplicated prostatic arteries and avoid non target embolization. During abscess drainage, CBCT confirms needle tip location after placement under ultrasound and confirms drain placement by revealing contrast injection into the desired location.
For adenoma adrenal vein sampling, contrast enhanced CBCT shows perfusion of the adrenal gland to confirm catheter placement for obtaining a satisfactory sample. During stent placement, CBCT improves the visualization of intracranial and extracranial stents. CBCT guides needle placement and allows diagnostic accuracy, sensitivity and specificity in lung nodules. After correction of vascular anomalies, CBCT sensitively detects small infarcts in tissue during the procedure to prevent further shunting.
Although it is a compact, faster and safer version of the regular CT, dental CBCT delivers more radiation than conventional dental X rays. Even properly shielded CBCT exposes patients to radiation many times more than 2D digital dental x rays. However, improved outcomes at lowered cost and time saving, reduced morbidity and reduced need for exploratory procedures and other such benefits of CBCT continue to make it popular with practitioners.