COMPUTED TOMOGRAPHY

 

ABSTRACT

    This presentation will enlighten us on what computed tomography scanning of the body is all about, what are some common uses of the procedure, how should a patient prepare, what does the equipment look like, how does the procedure work, how is the CAT scan performed, what will the patient experience during and after the procedure, who interprets the results and how do the patient get them, what are the benefits and risks, what are the limitation of CT scanning of the body.

 

INTRODUCTION

    WHAT IS COMPUTED TOMOGRAPHY SCANNING OF THE BODY?

        Computed Tomography (CT) is a powerful nondestructive evaluation (NDE)      technique for producing 2-D and 3-D cross-sectional images of an object from flat X-ray images. Characteristics of the internal structure of an object such as dimensions, shape, internal defects, and density are readily available from CT images.

    CT scanning—sometimes called CAT scanning—is a noninvasive medical test that helps physicians diagnose and treat medical conditions.

    CT scanning combines special x-ray equipment with sophisticated computers to produce multiple images or pictures of the inside of the body. These cross-sectional images of the area being studied can then be examined on a computer monitor, printed or transferred to a CD. CT scans of internal organs, bones, soft tissue and blood vessels provide greater clarity and reveal more details than regular x-ray exams.

    Using specialized equipment and expertise to create and interpret CT scans of the body, radiologists can more easily diagnose problems such as cancers, cardiovascular disease, infectious disease, appendicitis, trauma and musculoskeletal disorders.

CT imaging is:

 What are some common uses of the procedure?

•       one of the best and fastest tools for studying the chest, abdomen and pelvis because it provides detailed, cross-sectional views of all types of tissue.

•       often the preferred method for diagnosing many different cancers, including lung, liver, kidney and pancreatic cancer, since the image allows a physician to confirm the presence of a tumor and measure its size, precise location and the extent of the tumor's involvement with other nearby tissue.

•       an examination that plays a significant role in the detection, diagnosis and treatment of vascular diseases that can lead to stroke, kidney failure or even death. CT is commonly used to assess for pulmonary embolism (a blood clot in the lung vessels) as well as for abdominal aortic aneurysms (AAA).

•       invaluable in diagnosing and treating spinal problems and injuries to the hands, feet and other skeletal structures because it can clearly show even very small bones as well as surrounding tissues such as muscle and blood vessels.

      In pediatric patients, CT is rarely used to diagnose tumors of the lung or pancreas as well as abdominal aortic aneurysms. For children, CT imaging is more often used to evaluate:

•       lymphoma

•       neuroblastoma

•       kidney tumors

•       congenital malformations of the heart, kidneys and blood vessels

    Physicians often use the CT examination to:

•       quickly identify injuries to the lungs, heart and vessels, liver, spleen, kidneys, bowel or other internal organs in cases of trauma.

•       guide biopsies and other procedures such as abscess drainages and minimally invasive tumor treatments.

•       plan for and assess the results of surgery, such as organ transplants or gastric bypass.

•       stage, plan and properly administer radiation treatments for tumors as well as monitor response to chemotherapy.

     How should I prepare?

     You should wear comfortable, loose-fitting clothing to your exam. You may be given a gown to wear during the procedure.

     Metal objects including jewelry, eyeglasses, dentures and hairpins may affect the CT images and should be left at home or removed prior to your exam. You may also be asked to remove hearing aids and removable dental work.

     You may be asked not to eat or drink anything for several hours beforehand, especially if a contrast material will be used in your exam.

    You should inform your physician of all medications you are taking and if you have any allergies. If you have a known allergy to contrast material, or "dye," your doctor may prescribe medications to reduce the risk of an allergic reaction.

        Also inform your doctor of any recent illnesses or other medical conditions and whether you have a history of heart disease, asthma, diabetes, kidney disease or thyroid problems. Any of these conditions may increase the risk of an unusual adverse effect.

    Women should always inform their physician and the CT technologist if there is any possibility that they are pregnant.

 What does the equipment look like?

    The test component is placed on a turntable stage that is between a radiation source and an imaging system. The turntable and the imaging system are connected to a computer so that x-ray images collected can be correlated to the position of the test component. The imaging system produces a 2-dimensional shadowgraph image of the specimen just like a film radiograph. Specialized computer software makes it possible to produce cross-sectional images of the test component as if it was being sliced.

    The real diagram

   The CT scanner is typically a large, box-like machine with a hole, or short tunnel, in the center. You will lie on a narrow examination table that slides into and out of this tunnel. Rotating around you, the x-ray tube and electronic x-ray detectors are located opposite each other in a ring, called a gantry. The computer workstation that processes the imaging information is located in a separate control room, where the technologist operates the scanner and monitors your examination.

How does the procedure work?

         In many ways CT scanning works very much like other x-ray examinations. X-rays are a form of radiation—like light or radio waves—that can be directed at the body. Different body parts absorb the x-rays in varying degrees.

    In a conventional x-ray exam, a small amount of radiation is aimed at and passes through the body, recording an image on photographic film or a special image recording plate. Bones appear white on the x-ray; soft tissue, such as organs like the heart or liver, shows up in shades of gray and air appears black.

      With CT scanning, numerous x-ray beams and a set of electronic x-ray detectors rotate around you, measuring the amount of radiation being absorbed throughout your body. At the same time, the examination table is moving through the scanner, so that the x-ray beam follows a spiral path. A special computer program processes this large volume of data to create two-dimensional cross-sectional images of your body, which are then displayed on a monitor. This technique is called helical or spiral CT.

 

        CT imaging is sometimes compared to looking into a loaf of bread by cutting the loaf into thin slices. When the image slices are reassembled by computer software, the result is a very detailed multidimensional view of the body's interior.

        Refinements in detector technology allow new CT scanners to obtain multiple slices in a single rotation. These scanners, called multi-slice CT or multi-detector CT, allow thinner slices to be obtained in a shorter period of time, resulting in more detail and additional view capabilities.

     Modern CT scanners are so fast that they can scan through large sections of the body in just a few seconds, and even faster in small children. Such speed is beneficial for all patients but especially children, the elderly and critically ill.

     For children, the CT scanner technique will be adjusted to their size and the area of interest to reduce the radiation dose.

     For some CT exams, a contrast material is used to enhance visibility in the area of the body being studied.

 

     How is the CAT scan performed?

    The technologist begins by positioning you on the CT examination table, usually lying flat on your back or less commonly, on your side or on your stomach. Straps and pillows may be used to help you maintain the correct position and to hold still during the exam. Depending on the part of the body being scanned, you may be asked to keep your hands over your head.

    Many scanners are fast enough that children can be scanned without sedation. In special cases, sedation may be needed for children who cannot hold still.

 

     Motion will degrade the quality of the examination the same way that it affects photographs.

     If contrast material is used, it will be swallowed, injected through an intravenous line (IV) or administered by enema, depending on the type of examination.

         Next, the table will move quickly through the scanner to determine the correct starting position for the scans. Then, the table will move slowly through the machine as the actual CT scanning is performed. Depending on the type of CT scan, the machine may make several passes.

       You may be asked to hold your breath during the scanning. Any motion, whether breathing or body movements, can lead to artifacts on the images. This is similar to the blurring seen on a photograph taken of a moving object.

   When the examination is completed, you will be asked to wait until the technologist verifies that the images are of high enough quality for accurate interpretation.

   The CT examination is usually completed within 30 minutes. The portion requiring intravenous contrast injection usually lasts only 10 to 30 seconds.

CT scan: appendicitis

 CT scan: normal appendix

     What will I experience during and after the procedure?

         CT exams are generally painless, fast and easy. With helical CT, the amount of time that the patient needs to lie still is reduced.

   Though the scanning itself causes no pain, there may be some discomfort from having to remain still for several minutes. If you have a hard time staying still, are claustrophobic or have chronic pain, you may find a CT exam to be stressful.

       The technologist or nurse, under the direction of a physician, may offer you some medication to help you tolerate the CT scanning procedure.

        If an intravenous contrast material is used, you will feel a pin prick when the needle is inserted into your vein. You may have a warm, flushed sensation during the injection of the contrast materials and a metallic taste in your mouth that lasts for a few minutes. Some patients may experience a sensation like they have to urinate but this subsides quickly.

       If the contrast material is swallowed, you may find the taste mildly unpleasant; however, most patients can easily tolerate it. You can expect to experience a sense of abdominal fullness and an increasing need to expel the liquid if your contrast material is given by enema. In this case, be patient, as the mild discomfort will not last long.

    When you enter the CT scanner, special light lines may be seen on your body and are used to ensure that you are properly positioned.

 

       With modern CT scanners, you will hear only slight buzzing, clicking and whirring sounds as the CT scanner revolves around you during the imaging process.

   You will be alone in the exam room during the CT scan, unless there are special circumstances. However, the technologist will always be able to see, hear and speak with you at all times.

    With pediatric patients, a parent may be allowed in the room but will be required to wear a lead apron to minimize radiation exposure.

    After a CT exam, you can return to your normal activities. If you received contrast material, you may be given special instructions.

   

INDUSTRIAL COMPUTED TOMOGRAPHY SCANNING

        It is a process which uses x-ray equipment to produce three- dimensional representations of components both externally and internally. Industrial CT scanning has been used in many areas of components. Some of the keys uses for CT scanning have been flaw detection,failure analysis , metrology, assembly analysis and reverse engineering applications

 

 

TYPES OF INDUSTRIAL CT SCANNERS

•       FAN/LINE BEAM SCANNERS (TRANSLATE)

         Line scanners are the first generation of industrial CT scanners. X- rays are produced and the beam is collimated to create a line. The x-ray line beam is then translated across the part and data is collected by the detector. The data is then reconstructed to create a 3-dimension volume rendering of the part.

 

•       CONE BEAM SCANNERS (ROTATION)

        During the CT scan the part is placed on a rotary table. As the part rotates the cone of x-rays produce about 1300 2- dimension images which are collected by the detector. The 2D images are then processed to create a 3D volume rendering of the external and internal geomentries of the part.

 

    Benefits

MEDICALLY

•       CT scanning is painless, noninvasive and accurate.

•       A major advantage of CT is its ability to image bone, soft tissue and blood vessels all at the same time.

•       Unlike conventional x-rays, CT scanning provides very detailed images of many types of tissue as well as the lungs, bones, and blood vessels.

•       CT examinations are fast and simple; in emergency cases, they can reveal internal injuries and bleeding quickly enough to help save lives.

•       CT imaging provides real-time imaging, making it a good tool for guiding minimally invasive procedures such as needle biopsies and needle aspirations of many areas of the body, particularly the lungs, abdomen, pelvis and bones.

•       A diagnosis determined by CT scanning may eliminate the need for exploratory surgery and surgical biopsy.

•       No radiation remains in a patient's body after a CT examination.

•       X-rays used in CT scans usually have no immediate side effects.

 

 

 

INDUSTRIALLY

•       A non- destructive test for inspection and metrology.

•       Design requirements for both internal and external components are validated quickly and accurately.

•       Product quality is improved to reduce the risk of recalls

•       Internal complex features can be precisely measured without destructive testing.

•       Inspection and analysis costs from first article to production are significantly reduced

 

 

       Risks

MEDICALLY

•       There is always a slight chance of cancer from excessive exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk.

•         CT scanning is, in general, not recommended for pregnant women unless medically necessary because of potential risk to the baby.Women should always inform their physician and x-ray or CT technologist if there is any possibility that they are pregnant.

 

 

   This is necessary because radiation causes mutation( that is, a random change in a gene or chromosome) and other deformities to the baby.

•       Nursing mothers should wait for 24 hours after contrast material injection before resuming breast-feeding.

•       Because children are more sensitive to radiation, they should have a CT exam only if it is essential for making a diagnosis and should not have repeated CT exams unless absolutely necessary. CT scans in children should always be done with low-dose technique.

 

 

    What are the limitations of CT Scanning of the Body?

     A CT exam is not generally indicated for pregnant women.

    A person who is very large may not fit into the opening of a conventional CT scanner or may be over the weight limit—usually 450 pounds—for the moving table.

    For industrial usage  there is no limitation

CONCLUSION

        CT scanning has been largely used for medical purposes as an imagining tool to supplement medical ultrasonography and x-ray as well as for screening for disease and preventative medicine. For industrial CT scanning, the ability to see inside a components can be seen in their functioning position. Also, devices can be analyzed without disassembly.

          

REFERENCES        

 

 Herman, G. T., Fundamentals of computerized tomography: Image reconstruction from projection, 2nd edition, Springer, 2009

 "computed tomography – Definition from the Merriam-Webster Online Dictionary". Retrieved 2009-08-18.

 "Patient Page | ARRT – The American Registry of Radiologic Technologists". ARRT. Retrieved 2014-01-05.

 "Individual State Licensure Information". American Society of Radiologic Technologists. Retrieved 19 July 2013.

 Smith-Bindman R, Lipson J, Marcus R, Kim KP, Mahesh M, Gould R, Berrington de González A, Miglioretti DL (December 2009). "Radiation dose associated with common computed tomography examinations and the associated lifetime attributable risk of cancer". Arch. Intern. Med. 169 (22): 2078–86. doi:10.1001/archinternmed.2009.427. PMID 20008690.

Berrington de González A, Mahesh M, Kim KP, Bhargavan M, Lewis R, Mettler F, Land C (December 2009). "Projected cancer risks from computed tomographic scans performed in the United States in 2007". Arch. Intern. Med. 169 (22): 2071–7.