Tomography

  • Tomography is also recognized as computed tomography (CT). Specialists use CT scans to examine inside body structures(1). Mayo Clinic defines a computerized tomography (CT) scan as combining a series of X-ray images collected from various angles around a patient’s body with computer processing(2).
  • Unlike the conventional X-ray, which uses a stationary X-ray tube, a CT scanner has a motorized X-ray source that rotates around a circular frame known as a gantry(3). Then, the X-ray tube rotates around the patient’s part of the body while they rest on the bed, emitting small radiation beams.
  • Before doctors send a patient for a CT scan, it is necessary to establish that a CT scan is the proper diagnostic tool to confirm or rule out the suspected conditions(4). It is recommended to get professional advice from a radiologist if the patient is uncertain. Moreover, before obtaining a CT scan for a child or adolescent, it is essential due to their heightened radiosensitivity.

What Is a Computed Tomography (CT) Scan?

CT scans, also known as computed tomography, are used by medical practitioners to study internal body structures(5).

Mayo Clinic defined a computerized tomography (CT) scan as combining a sequence of X-ray pictures taken from different angles around the patient’s body parts with computer processing(6). 

The procedure aims to produce cross-sectional images (slices) of the bones, blood vessels, and soft tissues within the patient’s body. CT scan pictures give more detailed information than conventional X-rays.

CT is a noninvasive, painless imaging technique that a healthcare professional may use to help diagnose diseases and injuries(7). A CT scan is performed in a hospital or imaging facility.

A CT scan has various applications, but it is well suited for swiftly examining individuals who may have internal injuries due to auto accidents or other trauma(8). 

Moreover, CT has become an effective screening technique for spotting potential abdominal tumors or lesions(9). Likewise, when different forms of heart disease or abnormalities are detected, a CT scan of the heart may be recommended.

Note that tomography is not an MRI. CT and MRI (magnetic resonance imaging) scans enable physicians to see inside the patient’s body. 

However, CT and MRI scans are two distinct methods for generating precise images of inside body structures. The images may need analysis to discover abnormalities such as organ tumors, bone fractures, and joint damage(10).

How a CT System Works

The National Institute of Biomedical Imaging and Bioengineering briefly explains how CT systems work (11).

Unlike a traditional X-ray, which uses a fixed X-ray tube, a CT scanner uses a motorized X-ray source that moves around a circular structure called a gantry when the patient lies down. The X-ray tube moves around the bed, shooting narrow radiation beams at the body.

Instead of film, CT scanners use digital X-ray detectors(12). These detectors are positioned directly opposite the source of the X-rays, and they then pick up and transmit the CT imaging to a computer.

The computer then creates a 2D image, also called a slice, of the patient by analyzing the tissue in the slice(13). The computed image is stored, and the patient’s bed is moved incrementally into the circular structure.

The scanning process begins, and the images produced by the scanner are then repeated until the doctors reach their goal.

The computer then displays the slice in either a single or stacked form, producing a 3D image of the patient(14). This method gives the doctor a more realistic visualization of the skeleton, organs, and tissues. 

Another benefit of this technique is that it will enable the doctors to move the slice in space, making it easier to find the location of the problem.

Why CT Scan Procedure Is Done

The physician may prescribe a CT scan to assist with(15):

  • Determining the precise site of a tumor, an infection, or a blood clot
  • Diagnosing muscle and bone disorders, such as fractures and bone tumors
  • Guiding radiation treatment, surgical, and biopsies
  • Examining the efficacy of specific cancer therapy
  • Detecting and monitoring illnesses and conditions, including cardiovascular disease, cancer, liver masses, and lung nodules
  • Detecting internal bleeding and injuries

Types of Tomography

There are several types of tomography, namely(16):

  • X-ray computed tomography(17): An X-ray CT is a non-destructive method for gathering digital data on 3-D geometries and properties of solid things. 

X-ray tomography uses an X-ray source, detectors that measure X-ray intensity attenuation along several beam pathways, and rotating geometry. These standard components may be configured to produce CT scanners to image things of different sizes and compositions.

  • Ultrasound computed tomography (USCT)(18): It can locate metastases. USCT is a new digital imaging technology that reconstructs three-dimensional pictures of inhomogeneous media, such as soft tissue. It makes an effort to resolve the inverse-scattering field issue.
  • Seismic tomography(19). It is one of the principal geophysical techniques for determining the three-dimensional (3D) distribution of physical properties inside the Earth that affect seismic-wave propagation.

Advances in Technology and Clinical Practice

According to the FDA or U.S Food and Drug Administration, the majority of CT systems are capable of “spiral”, sometimes termed “helical“, scanning in addition to the more traditional “axial” mode(20). 

Note that the resulting images of the helical scan have a higher resolution and contrast, hence offering more information(21). Multidetector-row helical CT scanners may be utilized to collect data on calcium accumulation inside the heart’s coronary arteries.

Additionally, several CT systems can create images of multiple slices concurrently(22). These advancements enable imaging of relatively vast volumes of anatomy in a relatively short period. Another technological innovation is electron beam CT (EBCT). 

Consequently, the EBCT scanner acquires detailed images more quickly than traditional CT scanners(23).

In addition, Johns Hopkins Medicine noted other advances in CT technology(24): 

  • High-resolution CT: This provided greater details for lung disease. 
  • Combined CT and positron emission tomography (PET): The procedure can be for medical conditions such as coronary artery disease, epilepsy, and Alzheimer’s.
  • Ultrafast CT: This form of CT scan generates images quickly, generating a “movie” of moving bodily components, including the heart’s chambers and valves.
  • Computed tomographic angiography (CTA): Angiography is an X-ray of the blood vessels. A CT angiography employs CT technology instead of X-rays or fluoroscopy to scan blood vessels, such as the coronary arteries.

Expectations During a CT Scan

An hour is typical for a CT scan procedure(25). The time spent on tomography is mostly for preparation. The scan itself takes 10-30 minutes. Patients may typically resume normal activities following a scan and confirmation of clean images.

Patient Qualifications

Here are the patients’ qualifications for CT scans(26). 

Before sending a patient for a CT scan, the doctors need to ensure that a CT scan is the appropriate diagnosis to confirm or rule out the suspected condition. 

Patients may contact a radiologist for guidance if they are uncertain. It is particularly needed if there are possible risks for a CT scan on a child or teen due to increased radiosensitivity. Other methods may be more suitable for certain individuals.

Before referring a patient for a CT scan, it is essential to rule out early pregnancy in women of childbearing age since this is typically an absolute contraindication to CT scanning.

Meanwhile, patients with particular risk factors may need renal function testing. The factors to consider are(27): 

  • Advanced age
  • Diabetes
  • Present or previous history of abnormal kidney function
  • Single kidney or kidney surgery

The mentioned factors enhance the likelihood of kidney function impairment and may require renal function testing before CT scanning. Several other risk factors may improve the chance of contrast-induced renal failure. 

In any of these conditions, it is advisable to evaluate renal function before contrast delivery. Also, patients need to contact the radiology department if they are still uncertain whether contrast administration is necessary or if renal function testing is needed before their operation.

Preparation

According to Cleveland Clinic, here are some preparations when undergoing a tomography(28). 

The healthcare professional will provide the patients with preparation instructions for the CT scan, such as: 

  • Patients should schedule to come early. Arriving early assists in maintaining the testing schedule.
  • Patients should ask their healthcare professional whether they should take their regular medications before the CT scan.
  • Patients should abstain from food and liquids four hours before the test.
  • Patients need to wear comfortable clothing. Before the procedure, there is a need to wear a gown and remove the watch, jewelry, and any removable piercings. 
  • Patients may also need to remove their dentures and hearing aids. Moreover, zippers and metal items might impede the scanning process.

Also, according to Cleveland Clinic, the CT scan utilizes a contrast agent or dye(29). The healthcare practitioner may give the patient particular preparation instructions:

  • Patients may need a blood test before their CT scan. The blood test will ensure that the healthcare professional chooses the appropriate dye.
  • Suppose patients are allergic to the contrast agent used for CT (including iodine). In that case, the patient may need to take a steroid the night before and the morning of the operation. 
  • Four hours before the  CT scan, patients must be mindful of food and drink intake. Consuming just clear drinks helps minimize nausea associated with contrast dye administration. 
  • According to the technologist‘s or nurse’s instructions, patients should consume the oral contrast solution.

During the Procedure

The doctors may conduct CT scans on an outpatient basis or during a hospital stay(30). Procedures may differ depending on the patient’s situation and the physician’s methods. 

According to Johns Hopkins Medicine, this is how CT scans are performed(31):

  • Suppose the patients intend to have a procedure requiring contrast. In that case, the doctor will administer contrast material to put an intravenous (IV) line and place it in the hand or arm. For oral contrast, patients will ingest a liquid contrast agent. In some instances, the administration of contrast is through a rectal procedure. 
  • Patients will lay on a scan table that slips into the scanner’s substantial circular hole. The technician will be in a separate area containing the scanning controls. However, patients will have regular visual contact with the technician through a window. 

Speakers inside the scanner will allow the technician to hear and interact with the patient. Note that patients may have a call button to notify the technician if they have any issues throughout the process. The technician will constantly be observing the patients and communicating with them.

  • As the scanner circles around the patient, brief X-ray beams will travel through the body. The clicking noises that patients will hear are normal. The scanner will detect and transfer the X-rays absorbed by the body’s tissues to the computer. The computer will convert the data into an image for the radiologist to analyze.

Also, Johns Hopkins Medicine provides some reminders during the tomography procedure(32): 

  • During the treatment, patients must stay completely motionless. The patients may be requested to hold their breath at different points during the process.
  • Suppose the physician will use contrast media during the operation. Patients may experience some side effects when the contrast is administered via the IV line. 

These side effects include a salty or metallic taste in the mouth, flushing, a short headache, nausea, and vomiting. These effects often last a few seconds.

  • The patients should notify the technician if they have difficulty sweating, breathing, numbness, or have heart palpitations.
  • At the end of the tomography procedure, patients must be removed from the scanner.  
  • The line needs to be removed if an intravenous line is put in to provide contrast.

While the CT scan is not painful, the patient’s remaining position may cause discomfort(33). Pain is mainly in situations of a recent injury or invasive procedures such as surgery. 

Nevertheless, the technician will take every precaution to ensure the patient’s comfort. Also, the physician will conduct the treatment as fast as possible to minimize any discomfort or pain. 

After the Procedure

According to Johns Hopkins Medicine, if the physician uses contrast media, the patients will undergo observation for any adverse reactions(34). Side effects can be swelling, trouble breathing, itching, or rash.

Patients should tell the doctor if they experience any discomfort, redness, or swelling at the IV site after returning home. 

Typically, no particular treatment is necessary after a CT scan. Unless the doctor instructs the patients otherwise, they may resume their normal diet and activities.

Moreover, depending on the circumstances, the physician may provide additional or alternative instructions after the procedure. 

Results

According to Cleveland Clinic, the average turnaround time for CT scan findings is 24 hours(35). A radiologist, or a physician who specializes in reading and interpreting CT scans and other radiologic images, will evaluate the scan and create a report explaining its findings. 

Healthcare practitioners often obtain test results within an hour in emergency settings, such as hospitals and emergency rooms.

Meanwhile, after a radiologist and the healthcare practitioner have evaluated the findings, patients will either get a call or be scheduled for a follow-up visit. The healthcare professionals will discuss with the patients the results of the tomography. 

Risks of Tomography

CT scans are generally considered safe by healthcare professionals(36) and performed by AART-certified radiologists. CT scans are also regarded as safe for children. The CT technician may use precisely calibrated instruments for children to ensure that they get the least amount of radiation possible.

Like other diagnostic techniques, CT scans produce an image by exposing the patient to a minimal amount of ionizing radiation(37). Numerous risks associated with CT scans include the following:

  • All techniques of imaging that use radiation, such as X-rays, slightly increase the risk of developing cancer. The shift is too subtle to define precisely.
  • Individuals may sometimes have a moderate to a severe allergic reaction to the contrast agent.

If patients have any concerns regarding the health risks linked with CT scans, they should see the healthcare practitioner. These professionals will answer any concerns and guide the patients through making an informed decision regarding the scan.

What Is a Contrast Agent?

As with all X-rays, dense bodily structures, such as bone, are easy images to capture(38). However, soft tissues vary in their propensity to absorb X-rays and, as a result, may be dim or difficult to view. 

Therefore, intravenous (IV) contrast agents that are visible on an X-ray or CT scan and safe for use in patients have been created(39). 

Contrast agents include compounds that are more effective at obstructing X-rays and, as a result, are more apparent in X-ray images. 

Chest X-rays are the most prevalent kind of medical imaging(40). The heart, lungs, and other anatomical structures are captured on film during this examination.

Meanwhile, to evaluate the circulatory system, an iodine-based contrast agent is injected into the bloodstream to highlight blood vessels(41). 

This examination is intended to detect potential clogs in blood arteries, including the heart. For imaging the digestive system, including the esophagus, stomach, and GI tract, oral contrast agents, such as barium-based compounds, are utilized.

History of Tomography

The National Library of Medicine summarized the history of tomography(42). 

Conrad Röntgen’s discovery of X-rays in 1895 sparked interest in three-dimensional images. The clinical motivation was the driving force for the creation of this technology.

The clinicians demanded tomographic images instead of planar X-rays. Individuals rather than organizations created classical tomography between 1910 and 1940.

In 1914, Mayer, a Polish radiologist, suggested the use of tomography. A few years later, the idea was further developed by radiologists Vallebona, Grossman, and Bocage. In 1931, comprehensive clinical trials were published on the subject.

In the 1940s and 1950s, there was a pause in technological advancement and only adjustments to the current technology were made.

Frank and Takahashi established the essential ideas of axial tomography in the middle of the 1940s. However, Hounsfield, an English electrical engineer, could not create and sell the first axial computer tomography until 1972, when the requisite advances in electronics had occurred. 

Thus, the second, third, and fourth generations of CT scanners were quickly made accessible by the radiology industry’s major corporations.

A few years later, a new image generation method without the use of ionizing radiation was presented. Lauterbur and Damadian created the first low-quality magnetic resonance images, a technique dubbed zeugmatography by its developers. In 1974, the first photographs of a living subject were released. This led to the development of magnetic resonance that doctors now use. 

Regardless, it is hard to forecast the future. The expansion of networks and the rise in data capture and storage will cast fresh light on the area of expertise. Therefore, increased collaboration between clinicians, radiologists, pathologists, and a partial rethinking of the radiologists‘ role, may be necessary. 

  1. CT (Computed Tomography) Scan
    https://my.clevelandclinic.org/health/diagnostics/4808-ct-computed-tomography-scan
  2. CT scan
    https://www.mayoclinic.org/tests-procedures/ct-scan/about/pac-20393675
  3. Computed Tomography (CT)
    https://www.nibib.nih.gov/science-education/science-topics/computed-tomography-ct
  4. Computed Tomography (CT)
    https://www.insideradiology.com.au/computed-tomography-hp/
  5. CT (Computed Tomography) Scan
    https://my.clevelandclinic.org/health/diagnostics/4808-ct-computed-tomography-scan
  6. CT scan
    https://www.mayoclinic.org/tests-procedures/ct-scan/about/pac-20393675
  7. CT (Computed Tomography) Scan
    https://my.clevelandclinic.org/health/diagnostics/4808-ct-computed-tomography-scan
  8. CT scan
    https://www.mayoclinic.org/tests-procedures/ct-scan/about/pac-20393675
  9. Computed Tomography (CT)
    https://www.nibib.nih.gov/science-education/science-topics/computed-tomography-ct
  10. What is the difference between CT scans and MRI scans?
    https://opa.org.uk/what-is-the-difference-between-ct-scans-and-mri-scans/
  11. Computed Tomography (CT)
    https://www.nibib.nih.gov/science-education/science-topics/computed-tomography-ct
  12. Ibid.
  13. Ibid.
  14. Ibid.
  15. CT scan
    https://www.mayoclinic.org/tests-procedures/ct-scan/about/pac-20393675
  16. X-ray Computed Tomography (CT)
    https://serc.carleton.edu/research_education/geochemsheets/techniques/CT.html
  17. Ibid.
  18. Ultrasound Computed Tomography
    https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/ultrasound-computed-tomography
  19. Deep Earth Seismology
    https://www.sciencedirect.com/topics/earth-and-planetary-sciences/seismic-tomography
  20. What is Computed Tomography?
    https://www.fda.gov/radiation-emitting-products/medical-x-ray-imaging/what-computed-tomography#advances
  21. Computed Tomography (CT) Scan
    https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/computed-tomography-ct-scan
  22. What is Computed Tomography?
    https://www.fda.gov/radiation-emitting-products/medical-x-ray-imaging/what-computed-tomography#advances
  23. Ibid.
  24. Computed Tomography (CT) Scan
    https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/computed-tomography-ct-scan
  25. CT (Computed Tomography) Scan
    https://my.clevelandclinic.org/health/diagnostics/4808-ct-computed-tomography-scan
  26. Computed Tomography (CT)
    https://www.insideradiology.com.au/computed-tomography-hp/
  27. Ibid.
  28. CT (Computed Tomography) Scan
    https://my.clevelandclinic.org/health/diagnostics/4808-ct-computed-tomography-scan
  29. Ibid.
  30. Computed Tomography (CT) Scan
    https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/computed-tomography-ct-scan
  31. Ibid.
  32. Ibid.
  33. Ibid.
  34. Ibid.
  35. CT (Computed Tomography) Scan
    https://my.clevelandclinic.org/health/diagnostics/4808-ct-computed-tomography-scan
  36. Ibid.
  37. Computed Tomography (CT)
    https://www.nibib.nih.gov/science-education/science-topics/computed-tomography-ct
  38. Ibid.
  39. Ibid.
  40. What is Computed Tomography?
    https://www.fda.gov/radiation-emitting-products/medical-x-ray-imaging/what-computed-tomography#advances
  41. Computed Tomography (CT)
    https://www.nibib.nih.gov/science-education/science-topics/computed-tomography-ct
  42. The history of tomography
    https://pubmed.ncbi.nlm.nih.gov/8550391/
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