PET-CT Imaging: Purpose, Process, and Key Advantages

A PET-CT scan is a cutting-edge medical imaging tool that merges two technologies to efficiently detect certain types of cancer and identify if they have spread to other areas. Beyond that, PET-CT scans can reveal the body’s response to infections by illuminating inflammatory activity through the use of radioactive tracers.

This scanning technique enables healthcare professionals to precisely locate tumors and monitor how they evolve over time.[1]

Due to its ability to accurately track disease progression, PET-CT is frequently used to assess the success and effectiveness of treatments, including monitoring how cancer develops or spreads inside the body.

With the help of this technology, doctors can measure the size of abnormal growths, evaluate how they react to different therapies over time, and determine whether cancer is advancing or staying localized. A PET-CT scan can detect the exact position of metastases and even identify the tiniest tumors in their earliest stages.

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WHAT IS A PET-CT SCAN?

A PET-CT scan brings together two advanced imaging techniques: PET (Positron Emission Tomography) and CT (Computed Tomography). While each method offers its own distinct benefits, they generate different kinds of visual information. When combined, they provide powerful diagnostic insights, especially useful for detecting and monitoring certain cancers.[2]

In essence, PET-CT merges these two technologies into a single system, offering doctors a clearer, more detailed picture for accurate diagnosis.

How Does a PET Scan differ from a CT Scan

Positron Emission Tomography (PET) is a nuclear imaging method that uses short-lived radioactive tracers. These substances are injected into the body, where they accumulate in tissues based on metabolic activity. The PET scanner detects this distribution and converts it into detailed images showing biological processes.

Computed Tomography (CT), in contrast, uses X-ray technology to capture detailed anatomical images of the body, producing precise cross-sectional views of tissues and organs.

On its own, a PET scan cannot precisely determine the exact location or size of a tumor, nor track its physical development. CT, however, provides a structural map of the body. By combining both scans into one PET-CT machine, doctors receive highly precise, layered images that integrate metabolic data with detailed anatomical visuals, delivering the most complete diagnostic results.

How Does a PET-CT Scan Function?

To properly detect and diagnose a tumor, several tests are typically carried out in addition to a PET-CT scan. These may include a physical exam, blood tests, CT scans, mammograms, tumor marker tests, MRI scans, or even biopsies.

Before undergoing the PET-CT scan, the patient’s blood sugar level must be checked and should not exceed 200 units. Once this is confirmed, the patient is injected with a glucose-based solution and will need to rest quietly, lying down, for at least 45 minutes to an hour to allow the substance to circulate.

The scan itself generally lasts around 20 minutes, though the duration can vary depending on the area being examined and the specific type of scan. The output consists of standardized medical images, which can be stored locally or saved in a cloud PACS system for later viewing or comparison using a DICOM viewer.

After the scan is complete, the patient can return home but should follow a few important recommendations:

• Drink plenty of fluids over the next 24 hours, as the injected substance will naturally leave the body through urine, sweat, and feces during this period.
• Avoid close contact with young children (under age 7) and pregnant women.
• Ideally, stay in a separate room from other family members during this time.

Before the scan, the patient receives an injection of glucose combined with radioactive fluoride. Cancer cells absorb this glucose much faster than normal cells because they have a high demand for energy. The radioactive fluoride attached to the glucose allows these cancer cells to be easily seen on the PET-CT images. [3]

This process makes PET-CT scans especially valuable for doctors to detect cancer cells accurately and monitor their behavior and spread. It’s also useful in cases where metastases have been discovered but the original tumor site has not yet been identified.

Because the glucose absorption process is natural and affected by blood sugar levels, patients are instructed not to eat anything after 6:00 PM the evening before the scan.

PET Scan Diet

For best scan results, patients are advised to follow a high-fat, low-carbohydrate diet before the procedure. This includes eating high-protein foods such as meat, eggs, low-starch vegetables, hard cheeses, tofu, and butter. Foods rich in carbohydrates, like bread, pasta, sugary drinks, and alcohol, should be avoided.

It’s important to drink plenty of water and avoid strenuous activity the day before the scan. On the day of the scan, do not take over-the-counter cough syrups, cough drops, or antacids. Unless specifically required, it’s also recommended to skip taking supplements.

Why Avoid Caffeine Before a PET Scan?

Consuming caffeine can negatively impact the precision of a PET scan by altering how radioactive tracers spread through the body. This effect is especially important when evaluating the heart, as caffeine can influence cardiac activity and affect the interpretation of cardiac PET images.

Research indicates that individuals who ingested coffee prior to scanning showed notably increased tracer absorption in heart muscle compared to those who had minimal or no caffeine.

Primary PET-CT Aplication

PET-CT is widely used to diagnose and monitor a variety of serious cancers, such as: [4] [5]

• Lung cancer
• Breast cancer
• Cervical cancer
• Ovarian cancer
• Throat/laryngeal cancer
• Esophageal cancer
• Brain tumors
• Colon cancer
• Pancreatic cancer
• Melanoma
• Thyroid cancer
• Bladder cancer
• Prostate cancer
• Malignant lymphoma

Benefits of a PET-CT Scan

By combining PET and CT technologies, this approach integrates the advantages of both to deliver images far more informative than those from either technique used separately.

• It detects cancerous lesions throughout the body, regardless of their size or progression stage.
• The procedure is rapid, enabling physicians to act quickly in managing the disease. [6]
• Though the tracer contains radioactive material, it carries minimal risk and is naturally cleared from the body within one day after the test.

Risks of PET Scan

PET scans use a radioactive tracer, but the level of radiation exposure is very low. The radiation dose from the tracer is minimal, meaning the risk to the patient is extremely small. The potential risks are far outweighed by the benefits of accurate diagnosis for serious health conditions.

Individuals with allergies should inform their healthcare provider, especially if they have sensitivities to iodine, aspartame, or saccharin.[7]

For those allergic to iodine, an alternative contrast agent based on diluted barium can be used. People at higher risk for iodine allergies include those with heart disease, asthma, other allergies, kidney problems, or blood disorders like sickle cell anemia, polycythemia vera, and multiple myeloma.

Pregnant women require special consideration, as radiation exposure can harm the developing fetus. Therefore, PET-CT scans are generally avoided in women who are pregnant or may become pregnant.

Additionally, nursing mothers need to take precautions, as breastfeeding should be paused for 24 hours following the scan to avoid passing the radioactive material to the infant.

References:

• https://www.cancer.net/navigating-cancer-care/diagnosing-cancer/tests-and-procedures/positron-emission-tomography-and-computed-tomography-pet-ct-scans
• https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/positron-emission-tomography-pet
• https://www.radiologyinfo.org/en/info.cfm?pg=pet#how-its-performed
• https://www.medicalnewstoday.com/articles/154877#uses
• https://www.mayoclinic.org/tests-procedures/pet-scan/about/pac-20385078
• https://stanfordhealthcare.org/medical-tests/p/pet-ct-scan/what-to-expect.html
• https://www.healthline.com/health/pet-scan