Introduction
CAT scans and MRIs are common medical imaging techniques used to provide detailed internal views of the body. Both methods produce cross-sectional images of the body, but use different technologies:
CAT scans, also known as CT scans, combine a series of X-ray images taken from different angles to produce cross-sectional views of bones, blood vessels and soft tissues. The scans use ionizing radiation.
MRIs use strong magnetic fields and radio waves to generate detailed images of organs and tissues without using ionizing radiation.
This article will compare key factors like image quality, radiation exposure, scan time, cost, and availability to analyze the advantages and disadvantages of CAT scans versus MRIs for medical diagnosis.
Definition of CAT Scans
CAT stands for computed axial tomography. CAT scans are also known as CT scans or computed tomography scans.
A CAT scan is a medical imaging test that uses x-rays and computers to take cross-sectional images of the body (https://www.verywellhealth.com/what-is-a-cat-scan-189603). The scan provides detailed pictures of structures inside the body including bones, blood vessels and soft tissues.
During a CAT scan, the patient lies on a table that moves through a large donut-shaped machine. X-rays are sent through the body in different angles and are detected by special detectors in the machine. The x-ray data is processed by a computer to create cross-sectional images or “slices” of the body. These images provide more detail than typical x-ray images.
One of the main advantages of CAT scans over regular x-rays is the ability to see soft tissues. However, CAT scans do expose patients to radiation from the x-rays. The amount of radiation is generally small but cumulative over a lifetime (https://uoflhealth.org/articles/what-is-a-cat-scan/).
Definition of MRIs
MRI stands for magnetic resonance imaging. An MRI scan uses strong magnetic fields and radio waves to create detailed images of the inside of the body (National Institute of Mental Health, 2021).
MRIs use powerful magnets to align the protons in cells throughout the body. A magnetic field is then pulsed through the body, knocking the protons out of position. When the field is turned off, the protons realign, sending out radio signals. These signals are sent to a computer that analyzes the signals and converts them into a detailed image (Cleveland Clinic, 2022).
MRIs create highly detailed pictures using the natural magnetic properties of the body’s cells and tissues, without the need for potentially harmful ionizing radiation. The strong magnetic field causes hydrogen atoms in the body to line up. When the field is turned off, the atoms return to their normal positions, emitting faint radio signals as they realign. These signals provide information that is converted into images of the body (Cleveland Clinic, 2022).
Image Quality
When it comes to image quality and detail, MRI scans generally provide better visualization of soft tissues compared to CT scans. MRI vs. CT Scan. MRI utilizes magnetic fields and radio waves to generate detailed images, providing excellent contrast between the different soft tissues of the body. This makes MRI well-suited for examining organs, muscles, ligaments, cartilage, and tendons. The multiplanar capabilities of MRI also allow images to be taken in various planes. CT scans, on the other hand, use multiple X-ray beams to image the body. While CT excels at visualizing bone injuries, lung tissue, and detecting abnormalities in soft tissues, it cannot match the superior soft tissue contrast of MRI. Overall, MRI provides more detailed images with better resolution of soft tissues compared to CT.
Radiation Exposure
One of the biggest differences between CAT scans and MRIs is that CAT scans use ionizing radiation, while MRIs do not. During a CAT scan, the X-ray tube rotates around the body and sends out a narrow beam of X-rays. The levels of radiation exposure from a single CAT scan are considered low-risk, but it’s still radiation being absorbed by the body [1].
Repeated or cumulative exposure to radiation particularly at high levels has been shown to slightly increase cancer risk [2]. Thus, CAT scans are not recommended for pregnant women or children unless medically necessary. Ionizing radiation can potentially damage DNA and cause cell mutation.
In contrast, MRIs utilize strong magnetic fields and radiofrequency waves to produce images, without any exposure to ionizing radiation. This makes MRIs a safer imaging choice when radiation is a concern, such as for pregnant patients or pediatric cases [3].
Scan Times
One of the most noticeable differences between CAT scans and MRIs is the time each test takes to complete. CAT scans are generally very fast procedures. The actual CT scanning takes only seconds to complete. The entire process, including preparation, scanning and recovery, usually takes about 30 minutes.
MRIs require more time. The scans themselves can take up to 90 minutes or more, depending on the part of the body being imaged. Just the imaging portion of an MRI takes about 30-60 minutes. Adding in preparation and recovery time, the entire MRI process usually takes 60-90 minutes.
The longer scan times for MRIs are due to the way images are captured. CAT scans take a quick snapshot. MRIs require longer exposure times to capture enough data to construct detailed images. This makes MRIs better suited for completely scanning specific areas of the body, while CAT scans are preferred for quick overviews.
Cost Comparison
Generally, CAT scans are less expensive than MRIs. According to DocPanel, MRIs cost about twice as much as CAT scans. The average CAT scan costs around $1,200, while an MRI costs about $2,000. MedicineNet also reports that MRIs tend to cost nearly double the price of CAT scans. One reason for the price difference is that MRI machines are more complex and expensive to manufacture. The strong magnets required for MRIs also make them more costly to maintain. While both scans may be covered by insurance, the lower price point makes CAT scans the more budget-friendly choice for many patients.
Availability
CT scanners are more widely available and accessible than MRI scanners. This is because CT scanners are generally less expensive and require less specialized facilities to operate. CT scan vs MRI scan – What’s the difference? | Practice Plus Group
Most hospitals have at least one CT scanner, even smaller community hospitals. Larger hospitals may have multiple CT scanners. Because they are relatively affordable and easy to install, CT scanners can be found in a wide range of medical facilities.
In contrast, MRI scanners are large, complex machines that require extensive infrastructure. They need to be housed in shielded rooms and require specialized electricity and cooling systems. For these reasons, MRI scanners are less widely available than CT scanners and are more likely to be found in major hospitals and imaging centers.
The wider availability of CT scanners means patients usually have quicker and easier access to CT exams. Patients may need to travel farther for an MRI if a facility with an MRI scanner is not nearby. So when it comes to accessibility, CT scanners have an advantage over the less widely available MRI.
Patient Restrictions
MRIs tend to have more patient restrictions compared to CT scans. One major restriction for MRIs is claustrophobia, as the MRI machine is an enclosed tunnel that patients need to lie still inside of for up to 90 minutes (Source). This enclosed space can cause anxiety for those who have claustrophobia. CT scans on the other hand are more open and do not fully enclose the patient.
Another restriction with MRIs are metal implants. The strong magnetic field used in an MRI can interact with metal implants like pacemakers, stents, artificial joints etc, so these implants may preclude a patient from receiving an MRI (Source). Metallic tattoos and piercings may also need to be removed. CT scans do not have issues with metal implants or tattoos.
Overall, MRIs tend to have more restrictions when it comes to patient claustrophobia and the presence of metal in or on their bodies. CT scans are less restrictive when it comes to these factors.
When to Use Each Test
Both CAT scans and MRIs have their advantages, so determining which test to use depends on the specific medical need and what the scan aims to reveal. Some key differences in appropriate use cases:
- For traumatic injuries like fractures or internal bleeding, CAT scans are generally preferred due to their speed and ability to capture bone in detail. MRIs can take longer to perform.
- For abnormalities in soft tissue like tumors, cysts, or nerve damage, an MRI provides greater detail and contrast. The magnetic fields allow it to differentiate soft tissues better than a CAT scan.
- For strokes and other neurological conditions, MRIs are generally considered superior due to providing better visualization of the brain and more detailed images of blood vessels.
- For spinal conditions, MRIs allow multiplanar imaging and better differentiate between soft tissues. Some spinal conditions like disc herniations are better visualized on an MRI.
In cases of cancer, both CAT scans and MRIs may be used to provide a comprehensive view. A CAT scan provides a quick overview, while an MRI offers more specific soft tissue detail (Quizlet, n.d.). Ultimately a doctor will determine which test is most appropriate for the patient’s specific circumstances and diagnostic needs.
