Radiology Scans — Types and Potential Health Risks

11 min readAug 2, 2022

If you’re old enough (or perhaps had an injury), chances are you are familiar with radiology scans.

These imaging tests are extremely powerful tools that help doctors see the internal structures of the body, and to create images of those structures using various forms of electromagnetic energy such as radio waves and X-rays.

However, imaging tests are not the same, as each one serves its own unique purpose, and comes with its own strengths, weaknesses and risks.

Types of Scans
About Radiology
Structural Scans
Functional Scans
CT vs MRI — Which is Safer?

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Types of Scans

Generally speaking, radiology scans are used for 2 primary purposes, one is to investigate body structure, and the other to investigate bodily function.

Structural Scans: are used to uncover information about how organs look. The most popular structural scans include X-Rays, CT Scans, MRIs and MRAs
Functional Scans: are used to explore how organs work. The most popular functional scans include MEG, fMRI, NIRS, PET and SPECT

A key point to keep in mind is that each type of imaging scan is its own tool, with its own purpose, and different scans are often used in conjunction with one another to better illuminate medical conditions and inform diagnosis.

About Radiology

From Cost to Profit Center

It’s not widely known, but radiology services have been the primary profit engine for hospitals for quiet some time.

Between 1999 and 2009, imaging procedures increased from 117 million to 172 million, making outpatient radiology the biggest contributor to the profit margin of U.S. hospitals.
Today, imaging services account for $24.1 billion, or 37 percent of hospitals’ profit (that’s about three times greater than cardiology, the next closest service line)

A major reason for the profit surge, is that currently, 70 to 75 percent of patients referred to a hospital are prescribed imaging services, and that figure will likely increase as more than 75 million people are expected to turn 65 years of age or older over the next 18 years.

Science of Radiology

The field of radiology owes much of its success to the scientific discoveries that made scanning technologies possible, as all radiological scanners work according to the laws of physics underlying light, magnetism and energy.

As you take a look at the Electromagnetic Spectrum below, notice the tiny portion of the spectrum that constitutes visible light (i.e., these are the only wave lengths that the human eye can see).

Since all other wavelengths are invisible to the human eye, special scanners are needed to help doctors tap into the information carried by these waves.

1 foot = .3 meters
1 inch = .0254 meters
1 nanometer = 1 billionth of a meter (if earths diameter was shrunk to a billionth of its current size, we would be living on a planet with a diameter of 1/2 an inch)

Structural Scans

Ultrasound — X-Rays — CT Scans — MRI — MRA

1. Ultrasound

Strictly speaking, Ultrasound is not a Radiology scan (it uses sound waves rather than electromagnetic waves), but it was included in the list due to its popularity.

Ultrasound uses very high-frequency acoustical waves to image features inside the human body. These sounds waves are inaudible to the human ear due to the frequencies used.

The human hearing range is between 20Hz and 20,000 kHz, but medical ultrasound uses frequencies between 1 and 20 MHz.
Tissues inside the body reflect sound waves back to the scanner, producing an “echo” signal that the ultrasound machine processes into a live image (similar to a bat’s echolocation)

The following frequencies are typically used for ultrasound examinations:

2.5 MHz: deep abdomen, obstetric and gynecological imaging
3.5 MHz: general abdomen, obstetric and gynecological imaging
5.0 MHz: vascular, breast, pelvic imaging
7.5 MHz: breast, thyroid
10.0 MHz: breast, thyroid, superficial veins, superficial masses, musculoskeletal imaging.
15.0 MHz: superficial structures, musculoskeletal imaging.

2. X-Rays

An x-ray, also called a radiograph, sends beams of x-ray radiation through the body in order to generate an image.

Areas with high levels of calcium block the radiation, causing them to appear white on the image (x-rays are ideal for imaging hard tissues such as bone and teeth)
Soft tissues allow the radiation to pass through, appearing gray or black on the image (x-rays won’t show subtle bone injuries, soft tissue injuries or inflammation)

3. CT Scans

Computerized Tomography

Tomography comes from the Greek word ‘tomos’, meaning to cut, and true to its name, CT scans generate a picture that looks like a horizontal slice of the organ.

A CT scan combines a series of X-ray images taken from different angles around the body and uses computer processing to create cross-sectional images (slices) of bones, blood vessels and soft tissues
CT scans take longer than X-rays (but not as long as MRIs), and they provide more detailed images as compared to plain x-rays
The radiation doses of CT scans (a series of X-ray images from multiple angles) are 100 to 1,000 times higher than conventional X-rays

A CT scan has many uses, but it’s particularly well-suited to quickly examine people who may have internal injuries or other types of trauma.

4. MRI

Magnetic Resonance Imaging

While CT scans can create images of bones and soft tissues, they aren’t as effective as MRIs at exposing subtle differences between types of tissue.

In contrast to X-rays or CT scans, MRIs offer excellent contrast resolution for both bones and soft tissues. This is because unlike CT scans, which beam x-rays, MRI scans construct their imagines by passing a magnetic field over the body / head.

MRI scanners work by creating a magnetic field that locks hydrogen atoms in the body’s water-filled tissues into an aligned magnetic state. When a radio wave is applied, it knocks the hydrogen atoms out of alignment. The atoms in different tissues realign at different rates, producing radiofrequency signals that a computer converts into an image.

MRI images are typically black and white, but researchers have figured out a way to add the equivalent of color to MRI scans
People with metal implants, pacemakers or other implanted devices shouldn’t have an MRI due to the powerful magnet inside the machine

5. MRA

Magnetic Resonance Angiography

MRA is a type of MRI that looks specifically at the body’s blood vessels.

Unlike a traditional angiogram, which requires inserting a catheter into the body, magnetic resonance angiography is a far less invasive and less painful test.

In some cases, a special dye, called contrast, may be added to the bloodstream via IV to make blood vessels easier to see
Patients with kidney problems are potentially at risk of developing a severe reaction after receiving the MRI contrast dye that is used to make blood vessels more visible

A full MRA scan may take an hour or longer. This will depend on the type and number of blood vessels that your healthcare provider wishes to examine.

Functional Scans

MEG — fMRI — NIRS — PET — SPECT

1. MEG

Magnetoencephalography

Where EEG’s measure electrical activity in the brain, MEG scans create images of the brain’s magnetism (i.e., MEG measures the brain’s magnetic, rather than its electric activity).

The test takes about two hours and is performed in a specially shielded room, equipped with video and intercom systems so a technician can see, hear and communicate with the patient.

An advantage of MEG over EEG, is that the skull and tissue surrounding the brain affect magnetic fields measured by MEG much less than they affect electrical impulses measured by EEG. Due to minimal distortion of the signal, MEG has an advantage over EEG.

Test results results from MEG can be matched up with MRI images to create a “map,” or magnetic source image (MSI), that shows areas of normal and abnormal activity in the brain.

2. fMRI

Functional Magnetic Resonance Imaging

fMRI is based on the same technology as regular MRIs, but instead of creating images of organs and tissues like MRI, fMRI looks at blood flow in the brain to detect areas of activity. Changes in blood flow help doctors understand more about how the brain works.

fMRI measures how quickly oxygen is consumed by brain cells and has become the gold standard for in vivo imaging of the human brain, with an ability to pinpoint differences in brain activity to within a few millimeters.
with fMRIs, multiple scans are taken as the patient is asked to complete cognitive or behavioral tasks. By taking multiple scans, neuroscientists are able to watch which areas of the brain are activated in fulfilling the function under examination, in addition to seeing the overall structure of the brain.

Functional images don’t come the way they’re shown in magazines and journals, with reds and yellows splattered across the brain to show where the most neural activity occurred. The colors are added later by the researchers.

3. NIRS

Near Infrared Spectroscopy

NIRS is an optical brain imaging technique that investigates cerebral blood flow as well as the hemodynamic response in brain areas during activity.

comparable to fMRI, the NIRS method complements fMRI by providing measures of both oxygenated and deoxygenated hemoglobin concentrations and by measuring cortical activations.

NIRS presents several advantages relative to fMRI, such as measurement of concentration changes in both oxygenated- and deoxygenated hemoglobin, finer temporal resolution, and ease of administration, as well as disadvantages, most prominently inferior spatial resolution and decreased signal-to-noise ratio (SNR).

4. PET

Positron Emission Tomography

Positron emission tomography (PET) is a type of nuclear medicine procedure that measures metabolic activity of the cells of body tissues, and is a combination of nuclear medicine and biochemical analysis.

PET scans may detect biochemical changes in an organ or tissue that can signal the onset of a disease process before anatomical changes related to the disease can be seen with other imaging processes such as computed tomography (CT) or magnetic resonance imaging (MRI).

PET scans are used less often than fMRI scans, as these scans cannot be used on children or premenopausal women because its radioactive
In addition to exposing the patient to a radioactive substance, this technique has the lowest time resolution of all, because it takes time for the tracer to circulate and for changes to show up

With PET scans, the patient is injected with a radioactive substance and depending on the exact chemical chosen, this substance will accumulate in different parts of the organ (i.e., bind to specific molecules), which are typically parts of the organ that are most active and are thus drawing the most blood (e.g., brain).

The injected substance releases positrons (positively charged electrons), and the scanner records and maps the areas of positron emission.

The scanner then produces a multicolored image, that looks similar to a heat map, which highlights areas of functional activity.

5. SPECT

Single-photon emission computerized tomography

While imaging tests such as X-rays and CT scans can show what the structures inside your body look like, a SPECT scan produces images that show how your organs are functioning.

A SPECT scan is a type of nuclear imaging test, which uses a radioactive substance and a special camera to create 3D pictures of blood flow activity. Some of the most common uses of SPECT are to help diagnose or monitor brain disorders, heart problems and bone disorders.

While both PET and SPECT imaging use cameras that detect injected radiotracers, each type of imaging works differently and costs differently.

SPECT is much more widely available than PET and it also much more affordable, with the average camera costing between $400,000 and $600,000. PET is less widely available and much more costly to implement, with cameras running into the millions of dollars.

CT vs MRI — Which is Safer?

In the course of everyday life, we are constantly exposed to naturally occurring background radiation. This radiation occurs naturally in our environment and it is estimated that the average U.S. resident receives an effective radiation dose of about 3 mSv per year.

mSv (milliSievert) is how scientists measure radiation. It is used to quantify the average amount of radiation absorbed by the body

Johns Hopkins Hospital has created a reference chart showing how long it would take an adult to receive the same amount of radiation from naturally-occurring radiation exposure as they would from a particular radiology scan. Not many patients are aware of these figures, but they should be!

Here are some approximate comparisons of background radiation and effective radiation doses for several radiology procedures (these values can vary greatly, depending on the size of the patient and the type of imaging technology being used).