What are the different diagnostic imaging techniques and when are they used?

When we have a health problem, or we want to prevent it, many times our doctor tells us that we should do a diagnostic test to evaluate our state of health.

In most cases (it is always the preferred option) these tests will be diagnostic imaging tests, since they are little or not invasive, painless and allow us to evaluate our body quickly and accurately, without any health risks. Only when these tests are not enough or do not completely clarify the condition, will other invasive tests be performed such as analyses, biopsies, punctures or catheterizations, among others.

But what types of diagnostic imaging are there? What are they used for and when? Which ones are harmful to health? What drawbacks do they have?

Here we tell you.

Types of diagnostic tests

Ultrasound

Ultrasound is a diagnostic imaging technique that uses high-frequency sound waves (inaudible to humans) to create images of the inside of the body. It is a safe, non-invasive method that does not use ionizing radiation, so it can be used as much as needed without any risk to the patient or the health personnel who are making the diagnosis. It is especially useful in monitoring pregnancies, evaluating abdominal organs and monitoring the heart.

On the other hand, ultrasound is not useful to see bone problems, organs covered with bone such as the brain, organs filled with air such as the lungs, or in general any issue that is very deep within an organ or tissue.

The sensor that is placed on the skin (transducer) emits ultrasounds and receives them instantly. Depending on the characteristics of the tissues, the returned sound is attenuated and distorted in one way or another, so the returned signal is used to generate the image that is represented on the monitor. Before the test, a gel is applied to the skin so that there is no air between the transducer and the skin, since air makes it difficult to receive the ultrasound.

The main advantage is that it is a very accessible test (an ultrasound machine has a very low cost) and that it allows real-time monitoring, since what is seen on the screen is what is received immediately depending on the position of the transducer. . On the contrary, its results are more complicated to interpret since its precision is lower, so the analysis depends largely on the skill of who performs the test.

Curiosity: Ultrasound is not effective in hollow or air-filled tissues, such as the lungs, since air hinders the propagation of ultrasound and therefore only appears on the screen as a black area, which is why in abdominal ultrasounds it is recommended to drink a glass of water, since the empty bladder, but full of air, would act as a barrier that would not allow the rest of the organs to be seen through it (black zone), but when filled with water it behaves like a "transparent window" to ultrasound that allows you to see through it as if the bladder were not present.

Origin: Ultrasound uses the same technological concept as aviation radars or ship sonar. It has its origins in the 1940s, after the Second World War. Initially explored by Dr. Karl Theo Dussik in Austria to try to diagnose brain tumors, the medical application of ultrasound advanced significantly in the 1950s thanks to researchers such as John Wild, John Reid, and especially the Scottish obstetrician Ian Donald, who used in the field of obstetrics, leading the development of the first commercial scanners.

Doppler ultrasound

Doppler ultrasound is a type of ultrasound that has the same characteristics as traditional ultrasound, but that uses the Doppler effec present in the blood circulation to determine the flow of blood through the veins, their diameter, stenosis and even detect atheromas (accumulations of cholesterol).

The doppler effect, discovered by Austrian physicist Christian Dopple in 1842, describes how the frequency of a wave changes relative to its observer (or sensor) depending on whether it moves closer or further away from the source of the wave.

Curiosity: In addition to generating images that show the speed and direction of blood flow, doppler ultrasound can convert these measurements into audible sounds. This allows doctors to not only see, but also hear blood flow through arteries and veins, providing an intuitive way to detect abnormalities such as arterial stenosis or heart valve insufficiencies.

Origin: The integration of the doppler effect into ultrasound systems technology did not occur until the 1970s, where it marked a crucial advance, allowing real-time visualization of blood flow and transforming the diagnosis and treatment of cardiovascular conditions.

Source: diplomadomedico.com/principios-ecografia-doppler

Bone scan

Radiography is a very common diagnostic test, one of the most commonly used, and is used above all to evaluate bone, lung, and dental injuries and diseases or to detect foreign bodies, such as objects accidentally introduced into the body or to review the of internal implants, such as a pacemaker or prosthesis.

X-ray imaging works by emitting X-rays. The patient is positioned between the X-ray emitter and a receiving plate. Since X-rays pass entirely through the human body except for very hard surfaces like bones or metal objects, the receiving plate captures the emitted rays except for those blocked by bones, metals, or very dense tissues, thus coloring those areas in a lighter shade.

• The metal appears completely white (radiopaque)
• The bone appears almost white
• Fat, muscle and fluid appear as gray shadows
• Air and gas appear black (radiotransparent)

X-rays are a type of ionizing radiation, that is, when used in excess they can have harmful effects on health, such as the generation of cancerous tumors, but you can be VERY calm, since the amount of radiation received, for example, in a chest x-ray is equivalent to the natural radiation in the environment for 10 days (0.1 mSv), values ​​very far from the risk margins, so you can have as many x-rays as your doctor considers necessary.

Evolution: Traditional x-rays were printed on sheets composed of polyester and silver halide. These sheets were placed inside the receiving plate, which absorbed the ionizing radiation that had left the body. These sheets were then processed with chemicals to differentiate the areas of high radiation (soft tissues that the X-rays passed through), colored in black, from bones and hard materials (not crossed by the X-rays), which were colored in white. The process was very similar to developing photographic films in traditional analog photography.

Nowadays, with the digitalization of the world, this process is no longer carried out, since the receiving board is replaced by a board with thousands of sensors that allow the radiation from each point to be translated into an electric current, which is sent to the computer and generates the digital image, being a process also very similar to that of digital photography.

In this way the test is faster, easier to manage and cheaper, but above all it has 2 fundamental advantages: the resolution and quality is much higher, since it allows us to better distinguish areas of intermediate radiation and also avoids the contamination caused by x-rays. printed when thrown into the trash, because of the silver halide they contained. In less modern hospitals, some traditional radiodiagnostic machines are still found, although fortunately less and less.

Origin: On November 8, 1895, the German physicist Wilhelm Conrad Röntgen accidentally discovered X-rays while investigating the violet fluorescence generated by cathode ray tubes in his laboratory. Röntgen observed that a fluorescent material in his laboratory began to glow despite being protected from visible light by a black cardboard screen, indicating that it was being affected by an unknown type of radiation that was capable of passing through the screen, which he called X radiation, because he did not know where it came from. The first x-ray he took was of his wife, Bertha's, hand, clearly showing her bones and her wedding ring. Thanks to this discovery he won the first Nobel Prize in Physics in 1901.

Hand with rings. The first x-ray in history.

modern x-ray

Curiosity: During the First World War, X-ray cars equipped by Marie Curie crossed the battlefield to help surgeons detect the exact location of wounded soldiers' bullets before operating. This was so useful and important that once the Great War ended, radiology was recognized as an independent medical specialty and the first chairs were created in universities.

CT scan

Computed tomography (CT) is a radiodiagnostic technique that uses the same scientific basis as radiography, X-rays, so it also generates ionizing radiation.

This diagnostic test produces detailed cross-sectional images of the body, unlike conventional x-rays, which provide a flat and often overlapping image of internal structures.

CT offers an interactive 3D representation that allows organs, bones and other tissues to be seen in great detail from different angles, as it generates a complete image of the body in layers, with which this interactive 3D representation is generated by computer.

The tomograph is a giant ring that moves along the patient's body to generate the different layers, for which the patient lies on a stretcher that slides towards the center of the ring. Inside it, an x-ray tube rotates around the patient, emitting beams of x-rays from multiple angles. Detectors opposite the x-ray tube capture radiation waves that have passed through the body, and this information is sent to a computer. The computer processes this data to generate cross-sectional images of the body, which are stored in a file under a standard called DICOM, so they can be examined later by the specialist.

One of the main advantages of this technique is its ability to provide extremely clear images of different types of tissue, which is especially useful for detecting diseases and injuries in early stages. It is widely used to evaluate trauma, diagnose cancer, study blood vessels (CT angiography), guide biopsy procedures, plan radiation therapy treatments, and much more.

Although CT is a powerful diagnostic tool, it also involves greater radiation exposure compared to conventional x-rays. Therefore, its use is carefully justified in situations where the benefits of accurate diagnosis and treatment planning outweigh the risk associated with radiation exposure. Technological innovations continue to improve the efficiency of CT scanners, reducing the amount of radiation needed to obtain high-quality images.

The radiation dose absorbed by the patient is much higher than in an x-ray. To compare with the previous example, while a chest x-ray entails radiation of 0.1 mSv for the patient, a chest tomography entails radiation of about 7 mSv, that is, equivalent to taking about 70 x-rays. Despite what it may seem, it is still a completely safe test, far from the danger margins, so you should not fear anything if you have to undergo one of these tests. Even so, due to its greater exposure to radiation, this test is always recommended when the rest of the tests do not provide the necessary information to evaluate the patient's problem. In any case, the dose received will be increasingly lower with the continuous evolution of science. In 1972 the time spent on each scan was 5 minutes, it went to 2 seconds in 1977 and currently lasts on the order of milliseconds.

Origin: Inspired by the idea that a three-dimensional image of the body could be reconstructed from multiple x-rays taken from different angles, the South African physicist Allan MacLeod Cormack published the theoretical foundations of computed tomography in 1963, although without achieving a practical application.

Independently, English electrical engineer Sir Godfrey Newbold Hounsfield developed the first prototype of a brain X-ray tomograph in 1967, performing the first brain CT on a patient in 1971 in London. Hounsfield patented the CT scanner in 1972, beginning clinical trials in hospitals in the United Kingdom and the United States.

This incredible innovation earned them the Nobel Prize in Medicine in 1979, forever changing the world of medical diagnosis.

Tissues: As a tribute to Hounsfield, the units that define the different tissue attenuations studied in CT are called Hounsfield units (HU). These units vary from -1000 to 1000, with -1000 being air (absolute black), 0 being water and 1000 being bones (absolute white).

Source: https://www.scielo.org.co

Curiosity: A fascinating fact about CT scanning is that the development of this innovative technology was partially funded by the proceeds of a hit song. Sir Godfrey Hounsfield worked for EMI Laboratories in the United Kingdom, the same company that owned the Beatles' record label. In the 1960s and early 70s, the Beatles were at the peak of their popularity and generating enormous income. Part of this income was invested in research and development projects within EMI, including Hounsfield's pioneering work in computed tomography. Thus, the Beatles' hits not only left an indelible mark on music, but also indirectly helped finance one of the most significant advances in the history of diagnostic medicine.

Magnetic resonance

MRI and CT are often confused by the general public. They may seem similar since both obtain a three-dimensional image of the patient's body and both involve passing the patient through a hoop. But its scientific basis is completely different.

Unlike radiography and CT scans, which use x-rays, MRI uses powerful magnetic fields and radio waves to generate images of organs, soft tissues, and skeletal systems without exposure to ionizing radiation. Therefore, it does not generate any type of radiation or damage to the patient's body.

The MRI process involves placing the patient inside a long, narrow tube, surrounded by a giant magnet. When the magnet is activated, the hydrogen nuclei present in the human body, especially abundant in water and fat, align with the magnetic field. Radiofrequency pulses are then beamed toward the specific area of ​​the body being examined, briefly altering the alignment of the hydrogen nuclei. When the pulse is turned off, the nuclei return to their normal alignment, in turn emitting radio signals that are captured by detectors. The information collected is processed using computer algorithms to create detailed, cross-sectional images, which can be examined from different angles.

One of the main advantages of MRI is its exceptional ability to differentiate between different types of soft tissues, making it particularly useful in neurology to examine the brain and spinal cord, in orthopedics to evaluate injuries to the joints and ligaments, and in cardiology to visualize the heart and its functions. It is also widely used to detect tumors and to diagnose diseases at an early stage.

MRI is preferred to CT when more details about soft tissues are needed, for example to image abnormalities in the brain, spinal cord, heart, mammary glands, liver, spleen, pancreas, kidneys, uterus, ovaries, prostate, etc, since it is particularly useful to identify infections, hemorrhages, inflammations and tumors in these tissues. Injecting gadolinium-containing contrast dye into a joint allows the doctor to get a clearer picture of joint abnormalities, particularly if they are complex (such as injuries or degeneration of ligaments and cartilage in the knee, ruptures, or hernia). disc in the spine).

Source: Thomas Angus, Imperial College London, CC BY-SA 4.0 via Wikimedia Commons

Origin: Magnetic resonance imaging (MRI) evolved from nuclear magnetic resonance (NMR), discovered in 1946 by Felix Bloch and Edward Mills Purcell, who received the Nobel Prize in Physics in 1952 for their work.

The application of MRI in medicine began in the 1970s, with Raymond Damadian demonstrating that tumors can be differentiated from normal tissue using MRI. In parallel, Paul Lauterbur and Sir Peter Mansfield made crucial advances that enabled the generation of medical images using MRI, introducing the use of magnetic field gradients and developing algorithms for imaging, respectively.

These fundamental advances laid the foundation for the development of the first MR scanners in the 1970s, marking the beginning of magnetic resonance imaging as an essential technique in modern medical diagnosis, capable of providing detailed images without using ionizing radiation.

Lauterbur and Mansfield received the Nobel Prize in Medicine in 2003.

Tissues: Solid tissues such as hard bones or air areas provide low MRI signals since water is virtually immobilized or absent within them. For this reason, these tissues appear dark on MR images compared to fluids or soft tissues.

Fluids and soft tissues can be represented with different contrasts depending on the T1 or T2 weighting chosen.

T1 and T2 potentiations refer to two different relaxation times that characterize how the body's protons return to their normal state after being disturbed by a magnetic field and radio waves. T1 is the longitudinal relaxation time, which measures how long it takes for the protons to realign with the external magnetic field; It is associated with the recovery of energy. T2 is the transverse relaxation time, which indicates how long it takes for the protons to lose phase coherence with each other in a plane perpendicular to the magnetic field; It is related to the dispersion of energy. These properties are exploited to generate different contrasts in MR images, allowing us to distinguish between various types of tissues in the body.

The following image shows two identical MRIs, except that one is T1-weighted (image a) and the other is T2-weighted (image b). In the first we see how the tumor marked with the arrow is seen much better than in the T2 test. So it is very important to choose the correct configuration depending on the problem.

Source: https://www.researchgate.net/

Curiosities: Although mainly used for diagnosis in humans, MRI has also been applied in the study of ancient mummies, living and extinct animals (including fossils), and works of art, providing valuable information without damaging the object of study.

Some tattoo inks contain metals that can react to the magnetic field of the MRI, causing discomfort or even minor burns in rare cases.

Because the operation of the MRI is based on a very high-power magnet, it is absolutely necessary to remove any metallic object from the body, since there have even been cases of piercings that have been thrown towards the magnet, creating a wound when torn off. of the body. For this reason, patients who have pacemakers, implants or ferromagnetic prostheses cannot use this type of test.

Other diagnostic tests

Although they have not been mentioned until now, there are other diagnostic tests that are frequently used, but which are derived from the main technologies (ultrasound, x-rays, magnetism).

Echocardiogram: Ultrasound-based test. It is a specific variant of traditional ultrasound. It is performed with an echocardiograph, which is similar to an ultrasound machine but with a specific screen for reproducing the heart rhythm. It can generate both 2D and 3D images and also incorporates Doppler ultrasound for blood flow analysis.

Mammography: Reference test for the diagnosis of tumors in breast tissue. It is a specific application of the X-ray radiography technique.

Fluoroscopy: Uses x-rays to obtain real-time images of the inside of the body, allowing the movement of internal structures and fluids to be visualized. Unlike static x-rays, which provide a still image, fluoroscopy can show moving organs, such as the beating heart or the transit of contrast dye through the gastrointestinal tract. Depending on the test, the patient may be given a lead shield to protect the parts of the body that do not have to be analyzed from radiation.

DEXA (Bone Densitometry): Uses two x-ray beams of different energy levels to analyze bone density. Passing through bone, X-rays are absorbed to varying degrees by bones and soft tissues. The machine calculates the absorption of each beam and uses this information to determine the bone mineral density in the area examined. This procedure is quick, painless, and exposes the patient to a very low amount of radiation, significantly less than that of a conventional chest x-ray.

Functional magnetic resonance imaging (fMRI): It allows you to visualize and measure brain activity in real time, based on changes in blood flow and oxygen consumption in the brain when it performs a specific task or is at rest. It uses the same basic principles as magnetic resonance imaging (MRI), but instead of just generating static images of brain structure, fMRI captures brain function by detecting increased blood flow to active regions, a phenomenon known as brain effect. BOLD (Blood Oxygen Level Dependent)

Diffusion tensor imaging (DTI): An MRI technique that measures the diffusion of water along white matter fibers in the brain, providing images of neural pathways. It is useful for diagnosing brain diseases, traumatic brain injuries, and developmental disorders.

Tractography: Although technically part of DTI, it deserves a separate mention for its ability to visualize and trace the trajectories of nerve fibers in the brain, which helps in pre-surgical planning and the study of brain connectivity.

Angiography: An imaging procedure used to view the inside of blood vessels and organs in the body, especially to examine the arteries, veins, and heart. The goal is to identify narrowings, blockages, aneurysms (vessel dilations), vascular malformations, and other vascular abnormalities. The curiosity of angiography is that it can be performed using different techniques:

• X-ray angiography (most common):

It is the traditional method that involves the use of x-rays and an iodinated contrast medium, which is injected into the vascular system to make blood vessels visible on x-ray images. It requires insertion of a catheter through an artery, usually in the groin or arm, which is guided to the area of ​​interest.

• Computed tomography angiography (CT-Angio):

It uses CT scan along with intravenous contrast dye to obtain detailed images of blood vessels. It is less invasive than conventional angiography and can provide high-resolution three-dimensional images.

• Magnetic resonance angiography (MR-Angio):

It uses magnetic fields and radio waves instead of x-rays. It can be performed with or without contrast medium, depending on the type of examination. It is useful for patients allergic to iodine and for those in whom radiation exposure must be minimized.

Endoscopies

Endoscopy is a diagnostic technique, and sometimes also a treatment one, which, unlike the previous ones, does not use different technologies to reproduce the inside of the body but rather directly introduces video cameras inside the body to see the real image. It consists of a thin elongated tube with a lighted video camera at one end. This is introduced through the mouth, anus, urethra or through a small surgical incision to reach the area of ​​interest. Depending on the entry point and area of ​​interest, it has a specific name (gastroscopy, colonoscopy, bronchoscopy, cystoscopy, etc...) and when it is used to perform minimally invasive surgery it is called laparoscopy, which is the usual preferred technique. for most surgeries. By its very nature it does not generate any type of radiation or adverse effects.

Nuclear medicine

As can be predicted by its name, it does have ionizing radiation and in much higher doses than X-rays, so its purpose is much more specific and is applied when there is no less ionizing alternative.

The history of Nuclear Medicine dates back to the late 19th century formulation of X-rays Röentgen 1895 and discovery of the radioactivity of uranium (1896) and natural radioactivity (Marie Curie, 1896).

The multidisciplinary contributions of physics, chemistry, engineering, and medicine to this medical specialty make it difficult for historians to determine the birth of nuclear medicine.

It is considered that the most important steps for nuclear medicine were:

• The first use of radioactive tracers in biological exploration by George Hevesy in 1923.
• The discovery of the artificial production of radionuclides by Frédéric Joliot-Curie and Iréne Joliot-Curie in 1934
• The definition of the concept of emission and transmission tomography by David E. Kuhl and Roy Edwards in 1950

In 1948, Joseph Rotblat and George Ansell obtained the first diagnostic image of a thyroid gland after giving the patient a radiopharmaceutical and detecting gamma emissions outside the patient.

Nuclear medicine is a medical specialty that uses radiopharmaceuticals to diagnose and treat diseases. These compounds, which combine a radioactive isotope with a carrier drug, emit gamma radiation detectable at a distance, allowing diagnosis. After the radiopharmaceutical is administered to the patient, it is distributed throughout the organs and emits gamma rays, which are then captured by a gamma camera. These signals are converted into 2D and 3D images using a computer.

In essence, nuclear medicine offers images that show the function and molecular alterations of organs, in contrast to just their structure. This is particularly useful for detecting diseases such as cancer, where tumors can appear as points of greater or lesser absorption of the radiopharmaceutical, called “hot spots” or “cold spots.” This ability to discern cellular activity at the molecular level makes nuclear medicine a valuable tool in the field of medical diagnosis and treatment.

Types of tests in nuclear medicine

Scintigraphy: In this test, a radiopharmaceutical is injected intravenously and a gamma camera is subsequently used to capture the radiation emitted by the isotope and form 2D images. It is very similar to an x-ray, but the radiation source is the gamma decay of a radionuclide inside the body and not x-rays generated by an external device.

PET (Positron Emission Tomography): Tomographs create 3D images by detecting gamma photons emitted by the patient, the result of the annihilation between a positron (from the radiopharmaceutical) and an electron, generating mainly two photons. To form the image, both photons must be detected simultaneously, in an appropriate time window (nanoseconds) and come from the same directions and opposite directions, in addition to exceeding a minimum energy threshold that confirms that they have not been significantly scattered. These photons, captured in millions of pairs, are converted into electrical signals that, after a filtering and reconstruction process, result in the final image. PET is very useful for detecting Alzheimer's, since it allows us to identify cells with low glucose consumption and the presence of amyloid plaques, typical characteristics of the disease.

SPECT (Single Photon Emission Computed Tomography): The SPECT procedure is similar to that of PET, but in SPECT it is the isotope that directly emits the gamma ray, creating 3D images in a manner similar to scintigraphy. In contrast, in PET, the isotope emits a positron that, when annihilated with an electron, produces two gamma rays. SPECT is technically simpler, since it uses isotopes that are more accessible and have a longer half-life, although it offers lower precision in isotope detection compared to PET.

Curiosity: As the radiopharmaceuticals present in nuclear medicine tests sometimes have a life of several days, sometimes the patient can be isolated to avoid irradiating other people while the radiopharmaceutical does not disappear. Depending on the radiopharmaceutical and personal conditions, this isolation can be hospital, home or maintaining a certain social distance.

Summary

After having read this entire article, it is important that you understand the concept of ALARA .

ALARA is an acronym for "As low as reasonably achievable". This principle is fundamental in the practice of radiation protection and refers to keeping radiation exposures and doses as low as reasonably possible, taking into account 3 factors:

• Rationale: Any decision that increases radiation exposure must have more benefits than risks.
• Optimization: For exposures that have been justified, radiation doses should be optimized to be as low as possible.
• Dose Limitation: This concept is primarily applied in occupational settings, where workers may be exposed to radiation as part of their job. Maximum dose limits are set to ensure that no one is exposed to levels of radiation that could be harmful.

And what does all this mean? That as a patient, you can have peace of mind, since although there are tests that involve more or less amounts of ionizing radiation, they have low levels and very defined safety criteria, in addition to the fact that they will only be indicated when they are strictly necessary, for example. Therefore, performing diagnostic tests will not make you sick or harm you.

Below is a brief summary of what we have seen.

If you liked it, share :)