Noninvasive tests

ANATOMY OR SYSTEM AFFECTED: All

DEFINITION: Diagnostic techniques that do not involve the collection of tissue or fluid samples or the introduction of any instrument into the body and often involve imaging or the measurement of electrical activity

Indications and Procedures

Noninvasive tests are used in the initial diagnosis of a disease or abnormality and for the monitoring of certain conditions and body processes. Most such tests involve imaging techniques. Primary among them are x-radiology, computed tomography (CT) scanning, magnetic resonance imaging (MRI), electrocardiography (EKG or ECG), and ultrasound.

Diagnostic X-ray examinations are often the first step in complex technological solutions to medical diagnoses and health problems. New uses for diagnostic X-rays are constantly being devised, and hospital inpatients are usually given chest X-rays before admission or surgery.

Computed tomography (CT) scanning, also known as computed axial tomography (CAT) scanning, uses a computer to interpret multiple X-ray images to reconstruct a cross-sectional image of any area of the body. The inventors of the procedure for CT scanning were awarded a Nobel Prize in 1979.

After the patient is placed in the CT scanner, an X-ray source rapidly rotates around it, taking hundreds of pictures. The pictures are electronically recorded and stored by a computer. The computer then integrates the data into cross-sectional “slices.” The CT scanner can assess the composition of internal structures, which it is able to discriminate from fat, fluid, and gas. The scanner can show the shape and size of various organs and lesions and has the capability of detecting abnormal lesions as small as one or two millimeters in diameter.

Magnetic resonance imaging (MRI), unlike CT scanning (which uses X-rays), uses magnetic fields passing through the body to detect details of and physiology.

MRI equipment consists of a tunnel-like magnet that creates a magnetic field around the patient. This magnetic field causes the hydrogen atoms found in the body—water has two hydrogen atoms and one oxygen atom in the molecule—to line up. At the same time, a radio frequency signal is quickly transmitted to upset the uniformity of the formation. When the radio frequency signal is turned off, the hydrogen atoms return to their proper lineup, and a small current is generated. By detecting the speed and volume with which the atoms return, the computer can display a diagnostic image on a monitor.

MRI is noninvasive, and no pain or radiation is involved. The procedure takes from fifteen to forty-five minutes, depending on the number of views needed. Diagnostic X-rays rely on variations of density on film, and areas of soft tissue, for example, produce little or no shadow and are difficult to distinguish in any detail. MRI images, on the other hand, allow tumors, muscles, arteries, and vertebrae to be seen with great clarity.

Monitoring and providing electrical support to the heart constitute other useful techniques. A healthy heart generates electrical impulses rhythmically and spontaneously; this activity is controlled by the sinoatrial (S-A) node, the heart’s natural pacemaker. From there, the impulses pass through specialized conduction tissues in the atria and into the atrioventricular (A-V) node. Then the electrical impulses enter the ventricular conduction system, the bundle of His, and the right and left bundle branches. From the bundle branches, the impulses spread into the through the network of Purkinje fibers. The spread of electrical stimulation through the atria and the ventricles is known as depolarization. The standard electrocardiogram (ECG or EKG) records this activity from twelve different angles. The EKG records the heart’s electrical activity and provides vital information concerning its rate, rhythm, and conduction system status. Detecting changes in the EKG can help to diagnose ventricular conduction problems and ventricular hypertrophy.

The (SAECG) is another noninvasive procedure that is a promising diagnostic tool for many cardiac patients. Unlike the standard twelve-lead EKG, the SAECG can detect conduction abnormalities that often precede sustained ventricular tachycardia—which is second only to myocardial (heart attack) as the leading cause of sudden death. The SAECG records the heart’s electrical activity via six electrodes applied to the frontal and chest walls. The SAECG can often pick up repolarization delays that occur when ischemic (damaged) tissue impedes the passage of electrical impulses through a portion of the myocardium, a condition that can lead to ventricular tachycardia.

A valuable weapon in the battle against sudden cardiac death is the temporary pacemaker, which provides support for the heart’s electrical conduction system. Such devices can provide vital support when there is no time to prepare for an invasive procedure and are also used when invasive procedures are contraindicated.

Another method for diagnosing heart problems is echocardiography, a technique for recording echoes of waves when these waves are directed at areas of the heart. The principle is similar to that used in the sonar detection of submarines and other underwater objects. In this very simple and painless procedure, the patient lies on a table while a small, high-frequency generator (transducer) is moved across the chest. The instrument projects ultrasonic waves and receives the returning echoes. As the waves pass through the heart, their behavior differs, depending on whether there is any present, whether there is a blood or any other mass in the cavity of the heart, whether certain heart chambers are enlarged, whether the within the heart open and close in the proper fashion and whether any part of the heart is thicker than it should be.

Sonography, or ultrasound, imaging and the images produced are unique: patients can hear their blood flowing through the carotid of the neck, and physicians can see a or watch a human suck its thumb. This simple and inexpensive imaging technique has aided in the development of fetal medicine as a subspecialty. Sonography uses sound waves to look within the body by using a piezoelectric crystal to convert electric pulses into vibrations that penetrate the body. These sound waves are reflected back to the crystal, which reconverts them into electric signals. The use of ultrasound as a noninvasive procedure continued to develop in the twenty-first century.

In the twenty-first century, at-home diagnostic tests have emerged as a popular noninvasive method of testing for medical issues. Pregnancy tests and at-home drug testing have been available since the twentieth century, but technological advancements opened the door for different varieties of at-home testing, such as colon cancer screenings, blood sugar monitoring, and genetic testing for hereditary conditions. After the onset of the 2020 global COVID-19 pandemic, pharmaceutical companies developed at-home diagnostic methods to test for the virus. As pandemic lockdowns began to limit population movement, this allowed people to begin treatment without having to risk spreading the virus.

Uses and Complications

Historically, diagnostic X-rays have been used for the detection of metal objects, in teeth, and broken bones. Films of various parts of the body, such as the abdomen, skull, and chest, have been taken ever since X-rays were first discovered in the late nineteenth century. Dentists and orthodontists use X-rays to check for jaw fractures, tooth misalignment, gum disease, deposits, impacted teeth, and bone cancer. Chronic illnesses that can be detected by X-rays include arthritis, tuberculosis, osteoporosis, emphysema, ulcers, pneumonia, and urinary tract infections.

The CT scanner uses a series of narrow, pencil-like X-ray beams to scan the section of the body under investigation. CT scans allow the rapid diagnosis of brain abnormalities, cysts, tumors, and blood clots. Body scanners assist in the early detection of cancers and other diseases of the internal organs.

Magnetic resonance imaging has undergone an explosive growth in applications. In 1982, there were only six machines in operation. Hospitals often used a portable MRI device, which could be driven from place to place with a tractor-trailer truck. As the cost for MRI machines decreased, however, more hospitals purchased this equipment instead of sharing it. By 2021, the United States had about thirty-eight MRI machines per every million Americans.

The MRI machine is able to differentiate the brain’s gray matter (nerve cells) from the brain’s white matter (nerve fibers). Gray matter contains 87 percent water, and white matter contains 72 percent water. Thus, since MRI detects the protons in the hydrogen in water, a great difference in contrast between the two types of brain material is seen on the resulting scan. MRI is also useful in detecting and monitoring the progression of multiple sclerosis because the fatty tissue that normally exists around nerve fibers deteriorates, and these abnormal, fat-free areas can be clearly imaged.

MRI research seeks ways of analyzing the numerous chemical elements found in the body and aids in the study, diagnosis, treatment, and cure of a host of human diseases.

EKGs are useful in the detection of irregularities in the heart’s electrical conduction system. This technology can also help in the diagnosis of ventricular hypertrophy, emboli, and intraventricular conduction problems.

Echocardiograms, based on sound waves, are used to detect infarcts (areas of necrosis, or tissue death), valve closure between heart chambers, and abnormal thickening of myocardial muscle. Sonography is perhaps best known for its contribution to diagnostic medicine in the study of human fetal development. Determining the age of a developing is now standard procedure, and clear images can be obtained at five weeks of gestation when the embryo is only five millimeters long. Fetal weight can be determined by volume, and fetal anatomy can also be studied. Congenital heart defects can be spotted very early, and neural brain defects can be discovered as well. Sonography also became a boutique-style business for expecting parents in the twenty-first century. Expecting parents can visit businesses offering sonography and 3D sonography outside of a doctor’s office or hospital simply for their own interest.

The great advantage of ultrasound is that it emits no ionizing radiation and thus can be used on pregnant women without danger to the fetus. Ultrasound can also detect gallstones, kidney stones, and tumors and can monitor blood flow. Its applications have grown exponentially since its discovery.

Noninvasive tests such as X-rays, MRI, and CT scanning have become a crucial part of the detection and treatment of cancer. They are vital in determining the source and extent of the .

Mammography is a subset of X-ray imaging that is useful in detecting breast cancer. The equipment used in is designed to image breast tissue, which is usually soft and of uniform density. Very small changes in density can be identified in fine detail, including small areas of calcification. Radiation doses must also be kept to a minimum. The film interpretation of mammograms is difficult, but early detection of is often possible.

In the United States, the Public Health Service, in a memo dated June 1, 1993, delegated authority for implementing the Mammography Quality Standards Act (MQSA) of 1992 to the Food and Drug Administration (FDA). The MQSA is intended to ensure that mammography is reliable and safe. The act makes it unlawful for any facility to provide services unless it is accredited by an approved private nonprofit or state body and it has received federal indicating that it meets standards for quality. Each facility must also pass an annual inspection conducted by approved federal personnel. The law was enacted in response to the need for safe, early detection of breast cancer. Mammography is the most effective technique for early detection of this type of cancer.

Given a choice, most persons would prefer a noninvasive diagnostic tool. The earliest used diagnostic tool was the X-ray. X-rays were discovered in 1895 by a German professor named Wilhelm Conrad Röntgen. The first X-rays were produced in a Crookes tube, a pear-shaped glass tube in which two electrodes, the cathode (negative electrode) and anode (positive electrode), were placed at right angles to each other. The tube was then evacuated of gas. In Röntgen’s first experiment, the cathode was “excited” with an electrical current, producing a beam of cathode rays, or electrons. These electrons were directed across the tube from the cathode and struck the glass, causing it to glow and, at the same time, producing X-rays, which excited a fluorescent screen. In a modern X-ray tube, the cathode ray strikes a target in the anode rather than the glass. Modern equipment also uses high-energy electricity in order to energize the tube at the high voltages necessary for producing X-rays.

Radiology has come far. From a medical discipline with a limited but vital function (that of aiding diagnosis), it has become interventional. It is a field that has moved into therapy—repairing a growing variety of abnormalities, averting surgery, and sometimes achieving results beyond the reach of surgery.

In addition to the simple X-ray, physicians now have more powerful diagnostic devices: MRI, CT scanning, and sonography. Cardiac conditions and abnormalities are quite easily analyzed via the ECG or echocardiogram. Where once the diagnosis of required a two-day X-ray test and twelve grams of diarrhea-causing pills, now ultrasound allows a diagnosis to be made painlessly and noninvasively in ten to fifteen minutes.

The computer has been the core of the revolution in imaging. As more information becomes available and the density of information grows exponentially, larger and faster computers have been developed to assimilate this information. Computer visualization both interprets data and generates images from data in order to provide new insight into disease states through visual methods. Visualization and computation promise to play a key role in diagnostic medicine. Noninvasive medical tests continued to evolve in the twenty-first century. An example of an innovation was the HeartFlow Analysis device. This new type of CT scan proved a revolution in the detection of coronary artery disease as it was able to provide doctors with an improved view of coronary anatomy, view blockages more accurately, and determine the significance of the findings within one session.

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