Medical Uses

Medical Uses  

I understand that radiation sources are used for medical purposes. Is that true?Yes it is. In fact, the ionizing radiation that is emitted from radioactive atoms has many, many applications in the diagnosis and treatment of disease.

Where is radioactivity typically used?There are traditionally three branches of medicine that use ionizing radiation. The first is called "diagnostic imaging", which includes diagnostic x-ray and computed tomography. Magnetic resonance imaging and ultrasound are also included in diagnostic imaging, but do not use ionizing radiation.

And the other two branches?One is "nuclear medicine", which includes diagnostic nuclear medicine and radionuclide therapy. The other is "radiation therapy", which includes external beam therapy and brachytherapy.

Why would anyone want to use radiation in medicine since radiation exposure has some risks associated with it?Good question. Radiation makes the diagnosis of certain diseases and conditions, like broken bones, and the treatment of other diseases, like cancer, somewhat easier. The general goal in using radiation in medicine is to balance the risk of the exposure with the benefit of the diagnosis or treatment. The benefit of the exposure is usually obvious and personally relevant to patients undergoing procedures or their families. Therefore, the risks of these procedures are more readily accepted by the general population than other uses of radioactivity (i.e., industrial uses).

I have heard of an occupation called a Medical Physicist. What does this person do?Medical physicists are trained professionals who study the physical characteristics of the subject of diagnostic imaging or therapy and the human body. In diagnostic imaging and nuclear medicine, medical physicists work closely with the physician to reduce the purposeful radiation exposure in a way that does not lose the necessary diagnostic information. While any medically-related radiation dose can usually be reduced to lower and lower levels, there is always an accompanying loss of information for the physician. Eventually, the dose gets so low that there is not enough information to accomplish the objective. We call this a "wasted" dose.

Is the same thing true in radiation therapy?To a great extent, yes. In radiation therapy, the goal is to destroy malignant tissue while sparing healthy tissue. If the dose is minimized too much, there may be only negligible effect on the malignant tissue, again resulting in "wasted" dose.

What kinds of radiation are used in diagnostic imaging?X-ray machines are most commonly used for this purpose. The x-rays produced in the machines have energies ranging from about 20 kiloelectron volts, or "keV", to 125 keV. X-ray studies primarily reveal structural changes like broken bones, for example, rather than functional changes like a section of the lung that is not getting a supply of blood. The quality of the image produced is dependent upon the physical characteristics of the organ in question.

What do you mean by physical characteristics?Diagnostic imaging provides a "contrast" in the image which varies based on the density of the materials that make up the human body. For example, bone is quite dense, while soft tissue is not. Therefore, there is a distinct contrast between bones and tissue that is visible on an x-ray image. On the other hand, other body structures such as kidneys, blood vessels, intestines, etc. may not be visible in an x-ray image because there is not enough of a difference in the absorption of x-rays in these organs (i.e., less dense). However, other forms of diagnostic imaging, like computerized tomography or "CT Scans", are able to show differences between these less-dense structures.

Is there a way to improve the contrast for materials of similar densities?Yes. One technique is to fill these structures with contrast material. The contrast material is a stable compound (meaning that it is not radioactive) of greater density than the surrounding structures. As a result it will absorb more radiation and enhance the contrast and visibility of the image.

Can you give me an example, please?Certainly. A barium compound, serving as a contrast material, is often placed inside the gastrointestinal (GI) tract to image it. When barium is inside the colon, for example, an outline of the colon becomes clearly visible on the x-ray image. For that matter, other portions of the GI tract along with blood vessels, the urinary system of the kidney, the bladder, etc. can also be imaged with contrast material. Contrast material is also used in CT studies.

What is required to obtain good image quality?For good image quality, the characteristics of the radiation must be coupled with the characteristics of the subjects or organs being imaged.

What do you mean?Well, imaging geometry is an important factor that affects how structures will appear in the image. For example, a conventional x-ray tube is placed on one side of the patient and the image receptor, usually film, is placed on the other. In this geometry, a three-dimensional object is imaged on a two-dimensional image receptor. This results in many structures being superimposed on top of each other in the image.

That doesn"t sound too good.Actually, this is not a problem for a large number of routine x-ray studies. But, as you might imagine, there are circumstances where a "static" image would probably would be unacceptable.

You mentioned "image receptor". What is that?The image receptor is the material or device designed to capture the image or picture as the x-rays pass from the x-ray tube and through the patient.

What kinds of image receptors are there?Photographic film is still the most prevalent type of image receptor, but there are actually many others that will likely be in widespread use in the future. Some of these are fluorescent screens, video screens, computer monitors, laser discs, and phosphors which are "stimulated" upon exposure to radiation.

I take it a mammography machine is a type of imaging device, right?Most definitely. These are machines utilize x-rays for the difficult task of breast imaging. To accomplish this objective, the machine needs some pretty unique design features. There are definitely challenges in obtaining useful static images of this soft tissue.

Let"s move on to fluoroscopy. What is it and what does it accomplish?Fluoroscopy is a radiographic technique that is used to image organs in "real" time. This means that you can capture the organ while it is moving. These images, called "dynamic images", are recorded on special film or videotape. And, as you might imagine, fluoroscopy machines, just like other x-ray machine, come in different shapes and sizes.

How does fluoroscopy work?The patient is placed in a radiographic/fluoroscopic (R/F) x-ray room. The radiographic x-ray tube is positioned above the x-ray table, and the fluoroscopic x-ray tube is usually underneath the table. The image receptor for fluoroscopy, which is colloquially known as "fluoro", is a fluorescent screen assembly that is attached to the device that the radiologist moves over the patient. The fluoro beam is activated by a foot switch. The radiologist typically stands next to the patient, with one foot on the switch, eyes on the TV monitor, and his hand moving the image receptor and tube. The radiographic x-ray tube is used to make "static" images on an as-needed basis.

I notice that the radiologist wears a lead apron. Why is that?The radiologist must wear a protective lead apron during the procedure, as must any technologists or other people present. This is necessary because they perform this work day in and day out and, if not protected, could accumulate a significant amount of radiation exposure. In fact, you may also have observed radiologists wearing lead gloves if the procedure calls for him or her to reach into the x-ray beam to assist the patient during the procedure. In addition, you can also see a lead drape hanging from the image receptor assembly to the edge of the table. This drape is used to intercept radiation that "scatters" from the patient before it reaches the radiologist.

So, the medical staff takes radiation safety precautions to limit their exposures. What about the patient?Every effort is made to keep the radiation exposure to patients as low as possible, while making sure the radiologist gets as much information about the patient as possible. While there are legal dose limits for the medical staff, there are no limits to the amount of radiation exposure patients can receive, except in radiation therapy where higher doses are used to begin with.

Wow. That doesn"t seem quite fair.Before you jump to that conclusion, let me give you an example. Suppose there was a limit on the amount of radiation exposure you could receive, and you already reached that limit while being treated for a severe case of pneumonia. What if, on your way home from the hospital, someone ran a red light and broadsided your car, breaking some of your ribs or an arm or leg. It would be senseless to not permit the physician to use more x-rays to diagnose and treat you fractures in the best way possible, particularly when the radiation risk from those additional procedures would be small compared to not treating broken bones properly.

So there are no limits at all?Well, not quite. Some state agencies do have ceilings on the amount of exposure permitted per procedure, but there are no limits on the number of procedures performed. Similarly, regulations issued by the Food and Drug Administration (FDA) limit the entrance exposure rate (EER) to the patient for routine fluoroscopic procedures to ten roentgens per minute (10 R/min), but the duration of fluoro is not limited. For non-routine fluoroscopic procedures, such as angiographic (blood vessel-related) procedures or interventional procedures (such as balloon angioplasty), higher entrance exposure rates may be necessary, and can be used.

Should this concern me?The whole basis for our standard of medical care is that procedures are performed when medically necessary. If radiological procedures are required, the law states that the equipment must be checked by a physicist and a state inspector, and that all personnel involved in the procedure, like the radiologist (physician) and the technologist, are qualified by training and experience to perform the procedure. As a result, only the necessary amount of radiation will be delivered in order to achieve the medical objective. The risk of radiation exposure to the patient is really minimal when you compare it to the potentially dangerous consequences of not having the procedure. However, patients can help ensure their own radiation safety by asking questions of their physicians, radiologists, and physicists. While patients always have the right to refuse procedures, you should take care in making this request, as it might subject you to far greater risk than the procedure you are trying to avoid.

Okay. I"ll keep that in mind. In the meantime, would you please explain what vascular imaging procedures are?Vascular imaging procedures are another category of radiographic procedures. The word "vascular" simply refers to images of the blood vessels.

Do you have an example where this is utilized?Yes. One example is "arteriograms", where images of arteries are taken. These are semi-surgical procedures that are usually performed in rooms that are dedicated for this purpose.

Like how?The procedure involves placement of a catheter, or a hollow plastic tube, into the arterial system during fluoroscopy. The catheter has a "radiopaque" tip that allows it to be visible to the radiologist or vascular surgeon on the fluoro image. Once they see on the image that the catheter is correctly positioned in the desired artery, contrast material is automatically injected into the bloodstream. Images are then obtained in rapid sequence and recorded on film, video tape, or some sort of digital media. Special x-ray tubes are usually required for these studies because of the power output and heat loading demands of this type of rapid sequence x-ray production. In many angiographic procedures, not one, but two x-ray machines are used to make exposures simultaneously at 90 degrees from each other.

This is interesting. Give me some other applications of the vascular imaging technique.You got it. How about a selective renal arteriogram? In these studies, the catheter is introduced into the femoral artery, which is located in the upper thigh and groin area. From there it is "threaded" up through the aorta and into the right renal artery. The contrast material is then injected, and the images are obtained. The technique can be used to identify small blockages in the artery.

Any more?Another good example is a carotid arteriogram. The catheter is introduced into a carotid artery in the neck. (The carotid arteries supply blood to the brain). These images are difficult to interpret because abnormalities may be very small and subtle. In addition, the images are cluttered with bony details of the skull.

Is there any way to improve the diagnostic detail of vascular images?Actually, there are. Take the example of the angiogram we just described. A "subtraction" technique is utilized for this purpose. As originally conceived, the idea was that if all unnecessary images could be "subtracted" out of the original image, the vascular structures could be more easily seen. When first implemented, the procedures were labor intensive and time consuming. More modern equipment uses an automatic digital process where x-ray machines are designed to record and process images in pixels (picture elements). This process is called "digital subtraction angiography" (DSA).

In what other ways can the diagnostic power of radiographs be improved? Well, the "tomographic" technique provides another mechanism to accomplish this goal.

How does this work?In this technique, both the x-ray machine and the image receptor are moving during the exposure, but in opposite directions. As is the case when a camera is moved during a snapshot, blurring will occur. But if the area of the patient to be imaged is placed in a precise geometry relative to the x-ray tube and image receptor, a thin plane of tissue will be imaged very sharply, while all the other structures above and below this focal plane will be blurred. Sometimes computers are used to process the information obtained.

How has this technique been utilized?This technique is a valuable means of imaging areas such as the inner ear or chest lesions. It has also been used to identify medical conditions affecting the lumbar spine. Tomographic images can be used, for example, to confirm small, but potentially serious fractures which could cause damage to the spinal cord if not stabilized.

You said that computers are sometimes used to process information. Could you explain this a bit better?Be glad to. In the 1970"s, computer power was such that when combined with the tomographic principle, cross-sectional images of the body could be attained. This technique is widely used today and is called computerized tomography (CT).

Sounds impressive. Tell me about CT.In brief, a small, pencil-sized x-ray beam passes through the patient and into radiation detectors where it is measured. As the beam passes through, it is attenuated to a greater or lesser extent, depending upon what is in its way. This attenuation data is acquired 360 degrees (360 ) around the patient, meaning the x-ray tube travels completely around the patient, exposing a small volume of tissue each time. The accumulated attenuation data are stored by a computer then reconstructed into cross-sectional "attenuation maps" of the patient. The resultant images provide detailed cross- sectional anatomical information.

Why was the advent of CT so important in the field of medical physics?CT not only revolutionized imaging, but it revolutionized the study of anatomy by physicians! All physicians today study cross-sectional anatomy as shown by CT images.

If I have to have a CT scan, and I hope I don"t, what would the procedure be?Well, you would be asked to lie on a table, which then moves into an area called the "gantry" for imaging. The gantry, which looks like a big donut, houses the x-ray tube(s) and radiation detectors. You might hear some noise as the x-ray tube and the detector rotate around you, but other than that, you won"t feel a thing.

Does the table move fast?No. Because the exposed cross-sections of tissue are small (several millimeters), it is important for the table to accurately move small distances (millimeters) when holding a patient. Otherwise, cross-sections would overlap, resulting in unnecessary radiation exposure with no new information revealed. Knowing this, one of the quality control tests physicists make on CT units is testing of the table as it moves incrementally through the gantry.

You know, I think I had some kind of tomography when I saw the dentist, because the x-ray machine moved around my head. Right?Well, what you actually experienced was a "panoramic" dental x-ray. The machines that perform this procedure utilizes the tomographic principle for radiography of the jaw. The patient places his chin and forehead on "rests", and the x-ray tube then revolves around the patient"s head while the film also moves around the head. The radiation beam is "collimated", or restricted to a thin opening or slit, so that only a small volume of tissue is irradiated at one time.

We"ve spent a lot of time discussing diagnostic x-ray applications. What about nuclear medicine applications?Ok. In nuclear medicine, the patient is purposefully administered radioactive material. This now makes the patient the "source" of radiation. The radioactive material might be either injected, inhaled, or ingested by patients.

What"s the point of that?The objective is to get the radioactive material to a specific organ or organ system, then use an imaging device to find it and show its distribution. By chemically bonding ("tagging") a radioactive atom to various chemical compounds, the newly created radioactive compounds will seek out various organs of the body depending on how the body metabolizes the chemical compound. As a result, the organs that are not of interest to the physician do not receive much radiation dose, relatively speaking.

An example, please?Sure. The metastable form of technetium-99 (Tc-99m) is one of the most commonly used radionuclide in nuclear medicine. One of the reasons for this is that it has very favorable chemical properties. It can be bonded to a whole variety of chemical compounds that will be metabolized by the body in different ways. Tc-99m also has good radiological properties for imaging, such as a 140 keV gamma ray (with essentially no other radiations emitted) and a 6 hour half-life, which can help keep the radiation dose to the patient low.

What type of radiation detector is used to find the radioactivity and determine its distribution in the body? The radiation detector used is a large, stationary, sodium iodide (NaI) crystal. These detectors are known as "scintillation" detectors because they give off light "flashes" as radiation interacts with the solid crystal. (For more information, review the "Measuring Radioactivity" section of the IEM web page.) The light is then converted to an electronic pulse and the position (location) of the light flashes are recorded so that the count distribution (or image) can be displayed.

Do mobile scintillation cameras exist?Yes, they do as a matter of fact.

When would it be advantageous to use such a device?Take for example a patient who is in heavy traction as a result of a serious fracture. A person in this state cannot be easily moved to the nuclear medicine department for a bone scan. A bone scan is a very sensitive test that in this case would show early healing of the fractures. However, these mobile procedures are used sparingly.

Why is that?Well, its kind of a common-sense thing.  The fact that the radioactivity must leave the nuclear medicine department increases the chance for spills and/or exposures of other people. In other words, contamination control issues become a concern.

Tell me more about bone scans.Bone scans are commonly used to detect metastatic cancer, or cancer originating from another location that has spread to the bone. Cancers such as breast and prostate spread to bone, so a bone scan would be requested for patients who have been diagnosed with these cancers in order to determine how far it has progressed (i.e., "staging" the disease, or classifying its progression). Treatment options and prognosis will vary according to the stage of the disease.

I"ve heard about thyroid scans for illnesses of the thyroid. Is that a nuclear medicine study?Yes. Thyroid imaging for the detection of thyroid disease is another very common nuclear medicine study. A normal thyroid image is obtained using Tc-99m (found chemically as a "pertechnetate"). Sometimes isotopes of iodine are used.

What does a thyroid scan tell you?In hyperthyroidism, there is increased production of thyroid hormone, and increased uptake of iodine by the thyroid. The symptoms are nervousness and tremors. Images of the thyroid can be used to detect a hyperfunctioning (or "hot") nodule in a lobe of the thyroid. Hypothyroidism, on the other hand, results in the decreased production of thyroid hormone, and resultant decreased uptake of iodine. Hypothyroid patients are sleepy and tired all the time. Once again, thyroid imaging can detect a non-functioning (or "cold") nodule in a particular lobe.

Very interesting. What can you now tell me about lung scans?Lung scans are another common type of nuclear medicine procedure. Lung scans are performed to evaluate the blood supply to the lungs (perfusion studies) or the air supply to the lungs (ventilation). Often both are performed to obtain a diagnosis of pulmonary embolism, which can be a life-threatening condition. An abnormal lung perfusion scan, for example, shows the locations of decreased activity which indicate areas of decreased blood flow to the lungs.

I have heard of an isotope called Gallium-67, but do not know much about it. What application does it have?Gallium-67 (Ga-67) scans are used to image/locate sites of infection. For example, Ga-67 will concentrate in bone when a bone infection is present. So now it is used to image sites of infection (such as an infected tumor) or inflammation. Ga-67 scans are performed as part of the work-up for infections common in AIDS patients.

What is SPECT?Single Photon Emission Computed Tomography (SPECT) is the application of the tomographic principle in nuclear medicine. SPECT images are acquired in a 360 circle around the patient, and a computer reconstructs the data to produce cross-sectional images of planes of tissue. These studies require a little more administered activity than conventional scans, so the number of radiation counts in one cross-sectional "slice" will be adequate for image visualization.

So what does SPECT do for the patient?An amazing number of things. In a nutshell, SPECT can be used to identify conditions that are not visible on a conventional scan. In addition, the SPECT images can reveal much more detailed information to a surgeon, for example, about the extent and configuration of a tumor.

Tell me about the role of nuclear cardiology?This is a very exciting area of diagnosis. Nuclear cardiology has had a great impact on health care costs and surgical risks to patients by providing an excellent screening test for potential coronary bypass surgery candidates. For example, take the situation where a perfusion study is used to determine whether the heart muscle is getting adequate blood supply under stress (exercise) and at rest. The study begins with the patient on a treadmill. Then radioactive material is injected (most often thallium-201) and images of the heart are obtained. Then the patient is allowed to rest, and another set of images is acquired. These are known as the "rest" or "redistribution" study.

Sounds good. Now how is this information used?Let"s take two examples. The first involves an abnormal stress study, combined with a normal redistribution study, which indicates that the arteries supplying blood to the heart are open and the heart muscle is not damaged because of lack of blood supply, but that during exercise, the arteries are unable to meet the increased demand for blood. This type of pattern indicates a good candidate for bypass surgery. Following the surgery, post-by-pass stress and redistribution studies can be repeated to identify the benefits received by the patient from the bypass surgery. A poor surgical candidate would typically have both abnormal stress and redistribution studies, indicating that the blood supply to the heart muscle has been compromised to the degree that there is muscle damage, and that resupplying the muscle with blood will not reverse the damage.

You"ve given me a lot of information. Is there anything we"ve missed?Well, yes. Positron emission tomography (PET) is another unique area of nuclear medicine. This technique utilizes the principles of coincidence counting of annihilation radiation from positron (electrons with a positive charge) emitters for the creation of tomographic images. The most common positron emitters used are Fluorine-18 (F-18), Oxygen-15 (O-15), Carbon-11 (C-11), and Nitrogen-13 (N-13). With the exception of F-18 which has a two (2) hour half-life, the remaining radionuclides must be produced in an on-site cyclotron (accelerator) and delivered immediately to the patient before significant radioactive decay occurs.

Whoa, hold the phone. Coincidence counting? Annihilation radiation? You"re losing me.Sorry. Perhaps this explanation will help. Annihilation radiation results when two electron masses (of opposite charges) collide and subsequently are converted into two gamma rays of 511 keV. These rays travel in completely opposite directions. As a result, a "coincidence" count is recorded if it both radiations are detected simultaneously (in "coincidence") by detectors that are 180 degrees opposed to each other . Radiation counts not observed in this manner are not accepted as a "true event".

Why aren"t there PET machines everywhere?Well, for one thing, the half-lives of the positron emitters used are extremely short (on the order of tens of minutes). Therefore, the radionuclides and the radiopharmaceuticals used for these procedures must essentially be produced on- site (or very close by to the medical facility). If not, they decay away before they can be used.

Can you provide an example?Certainly. At the University of Tennessee Medical Center in Knoxville, Tennessee (UTMCK), the cyclotron that produces these materials is located right across the hallway from the scanning rooms. The radiochemistry laboratory is located next to the cyclotron room. The laboratory prepares the radiopharmaceuticals for administration to the patient, after which quality control tests are performed.

What do PET machines look like?PET uses an octagonal ring design of scanners where individual detectors arranged within a bank of detectors are connected in coincidence with all of the detectors in an opposing bank.

What detectors are used?PET scanners use "scintillation" detectors, such as bismuth germanate (BGO). The detector responds to ionizing radiations and produces light flashes. The light is then converted into an electrical signal and finally a radiation count

You know, I don"t think we"ve talked about radiation therapy yet. What can you tell me about it?Radiation therapy is used either alone or in conjunction with surgery and chemotherapy to treat cancer.

I take it radiation therapy has different goals than radiation diagnostics, right? You"re correct. We can divide radiation therapy objectives into palliative and curative therapy. In "palliative" therapy, the goal is to relieve pain in terminally ill patients. Palliative therapy usually consists of a single dose of radiation which is not large enough to cause any associated complications. In "curative" therapy, the goal is to achieve 90% tumor control/destruction with only about 5% normal tissue damage. To achieve a cure, higher radiation doses are used, on the order of about 1000 rads/week. But these are delivered in fractional amounts to spare healthy tissue as much as possible. A typical treatment course would last about two weeks, with the patient visiting the radiation therapy department every day for a treatment. In curative therapy, one is usually willing to tolerate some of the side effects of the high exposure if it leads to an eventual cure.

How sensitive are tumors to radiation?Tumors are more sensitive, in general, to radiation damage than normal tissue. Some tumors are more resistant than others; others respond well because they are rapidly growing, and not highly differentiated.

What types of radiation therapy exist?There are four principal types: external beam therapy using linear accelerators, low- and high-dose rate brachytherapy, radionuclide therapy, and stereotactic radiosurgery.

Isn"t radioactive cobalt used for external therapy?  I believe I"ve read about it in the newspaper.Yes. But this type of therapy is somewhat outdated, at least in the United States. However, in other countries, where the stable sources of electrical power necessary for accelerator use is unavailable, Cs-137 and Co-60 teletherapy is still used.

Tell me more about external beam therapy with accelerators and why is it advantageous?External beam therapy is most widely used for two reasons: 1) Linear accelerator beams provide some measure of protection or sparing of superficial, healthy skin tissue. In other words, the skin is not receiving the maximum dose; 2) Higher energy radiations from linear accelerators are effective at deeper depths in the body where most tumors occur. Linear accelerators can also produce multiple (photon and electron) radiations.

How do linear accelerators basically work to the patient"s advantage?In the case of a tumor, the tumor is positioned in the beam and the treatment delivered from several entrance points, or ports. For example, a treatment might be delivered from four ports: front, back and each side. With this technique, the tumor gets the total dose, but the healthy tissue surrounding the tumor gets lower doses than if the treatment were delivered from only one port.

What types of activities occur before the patient is actually treated?A lot of effort goes into treatment planning, simulation, and verification before the patient is irradiated. First, a treatment plan is made which consists of the type of radiation, machine, tumor dose, doses to surrounding organs, the size of the radiation field, design of shielding blocks, patient set-up, etc. A radiation therapy "simulator" is used before the treatment to locate, define, and verify the treatment field after the planning stage. It is essentially an x-ray machine, and may produce either fluoroscopic (dynamic/moving) or static images.

I would assume that the positioning of the patient is very important. Am I correct? You certainly are. Proper patient positioning is critical since the patient may be returning for a daily treatment for several weeks. Even a skin fold from lying on the treatment couch in a slightly different position could lead to skin effects. Every effort is made to ensure that the treatment can be reproduced from one time to another. Sometimes skin markings are necessary to define the radiation field on the patient"s skin, since tumors may shrink, or patients may lose weight during a course of therapy.

What does brachytherapy refer to?Brachytherapy is another type of radiation therapy where radioactive materials are directly implanted into tumors to irradiate them. It is often performed on tumors that are accessible from outside the body. For example, gynecological and prostate tumors and tumors of the head and neck are treated with brachytherapy. Often, the therapy involves surgical procedures to implant hollow needles into the tumor, and after the surgery, the radioactive material can be "loaded" into the hollow needles.

What kinds of radioactivity is used?Cs-137 and I-125 are common radioactive materials used in low dose rate brachytherapy.

What type of verification approach is required prior to the actual treatment?For brachytherapy, the hollow needles must be verified to be in the correct position in relation to the tumor and according to the treatment plan before they are "loaded" with radioactive material.

Where is medical imaging going in the future? As you might have suspected, 3D imaging is just around the bend!

How will this help?True 3D imaging will greatly benefit radiation therapy, but also will improve diagnostic imaging and nuclear medicine procedures. Computer programs can take cross-sectional images from CT, magnetic resonance imaging (MRI), SPECT, and PET, and composite them into a whole image of the patient that can then be manipulated at a computer workstation. Since these imaging techniques yield different types of information (i.e., structural vs. functional), a composite image might be very insightful and useful in understanding the particular disease process, and planning a course of action.

An example? Well, a surgeon might use a composite image from cross-sectional images of the head to study and plan a surgical approach at a computer workstation before actually performing the surgery.

It sounds like there have already been great strides in medical imaging over the years.There sure has. Considering that one of the first radiographs (1896) involved the direct exposure of human hands, rumor has it that it was the hands of Wilhelm Roentgen"s spouse that lead him to discover the potential of these mysterious "x-rays". And now here we are today, on the cutting edge of 3-D imaging. We have definitely come a long way.

Any final words for me?Yes. Medical radiation exposures are the largest single contributor to the annual average exposures people in the United States receive from man-made sources. The average medical contribution to an individual is about 65 mrem per year, which represents about 18% of the total average background dose (both from natural and man-made contributors) of about 360 mrem. However, the use of radiation in medicine is extremely important and serves a vital role throughout the world. Keep in mind that while the dose received by a patient may be higher than the average values cited above (depending on the medical procedure), the benefit outweighs any potential disadvantages from receiving a radiation dose. Our good health is dependent upon this important use of radiation and radioactivity.

Where can I learn more about medical uses of radioactivity?First of all, be sure to speak with your physician if you are scheduled for diagnostic or therapeutic procedures. There you can obtain not only a wealth of information on the procedure and its advantages and disadvantages, but that information will be focused on your explicit needs. You may also wish to review some of the documents that appear in the "Bibliography" section of the IEM "Tool Box" (red button to the left).

 

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