How It Works - CT Scanners

The next installment of my ongoing series called “How It Works” has to do with Computed Tomography, frequently referred to as CT imaging. Like conventional x-ray imaging, CT imaging uses x-rays to make images of the human body. However, CT imaging uses computers and a moving x-ray tube to obtain 3-dimenional, high-resolution, high-detail images of anatomical structures.

History

The CT scanner was developed and demonstrated by Godfrey Hounsfield, a British physicist working for EMI, Ltd. Originally developing the idea in 1967, the first working prototype was unveiled in 1972. Atkinson Morley's Hospital in Wimbledon, England was the first institution to use a CT scanner to scan a patient. The first CT scanner sold in the US was to Massachusetts General Hospital and George Washington University for $390,000.

CT Technology

The first CT scanners were very limited in their applications compared to those used today. Primarily used to scan the brain, the earliest scanners could only form axial (horizontal) images of the human body; that is, a slice from side-to-side, similar to a slice of bread (see picture below). Thus the name Computed Axial Tomography, or CAT scan, was used to describe a scan from this machine. However, this name is no longer accurate, as today’s versions make it possible to see almost every structure in the body in a coronal, sagittal or axial plane, often in a clear 3-D view. Therefore, the term Computed Tomography, or CT imaging, has been adopted.

Axial, Coronal and Sagittal planes of the body

CT - Axial View

CT - Coronal View

CT - Sagittal View

The CT scanner is a complex machine that relies on electronic/digital as well as mechanical equipment to make an image. The patient is placed on a movable platform that is raised and “inserted” into a short tube that looks something like a large donut. Within this tube is a revolving x-ray tube and image receptor (IR), or sensor. As the scan begins the x-ray tube begins to spiral around the patient emitting a thin curtain of x-rays as it moves. Directly across from the tube (on the other side of the patient) is a sensor that picks up the x-rays after they have passed through the patient, collects the data and transfers it to a computer. The computer then uses complex algorithms to form a visual image from the data and projects it onto a computer screen.

View of inner workings of a CT scanner; tube revolves around patient.

With conventional x-ray, different anatomical structures are superimposed on top of each other and often cannot be clearly seen on the x-ray image. However, with CT, because the x-ray tube and IR rotate around the patient’s body scanning it from all angles, it is able to combine all the data it receives from the scan into a comprehensible image for the doctor to evaluate. This is one of the reasons CT imaging is often considered “superior” to conventional x-ray imaging. However, there are some considerations to keep in mind.

A patient generally receives a higher dose of radiation when receiving a CT scan than a conventional x-ray. This is because the patient is being exposed to radiation during the entire time the CT is making its scan, which can last up to several minutes. However, with conventional x-ray the patient is exposed to just a brief emission of x-rays, often measured in just fractions of a second. This is why conventional x-ray is still used for simple imaging procedures such as a broken arm or finger or chest x-rays. Also, CT machines are not portable, so the patient must come to the machine, where as mobile x-ray units allow the machine to come to the patient’s room to make the image.

Conclusion

Overall, the computed tomography has proved to be an invaluable asset to medical imaging and has saved countless lives, whether from helping a doctor diagnose a brain tumor or allowing a surgeon to identify a brain bleed in a car accident victim. As technology advances it is likely that CT scanners will become faster, more precise and more compact, and will continue to allow medical professionals to save lives.

Patient Obesity Is Obscuring Medical Scans

An article from Forbes online magazine. here's the direct link to the article.

07.25.06, 12:00 AM ET

TUESDAY, July 25 (HealthDay News) -- In yet another example of how obesity is playing havoc with Americans' health, a new study finds that the number of inconclusive diagnostic imaging exams has doubled in the last 15 years -- a phenomenon experts attribute to all those extra pounds.

"Obesity is affecting the ability to image these people. We're having trouble finding out what's wrong," explained Dr. Raul N. Uppot, lead author of the study, and an assistant radiologist at Massachusetts General Hospital and an instructor in radiology at Harvard Medical School, both in Boston.

"When they come to the hospital, people are so concerned about the disease they have that they don't realize that being obese could hinder the ability to deliver health care," he said.

In fact, it could hinder it considerably, given medicine's ever-growing reliance on imaging technology such as X-rays and ultrasound.

"In the past 10 years or so, medicine has become so dependent on imaging," Uppot said. "Instead of doing very meticulous clinical examinations, a lot of doctors now rely on CT scans, ultrasounds, etcetera, to tell them what's happening inside the body. What happens when you're too big to fit on a table? Or you can fit on a table but the image is poor quality?"

The new study is published in the August issue of the journal Radiology.

The findings did not come as a surprise to outside experts. "The study shows more systemically what all of us felt was true anyway," said Dr. Levon Nazarian, professor of radiology and vice chairman for education at Thomas Jefferson University Hospital, in Philadelphia.

"Patients may not realize that there are two aspects to being overweight, one of which is the increased risk of a number of different diseases," Nazarian added. "They may not realize that once they actually get sick, their size is going to limit the ability to even tell them what's wrong."

According to official estimates, about two-thirds of adult Americans are overweight or obese, and the effect on individual health and the health-care system is considerable. Obese people are more likely to develop illnesses such as cancer, diabetes and heart disease. Hospitals have also had to "super-size" their wheelchairs and beds to accommodate the new generation of sick and overweight Americans.

To assess the effect of obesity on the quality of imaging exams, the researchers reviewed all radiology records from tests performed at Massachusetts General Hospital between 1989 and 2003. Specifically, they were looking at incomplete exams due to patient size.

"We looked at people who were able to fit on the imaging equipment and get the scan," Uppot said. "When radiologists read the film, they had trouble interpreting the film because the quality of the image was not very good because of [the patient's] size."

In 1989, 0.10 percent of inconclusive exams were due to patient size. By 2003, that number had almost doubled to 0.19 percent.

"What was most alarming was the increase," Uppot said. "The number itself was small."

Difficulties varied according to the type of imaging. By 2003, abdominal ultrasounds exhibited the most difficulty in giving a proper diagnosis (1.9 percent), followed by chest X-rays (0.18 percent), abdominal computed tomography (CT), abdominal X-rays, chest CT and magnetic resonance imaging (MRI).

Ultrasound sends high-frequency sound waves through the patient, where they bounce off internal organs and come back, like a submarine's sonar. But the thicker the fat, the less able the waves are to penetrate. A similar phenomenon is at work with X-rays, the study authors said.

CT scans and MRI have a different problem -- weight limitations of the table that holds the patient and the size of the opening on the imager.

"Many manufacturers have started to address the issue by increasing table weights," Uppot said.

The weight limit for CT scans has been increased from 450 pounds to 550 pounds. For MRI, the weight limit went from 350 to 550 pounds, he said.

But that doesn't solve the bigger problem. "We are now able to fit people on the machine. Then the issue is, what do you do?" Uppot said.

The imaging power can be increased on standard X-ray and CT machines, but this leads to an increase in radiation dose as well, he said.

"What we're realizing is that not only do obese people have increased health problems but our ability to deliver quality diagnostic imaging to them is limited," Uppot said. "A large patient can no longer walk into a hospital and say, 'I want the best quality care, let me get imaged and operated on.' If you're that big, there will be issues."

The problems don't stop with diagnosis. "It puts stress on personnel," said Dr. Jorge Guerra, professor of radiology at the University of Miami Miller School of Medicine. "X-ray personnel will be more prone to injury. We receive patients who are 400, 500, 600 pounds. It paralyzes our ability to provide care for other patients. We need special equipment, special beds, the imaging is lower quality so it takes longer to complete." Size also affects interventional radiology, or procedures meant to treat a patient, which is Guerra's specialty.

And as the University of Miami builds a new hospital, it is having to take into account that more than one-third of the patient population will be more than 350 pounds, he said.

How It Works - X-ray Machines

Almost everyone has heard of x-rays before. Some people have even had images made using x-rays, but most people don’t understand how x-rays work and how they are produced.

This is the first of a series of posts called “How It Works” in which I will attempt to explain how various imaging modalities work. This first post explains in layperson’s terms what exactly an x-ray is, how it is produced, and how it is used for medical imaging. I will do my best to keep it from being too dry, but lets face it, it may get a little technical at times, I mean we are dealing with physics here. So….

X-rays were first discovered by a German physicist named Wilhelm Roentgen (pronounced “RANK-in”) in 1895. While experimenting with electron beams, he found that when exposed to this electron beam a piece of phosphorescent paper would glow. This in itself was not ground breaking. However after experimenting by placing different types of material between the beam source and the paper, to determine the beams penetration ability, he found that the beam passed easily through most material. Finally, he passed his hand through the beam and discovered that it produced a “shadow” on the phosphorescent paper in which he could make out the bones of his hand. Within weeks other scientists were experimenting with the various possible uses for x-rays, most within the medical field. And the rest is history.

X-rays

X-rays themselves are actually a form of radiation closely related to visible light, infrared and ultraviolet radiation. X-ray radiation is very similar to visible light but with a much higher energy level. This elevated energy level allows x-rays to easily penetrate less dense materials (such as clothing, plastic or skin) and pass through to the other side. However, materials of a more dense nature absorb some or all of the radiation hitting them. Therefore when objects composed of materials of varying densities (e.g. human bodies) are exposed to x-rays, the shadows produced mimic these density variations.

X-ray Images

Although today’s digital imaging technology is quite advanced, the first x-ray images were produced with relatively simple equipment. The source of x-rays is the x-ray tube, which produces x-rays using a vacuum chamber and high amounts of electricity. The x-ray tube will be discussed later. Also needed are phosphorescent or fluorescent paper, unexposed film, a light-tight cassette to house the paper and film and of course a patient. The film and paper are placed in the cassette and then placed within the x-ray beams trajectory on the opposite side of the patient as the emitting tube.

When the x-rays are produced they pass through the patient and hit the phosphorescent paper causing it to fluoresce or glow, which in turn exposes the film below it. The film is then removed from the cassette in a dark room and developed just like film from a 35mm camera would be. The areas of the paper, which receive more x-ray radiation glow more brightly causing more of an exposure on the film directly under it. So variations in densities of materials through which the x-rays are passed show up as variations of light and dark gray on the film.

X-ray Tube

The process for producing the x-ray radiation, however, is much more complex. X-rays are produced in an x-ray tube, which is composed of an electrode pair (a cathode (positive) and an anode (negative)) and a vacuum tube. A large amount of electrical current is passed through the cathode heating it up to a very high temperature, which causes it to release electrons into the vacuum chamber. The anode, which is a negatively charged metal plate located several inches away from the cathode, attracts the electrons and causes them to hit the anode plate at a very high rate of speed. The collision causes the electrons to release photons, the basic particle of which most radiation is composed. The high energy photons manifest themselves in the form of x-ray radiation, which is then directed down and out of the machine.

Since its discovery, x-ray radiation has been used for many different purposes, many of which are in the medical field. Diagnostic and interventional radiography, fluoroscopy and Computed Tomography (CT) are just a few modalities that use x-rays. After more than a century of research, we are now able to harness and use x-rays to diagnose many types of illness in a manner that is safe for not only the patient but also the healthcare workers employing them.

Because of my desire to NOT bore my readers to death, I have left out the nitty-gritty physics of the machine, but the above explanation should give you a general idea of how x-rays are produced and used in medical imaging. If you have any questions about this post please feel free to leave them in my comments section, and I will respond to them to the best of my ability.

How MRI Machines Work

Here's a link to an explanation on how MRI machines work, that was passed on to me by fellow X-ray Tech student Mike. Heres a link to his blog. On the MRI page click the link at the bottom that says "Go To MRI Introduction". A new window will pop up that will give you a nice little animated demo of how Magnetic Resonance Imaging works. It gets a bit technical, so be sure to put on your thinking cap first. :-P

Also, a webpage entitled, The Basics of MRI, gives a good explanation of how the technology works as well as a little background on its development. Its mostly text.

If any one else has links to radiography related sites, please don't hesitate to mention them here. Just leave them in my comments section, I check it frequently. Thanks.

T is for Technologist

TECHNOLOGIST v. TECHNICIAN. What's the difference, you ask? In radiography circles, the difference is huge!

For many years the term X-ray Technician, or radiology technician, was used to describe the healthcare worker who was in charge of creating x-ray images of sick or hurt patients. They had little, or no, formal education, were trained on the job and were not licensed or credentialed in any way.

That has all changed. Although still misused by the lay-person, and even some people within the healthcare field, x-ray technician is no longer an accurate title for the personnel who are involved in creating medical images.

Currently, we are in a period of transition. Although the term technician is no longer used, a solid, universally-accepted title has not yet been estabished. I guess the most commonly used title in the US, and one endorsed by our major certifying organization the ARRT, is Radiologic Technologist. The title is right there in their name (American Registry of Radiologic Technologists). After taking a nationally recognized exam administered by the ARRT, a student becomes certified as a Technologist, is registered with the ARRT, and can later take another exam to be licensed in the state in which the tech works.

However, that's not to say other names are not used in everyday conversation. X-ray Technologist is still common, as is Rad Tech and RT. Radiographer is commonly used in Great Britain and is likely derived from our common use of the word photographer (a person who make pictures with light rather than x-ray radition). Imaging Tech is more general, including techs who work in CT, MR and ultrasound, and more accurate in that these modalities all produce images of the human body, but they do not all use x-ray radiation to do it.

Presently, radiology departments are employing a level of imaging worker that is similar to the antiquated X-ray Technician, called a Practical Tech or X-ray Tech of limited scope. This position requires less education than an Radiologic Technologist and is much more limited in their scope of practice, as the name would imply. They are licensed to image parts of the distal extremeties, the shoulder girdle, the chest, skull and spine. They are NOT able to image the GI tract, the pelvis, the reproductive tract, the urinary tract or work in Specials. Also, they can NOT use fluoroscopy, CT, MR or bone densitometry. And because of their limited capacity this position is being phased out in many of the hospitals around the United States.

Still a little confused? One way to look at it is comparing a Radiologic Technologist to a Technician is like comparing an RN with an LPN or a physician with a physician's assistant. While all positions in healthcare are important and worthly of respect (right down to the guy who mops the floors), there are often vast differences in education, experience and scope of practice between the different branches in the hierarchy.

Another way to look at it (and I can't take credit for this, since it's something my instructor told us) is that:

A Technician is TRAINED
A Technologist is EDUCATED

or

A Technician can push the button
and a Technologist knows why.

I hope this information has helped clear up the difference between a technician and a technologist. Keep in mind terminology and practices differ from region to region and between institutions, so this information is not exactly accurate. But in a general way it should help you to realize that a difference exists between the two terms and it is important to use the correct one when referring to a Radiologic Technologist.

Prospective X-ray Tech Students

This blog is meant to be a resource for people who are considering entering into a career as an x-ray technologist. On the right of the screen you will see several lists of links to websites with information on radiography. Please make use of them, I found them very helpful while researching for my new career.

Those working in radiography go by many names: x-ray tech (short for TECHNOLOGIST not technician!), radiographer, Radiologic Technologist, imaging technologist, Rad Tech and RT. Also, if one chooses to specialize in one of the many modalities within medical imaging, there are still more titles: MR tech, CT tech, sonographer, ultrasound tech, Nuc Med tech, mammographer, cath. lab tech, etc.

First lets talk about the difference between radioLOGY and radioGRAPHY. These two terms are often misused by laypeople, and can cause a lot of confusion if not properly used.

Radiology literally means the study of radation (radio=radiation, ology= study of), but is usually used in reference to the interpretation of diagnostic images, which are obtained in several ways. This interpretation is done by a radioLOGIST, who has gone through many years of medical school and residency and are considered MDs, and rightly so. They receive medical images (aka x-rays) and are able to identify anomalies or pathologies in the patients anatomy. They are paid quite well, but have worked long and hard to get to their position within the medical hierarchy.

RadioGRAPHY, on the other hand is quite different. It is the art/science of producing images of the human body using x-ray radiation. Literally translated it means radiation picture-making (radio=radiation, graphy=representation of an object). It has a long history in medical science, most of which I will not go into here, and has been used in many ways to diagnose and even treat human diseases. An x-ray technologist, or radiographer, is the person who works with the patient to produce a quality x-ray image of a specified body part or system. X-ray techs must be educated in a number of different subjects (human anatomy, radiation safety, patient positioning, patient care, basic life saving, radiation physics, medical terminology, etc.) in order to properly and safely do their job.

Education and training to become an x-ray tech involves at least 2 years of formal education, which includes classroom instruction and clinical experience. Once the education has been completed, the student is eligible to take the national board exam given by the American Registry of Radiologic Technologists (ARRT) to become licenced to practice radiography. Some states require an additional exam to be certified in their state, however usually the national exam is sufficient to find work.

Time management, computer skills and patient interaction are all big parts of being an x-ray technologist. When a patient enters the Radiology Department, the x-ray tech is responsible getting their procedure done in a safe and timely manner. Although most imaging procedures are relatively non-invasive, some require patients to undergo intravenous injection, sedation, colonic retrograde filling (contrast enemas) and urethral catheterization. These procedures are often very uncomfortable and embarassing for the patient, so it is important that the x-ray tech have the ability to empathize with the patients and make their experience as pain and discomfort free as possible.

Technology has become a very important part of medical imaging. General radiography is no longer the only imaging modality employed in the medical field. CT (computed tomography), MR (magnetic resonance), ultrasound, PET (positron emission tomography), DEXA (dual-energy x-ray absorptiometry), nuclear medicine, mammography and vascular radiography are all commonly used to diagnose disease today. Radiography is one of the fastest growing and advancing areas of medicine due, in large part, to advances made in imaging technology. Inventions like high speed computers, expanded memory servers, the internet, high resolution monitors, and digital photography have all had an effect on how medical imaging is used. So it is very important the x-ray technologist stays familiar with new advancements and makes an effort to continually learn throughout his or her career.

Hopefully this first post has given you at least a basic understanding of radiography and what a career as an x-ray technologist is all about. I will continue to update this blog periodically with new posts on various subjects regarding radiography. **See below this post for additional postings.** You may also consider visiting my other blog, Desert Imaging: An X-ray Tech Student in Phoenix, which chronicals my progress through a radiography program at a school in Phoenix, AZ.

Also, please feel free to email me with any questions or concerns you have regarding radiography or this site. My email address is arizonadb2005 @ yahoo dot com. I have written it a little strangely to avoid getting spam.