Wednesday, April 23, 2008

Planning Imaging Areas (Non X-Ray)

If my experiences are representative of most medical equipment planners, the design team members who are unfamiliar with all of the imaging modalities may assume that every imaging device uses X-rays. The need to provide shielding for the imaging rooms, even the ones that do not employ x-rays, only reinforces this mistaken belief.

There are in fact several imaging modalities that do NOT use X-rays. MRI uses a combination of magnetic field and radio-frequency waves to create an image; An ultrasound unit uses sound waves; and several devices under the umbrella of "Nuclear Medicine" utilize radioisotopes to create images of the internal structures of the body.

Nuclear Medicine: These machines generate images by detecting the emittance of radioisotopes that have been given to a patient. These radioisotopes can be injected directly, via an IV, or they may be inhaled or ingested. These devices include:
Gamma Camera (Single, Dual or Triple Head)
PET Scanner (Positron Emission Tomography)
SPECT (Single Positron Emission Computed Tomography)

The rest of this blog entry will focus on nuclear medicine imaging. If you are interested in learning more about MRI or Ultrasound, follow these links:
MRI (Magnetic Resonance Imaging) See blog entry for MRI
Ultrasound See blog entry for Ultrasound

Each of these modalities are what I would call "passive" or "listening" devices. They create an image by detecting the signals or activity emitted within the patients body. (MRI and Ultrasound units are covered in greater depth within their respective posts in this blog.) The Nuclear Medicine modalities mentioned above rely upon the rapid decay of radioisotopes to emit energy, which these devices capture to generate an image.

So while an x-ray device will generate x-rays to pass through the body to create the image, these "passive" devices are highly efficient listening devices that detect and capture the activities occurring inside of the body. You could spend a week lying on the table of a gamma camera and it would have no effect on you. So if you were a fan of "The Incredible Hulk" growing up (or still are), you will be relieved to know that undergoing a nuclear medicine test in a gamma camera has zero risk of turning you green or morphing your into a Mr. Universe contestant. It can however affect your mood.

Patient anxiety is common among those undergoing tests for a variety of reasons:
1. They are having a medical test in a hospital.
2. The equipment is large, imposing, and looks similar to that thing that turned Bill Bixby into The Incredible Hulk.
3. The sign on the door has a big "Radiation" symbol on it.

These rooms require radiation shielding to prevent the clinicians, technicians, and other staff from being exposed to the cumulative effects of these low-dose radiation exposures. The patient will either ingest, inhale, or be injected with a radioactive isotope. (The individual dosage level is not dangerous) The room shielding simply addresses the need to shield others from the cumulative effect of repeated exposures. For a nuclear medicine tech, they may see 5-8 patients per day, 5 days per week. So they have the potential for exposure at levels 100 times what a patient receives in their single study. Patients carry the radioisotope in their blood stream, which then exits the patients body via breath or through the skin. As it disperses, the tech and any others in the room will be exposed to trace amounts of radiation. The room shielding simply "holds" these low levels of radiation in the room until its energy is dispersed. Each of these radioisotopes lose their radioactive properties very rapidly.

Most of the radiation exposure that a technician is exposed to is in the "Hot Lab" where the actual dosage of the radioisotope to be given to the patient it prepared. This room has lead-lined cabinets for storage of the radioisotopes, and for disposal of any left-over material in the syringe.

Here are photos of the devices mentioned above:
Positron Emission Tomograpghy (PET)

SPECT Camera

Upright SPECT (Specialized for cardiac studies)

Gamma Camera (Single Head)

Gamma Camera (triple head)

A note about the number of heads on a Gamma Camera:
The number of heads on a gamma camera influences the speed of the image acquisition process. The camera head(s) rotate around the patient, capturing data to create the image. A single head camera must make a 360 degree rotation while a 2-head camera must rotate 180 degrees and a 3-head camera only 120 degrees to capture the same amount of information.

There are also hybrid units that will be discussed in later blogs:
SPECT/CT (SPECT Camera and CT Scanner)
PET/CT (Positron Emission Tomography and CT Scanner)

For each of these imaging modalities, the actual source of the radiation is the radioisotope, not the equipment itself. There are several radioisotopes that are comonly used, each having a specific property that makes it uniquely suited for various studies. The purpose of this blog is to understand the basics of room planning criteria, not the actual science behind how radioisotopes work. If you are interested in learning more about radioisotopes and their uses, visit Wikipedia.

Of great importance to the planner should be an understanding the movement of these radioisotopes through the facility. Some hospitals and clinics have an outside service deliver them on a just-in-time delivery schedule. Others have a cyclotron to manufacturer them on-site. It is important to understand the deliver method and ensure that adequate security, storage and containment is available at every step of the process. A later blog post called "Planning for cyclotrons and radioisotopes" will be dedicated to this subject.

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