Radiation from Alternative Imaging

Ionizing radiation is used in several forms of diagnostic testing, such as X-ray imaging, computed tomography (CT or CAT scans), PET, radionuclide (nuclear medicine/SPECT) imaging, and angiography.  There is no radiation exposure from ultrasound (including CEUS) and magnetic resonance imaging (MRI).

All forms of diagnostic imaging may be useful tools for pinpointing disease and providing optimum medical care when medically indicated.  In many cases, the medical benefits of diagnostic tests may outweigh their inherent risks.  Nevertheless, radiation exposure from diagnostic imaging may increase cancer risk even at low levels, and may be cumulative over an individual’s lifetime.  According to the Joint Commission, which accredits health care programs in the US, exposure to ionizing radiation has nearly doubled over the past two decades, and physicians may order tests involving exposure to radiation “with no knowledge of when the patient was last irradiated or how much radiation the patient received.”

Diagnostic radiation is an effective tool that can save lives.  The higher the dose of radiation delivered at any one time, however, the greater risk for long-term damage. … The risks associated with the use of ionizing radiation in diagnostic imaging include cancer, burns and  other injuries.

Many experts now believe that ultrasound imaging (including CEUS) and MRI should be preferred where they would provide similar diagnostic information to radiation-based diagnostic exams.   According to the Joint Commission:

In order to reduce the exposure of the patient to ionizing radiation, use other imaging techniques, such as ultrasound or MRI, whenever these tests will produce the required diagnostic information at a similar quality level.

The following information describes concerns relating to radiation-based imaging.  Additional information on imaging tools follows.

Science Advisory - American Heart Association Committee on Cardiac Imaging 
of the Council on Clinical Cardiology and 
Committee on Cardiovascular Imaging and Intervention 
of the Council on Cardiovascular Radiology and Intervention

“Medical imaging is the largest controllable source of radiation exposure to the US population, and its most important determinant is the ordering healthcare provider.”

“Considerations should include options for answering the clinical question at hand by means that do not use ionizing radiation or choosing the type of study that exposes the patient to the lowest amount of radiation.”

“Therefore: Physician education should emphasize that cardiac imaging studies that expose patients to ionizing radiation should be ordered only after thoughtful consideration of the potential benefit to the patient and in keeping with established appropriateness criteria.”

Health care professionals are obligated to provide prudent advice that includes appropriate decisions regarding the implementation of high-yield, diagnostic imaging testing. Importantly, the associated, inherent risks must be considered when scheduling these imaging studies including the indiscriminate use of ionizing radiation.

The intrinsic value of performing a high quality TTE with contrast if clinically indicated must be viewed in the context of performing alternative or consecutive and comparable imaging studies.

If the TTE study is deemed inadequate for technical reasons, the patient is often referred for an additional test and includes additional risks which are as follows: (1) TEE has an associated risk of death of 1:10,000; (2) nuclear imaging test including Sestamibi = 9mSv or Thallium = 41 mSv imaging test; (3) CT-angiogram (mSv = 12-18), and (4) a coronary angiogram (2-16 mSv).

Thomas C. Gerber, J. Jeffrey Carr, Andrew E. Arai, Robert L. Dixon, Victor A. et al., Circulation Online Feb 2, 2009: DOI10.1161/CIRCULATIONAHA.108.1916502009

• X-rays are invisible beams of ionizing radiation that create 2-dimensional images of various parts of the body, such as bones, lungs, and organ systems.  X-rays are not painful, and lead shields may decrease radiation exposure to areas that are not imaged.
   
• CT scans use X-rays rotating around the body to create image “slices” that are transformed into 3-dimensional images.  CT provides superior data when compared to a single X-ray, but does so using more radiation.  Patients undergoing a CT scan are required to lie still on a table while the table moves through the CT scanner.  CT scans are painless but sedation may be required.  CT contrast agents are iodinated solutions that are administered intravenously to enhance visualization of organs and blood vessels.
   
• PET (positron emission tomorgraphy) imaging uses injectable radionuclide (radioactive) agents that emit gamma ray signals measured by PET scanners.  PET is often used to detect and evaluate cancerous tumors, neurological conditions and cardiovascular disease.
   
• Nuclear (SPECT) studies use small amounts of radioactive drugs that are administered intravenously and emit  gamma rays detected by a camera, which then converts the rays to electronic signals to create an image. The amount of radiation exposure depends on the type of study being performed.  SPECT studies are not painful, but require patients to lie still while images are being obtained.  Sedation may be required for some patients.
   
• Angiography is an invasive procedure that produces X-ray images of the inside of blood vessels to evaluate blockages or other damage.  During an angiogram, a radio-opaque dye (which absorbs the x-rays) is injected into arteries using flexible catheter tubes and guide wires.   
   
• MRI machines use powerful magnetic fields and radio-frequency transmitters to produce 3-dimensional images throughout the body, including the brain, muscles, heart and cancerous tumors.  MRI procedures do not expose patients to ionizing radiation.  While MRI scans are painless, some patients complain of claustrophobia and noise, and MRI contrast agents (gadolinium) used to enhance images may have associated risks.  In addition, pacemakers, implantable cardioverter-defibrillators, insulin pumps, cochlear implants, and certain other medical or biostimulation implants are generally considered contraindications for MRI imaging.  

 “Sentinel Event Alert,” August 24, 2011.  The Joint Commission (TJC), formerly the Joint Commission on Accreditation of Healthcare Organizations (JCAHO), accredits more than 19,000 health care organizations and programs in the United States.  See: HYPERLINK "http://www.jointcommission.org/sea_issue_47/"http://www.jointcommission.org/sea_issue_47/