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Pharmacology / Nuclear Medicine

SPECT/CT adds anatomic detail to improve diagnostic utility of SPECT images

08/01/2008

Pairing nuclear medicine with high-quality computed tomography (CT) imaging adds anatomic landmarks to the isotope uptake information nuclear medicine studies provide, improving diagnostic capabilities by helping physicians localize disease. PET/CT was the first procedure widely used to exploit this ability. More recently, SPECT/CT has developed to offer the same advantages. SPECT/CT equipment is now available using high-speed, multi-slice CT technology to provide diagnostic-quality anatomical imaging combined with functional SPECT information.

How it works

SPECT (Single Photon Emission Computed Tomography) relies on radioisotopes that accumulate very selectively in specific target tissues — and only to a smaller degree in other tissue. When an isotope accumulates in the target tissue, it appears as a bright-colored spot on the SPECT image. The problem is that the image lacks information on exactly where that tumor is located. When physicians acquire SPECT and CT images at the same time, this functional information is projected onto the anatomical background of the body, enabling nuclear medicine specialists to provide more precise and informed diagnoses to referring physicians.

Current clinical applications

SPECT/CT is currently used to aid in the diagnosis of coronary artery disease, inflammatory diseases, tumors, bone diseases and others. Stress/rest myocardial perfusion imaging is used to test for coronary artery disease. An injected radioisotope highlights areas of atherosclerotic narrowing of the arteries and areas of inadequate muscle perfusion during stress. SPECT/CT offers physicians unusually exact location and severity information. The SPECT/CT studies can also be completed in a shorter time than traditional SPECT imaging studies, offering greater comfort and convenience to patients.

Another current diagnostic use for SPECT/CT is in tumor imaging. SPECT
isotopes have been developed that selectively bind to certain features of specific tumors. SPECT provides highly accurate images of these tumor areas, but does not show their location in the body. SPECT/CT adds anatomical detail to help localize the tumor. SPECT isotopes have been developed to image many tumor types for which PET isotopes do not exist.  Bone imaging is another SPECT/CT application. SPECT isotope uptake in bone can indicate tumor, infection or trauma, but it can be difficult to distinguish among them. CT provides additional information to help determine what is causing the bright spot on the SPECT image.

SPECT/CT and attenuation artifacts

A traditional shortcoming of SPECT technology is gamma ray attenuation in the surrounding tissue. When the isotope accumulates in its target, it radiates gamma energy. As the gamma radiation travels through surrounding tissue, some is absorbed, resulting in reduced signal detection from sources deeper within the body than those closer to the periphery. This distortion of the SPECT image can reduce its diagnostic value.

Attenuation artifacts in coronary artery SPECT imaging reduce diagnostic accuracy in women because of their intervening breast tissue. The problem of attenuation artifacts is particularly acute in obese patients because the gamma radiation must traverse additional fatty tissue.  SPECT/CT can measure the density of the intervening tissue and correct for this signal attenuation, improving the diagnostic accuracy of the procedure.

Research

UCLA will be conducting clinical research using SPECT/CT, establishing the best protocols for its use and determining how the technology improves clinical diagnosis.

Adding anatomic landmarks to functional SPECT images

SPECT/CT, like PET/CT before it, came about to address a difficulty in interpreting the results of nuclear medicine studies. According to Johannes Czernin, M.D., UCLA professor of molecular and medical
pharmacology/nuclear medicine, “Nuclear medicine traditionally provides excellent information about functional processes in the body, but does not provide adequate anatomic orientation.” Nuclear medicine technology can, for example, identify a tumor, but it cannot show precisely where that tumor is located relative to other body structures.

SPECT/CT combines the nuclear medicine image with a diagnostic-quality CT image to provide anatomic landmarks to allow precise and informed diagnosis.

Physicians

Johannes Czernin, M.D.
Professor, Molecular and Medical Pharmacology/Nuclear
Medicine Director, Ahmanson Biological Imaging Center

Martin Allen-Auerbach, M.D.
Assistant Professor, Molecular and
Medical Pharmacology/Nuclear Medicine

Heinrich Schelbert, M.D., Ph.D.
Professor, Molecular and
Medical Pharmacology/Nuclear Medicine

Christiaan Schiepers, M.D., Ph.D.
Professor, Molecular and
Medical Pharmacology/Nuclear Medicine

Daniel H. Silverman, M.D., Ph.D.
Associate Professor, Molecular and
Medical Pharmacology/Nuclear Medicine

Contact Information

Referral and appointments
(310) 794-1005
Consultation and faculty contact
(310) 825-4829
Fax (310) 206-4899
www.nuc.uclahealth.org

 

 





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