SPECT/CT Scanners Improve Imaging, Offer Options
Single photon emission computed tomography (SPECT) nuclear imaging and computed tomography (CT) scanners have been used separately for cardiology, oncology and neurologic imaging for more than 20 years. In recent years there has been a trend toward combined SPECT/CT systems to enable faster and more accurate functional and anatomic assessment using a single imaging system in one imaging session.
Integrated SPECT/CT systems can perform both functions on one gantry and allow anatomic localization of nuclear imaging findings. These systems also allow accurate and rapid attenuation correction of SPECT studies. These attributes have proved useful in many cardiac, general nuclear medicine, oncologic and neurologic applications when the solitary SPECT results were inconclusive.
The CT Component
Hybrid imaging systems now use 16- or 64-slice CT systems. These acquire data faster than the previous generation single-slice hybrids.
CT provides three important features: attenuation correction, anatomical guideposts to put the low-resolution SPECT image into context with surrounding tissue, and calcium scoring capability.
CT imaging corrects photon attenuation and improves diagnostic accuracy. SPECT images are inherently susceptible to attenuation artifacts, which are caused by the gradual loss in signal intensity of photons as they pass through soft tissue. Differing scatter and absorption of photons between emission and detection can distort the final picture. Attenuation artifacts may be confused with perfusion defects and obscure genuine coronary artery disease.
SPECT/CT offers anatomic sign posts so clinicians can accurately locate and identify the affected tissue in a nuclear image. However, while some nuclear cardiologists say the anatomical guideposts offered by the CT image are helpful, unlike oncology, in cardiac perfusion imaging it is less important. They say cardiologists already know what part of the heart’s anatomy they are looking at. Also, with cardiac perfusion imaging, it is usually pretty easy to determine which vessels are likely occluded in a patient suffering from heart disease.
Precise anatomical mapping is more important for oncology. It helps pinpoint the exact location of a tumor and its relation to surrounding tissue.
Cost Effectiveness of Hybrids
In these challenging economic times, hospitals are seeking to maximize their investment in technology. To justify purchasing any imaging system, a facility has to have sufficient patient volume to pay for the investment. One way to assure patient throughput covers the cost of technology is to optimize the use of a modality by applying it to several clinical indications, such as SPECT for oncology and cardiology, and CT alone for general radiology once the nuclear exams are concluded for the day.
This strategy is driving the trend toward multipurpose hybrid imaging systems with full capacity in both modalities. Some hospitals are finding it more economical to purchase one hybrid system rather than two separate imaging systems. Busy imaging departments find hybrid systems rarely sit idle because they can be used for multiple applications.
Image Quality Without Compromises
No clinician wants to compromise image quality for efficiency, but it is important to shorten exam times. By using two high-end imagers for a single scan, not only are scan times shorter, but also image quality is superior.
GE Healthcare’s Discovery NM/CT 670 system is designed to shorten acquisition times and improve dose management, compared to using separate, conventional SPECT and CT exams.
“We understand that a clinician does not want to compromise,” said Nathan Hermony, general manager of GE Healthcare’s nuclear medicine business. “With the Discovery NM/CT 670, we are providing clinicians the ability to discover and explore new capabilities, while continuing to perform advanced hybrid and standalone CT procedures.”
This full-featured SPECT/CT system is engineered to reduce scan time. Bone imaging protocols, including planar whole body, 3-D SPECT and CT attenuation correction/localization, are among the most frequently performed nuclear medicine procedures. With conventional nuclear hybrid imaging, a traditional bone imaging protocol can take up to 55 minutes. With the Discovery NM/CT 670, the imaging time is reduced to as little as 16 minutes. Shorter scan times result in less patient movement, which minimizes artifacts in the images.