SPECT/CT is making notable inroads in imaging infection. It allows the detection of unsuspected infectious foci, especially in areas that are not well investigated by other imaging modalities. It is improving diagnostic performance and treatment management for specific infections such as in bone, the diabetic foot, post-device implantation, fever of unknown origin (FUO), orthopedics and in post transplant patients. A wide cross-section of physicians are starting to take notice—and referring more cases to gain the combined strengths of SPECT and CT to investigate infection.
SPECT/CT is an integral part of infection imaging. “Just like PET/CT, we no longer do SPECT without the CT,” says Jerry Froelich, MD, director, nuclear medicine and molecular imaging at the Imaging Center for the University of Minnesota in Minneapolis.
“I cannot imagine going back to do SPECT without the CT now that I do it every day or all the time,” says Froelich.
SPECT/CT’s imaging advantage
SPECT/CT combines the advantages of molecular imaging to detect infection and anatomical imaging to localize it, says Anne Hitzel, MD, Nuclear Medicine Department, University Hospital of Toulouse, Place du Docteur Baylac, Toulouse, France. The new generation of SPECT/CT scanners with iterative reconstruction allows us to find smaller areas of lower activity that relates to infection or disease, adds Froelich.
SPECT/CT allows the detection of unsuspected infectious foci, especially in areas that are not well investigated by planar scans—such as areas surrounding prothesis or infected areas without abscess, vascular prosthesis or left-ventricular-assist devices, Hitzel says. “We frequently use it to help the surgeons determine what is the next logical step to do with the patient, be it aspiration biopsy or even surgery,” adds Froelich. In pediatric populations, neuroblastomas can be located with mIBG (meta-iodobenzylguanidine) scans as they are not FDG positive and SPECT/CT provides information on where the neuroblastoma is located, while PET/CT cannot, he says.
|Evaluation of Diabetic Foot Infection by Dual-Isotope SPECT/CT|
Dual-isotope SPECT/CT is a more highly accurate imaging protocol for evaluating the diabetic foot than Tc-99m hydroxymethylene-diphosphonate (HDP) 3-phase bone (BS) or Indium-111 leukocyte scanning (WBCS) alone, says Sherif I. Heiba, MD, associate professor of radiology, Mount Sinai Medical Center in New York City. Diagnosis of diabetic foot infection is a difficult task and single modality imaging, whether it be a bone scan, MR or CT scan, is not very successful in accurately determining the infection and its precise location, he says.
Heiba and his colleagues investigated a method that combined BS/WBCS, and if needed, WBCS/bone marrow scanning (BMS) using SPECT/CT to accurately diagnose/localize infection in a protocol which was published online September 20, 2010, in the Journal of Foot & Ankle Surgery.
Blood flow/pool images were obtained followed by WBC reinjection and dual-isotope BS/WBCS planar and SPECT/CT were performed approximately 24 hours later. BMS/WBCS SPECT/CT (step 2 dual isotope) was obtained on the following day when images were suspicious for mid/hindfoot osteomyelitis.
The use of SPECT/CT in this protocol improves the diagnostic confidence and helps to discriminate between soft-tissue infection and osteomyelitis, while providing precise anatomic localization. When needed, step 2 dual-isotope SPECT/CT (BMS/WBCS) can yield additional information for a more definitive diagnosis.
Combined radioisotope SPECT/CT imaging technique also can beneficially impact diabetic patient management. Heiba’s group has seen encouraging results in an unpublished study involving 200 patients where the combined radioisotope SPECT/CT imaging helps not only in diagnosis, but also the precise management of diabetic foot infection.
Moreover, conventional planar and SPECT images are often unable to precisely locate the site of infection. Hybrid SPECT/CT system delivers the high sensitivity of scinitigraphic technology with the high specificity of CT and overcomes the partial limitations of each technology alone. SPECT/CT has been widely used to detect and localize