HYBRID SPECT/CT USEFULL

Hybrid SPECT/CT

Hybrid SPECT/CT

Introduction

To assess the usefulness of a hybrid imaging system (single-photon emission computed tomography/computed tomography, SPECT/CT) for functional anatomical mapping (FAM) using various radiotracers and the additional value of fused SPECT/CT images compared with SPECT alone.

Discussion

Eighty-one consecutive patients studied for various clinical situations were evaluated: 10 with 111In-pentetreotide, four with 123I-meta-iodobenzylguanidine (I-MIBG), five with 99mTc-labelled red blood cells, two with 99mTc-antigranulocyte antibodies, four with 99mTc-nanocolloids, 10 with 67Ga, seven with 99mTc-methylene diphosphonate (99mTc-MDP), nine with 99mTc-sestamibi, 21 with 99mTc-tetrofosmin, two with 201Tl, three with 99mTc-ethylcysteinate dimer (ECD), one with 99mTc-hexamethylpropyleneamine oxime (99mTc-HMPAO) and three with 123I-N-w-fluoropropyl-2-beta-carbomethoxy-3-beta-(4-iodophenyl) nortropanel (FPCIT). The acquisition of both anatomical (CT) and functional (SPECT) data was performed during a single session. SPECT data were first interpreted alone and then re-evaluated with the addition of FAM (Schillaci 2004 pp.25-30).

Transmission anatomical maps allowed for the precise anatomical localization of SPECT images in 79 of the 81 cases. SPECT/CT had a significant impact on the results in 33 (40.7%) of the 81 patients: FAM provided the correct localization of SPECT findings in 23 cases, allowed the definition of the functional significance of CT lesions in two and enabled the exclusion of disease in sites of physiological tracer uptake in eight. (Studholme 2006 p.12)

SPECT/CT with this hybrid system is a feasible technique yielding co-registered dual-modality images. FAM allows a more precise interpretation of scintigraphic studies in several cases and fused images can improve the diagnostic accuracy of SPECT in various clinical situations.

Radiotracers used for brain single photon emitted computed tomography (SPECT) pass the blood-brain barrier and bind intracellularly on their first pass through the circulation, providing a "snapshot" of cerebral perfusion at a particular timepoint. When injected during a focal epileptic seizure, an area of significantly increased radiotracer uptake typically corresponds to the region of maximal abnormal activity, often the seizure focus. This ictal pattern of cerebral blood flow can be compared to an interictal/baseline pattern obtained when the patient is not having a seizure, to provide unique information about the nature and location of a patient's epileptic focus, which can be used to guide therapy(Saposnik 2005 p.30).

A previously-healthy young woman developed behavioral changes followed by seizures and refractory status epilepticus. She was diagnosed with encephalitis and treated with antiviral and multiple antiepileptic agents. She required nasotracheal intubation and mechanical ventilation for respiratory support. She experienced persistent episodes of facial twitching resembling seizures. These episodes were not however associated with an ictal EEG pattern on continuous video/EEG monitoring. To clarify the nature of these episodes, 99mTc-HMPAO was injected during a period of frequent twitching. Brain SPECT showed a prominent focus of increased uptake interpreted by the radiologists and clinical team as arising in the upper brainstem repeat study (using 99mTc-ECD) two weeks later, when twitching was no longer occurring, showed resolution of this increased uptake. These findings were considered to support a diagnosis of seizures/repetitive myoclonus originating from the brainstem. Although brainstem seizures in humans remain a controversial entity, there are reports in the ...