Abstracts

Rationale: Single photon emission computed tomography (SPECT) has been used in the evaluation of patients for epilepsy surgery. As part of a pre-surgical evaluation, an ictal SPECT scan, which requires injection of the isotope being used (usually Tc-99m) at the onset of the seizure, can be compared with an inter-ictal study completed when the patient is not having a seizure. Electronic subtraction of the studies may reveal a region of increased cerebral blood flow identifying the seizure focus. A quality study requires an immediate injection when the seizure electrographically begins. Delayed injections may falsely localize the seizure onset. An automatic injector which could be remotely activated by a technologist monitoring the electroencephalogram (EEG) would improve the quality of the ictal study by decreasing the injection time. An automated system that does not require a nurse to directly handle the radioactive isotope and inject into a seizing patient should also improve safety and decrease spillage of the isotope. To test this hypothesis we have worked with a local company (Medrad) and adapted a commercially available injector for use with ictal SPECT studies in pediatric patients. Methods: Medrad Corporation manufactures injectors primarily used during radiologic studies such as MRI and CT scans. We have adapted the Solaris injector, originally designed for MRI contrast injections, to be used for ictal SPECT studies. No modifications were made to the injector or the software, a lead shield was designed and added to the syringe containing the isotope. The Solaris injector was chosen due to a KVO mechanism which ensures a patent IV for the injection. If the IV line is not functional an alarm sounds and the nursing staff can correct the problem. The isotope is loaded into the syringe by nuclear medicine staff and delivered to the patient s room twice per day. The injection is activated remotely buy a technologist monitoring the EEG of the patient. When the seizure begins the EEG, the technologist presses a button on the control panel positioned next the EEG monitoring computer and the isotope is injected followed immediately by a saline flush. Results: Since our institution began using the automatic SPECT injector, 5 patients have had successful studies. No spillage or leakage of isotope occurred. Injection times ranged from 5-20 seconds with an average of 10 seconds. Injection times have decreased as staff has become more comfortable with the injectors. Conclusions: An automatic SPECT injector can be easily made by adapting the Medrad Solaris MRI injector without any software or hardware changes required. By adding fiber-optic cable to our patient rooms and working with our radiation safety personal to develop a custom lead shield we have been able to use the injector without difficulty. With the injector we have had no spillage of isotope and our injection times have decreased to an average of 10 seconds improving the quality of the studies. Improved quality of ictal SPECT studies allows more patients to have successful epilepsy surgery.