Experimental validation of a new coronary guide wire labeled with rubidium81/krypton 81m for continuous assessment of myocardial blood flow

Background. The rubidium 81/krypton 81m method was suggested for assessment of myocardial blood flow (MBF) three decades ago. This study investigates the novel concept of using Rb-81-/Kr-81m-labeled coronary guide wires with wire-attached Rb-81 activity and diffusable Kr-81m gas for assessment of le sion-specific impairment of MBF by evaluation of the Rb-81/Kr-81m activity ratio. The feasibility of wire production is tested, and application of the method is investigated in the canine model. Methods and Results. Conventional coronary guide wires for angioplasty (0.0 14 in) were labeled with radioactive Rb-81/Kr-81m by ion bombardment of the wire tip. A total of 16 of the 18 wires labeled in series showed successfu l Rb-81 fixation in combination with free Kr-81m gas diffusability during q uality control measurements. The suitability of the wires to assess MBF in combination with an external gamma ray detector was investigated in open-ch ested dogs. Electromagnetic measurement of coronary blood flow (CBF) was us ed as reference, providing a signal that is directly linked to volumetric M BF. The Rb-81/(81)mKr ratio tracked changes in CBF reliably in all 6 dogs. The found linear dependence of measured Rb-81/Kr-81m count rates on measure d CBF supports the modeling assumptions made to apply the theoretic basis o f the Rb-81/Kr-81m technique to Rb-81-labeled coronary guide wires. Conclusion. Rb-81-/Kr-81m-labeled coronary guide wires provide a signal tha t indicates volumetric MBF directly. This unique capability may qualify the technique as a valuable tool for research purposes and as an attractive me thod for invasive cardiology at centers where the logistic arrangements for short-lived isotope supply are provided.