Methods and systems are provided for improving accuracy of delta pressure over valve based EGR flow measurement during low valve lift conditions by learning errors in EGR valve lift andor EGR valve flow transfer function. The medical system an implantable lead configured to deliver an electrical stimulation therapy for a patient. The scanning optical system includes a first lens group having a positive refracting power and a second lens group having the positive refracting power in this order from the scanning part. Depending on the type of material in the region of interest, the correction factor may be the material specific phase difference of the materials in the region, e. The capacitors are optionally divided into separate capacitor banks.