A method for detecting a test gas present at a measuring location, using an infrared gas analyzer having a cuvette, an infrared light source, an infrared detector, and two gas lines. Another object of the present invention is to provide a compound which is highly specific to tau and can image tau with satisfactory sensitivity, and also has high brain transition, low or non-recognized bone-seeking properties and low or non-recognized toxicity. The handle determines a water flow rate and temperature. A blocking voltage may be provided at the input of the transistor to provide a voltage bias, blocking a range of input voltages to the transistor.