The present invention relates to a catheter head comprising: means (104, 108; 306, 304; 320; 322; 326; 338) for directing of radiation to a blood detection volume (220; 310), means (104, 108; 306, 304; 320; 322; 326; 332, 334, 330; 338) for receiving of return radiation from the blood detection volume, means (104; 306; 330) for transmitting of the return radiation to means (122) for analysis of the return radiation for determination of at least one property of the blood.