The Millar Catheter equipment consists of a miniature transducer-tipped catheter in which the sensor is side-mounted at the tip. The transducer is inserted into the tumor tissue through a hypodermic needle. The sensor is positioned in the center of the tumor. A pressure transducer converts the IFP to a voltage that is logged by a computer.
The wick-in-needle equipment consists of a hypodermic needle probe connected to a pressure transducer via a tubing filled with saline. The needle is inserted into the tumor tissue manually. The hole of the needle is filled with nylon threads to improve the fluid communication between the tumor tissue and the probe. The pressure transducer converts the IFP to a voltage that is logged by a computer.
The micropipette system consists of a micropipette, a micromanipulator, a servo-null device, a pressure transducer, an amplifier, and a computer. A pipette puller device is used to prepare micropipettes from thick-walled capillary tubings. The micropipettes have a diameter of 2-4 µm, and are filled with 1M NaCl solution. They are positioned in the tumor tissue with the micromanipulator, under guidance of a stereomicroscope. The servo-null device produces a counter pressure to the IFP at the tip of the micropipette. The pressure generated in the servo-null device equals the IFP, and is transferred to the signal amplifier. The micropipette technique is substantially more sensitive than the wick-in-needle technique.