Experimental Setup

The twilite measures the radioactivity in a catheter which runs between two LYSO crystals. In animals a very efficient solution is to install a shunt between the femoral artery and the femoral vein. This allows continuous measurement of the whole blood activity without any loss of blood. Such arteriovenous shunts can be placed in animals as small as a mouse, using catheters differing in size. A typical setup and schematic are shown below.

In humans, the withdrawn blood should not flow back into the body. One usually places a catheter into the radial artery, runs the catheter through the twilite measuring head and directs the blood into a waste container. A schematic is shown below.

In humans the blood flow in the catheter is always controlled by a suitable certified infusion pump. In animals it is also advisable to control the blood flow in the shunt with a peristaltic pump. However, it is also possible to let the shunt run freely driven only by the arteriovenous pressure difference.

The appropriate catheter diameter differs according to the size of the animals. Swisstrace delivers templates to guide the catheter through the measuring head for each catheter size, such that a well-defined geometry is established. The characteristics of the shunt are described in a paper published by Weber and co-workers [1], and further information on shunt and general twilite setup can be found in [2] and [3].

A typical setup for a quantitative rat PET experiment is illustrated below:

1. Shunt running from the femoral artery to the femoral vein.
2. Peristaltic pump to control blood flow in the shunt.
3. Twilite measuring head made of tungsten.
4. Light guides carrying the photons from the crystals to the PMT‘s. These guides have a standard length of 2m; they can be as long as 20m in MR compatible systems.
5. Data acquisition box with coincidence electronics.
6. Touch screen for device setup and start/stop.
7. Not seen here: TCP/IP connection on rear panel of data acquisition box, computer with PMOD PSAMPLE data acquisition and data analysis software.

Schematic:

1. Catheter running femoral artery to the femoral vein.
2. Peristaltic pump.
3. Twilite measuring head made of tungsten.
4. LYSO crystal 1.
5. LYSO crystal2.
6. Light guides carrying the photons from the crystals to the PMT‘s. These guides have a standard length of 2 m, they can be as long as 10 m in MR compatible systems.
7. Data acquisition box with coincidence electronics.
8. TCP/IP connection to computer with PMOD data acquisition tool PSAMPLE.
9. Computer with PMOD data acquisition and analysis.

The arteriovenous shunt can serve several additional functions, such as blood pressure monitoring, tracer injection as well as the collection of blood samples for metabolite analysis. The following procedure is recommended for collection of blood samples: a small cut is made into the catheter using a scalpel. In normal operation the catheter is bent upwards, so that the cut is closed and blood circulates. To obtain blood samples the shunt is briefly pressed downwards in order to open the cut and blood drops can be collected with minimal dead volume.

In humans there is no return of arterial blood. Schematic:

1. Catheter running from the radial artery to the waste container.
2. Twilite measuring head made of tungsten.
3. LYSO crystal1.
4. LYSO crystal2.
5. Light guides carrying the photons from the crystals to the PMT‘s. These guides have a standard length of 2m, they can be as long as 20m in MR compatible systems.
6. Data acquisition box with coincidence electronics.
7. TCP/IP connection to computer with PMOD data acquisition tool PSAMPLE.
8. Computer with PMOD data acquisition and analysis.
9. Peristaltic pump.
10. Waste container.