Page 334 - Biomedical Engineering and Design Handbook Volume 2, Applications

312 DIAGNOSTIC EQUIPMENT DESIGN

FIGURE 10.56 Cold-stage block assembly.

platinum resistance heat exchanger coolant
counterweight
thermometer
sprocket and chain

dry gas bleed
cold-stage block
16W heater
70W thermoelectric
cold-stage block coolers miniature slide
x-ray path pitch/roll plate pitch/roll plate
heat exchangers

(a) (b)
FIGURE 10.57 Thermal control stage assembly. (a) Top view; (b) rear view with counter weight removed.

Platinum resistance thermometers monitor the temperature, and a three-term tunable PID con-
troller, which is RS232-linked to a PC, stabilizes the value at the set point to an accuracy of at least
0.1°C by regulating the secondary heat transfer. The set point temperature can be programmed, so
that precise thermal cycling is available, or manually entered for step variation. The working tem-
perature range is ±50°C with a thermal response ~0.2°C/s.
The system is ideal for examining the rearrangement of microstructural composition of soft-solid
materials with variation in temperature. An example of a material that is practically impossible to
image in the natural state by conventional optical microscopy is shown in (Fig. 10.58a). The volumes
depicted are child volumes, containing a region of interest (ROI), extracted from the reconstruction
of a frozen four-phase soft-solid structure. The reconstructed volume is derived from 720 filtered and