With sonomicrometry, it is necessary to attach the crystal transducers to (or implant them in) the myocardium in order to measure the axial dimensions of the heart chambers. If thoracic surgery is part of the experimental protocol (to perform coronary occlusions, implant pressure or flow transducers, etc) then the application of sonomicrometer crystals to the heart will actually take less time (and less trauma) than the insertion and adjustment of a conductance catheter.

In addition to the computation of volume by measuring chamber dimensions, sonomicrometry can give a direct measure of contractility (both regional and global) and wall thickness. Conductance catheters can not perform any of these measurements. Sonomicrometry can be used in conjunction with cardiac pacing and defibrillation with no interfering effects. In fact, the instrumentation made by Sonometrics is so well designed that defibrillation shocks can be applied directly to the heart without disconnecting the crystals or turning the instrument off. Some researchers make it a point to record the mechanical activity of the heart during defibrillation.

For chronic studies, the advantage of sonomicrometry is that the reproducibility of the measurement of chamber dimensions is guaranteed because of the fixed placement of the crystals on the heart. Sonomicrometer measurements made on chronic animals can be done while the animal is fully conscious, and occasionally measurements have been done while the animal is active (on a tread-mill, for example). Naturally, should any wires break inside the animal, then the number of measurements would be reduced, possibly preventing the accurate measurement of volume. It should also be noted that the sonomicrometer crystals themselves are MRI compatible, along with their copper wiring, making it ideal for contractility and volume studies which involve MRI imaging.

Recent advances in sonomicrometry can now enable the researcher to accurately model the geometry of any soft-tissue organ by using as few as 6 or as many as 32 sonomicrometry crystals. This enables a more comprehensive geometrical model of such structures as the RV, LV, septal wall, and valvular apparatus. Previously this was possible only with bi-plane X-ray or MRI scanners, but now such studies of cardiac wall motion can be done at a fraction of the cost, with superior temporal resolution.

The Conductance Catheter:

no major surgery needed
general anesthesia needed during placement and usage
positioning aided or verified with fluoroscopy
measurements limited to several hours per experiment
must be re-introduced for chronic studies
reproducibility of placement (acute and chronic) is a factor
measurements on conscious animals are difficult or impossible
non-sterile catheter is a major source of sepsis during long acute studies
can't measure myocardial contractility (segment lengths)
can't measure regional function or wall motion, wall thickness
used and validated almost exclusively for LV volume
possibility for interference or damage from pace-makers, defibrillators, etc
cost (including hardware & software) is at least $26,000 US Dollars (no computer).

Sonometrics Sonomicrometer:
surgery is needed to implant crystals
no time limitation for measurements (chronic or acute)
no placement variability during or between experiments
measurements can be performed during conscious activity
contractile measurements other than volume can be made
ability to perform regional contractility measurements
volumes of complex shapes (RV) can be geometrically computed
crystals are a minimal source of infection during acute studies
not affected by weak or strong electrical devices (defibrillators, etc)
multi-animal (mice/dogs/horses) multi-purpose (valves, atria, vascular)
cost (software and hardware and computer) is from $16,500 to $18,000 US dollars