SALSA III
System for the Automatic LAbeling of SAline.
While pursuing my PhD at MIT, I worked at the Pulmonary Imaging and Bioengineering Laboratory (PImBeL) at the Massachusetts General Hospital and Harvard Medical School. At PImBeL we imaged the lungs using high resolution computed tomography (HRCT, which gives a high resolution static image of the lungs) and positron emission tomography (PET, which provides low resolution movies of tracers moving throughout the body).
For the lungs to perform their function, the blood must bring CO2 to the lung and exit the lungs with O2. The blood flow to the lungs is called perfusion. For this exchange to happen fresh air must be continually ventilated in and out of the lungs, which brings in fresh O2 and removes the CO2 that is brought in by perfusion. For the last 20 years at PImBeL, scientists have been using a technique called nitrogen washout to image both the perfusion and ventilation of the lungs.
Nitrogen washout uses 13NN gas (radioactive nitrogen) that is dissolved in saline. The saline is injected into the patient. Because nitrogen is very poorly soluble in both saline and plasma, as soon as it reaches the lungs and gets a chance to move into air, it jumps from the circulation to the airspace. The buildup of the radioactive gas in a region of the lungs during a breath hold is a measure of the amount of blood that arrived at tha t region, and thus perfusion, Once the tracer is entirely in the gas space the subject resumes breathing. From the rate that the tracer is eliminated, the ventilation of each region of the lungs can be evaluated.
Changes in ventilation and perfusion after bronchoconstriction measured with NN13 PET.
The trick is getting the radioactive nitrogen (produces by bombarding deuterons into CO2) into the saline it doesnt like to be in the first place. This needs to be done rapidly (the half life of 13NN is ten minutes!), and without exposing the operator to radiation. This is done by a System for the Automatic LAbeling of SAline (SALSA) device. This automated system isolates the radioactive 13NN from other gasses and pushes it into degassed saline.
The requisite steps for creating injectable NN13 saline. The grey dotted line encloses steps performs by the SALSA.
I designed and built the third generation SALSA III device. This generation automates many of the manual steps required in earlier generations, and uses off the shelf components to construct a device that delivers a higher radionuclear yield with lower operator exposure. The user interface allows for a highly automated approach, with the flexibility for operator intervention at any point. The components of SALSA three communicate on many levels, from basic transistors and relays to TCP/IP connectivity.
Schematic of the information flow in SALSA III.
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