Someone who had just undergone several medical diagnostic procedures suggested, “Why don’t you write about medical technology—or do you? I could have missed it, but I read most of your technology columns.”
Medical records technology has been discussed, but medical technology, not so much. And my son is a medical physicist, dealing with nuclear medicine tech all the time!
In this space a lot of what is discussed in computer-related, and most of the time we are “speaking digital”—as opposed to analog.
In medical diagnostic technology analog inputs are involved, but digital analysis is involved too.
Analog inputs are received in many diagnostic procedures. The equipment we patients are most familiar with is analog, particularly at the patient end.
For instance, there is the well known, but seldom pronounced, sphygmomanometer. We patients tend to call them blood pressure monitors. (Doctors could call them that too, couldn’t they?) Well, they are analog.
Basically, a sphyg—a BP thingy, that is, consists of an inflatable, calibrated cuff, to be put on the patient’s upper arm or wrist. The operator pumps it up to the point that blood flow in the arteries is brought to a halt, and the patient considers the things he/she has read about how if they leave a tourniquet too tight long enough, it may be necessary to amputate your arm or leg (but you will survive the snake bite).
But then the operator begins to release the pressure, and circulation is restored. The pressure at which the blood starts to move is the systolic pressure; the pressure at which there is no restriction is the diastolic pressure.
The person taking the blood pressure (and giving it back, at last, thank heavens!) can use the auscultatory method to listen to arterial wall sounds, employing a stethoscope, or can pick up on arterial wall vibrations in the oscillometric method.
The auscultatory method works fine for skilled and experienced operators, but the oscillometric method calls for readings from a pressure sensor, which would seem to be somewhat more straightforward.
The pressure sensor is conditioned with an analog front end, or AFE, and it is applied to an analog-to-digital-converter, or an ADC. At that point the systolic and diastolic pressures and the heart rate or pulse are digitized. They have been brought into the digital world.
It isn’t just blood pressure that has to be checked out. Sometimes we have to have ECGs, or electrocardiographs. (They used to be called EKGs, it seems to me. Why was that?)
Anyway, for an ECG we have electrodes taped to our bodies, with leads going to something that records them.
Heart signals aren’t all that powerful even in the heartiest individuals. They are measured in millivolts of amplitude. There are changes in these readings all the time, and those patterns of changings are traced, yard after yard.
Analysis of differences in signals from a number of locations tells doctors a lot about our heart functionality. They can look at an array of tracings from different locations and deduce important truth.
Each trace represents the voltage differential between two electrodes, or the voltage differential between one electrode and the average of several others.
Each channel is called a lead, but that isn’t because the number of leads is the same as the number of wires hooked onto the patient.
Often the number of leads is 12, but there are 10 electrodes. Nine leads monitor heart voltages across different areas of the body. The “right leg” electrode (RL) is electrically driven to reduce common-mode voltage.
How about the nine? Those are right arm (RA), left arm (LA), left leg (LL), and V1 through V6, the six precordial electrodes (chest electrodes, to us laypersons).
RA, LA and LL are grouped and averaged for six leads and are used as one side of the differential pairs, teamed with the chest electrodes V1 through V6.
Also, three measure differential voltage between RA, LA, and LL and the average of the other two.
More involved ECGs may have pace signals (from pacemakers where present) and non-heart signals such as “lead-off,” a fault situation. Impedance measurements can provide an input for respiration rate, because the chest rising and falling changes the thoracic impedance.
The AFE, with the ADC, allows the rest of the system to sort and sift those differential signals.
Analog inputs are digitized in ultrasound imagers, blood glucose readers, wearable or portable insulin pumps and digital thermometers, to mention just a few.
“It’s all computerized now,” said a medical tekkie, when we were discussing some of these matters.
Then he added, “Well, there’s still analog, but everything gets digitized.”