CHAPTER 1 MODELING BIOSYSTEMS 1

Chapter 1 Modeling Biosystems

Problem 1.1 List five applications of computers in biomedical engineering and briefly describe each application.

Solution

• Computers are used in Medical Imaging and in particular, Computed Tomography or Magnetic Resonance Imaging. The computer controls the positioning of the patient, is the interface to the technician and computes the reconstruction.

• Computers are also used in blood pressure monitors, to control the interface to the operator (who may be the patient), to control the air pump and to read the pressure sensor.

• Confocal and other sophisticated microscopes, which are used by biomedical engineers, are controlled by computer. The computer controls turning the laser(s) on and off, the positioning of the x-y stage and shows the image to the user on a monitor.

• Prosthetics, such as dental implants, are designed and manufactured under computer control. The implant is designed using a CAD tool such as Pro-Engineer or AutoCAD and the design, as a set of 3D coordinates is then used by a computer controlled machine to make the implant.

• Computers can be used in sports medicine to study high performing athletes. Computers are used to capture images as an athlete may be running, swimming or bicycling, for example. These images are then analyzed by computer.

Problem 1.2 You have been assigned the task of designing a computerized patient-monitoring system for an intensive-care unit in a medium-sized community hospital. What parameters would you monitor? What role would you have the computer play?

Solution

In an intensive care facility, one would want to monitor and record vital signs, most importantly blood pressure, pulse, respiration and temperature, for each patient. In addition to these vital signs, one might also have the system record the patient's electrocardiogram. The design engineer would have to decide whether or not to have individual units for each bed in the ICU or units that would transmit the data back to one control station – known as telemetry. In either case, the

2 NUMERICAL METHODS IN BIOMEDICAL ENGINEERING – SOLUTIONS MANUAL

computers are used to read settings input by the clinician, collect data from each sensor, display the results and possibly save and/or transmit the results to a remote control station. Problem 1.3 Why is a computer-averaged, EEG-evoked response signal easier to analyze than a raw signal?

Solution

Data collected from biomedical instruments is noisy, meaning that any given sample value is only an approximation of the real value. A reasonable assumption that is often made is that the noise is random and uniformly distributed. Therefore, if one collects a set of measurements, then the values are as likely to be greater than the real values as they are likely to be less than the real value.

If a set of ECG signals are collected and then the digital samples are averaged, these measurements will yield a better approximation of the desired ECG signal. A discussion of noise, variability and averaging, which is often covered in instrumentation and/or systems courses, is in Chapter 9. Problem 1.4 What advantage does a computer give in the automated clinical laboratory?

Solution

Computers provide reproducible results for the same inputs. In a clinical laboratory where blood is analyzed, it would be very important to produce the same results if both samples have the same composition. Problem 1.5 List the types of monitoring equipment normally found in the ICU/CCU of a hospital.

Solution

The answer to this question can be found from a number of textbooks such as Enderle et al (2005) or from resources on the web. A sample of the type of computer controlled monitoring equipment might be for:

• ECG measurement • Pressures measurement • Temperature and Cardiac Output measurement • Pulse Oximetry. and CO2

• Some units may have defibrillators • Telemetry units (see Problem 1.2). • There might be a printer so that the clinician can generate hard copy for patient records

CHAPTER 1 MODELING BIOSYSTEMS 3

Problem 1.6 Are computer systems always applicable in biomedical equipment?

Solution

One example are biomedical engineers work in prosthetics and orthotics do not necessarily use nor do they design and build computer controlled equipment. Problem 1.7 Describe three computer applications in medical research.

Solution

• Bioinformatics is a field where computers are used to organize and analyze volumes of data that come from high throughput experiments. DNA microarray experiments are one example and computers are used to try to discover gene regulation networks.

• Medical Image Analysis is a discipline where researchers develop computer algorithms to detect, identify or measure normal or pathological structures in images. The images may be traditional MRI or CT studies, video microscopy or bio-optics.

• Computers are also used to compute statistics and manage data for clinical trials. Such trials might be tests of therapies, or they may be experiments to study human behavior or performance.

Problem 1.8 On a biomedical engineering examination, a student named George computes in feet and inches the maximum distance that a certain artificial heart design could pump blood upward against gravity. Unfortunately, in recording this distance on his examination paper, he reverses the numbers for feet and inches. As a result, his recorded answer is only 30% of the computed length, which was less than 10 feet with no fractional feet or inches. What length did George compute in feet and inches?

Solution

This problem is due to Professor HW Corley of the University of Texas at Arlington and included here as a simple example for getting students to think about setting up equations to model a system.

First, let George's recorded answer be x feet and y inches; the true measurement is then y feet and x inches. Both measurements should be converted to inches; the recorded answer is (12x+y) and the computed length is (12y + x). Since the recorded answer is 30% of the computed length,

12 .30 (12 )x y y x+ = ⋅ + 11.7 2.6x y=

and then y = 4.5 (feet) and x=1 (inch). Make sure that the students get the units correct.