Lesson: Bone Mineral Density Math and Beer's Law

Contributed by: VU Bioengineering RET Program, School of Engineering, Vanderbilt University

X-ray showing an Ap and laterial of an elbow.
How do we find the bone mineral density of bones?
copyright
Copyright © 2007 Glitzy queen00, Wikimedia Commons http://commons.wikimedia.org/wiki/File:Ap_lateral_elbow.jpg

Summary

Students revisit the mathematics required to find bone mineral density, to which they were introduced in lesson 2 of this unit. They learn the equation to find intensity, Beer's law, and how to use it. Then they complete a sheet of practice problems that use the equation.

Engineering Connection

Students see the real-world connection with this material right away. Beer's law and the other equations that they learn in this lesson are mathematical tools that biomedical engineers use every day when they make bone mineral density readings. Environmental engineers also use light intensity measurements when designing solar panels and other forms of energy storage. Almost every type of engineer knows and uses Beer's law.

Learning Objectives

After this lesson, student should be able to:

  • Apply their knowledge of logarithms to solve Beer's law problems.
  • Explain the breath of the applications of logarithms.

More Curriculum Like This

Bone Density Math and Logarithm Introduction

Students examine the definition, history and relationship to exponents; they rewrite exponents as logarithms and vice versa, evaluating expressions, solving for a missing piece. Students then study the properties of logarithms (multiplication/addition, division/subtraction, exponents).

Light Intensity Lab

Students complete this Beer's law activity in class by examining the attenuation of various thicknesses of transparencies. From this activity, they come to understand that different substances absorb light differently.

High School Activity
Bone Mineral Density and Logarithms

Students examine an image produced by a cabinet x-ray system to determine if it is a quality bone mineral density image. Students learn about what bone mineral density is, how a BMD image can be obtained, and how it is related to the x-ray field.

A Tale of Friction

High school students learn how engineers mathematically design roller coaster paths using the approach that a curved path can be approximated by a sequence of many short inclines. They apply basic calculus and the work-energy theorem for non-conservative forces to quantify the friction along a curve...

High School Lesson

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • Interpret expressions that represent a quantity in terms of its context (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Interpret parts of an expression, such as terms, factors, and coefficients. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Solve simple rational and radical equations in one variable, and give examples showing how extraneous solutions may arise. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Solve linear equations and inequalities in one variable, including equations with coefficients represented by letters. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Choose and produce an equivalent form of an expression to reveal and explain properties of the quantity represented by the expression. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • (+) Understand the inverse relationship between exponents and logarithms and use this relationship to solve problems involving logarithms and exponents. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • For exponential models, express as a logarithm the solution to abct = d where a, c, and d are numbers and the base b is 2, 10, or e; evaluate the logarithm using technology. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Use the properties of exponents to transform expressions for exponential functions. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Rearrange formulas to highlight a quantity of interest, using the same reasoning as in solving equations. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • Technology transfer occurs when a new user applies an existing innovation developed for one purpose in a different function. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
  • (+) Understand the inverse relationship between exponents and logarithms and use this relationship to solve problems involving logarithms and exponents. (Grades 9 - 12) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Introduction/Motivation

Recall from lesson 1 that you are working for a company that makes small specimen cabinet x-ray machines for medical research. Today you will learn how to do some calculations with the data that you might collect from such a machine.

Lesson Background and Concepts for Teachers

Calculation of Bone Mineral Density:

The basic equations for dual-photon absorptiometry can be derived from a number of underlying assumptions. First, it is assumed that the material is composed of varying amounts of only two substances (in this case bone and soft tissue). Second, it is assumed that scatter can be ignored. Under these circumstances, for any given photon energy, the number of photons striking the detector (N) can be calculated from the number of incident photons (No) using Beer's law.

Beer's law:

Beer's law equation.

where μs and μb represent the mass attenuation coefficients (cm2/g) of soft tissue and bone (respectively) and Ms and Mb represent the area densities (g/cm2) of the two tissue types.

I = I o e -μl

I = Intensity.

I0 = Intensity with no object.

μ = attenuation coefficient (depends upon material and x-ray energy).

l = length of the x-ray path.

Lecture Information

Present to students the BMD Math Presentation, a PowerPoint® file. Then have students complete the BMD Math Practice Problems. Administer the Log Quiz 2. Then students are ready to conduct the associated activity, Light Intensity Lab.

To answer the Challenge Question introduced in lesson 1, students next must Go Public. Refer to the Pamphlet Poster Paper Instructions for how students are to present all that they have learned about logarithms and bone mineral density during the course of the entire unit.

Associated Activities

  • Light Intensity Lab - In this lab exercise, students learn how to measure light intensity through transparencies.

Attachments

Assessment

Post-Introduction Assessment

Practice Problems: At lesson end or as homework, assign students to complete the BMD Math Practice Problems. Review their answers to assess the depth of their understanding.

Lesson Summary Assessment

Quiz: At lesson end, administer the 13-question, multiple-choice Log Quiz 2, which covers all types of logarithmic problems covered in this unit. Review students' answers to gauge their comprehension.

Student Presentations: In order to answer the unit challenge question first posed in lesson 1, have students create posters, pamphlest or papers, as described in the Pamphlet Poster Paper Instructions.

Contributors

Kristyn Shaffer; Megan Johnston

Copyright

© 2013 by Regents of the University of Colorado; original © 2006 Vanderbilt University

Supporting Program

VU Bioengineering RET Program, School of Engineering, Vanderbilt University

Acknowledgements

The contents of this digital library curriculum were developed under National Science Foundation RET grant nos. 0338092 and 0742871. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.

Last modified: July 20, 2017

Comments