Agenda

Introduction to Medical Imaging
- What is medical imaging ?
- Roles, Players, Modalities
- Anatomical vs Functional Imaging
- Ionizing vs Non-ionizing Radiation
Nuclear medicine
- Basic concepts

Tomorrow

X-ray Physics
- Basic concepts
- X-ray production
- X-ray interaction with matter
- X-ray detectors
Diagnostic Radiology

GE Healthcare

+1800 employees

R&D ($35\%$)
Production ($22\%$)
European Center for Maintenance ($16\%$)
Support Functions & Other ($27\%$)

Introduction

A recent history

1895: discory of X-rays, first applications
1958: First gamma camera, Nuclear Medicine
1962: First UV of fetus
1967: First CET head scanner
1972: First head MR scanner
1990: first PET scanner

2000’s-2010’s: Digital Age
- IA

What is medical imaging ?

Process

Roles

Players

Who are diagnostic imaging customers ?

Healthcar systemes, hospitals, and clinics
Governmnent officials
Pharmaceutical firms
Genetics & Bio-science researchers

Modalities overview

Ionizing vs non-ionizing radiation

Anatomix vs Functional Imaging ?

Contrast Agents

Contrast agents are substances used to enhance visibility of internal structures in X-ray or MR-based imaging techniques

Iodine-based
- Injected in the bloodstream to highlight blode vessels
Gaolinium-based
- Vascular ferromagnetic contrast agent visible in MRI
Baarium-based
- orally to help imaging digestive system, including esophagus, stomach and GI tracks

Radioisotope Contrast Agents

Radioisotope contrast agents are based on atmos with excess nuclear energy, making it unstable. They emit the excess energy to highlight body functions

Tc-99m
- Injected in the bloodstream to study brain, myocardium, thyroid, lungs, liver, gallblader
$^{18}$F-FDg
- Mark the glucose metabolism

Nulcear imaging

Key components

Nuclear Medicine

Anatomical vs Functional Imaging

Gamma-rays Physics

Basics Concepts

Quanta

Atomic Model

Characteristic Radiation

Product of electron transistions between 2 electric shells:

Two steps:

Electrons (or photons) collid with a shell electron, which is removed from orbit
Electrons from higher energy shell fills the vacancy and an X-ray photon is emitted

Exponential Behavior

Exponential decay/growth:

\[\frac{\Delta N}{\Delta t}=\pm\lambda N\\ \text{provided: }\lambda\Delta t\lt\lt1\\ \text{then: } N=N_0e^{\pm\lambda\Delta t}\]

Attenuation

Z-ray photon life span:

Photon is transmitted through the matter
Photon is absorbed (end of life)
Photon is scattered ($E_{new}\le E$)

If $E_{new}\gt0$, then more A, B or C

Transmitted photons:

\[I(E)=I_0(E)\cdot e^{-\mu(E)\cdot t}\quad\text{Berr-Lambert lawa}\]

Isotopes Decay

Glossary:

IsotoPes = atoms with the same number of protons (Z)
IsotoNes = atoms with the same number of neutrons
Nuclides = nuclei with differing numbers of protons and neutrons are called nuclei
Radioisotopes = atoms with unstable nuclei

Isomeric Transition

Nucleus in an excited state returns to the more stable state release of a photon (gamma, $\sim88\%$)

Sometimes the nucleus energy may eject an electron (ionized radiation $\sim12\%$) which deposes radiation dose to the patient

Example: $^{99m}{43}Tc\to^{99}{43}Tc+\gamma$

Beta-plus decay Proton converted to a neutron by releasing positron $(\beta)+$ and a neutrino

Since positron is an antimatter analog

Electron capture Proton converted to a neutron by capturing an electron and releases a neutrino. It happens in nuclei with too few neutrons

Since the electron is removed from the shell, it releases characteristic X-rays

Summary

Radiopharmaceuticals

Production

Ideal characteristics

Ideal Characteristics

Short-half life (but not too short)
Monochromatic Gamma-ray production
Gamma-ray energy high enough to easily cross patient body (deposing minimal dose)
Gamma-ray energy low enough to be stopped by the detector
Have minimal production of other particles (add noise to our measurements)
Localize to the organ of interest, non toxic, …
Inexpensive and readily available

Technetium-99m

Close to ideal characteristics
Decays with $88\%$ in emission of 140.5 keV photon
$12\%$ internal conversions (electrons, characteristic x-rays, …)

Transport Issues

Common Isotopes

Diagnostic Radiology

Instrumentation

Gamma Camera

Nuclear Imaging $\Leftrightarrow$	X-ray Imaging
Radioctive isotope	X-ray tube
Collimator	Anti-scatter grid
Gamma camera	X-ray detector

Nuclear Medicine detector also measures not only the number of events, but the time and energy of each detected event
Ideally imaging is performed from unscattered photons that undergo photoelectric absorption in the detector
Scintillator + Electronics must be very fast to detect individual events

Pulse Height Analyzer with Nal Crystal

Collimators

Efficiency

Resolution = bar patterns, MTF, FWHM of point source, …
Sensitivity = fraction of gamma rays the pass through the holes (typically $0.01\%$)
Increasing blades/holes length: Res $\uparrow$, Sen $\downarrow$
Type (parallel, convergence, …) modulates Res & Sen
Increasing blades/holes

Clinical application

Single Photon Emission CT

Characteristics

Long decay isotope
Single photon emitted and captured by camera
Tomography technique generates 3D volume of radioactivity density
Multi-head cameras allows for faster acquisitions
Poor spatial resolution VS excellent contrast resolution
Noise is a major factor

Reconstruction (same as CT)

Filtered Back-Projection
Iterative techniques

Applications

Positron Emission Tomography