Basic Imaging Principles PDF

Basic Imaging Principles  Medical Imaging The overall objective of medical imaging is to acquire useful information about physiological processes or organs of the body by using external or internal sources of energy.  The Modalities Different types of medical images ca...

Basic Imaging Principles  Medical Imaging The overall objective of medical imaging is to acquire useful information about physiological processes or organs of the body by using external or internal sources of energy.  The Modalities Different types of medical images can be made by varying the types of energies and the acquisition technology used. The different modes of making images are referred to as modalities. Each modality has its own applications in medicine.  Modalities Fluoroscopy Mammography X- Computed Tomography (CT) RAY Nuclear Medicine Imaging Single Photon Emission Computed Tomography (SPECT) Positron Emission Tomography (PET) Magnetic Resonance Imaging (MRI) Ultrasound Imaging Doppler Ultrasound Imaging What does the human body look like on the inside? Invasive Techniques: Operation Endoscope Noninvasive Techniques: Magnetic Resonance Imaging (MRI) Ultrasound Imaging x-ray Computed Tomography (CT) Nuclear Medicine Functional Magnetic Resonance Imaging (fMRI) Positron Emission Tomography (PET)  Image quality determined by:  Resolution When we say resolution in medical imaging we are typically referring to spatial resolution or what is sometimes called high contrast resolution.  Noise Noise is the random fluctuation in image intensity about it’s true value  Contrast It allow the human observer to differentiate between regions.  X-ray Physical Principle: Variation in X-ray attenuation of different tissues Methodology: A beam of X- rays is directed through a patient onto a film. Image: An X-ray “shadow” of the patient. History: – Roentgen’s discovery - 1895 – Application to medicine – 1896 X-Ray tube The X-rays are produced from electrons that have been accelerated from in vacuum from the cathode to the anode. Emission occurs when filament is heated by passing current through it. When the filament is hot enough, the electrons obtain thermal energy sufficient to overcome the energy binding the electron to the metal of the filament. After accelerated they will be stopped at a short distance. Most of the electron energy will produce heat at the anode. Some percentage will be converted to X-ray by two main methods. Deceleration of charged particle results in the emission of electromagnetic field  X-ray Production. High Electrical Potential Electrons + - Electrons from cathode filament are accelerated towards and impact the Radiation Penetrate rotating anode. the Sample Rapid deceleration Exposure Recording Device  X-Rays Used to visualize hard bony structures and locate abnormally dense objects like tumors or tuberculosis nodules in lungs  X-Ray using contrast media Contrast agents usually contains barium or iodine which absorb more x-rays than the surrounding tissue