Imaging Modalities PDF

DEPARTMENT DIAGNOSTIC IMAGING AND RADIOTHERAPY KULLIYYAH OF ALLIED HEALTH SCIENCES IMAGING MODALITIES INTRODUCTION TO MEDICAL IMAGING HSMI 1211  Historical development of medical imaging modalities Principles of imaging...

DEPARTMENT DIAGNOSTIC IMAGING AND RADIOTHERAPY KULLIYYAH OF ALLIED HEALTH SCIENCES IMAGING MODALITIES INTRODUCTION TO MEDICAL IMAGING HSMI 1211  Historical development of medical imaging modalities Principles of imaging modalities (General LEARNING Radiography, CT, MRI, US, RNI) OBJECTIVES Imaging parameters specific to imaging modalities Advantages and disadvantages of each modality. HISTORICAL DEVELOPMENT GENERAL X-RAY PRINCIPLES IMAGING PARAMETERS ADVANTAGES AND DISADVANTAGES GENERAL X-RAY PRINCIPLE X-ray is based on the interaction of x-rays with tissues as they pass through the body. The interaction of x-rays encompasses transmission and absorption. Transmission - X-rays passes through less dense tissues (e.g. air or soft tissue) Absorption – X-rays are absorbed by denser tissues (e.g. bone) GENERAL X-RAY PRINCIPLE Transmission - X-rays passes through less dense tissues (e.g. air or soft tissue) Transmission Absorption – X-rays are absorbed by denser tissues (e.g. bone) GENERAL X-RAY PRINCIPLE-3 components 1. X-ray tube : provides the x-ray beams that is projected in specific direction. 2. Patient: The medium where the x-rays interact with tissues to generate image based on attenuation characteristics of the tissues. 3. Image receptor: The material to receive the remnant beam that interacted with the body tissue. GENERAL X-RAY IMAGING PARAMETERS (kVp) PARAMETER DESCRIPTION EFFECT Increase in kV results in more penetrating beam (leading to overpenetration) reducing the contrast of the image Kilovoltage Determines the penetrating power of while increasing the blackness of the image. (kV) the radiation beam Increase in kV results in less radiation will be absorbed by the tissues. Hence less radiation dose to the patient. Difference in charge between anode and cathode is called as tube potential. The tube potential is measured in unit kilovolts. When we use HIGH kVp, larger voltage Negatively difference across x-ray tube is created (electron Positively charged move quickly, become more energy thus charged priducces higher energy x-ray beam). GENERAL X-RAY IMAGING PARAMETERS (mA) PARAMETER DESCRIPTION EFFECT Increase in mA, increases the intensity of the beam Denotes the applied tube current. resulting in increase blackness of the image milliAmpererage The movement or the flow of (overexposed). (mA) electron in the x-ray tube. Increase in mA means increase in radiation intensity and this increases radiation dose to the patient This movement of electron in the X-ray tube is called as tube current. The tube current is measured in units of miliamperes (mA). GENERAL X-RAY IMAGING PARAMETERS PARAMETER DESCRIPTION EFFECT Relates to the duration of radiation Increase in exposure time, increases the amount of exposure. radiation reaching the patient, increasing the blackness Note: This relationship is only of the image (overexposed). Seconds (s) applicable to Projection Radiography Increase in exposure time increases the radiation dose techniques involving Fluoroscopy. to the patient. GENERAL X-RAY IMAGING PARAMETERS PARAMETER DESCRIPTION EFFECT Follows the Inverse Square Law. Increase in the Source to Denotes the distance between the x- distance reduces the intensity of radiation. The image Image ray source and the image receptor. will be less black (underexposed) Receptor Distance (SID) GENERAL X-RAY IMAGING PARAMETERS PARAMETER DESCRIPTION EFFECT Increase in the speed of the system (i.e, more sensitive) systems can give rise to overexposed images if other Responsible to record the image. Image receptor imaging parameters remain constant. Depends on the sensitivity of the (IR) Increase in the speed of the system requires less particular system being used. radiation to give the same image density compared to systems of lower speed. Patient dose is reduced. GENERAL X-RAY IMAGING PARAMETERS PARAMETER DESCRIPTION EFFECT Presence of filters in the x-ray tube Increase in filtration reduces the intensity of radiation assembly filters low energy x- reaching the image receptor. The image will be less radiation. Filtration absorbs the black (underexposed) Filtration lower energy radiation, preventing Increase in filtration reduces the radiation dose to the this type of radiation from reaching patient. the patient. GENERAL X-RAY IMAGING PARAMETERS PARAMETER DESCRIPTION EFFECT Increase in OID results in less radiation reaching the IR, Object to giving rise to underexposed image. Image The distance between the patient Receptor and Image receptor. Increase in OID also results in magnification of the Distance (OID) image, resulting in poor detail of images. GENERAL X-RAY ADVANTAGES AND LIMITATION LACKS DEPTH INFORMATION Resultant radiograph is a 2D image depiction of 3D object (all structures are superimposed each other) The chest x-ray image shows among others, the clavicle, lungs, ribs, spine, heart, etc. However, one might not be able to appreciate the position of the heart relative to the lung; how far anterior or posterior is it to the spine? Conversely, how much anterior or posterior the clavicles are to the spine? GENERAL X-RAY ADVANTAGES AND LIMITATION Solution for the lack of depth information: This makes it difficult for the exact localization of lesions to be made. This difficulty can be reduced slightly when another projection that is 90 degrees to the first projection is made. Hence with the above chest x-ray, a lateral view can help to identify the location of lesions from a different perspective. GENERAL X-RAY ADVANTAGES AND LIMITATION LIMITED TISSUE DIFFERENTIATION Understanding of how the concept attenuations works enable radiographers achieve best tissue differentiation. FALSE SIZE Influenced by magnification The nearer the organ to image receptor, the less magnification appearance in the image. Mammography Equipment still relies on the use of an x-ray tube which delivers the necessary radiation to image the breast. The main difference between the Mammography and the common Projection Radiography equipment will be the use of specific anode (in the x-ray tube) that is made of Molybdenum or Molybdenum/Tungsten alloy. This is to enable the energy of the beam that is used in Mammography, in the region of 28-32 kV, to be generated, as compared to 50 – 120kV employed in imaging the other regions of the body. The common projections are Medio-lateral oblique (MLO) and Cranio-Caudal (CC) projections, while there are other projections that can be used when indicated Fluoroscopy This modality is an extension of Projection Radiography, for it still depicts a 2 dimensional image of a 3 dimensional object. One very important difference with Fluoroscopy when compared to the other Projection Radiography sub-modalities (conventional Radiography, Mammography and Orthopantomography) in imaging the Summary of the signal conversion stages during fluoroscopy anatomy is the ability of Fluoroscopy to show Real-time imaging. Mobile Permits Projection Radiography to be performed in places other than the Imaging departments. Image quality could be less, though diagnostic enough, for some of the examinations. This is due to the fact that mobile X-ray equipment has lower specifications compared to the static Projection Radiography equipments available in Imaging departments. COMPUTED TOMOGRAPHY (CT) SCAN PRINCIPLES IMAGING PARAMETERS ADVANTAGES AND DISADVANTAGES CT scan PRINCIPLE The computer assisted generation of cross-sectional images of the body that results from multiple projections of the anatomy based on the attenuation of radiation as its transverses the body. A schematic diagram depicting the principle of CT Image generation CT scan CT scan Factors driving CT innovation 1. The difficulty to fully appreciate the location of lesions based on a 2D representation of a 3D object as evident on Projection Radiography images. 2. The inability to fully appreciate the image from various perspectives other than the AP, PA, lateral and / or oblique projections. 3. The poor contrast differentiation between tissues in Projection Radiography due to the superimposition of the tissues makes it difficult to outline the individual tissues effectively. CT scan CT system Control system Data acquisition Data processing patient couch To ensure the computer system that is gantry (x-ray tube, smooth running of responsible to reconstruct detectors, s-ray the system the digital data gathered into generator and an image support electronics Data archive or Data Data display storage communication a monitor that is used to display the a system that permits the a system that permits the image data and the images to be images to be sent elsewhere stored for future use. to be viewed at monitors distant from the examination room. CT scan IMAGING PARAMETERS Kilovoltage (KV) Miliampere (mA) Exposure time Collimation Slice thickness Type of scan acquisition Multi-planar reformation MAGNETIC RESONANCE IMAGING (MRI) PRINCIPLES IMAGING PARAMETERS ADVANTAGES AND DISADVANTAGES MRI PRINCIPLE MRI works by utilizing a strong magnetic field to align hydrogen protons in the body, which are abundant in tissues due to the water content. The magnetic strengths used in MRI for medical purposes are between 0.2 – 4T MRI MRI IMAGING PARAMETERS Repetition time (TR) Echo time (TE) Inversion time (TI) Flip Angle (FA) Spin-lattice relaxation time (T1) Spin-spin relaxation time (T2) MRI ADVANTAGES AND DISADVANTAGES MRI ULTRASOUND PRINCIPLES IMAGING PARAMETERS ADVANTAGES AND DISADVANTAGES ULTRASOUND PRINCIPLE the propagation of sound as it interacts with matter. The transducer, also called a probe, generates sound waves and receives the echoes reflected back from tissues. Ultrasound uses high-frequency sound waves (typically 2-18 MHz) to create images of the internal body structures. ULTRASOUND Image generation in Ultrasound ULTRASOUND Imaging Parameter High frequency (7 – 18mHz) : for superficial structures such as tendons, muscles, testis and breasts while Lower frequency (1 – 6mHz) : offers greater penetration for deeper structures like the kidney and liver. FREQUENCY However lower frequency results in lower resolution but this lower frequency means greater penetration that permits visualisation of the deeper structures. “Gain” refers to the necessary adjustment that can be made to improve the quality of an ultrasound image. GAIN Echoes from the tissues further from the transducer have reduced amplitudes as the sound has covered uniform amplification of the greater distance. ultrasonic signal that is returning to the transducer after it travels through Special circuits amplify these attenuated echoes to the tissue. correct the amplitude loss from tissue attenuation. ULTRASOUND FREQUENCY ULTRASOUND GAIN ULTRASOUND ADVANTAGES AND DISADVANTAGES RADIONUCLIDE IMAGING (RNI) PRINCIPLES IMAGING PARAMETERS ADVANTAGES AND DISADVANTAGES RADIONUCLIDE PRINCIPLE The detection of radiation released by radionuclides that are introduced into the body. Radioactive Tracers: Radionuclide imaging uses small amounts of radioactive substances called tracers (radiopharmaceuticals) that are injected, inhaled, or ingested into the body. Gamma Radiation Detection: The tracers emit gamma rays (or sometimes positrons), which are detected by special cameras (gamma cameras or PET scanners) outside the body. Physiological Imaging: Unlike CT or MRI, which mainly provide structural images, radionuclide imaging is used to visualize physiological processes (e.g., metabolism, blood flow, organ function) by tracking how the body absorbs and processes the tracer. RADIONUCLIDE IMAGING PARAMETERS Single Photon Emission Computed Tomography (SPECT): ⚬ Uses gamma cameras to detect gamma rays emitted by the tracer. ⚬ Provides 3D images by rotating the gamma camera around the patient, capturing multiple angles to form cross-sectional images. ⚬ Commonly used for imaging the heart, brain, liver, bones, and detecting cancer metastases. Positron Emission Tomography (PET): ⚬ Tracers emit positrons, which annihilate with electrons, releasing gamma rays that are detected by PET scanners. ⚬ Provides high-resolution functional images, particularly useful in oncology for detecting and monitoring tumors, assessing brain function, and evaluating heart diseases. ⚬ PET/CT: Combines PET with CT to merge functional and anatomical imaging, allowing precise localization of abnormal tracer uptake. RADIONUCLIDE ADVANTAGES AND DISADVANTAGES CHOICE OF IMAGING MODALITY The selection of imaging modality to demonstrate a certain medical condition could be based on the following considerations: Depends on the intended information. For example : MRI and Ultrasound could not depict bony pathology Depends on patient factors: MRI not for those who are claustrophobia Trauma patients may not be indicated for MRI because of long examination time End…