Medical Imaging Imagining Modalities

Learning Objectives By the end of this Lecture the student will be able to: Understand the origin of electromagnetic radiation . Identify the different modalities ultrasound, X-ray, CT, MR, and PET scanning. Understand the basic principles for each imaging modality. Differentiate between ionizing and non ionizing radiation. Understand the general concept of using each modality in the demonstration of anatomy and physiology of body parts.

Imagining Modalities Radiography (X-Ray) Fluoroscopy (guided procedures) Diagnostic / Interventional imaging Computed Tomography (CT) Ultrasound (US) Gray-Scale /Color Doppler Magnetic Resonance Imaging (MRI) Nuclear Medicine .

Conventional X-ray Imaging. X-ray Production. High Electrical Potential Electrons - + Exposure Recording Device Radiation Penetrate the Sample Electrons from cathode filament are accelerated towards and impact the rotating anode. Rapid deceleration produces heat ( ~ 98 %) and x-rays (~ 2%)

Table, and cassette holder Overcouch X-ray Tube and Table High Tension Cables X-ray Tube housing Controls Light Beam Diaphragm Table, and cassette holder

Conventional X-ray Image of a Hand Normal Arthritic

Chest X-ray

(for digital screening) Fluoroscopy TV CAMERA (for digital screening) IMAGE INTENSIFIER X-RAY TUBE Allows dynamic imaging of Blood vessels ( angiography ) and ‘interventional’ procedures CONTROLS

(rare-earth doped ceramics Computed Tomography (CT) X-ray tube Rotation gives multiple projections Thin fan beam of x-rays Patient (stationary) Array of detectors (rare-earth doped ceramics with photodiodes)

CT Scanner

CT Image of Abdomen Axial image looking up from the feet.

Radioisotope Imaging Nuclear medicine(NM) Gamma camera head

Gamma Camera Scan.

Ultrasound Imaging (US) Ultrasound imaging is a common diagnostic medical procedure that uses high-frequency sound waves to produce images sonograms) of organs, tissues, or blood flow inside the body. The procedure involves using a transducer, which sends a stream of high-frequency sound waves into the body and detects their echoes from internal structures. The sound waves are then converted to electric impulses, which are processed to form an image displayed on a computer monitor. It is from these images that videos and portraits are made. Ultrasound probe

Ultrasound Image of 19 Week Old Foetus

Magnetic Resonance Imaging (MRI) MRI imaging uses a powerful magnetic field, radio frequency pulses and a computer to produce detailed pictures of organs, soft tissues, bone and all other internal body structures. The images can then be examined on a computer monitor, printed or copied to CD. MRI does not use ionizing radiation (x-rays). Big superconducting magnet (~ 1.5 tesla). Gradient coils. Radiofrequency coils.

Magnetic Resonance Imaging (MRI) Axial Brain Images T1-weighted T2-weighted Proton density weighted

} } Safety Ionising Radiation Non-ionising Radiation Modality Type Comments } X-ray imaging Radioisotope scanning Ultrasound Imaging MRI Biological effect , need protection against unnecessary doses Ionising Radiation } Non-ionising Radiation Less harmful effects. Better for the foetus.

What are they good at (or not)? Summary What are they good at (or not)? Imaging Technique Advantage Disadvantage X-ray Bone-soft tissue interfaces. High spatial resolution. Quicker and cheap. Poor soft tissue contrast. Planar – except CT. Ultrasound Good soft tissue contrast. Quick and cheap. Can be 3-dimensional. Mainly anatomical. Only ‘reasonable’ spatial resolution. Nuclear Medicine Functional rather than anatomical. PET – very sensitive metabolic tool. Functional rather than anatomical. Poor spatial resolution. PET very expensive. Long scan times. Magnetic Resonance Outstanding soft tissue contrast. Ability for functional imaging and 3 (or 4) dimensional.