MEDICAL IMAGING Dr. Hugh Blanton ENTC 4390

Dr. Blanton ENTC Introduction 2 There has been an alarming increase in the number of things I know nothing about!

Lecture 1 INTRODUCTION

Dr. Blanton ENTC Introduction 4 INTRODUCTION TO MEDICAL IMAGING Medical imaging of the human body requires some form of energy. In radiology, the energy used to produce the image must be capable of penetrating tissues. The electromagnetic spectrum outside the visible light region is used for x-ray imaging, magnetic resonance imaging, and nuclear medicine. Mechanical energy, in the form of high-frequency sound waves, is used in ultrasound imaging.

Dr. Blanton ENTC Introduction 5 INTRODUCTION TO MEDICAL IMAGING With the exception of nuclear medicine, all medical imaging requires that the energy used to penetrate the body’s tissues also interact with those tissues. Absorption, Attenuation, and Scattering.

Dr. Blanton ENTC Introduction 6 INTRODUCTION TO MEDICAL IMAGING If energy were to pass through the body and not experience some type of interaction (e.g., absorption, attenuation, scattering), then the detected energy would not contain any useful information regarding the internal anatomy, and thus it would not be possible to construct an image of the anatomy using that information.

Dr. Blanton ENTC Introduction 7 INTRODUCTION TO MEDICAL IMAGING In nuclear medicine imaging, radioactive agents are injected or ingested, and it is the metabolic or physiologic interactions of the agent that give rise to the information in the images.

Dr. Blanton ENTC Introduction 8 The power levels used to make medical images require a balance between patient safety and image quality.

Dr. Blanton ENTC Introduction 9 History, Basic Principles, & Modalities Class consists of: 1)Deterministic Studies - distortion - impulse response - transfer functions All modalities are non-linear and space variant to some degree. Approximations are made to yield a linear, space- invariant system. 2)Stochastic Studies SNR (signal to noise ratio) of the resultant image - mean and variance

Dr. Blanton ENTC Introduction 10 Nov – Announces X-ray discovery Jan. 13, 1896 – Images needle in patient’s hand – X-ray used presurgically 1901 – Receives first Nobel Prize in Physics – Given for discovery and use of X-rays. Wilhelm Röntgen, Wurtzburg Radiograph of the hand of Röntgen’s wife, 1895.

Dr. Blanton ENTC Introduction 11 Röntgen’s Setup Röntgen detected: No reflection No refraction Unresponsive to mirrors or lenses His conclusions: X-rays are not an EM wave Dominated by corpuscular behavior

Dr. Blanton ENTC Introduction 12 Projection X-Ray Disadvantage:Depth information lost Advantage:Cheap, simple attenuation coefficient Measures line integrals of attenuation Film shows intensity as a negative ( dark areas, high x-ray detection

Dr. Blanton ENTC Introduction 13 Sagittal Coronal

Body Structure

Dr. Blanton ENTC Introduction 15 Directional Terms Anatomical position Beginning reference point Body upright Facing front Arms at side, palms forward Feet parallel

Dr. Blanton ENTC Introduction 16 Directional Terms

Dr. Blanton ENTC Introduction 17 Planes of Division Frontal plane Coronal plane Divides body into anterior, posterior parts

Dr. Blanton ENTC Introduction 18 Planes of Division Sagittal plane Divides body into right, left portions If plane cuts midline, called midsagittal or medial plane

Dr. Blanton ENTC Introduction 19 Planes of Division Transverse plane Divides body into superior, inferior parts

Dr. Blanton ENTC Introduction 20

Dr. Blanton ENTC Introduction 21 Anatomical Directions Anterior (ventral) = toward front of body Posterior (dorsal) = toward back of body Medial = toward midline of body Lateral = toward side of body Proximal = nearer to reference point Distal = farther from reference point

Dr. Blanton ENTC Introduction 22 Body Cavities Dorsal cavity contains: Cranial cavity Spinal cavity

Dr. Blanton ENTC Introduction 23 Body Cavities (cont’d) Ventral cavity contains: Thoracic cavity Diaphragm Separates thoracic cavity and abdominal cavity

Dr. Blanton ENTC Introduction 24 Body Cavities (cont’d) Abdominopelvic cavity: Abdominal cavity Pelvic cavity Peritoneum

Dr. Blanton ENTC Introduction 25 Body Regions Imaginarily divided into 9 regions

Dr. Blanton ENTC Introduction 26 Body Regions Midline sections: Epigastric = above stomach Umbilical = umbilicus or navel Hypogastric = below the stomach

Dr. Blanton ENTC Introduction 27 Body Regions (con’t) Lateral sections: Right and left hypochondriac Positioned near ribs, specifically cartilages

Dr. Blanton ENTC Introduction 28 Body Regions (con’t) Right and left lumbar Positioned near small of back (lumbar region)

Dr. Blanton ENTC Introduction 29 Body Regions (con’t) Right and left iliac Named for upper bone of hip (ilium) Also called inguinal region (referring to groin)

Dr. Blanton ENTC Introduction 30 Body Positions Anatomical Standing erect, facing forward, arms at sides, palms forward, toes pointed forward Prone Lying face down Supine Lying face up

X-Ray

Dr. Blanton ENTC Introduction 32 Early Developments Intensifying agents, contrast agents all developed within several years. Creativity of physicians resulted in significant improvements to imaging. - found ways to selectively opacify regions of interest - agents administered orally, intravenously, or via catheter

Dr. Blanton ENTC Introduction 33 Later Developments More recently, physicists and engineers have initiated new developments in technology, rather than physicians. 1940’s, 1950’s Background laid for ultrasound and nuclear medicine 1960’s Revolution in imaging – ultrasound and nuclear medicine 1970’s CT (Computerized Tomography) - true 3D imaging (instead of three dimensions crammed into two) 1980’s MRI (Magnetic Resonance Imaging) PET ( Positron Emission Tomography)

Dr. Blanton ENTC Introduction Hounsfield announces findings at British Institute of Radiology 1979 Hounsfield, Cormack receive Nobel Prize in Medicine (CT images computed to actually display attenuation coefficient  x,y  Important Precursors: 1917 Radon: Characterized an image by its projections 1961 Oldendorf: Rotated patient instead of gantry Computerized Tomography (CT) Result:

Dr. Blanton ENTC Introduction 35 First Generation CT Scanner Acquire a projection (X-ray) Translate x-ray pencil beam and detector across body and record output Rotate to next angle Repeat translation Assemble all the projections.

Dr. Blanton ENTC Introduction 36 Reconstruction from Back Projection 1.Filter each projection to account for sampling data on polar grid 2. Smear back along the “line integrals” that were calculated by the detector.

Dr. Blanton ENTC Introduction 37 Modern CT Scanner From Webb, Physics of Medical Imaging

Dr. Blanton ENTC Introduction 38 Computerized Tomography (CT), continued Early CT ImageCurrent technology

Dr. Blanton ENTC Introduction 39 Inhalation

Dr. Blanton ENTC Introduction 40 Exhalation

Dr. Blanton ENTC Introduction 41 Nuclear Medicine a)Radioactive tracer is selectively taken up by organ of interest b)Source is thus inside body! c)This imaging system measures function (physiology) rather than anatomy. - Grew out of the nuclear reactor research of World War II -Discovery of medically useful radioactive isotopes 1948 Ansell and Rotblat: Point by point imaging of thyroid 1952 Anger: First electronic gamma camera

Dr. Blanton ENTC Introduction 42 Nuclear Medicine, continued Very specific in imaging physiological function - metabolism - thyroid function - lung ventilation: inhale agent Advantage:Direct display of disease process. Disadvantage:Poor image quality (~ 1 cm resolution) Why is resolution so poor? Very small concentrations of agent used for safety. - source within body Quantum limited: CT 10 9 photons/pixel Nuclear ~100 photons/pixel Tomographic systems: SPECT: single proton emission computerized tomography PET: positron emission tomography

Dr. Blanton ENTC Introduction 43 Combined CT / PET Imaging

Dr. Blanton ENTC Introduction 44 Comparison of Modalities Why do we need multiple modalities? Each modality measures the interaction between energy and biological tissue. - Provides a measurement of physical properties of tissue. - Tissues similar in two physical properties may differ in a third. Note: - Each modality must relate the physical property it measures to normal or abnormal tissue function if possible. - However, anatomical information and knowledge of a large patient base may be enough. - i.e. A shadow on lung or chest X-rays is likely not good. Other considerations for multiple modalities include: - cost- safety - portability/availability

Dr. Blanton ENTC Introduction 45 Measures attenuation coefficient Safety: Uses ionizing radiation - risk is small, however, concern still present individual lesions per population risk > individual risk i.e. If exam indicated, it is in your interest to get exam Use: Principal imaging modality Used throughout body Distortion: X-Ray transmission is not distorted. X-Ray

Dr. Blanton ENTC Introduction 46 Ultrasound Measures acoustic reflectivity Safety: Appears completely safe Use: Used where there is a complete soft tissue and/or fluid path Severe distortions at air or bone interface Distortion: Reflection: Variations in c (speed) affect depth estimate Diffraction: λ ≈ desired resolution (~.5 mm)

Dr. Blanton ENTC Introduction 47 Magnetic Resonance (MR) Multiparametric M(x,y,z) proportional to ρ(x,y,z) and T 1, T 2. (the relaxation time constants) Velocity sensitive Safety: Appears safe Static field - No problems - Some induced phosphenes Higher levels - Nerve stimulation RF heating: body temperature rise < 1˚C - guideline Use: Distortion: Some RF penetration effects - intensity distortion

Dr. Blanton ENTC Introduction 48 ChestAbdomenHead X-Ray/ CT + widely used + CT - excellent – needs contrast + CT - excellent + X-ray - is good for bone – CT - bleeding, trauma Ultrasound– no, except for + heart + excellent – problems with gas – poor Nuclear+ extensive use in heart Merge w/ CT+ PET MR+ growing cardiac applications + minor role+ standard Clinical Applications - Table

Dr. Blanton ENTC Introduction 49 CardiovascularSkeletal / Muscular X-Ray/ CT + X-ray – Excellent, with catheter-injected contrast + strong for skeletal system Ultrasound+ real-time + non-invasive + cheap – but, poorer images – not used Nuclear+ functional information on perfusion + functional - bone marrow MR+ getting better High resolution Myocardium viability + excellent Clinical Applications - Table

Dr. Blanton ENTC Introduction 50 Economics of modalities: X-Ray:Cheapest Ultrasound: ~ $100K – $250K CT: $400K – $1.5 million (helical scanner) MR: $350K (knee) - $4.0 million Service: Annual costs Hospital must keep uptime Staff: Scans performed by technologists Hospital Income: Competitive issues Significant investment and return