MRI Prelims PDF

Trisha Jane Andriane D. Pardillo, RRT 08/017/2024 MAGNETIC RESONANCE IMAGING RDT 116 WHAT IS MRI? Trisha Jane Andriane D. Pardillo, RRT WHAT IS MRI? Trisha Jane Andriane D. Pardillo, RRT The use of...

Trisha Jane Andriane D. Pardillo, RRT 08/017/2024 MAGNETIC RESONANCE IMAGING RDT 116 WHAT IS MRI? Trisha Jane Andriane D. Pardillo, RRT WHAT IS MRI? Trisha Jane Andriane D. Pardillo, RRT The use of MAGNETIC FIELDS (MF) and RADIOWAVES (RF) to obtain mathematical RECONSTRUCTED image. WHAT IS RADIOFREQUENCY? Radiofrequency (RF) electromagnetic radiation (EMR) is the transfer of energy by radio waves. RF EMR lies in the frequency range between 3 kilohertz (kHz) to 300 gigahertz (GHz). RF EMR is non-ionizing radiation, meaning that it has insufficient energy to break chemical bonds or remove electrons (ionization). WHAT IS MRI? Trisha Jane Andriane D. Pardillo, RRT  MAGNETIC RESONANCE IMAGING Trisha Jane Andriane D. Pardillo, RRT HISTORY OF MRI DEMOCRITUS – A Greek philosopher, in 400 B.C. theorize that all matter is made of both indivisible and invisible particles “atoms” Magnesia- West Turkey, discovered “lodestones” - used for navigation, religious and magical purposes MAGNETIC RESONANCE IMAGING Trisha Jane Andriane D. Pardillo, RRT HISTORY OF MRI Hans Christian Oersted- in 1819 discovered that electricity produces magnetism Michael Faraday- 1831, twelve years after the discovery of Oersted discovered the electricity. MAGNETIC RESONANCE IMAGING Trisha Jane Andriane D. Pardillo, RRT A magnetic field is generated by a moving charge (electrical current). The direction of the magnetic field can either be clockwise or counter-clockwise with respect to the direction of flow of the current. JEAN-BAPTISTE-JOSEPH FOURIER - made the heart of MRI mathematics “the Fourier Transform” MAGNETIC RESONANCE IMAGING  MAGNETIC RESONANCE IMAGING Trisha Jane Andriane D. Pardillo, RRT HISTORY OF MRI Sir James Clerk Maxwell of Scotland- 1860 discovered magnetic lines of force could be mathematically expressed. Electrical and magnetic fields coexist at a 90 degree angle. Heinrich Hertz of Germany- 1868 discovered invisible electromagnetic waves exist with varying wave frequencies. Nikola Tesla- Discovered Rotating Magnetic Field MAGNETIC RESONANCE IMAGING Trisha Jane Andriane D. Pardillo, RRT Section 01 Trisha Jane Andriane D. Pardillo, RRT A START OF A MAGNETIC ERA MAGNETIC MOMENTS OF NUCLEUS MAGNETIC MOMENTS OF NUCLEUS Trisha Jane Andriane D. Pardillo, RRT ISIDOR ISAAC RABI First described and measured in molecular beams of NUCLEAR MAGNETIC RESONANCE Rabi’s method involved using an electromagnet of approximately 0.2T and a hairpin coil producing an oscillatory RF-field of about 3.5 MHz. The RF- field was maintained at constant frequency and the main magnetic field was varied by changing its current. Rabi then passed a "molecular beam" of lithium chloride (LiCl) molecules through a vacuum chamber and subsequently into the magnetic apparatus. In 1938 he and his team reported energy absorption/resonance peaks for both Li and Cl as predicted. Rabi named this phenomenon "nuclear magnetic resonance." Provides a frequency spectrum of a given tissue based on the molecular and chemical structures of that tissue- NMR Spectroscopy MAGNETIC MOMENTS OF NUCLEUS Trisha Jane Andriane D. Pardillo, RRT ISIDOR ISAAC RABI MAGNETIC MOMENTS OF NUCLEUS Trisha Jane Andriane D. Pardillo, RRT ISIDOR ISAAC RABI Although Isidor Rabi is generally credited for the discovery of NMR, he did so in an inherently "unnatural" context — using a molecular beam in a vacuum where individual nuclei were isolated from each other and their environment. It would not be until late 1945 that independent teams led by …… MAGNETIC MOMENTS OF NUCLEUS Trisha Jane Andriane D. Pardillo, RRT. BASIC SCIENCE OF Trisha Jane Andriane D. Pardillo, RRT NMR PHENOMENON Felix Bloch and Edward Purcell their development of new ways and methods for nuclear magnetic precision measurements. expanded the technique for use on liquids and solids in NMR, for which they shared the Nobel Prize in Physics in 1952. BASIC SCIENCE OF Trisha Jane Andriane D. Pardillo, RRT PURCELL DIAGRAM In the late 1930's Edward Purcell was just beginning his career at the Massachusetts Institute of Technology and had only written a handful of papers prior to interruption of his research by World War II. Back at work in the winter of 1945, he, Henry Torrey, and Robert Pound filled an electromagnetic cavity with 850 cc of solid paraffin and placed the device in an electromagnet at Harvard's Research Laboratory of Physics. Driving the cavity with an oscillating current of about 30 MHz, the magnetic field strength was slowly increased until at about 0.7T when a sudden, 20-fold sharp increase in the cavity's absorption of radiation occurred, verifying the predicted nuclear magnetic resonance of hydrogen nuclei at that field strength and frequency. BASIC SCIENCE OF Trisha Jane Andriane D. Pardillo, RRT BLOCH APPARATUS About 1 month later at Stanford, Felix Bloch, William Hansen, and Martin Packard demonstrated NMR in a different substance and using a much smaller apparatus. They placed about 1 cc of water in a small glass bulb, around which were wrapped separate transmitter and receiver coils optimized for radio frequencies in the range of 8 MHz. The receiver coils were placed perpendicular to the transmitter coils so that the input waves would not be detected. The RF-specimen device was then placed between the poles of an adjustable electromagnet operating at approximately 0.18T. Like Purcell's group, Bloch's team slowly changed the magnetic field until resonance was achieved. Rather than measuring absorption, however, Bloch et al. detected a nuclear induction signal in the receiver coil as a manifestation of the NMR phenomenon.  DR. PAUL LAUTERBUR Trisha Jane Andriane D. Pardillo, RRT ZEUGMATOGRAPHY 1952 demonstration of use of magnetic gradients for spatial localization and actual demonstration of 1-D imaging (1D MR image) Which leads to the experiment of…… Dr. Paul Lauterbur- designed the gradient coils. Developed a way to generate the first MRI images, in 2D and 3D, using gradients  DR. PAUL LAUTERBUR ZEUGMATOGRAPHY In 1973, Paul Lauterbur (State University of New York) described a new imaging technique that he termed Zeugmatography. By utilizing gradients in the magnetic field, this technique was able to produce a two-dimensional image (back-projection). ENCODING DATA Trisha Jane Andriane D. Pardillo, RRT RICHARD ERNST In 1975, Richard Ernst introduced 2D NMR using phase and frequency encoding. Encoding of Data in NMR paves way on finalizing image signal localization ENCODING DATA Trisha Jane Andriane D. Pardillo, RRT RICHARD ERNST ENCODING DATA Trisha Jane Andriane D. Pardillo, RRT RAYMOND DAMADIAN Up until the 1970s, MRI technology was only being used for chemical and physical analysis. Raymond Damadian, a doctor, who wondered if the same methods could be used on living organisms to detect disease. In 1971, he concluded that since cancerous tissue contained more water than healthy tissue, it could be detected by scanners that bathed a part of the human body in radio waves and measured the emissions from the local hydrogen atoms. ENCODING DATA Trisha Jane Andriane D. Pardillo, RRT RAYMOND DAMADIAN Dr. Raymond Damadian – physician/physicist July 3, 1977 performed the 1st MRI whole body transaxial proton density weighted slice image. It took four hours and 45 minutes for the first scan Indomitable name of Damadian’s whole body scanner. ENCODING DATA Trisha Jane Andriane D. Pardillo, RRT RAYMOND DAMADIAN The crude image, reconstructed first with colored pencils and then by computer from 106 data points, revealed a two- dimensional view of Minkoff's chest — including his heart and lungs. Damadian trumpeted Indomitable's success to the media, asserting, perhaps a bit rashly, in a July 20,1977 press release that titled "a new technique for the nonsurgical detection of cancer anywhere in the human body has now been perfected.“ Even then, the machine was still in progress and too slow THE EQUATION Trisha Jane Andriane D. Pardillo, RRT MEDICALLY PRACTICABLE With Lauterbur’s concept and Mansfield’s experiments, the MRI era begins in the clinical world. In his writings, Paul Lauterbur reflects on how the idea of the MRI came to him at a Pittsburgh Eat’n Park Big Boy Restaurant, with the MRI’s first model scribbled on a coffee bar table napkin, while he was a student and researcher. Meanwhile, Sir Peter Mansfield came up with the inspiration that would advance the dream of MRI during a break in the tea room of the Physics Department at the University of Nottingham. THE EQUATION Trisha Jane Andriane D. Pardillo, RRT HOW? Mansfield took Lauterbur’s initial work a step further at the University of Nottingham, replacing the slow projection- reconstruction method with a method that used frequency and phase encoding by spatial gradients of magnetic field. He further developed the utilization of gradients in the magnetic field and showed how the radio signal from MRIs could be mathematically analyzed, which made it possible to develop a useful imaging technique. THE EQUATION Trisha Jane Andriane D. Pardillo, RRT THE CONTROVERSY Despite Dr. Damadian's contribution to medicine, widespread peer acceptance, and now the Nobel prize, have eluded him. He has taken a typically defiant stance and to voice his recent disappointment, he took out several full-page advertisements in the Washington Post, the New York Times, and a Swedish newspaper, Dagens Nyheter, after the announcement was made. He has allowed me to provide a smaller version of this for the Irish Medical Times. WHY MRI? ADVANTAGES Best low contrast resolution (main advantage) No ionizing radiation Direct multiplanar imaging No bone or air artifact Direct flow measurements Totally noninvasive CM is not necessarily required and relatively safer than iodinated CM MRI VS CT COMPARISON BETWEEN MRI AND CT SCAN MRI CT Non - Ionizing radiation Use of ionizing radiation Generally considered safe for Not desirable for pregnant patients pregnancy and pediatric patients Better suited for imaging the CNS, Better suited for visualization of soft tissues and in the evaluation of bone, lungs and in oncology ligaments and tendons MRI VS CT COMPARISON BETWEEN MRI AND CT SCAN MRI CT Capable of generating in several planes Capable of generating images in planes Generally needs a longer imaging time Generally needs shorter imaging time Scanner and hence imaging Scanner and hence imaging investigation are very expensive investigation are not very expensive MRI VS CT COMPARISON BETWEEN MRI AND CT SCAN MRI CT Contraindicated in patients with Can be performed to patient with metal implants implants WHY MRI? DISADVANTAGES Cost of the scanner High cost limit its universal availability More expensive than other procedures Not very useful in the assessment of bones Contraindicated to patient with claustrophobia (sedation is required) Contraindicated to patients with metal implants TIMES OF MILESTONE DEVELOPMENT OF AN MRI SCANNER In 1974, selective excitation or sensitization of tomographic image slice was invented by Sir Peter Mansfield’s group In 1975, Richard Ernst’s group invented the two dimensional Fourier Transformation 1977- Mansfield Examines the MRI Finger 1978-Mansfield Examines the MRI Abdomen Around 1984, General Electric introduced high field 1.5 Tesla systems 1990 FMRI 1991: Richard Ernst for his contributions to the development of the methodology of high resolution nuclear magnetic resonance TIMES OF MILESTONE DEVELOPMENT OF AN MRI SCANNER In 1974, selective excitation or sensitization of tomographic image slice was invented by Sir Peter Mansfield’s group In 1975, Richard Ernst’s group invented the two dimensional Fourier Transformation 1977- Mansfield Examines the MRI Finger 1978-Mansfield Examines the MRI Abdomen Around 1984, General Electric introduced high field 1.5 Tesla systems 1990 FMRI 1991: Richard Ernst for his contributions to the development of the methodology of high resolution nuclear magnetic resonance  Trisha Jane Andriane D. Pardillo, RRT MRI THE BASICS STEPS OF MRI FUNDAMENTALS OF MRI ELECTROMAGNETISM OERSTED LAW OF INDUCTION FARADAYS LAW OF INDUCTION MRI ACTIVE NUCLEI: - Odd atomic number - Even atomic number FUNDAMENTALS OF MRI RATIONALE The spin of hydrogen atom is ½ Nuclei with odd numbers are said to be MR ACTIVE FUNDAMENTALS OF MRI 1. HYDROGEN NUCLEI AS MAGNETS FUNDAMENTALS OF MRI 2. PRECESSION FUNDAMENTALS OF MRI 2. PRECESSION LARMOR EQUATION fo = γ Bo FUNDAMENTALS OF MRI 3. TRANSEVERSE MAGNETIZÅTION FUNDAMENTALS OF MRI 3. TRANSEVERSE MAGNETIZÅTION FUNDAMENTALS OF MRI RESONANCE FUNDAMENTALS OF MRI 4. RELAXATION Section 02 Trisha Jane Andriane D. Pardillo, RRT TYPES OF MAGNETS USED IN MAGNETIC RESONANCE IMAGING TYPES OF MAGNET PERMANENT MAGNET A magnet whose magnetic field originates from permanently ferromagnetic materials (permanent magnets) to generate a magnetic field between the two poles of the magnet. There is no requirement for additional electrical power or cooling, and the iron-core structure of the magnet leads to a limited fringe field and no missile effect. Due to weight considerations, permanent magnets are usually limited to maximum field strengths of 0.3 T-.5T. ( old books.2T-.3T) MF: 50-10ppm The main disadvantages of a permanent magnet are the cost of the magnet itself and supporting structures and the varying changes in the magnetic field. Field homogeneity and limitation can be an on-going problem in permanent magnets and the weight 20-100tons TYPES OF MAGNET PERMANENT MAGNET A magnet whose magnetic field originates from permanently ferromagnetic materials (permanent magnets) to generate a magnetic field between the two poles of the magnet. There is no requirement for additional electrical power or cooling, and the iron-core structure of the magnet leads to a limited fringe field and no missile effect. Due to weight considerations, permanent magnets are usually limited to maximum field strengths of 0.3 T-.5T. ( old books.2T-.3T) MF: 50-10ppm The main disadvantages of a permanent magnet are the cost of the magnet itself and supporting structures and the varying changes in the magnetic field. Field homogeneity and limitation can be an on-going problem in permanent magnets and the weight 20-100tons TYPES OF MAGNET PERMANENT MAGNET TYPES OF MAGNET ELECTROMAGNETS OR RESISTIVE SYSTEMS A type of magnet that utilizes the principles of electromagnetism to generate the magnetic field. Typically large current values and significant cooling of the magnet coils is required. The resistive magnet does not require cryogens, but needs a constant power supply to maintain a homogenous magnetic field, and can be quite expensive to maintain. Resistive magnets fall into two general categories - iron-core and air-core. Less than. 3T TYPES OF MAGNET ELECTROMAGNETS OR RESISTIVE SYSTEMS TYPES OF MAGNET ELECTROMAGNETS OR RESISTIVE SYSTEMS TYPES OF MAGNET ELECTROMAGNETS OR RESISTIVE SYSTEMS TYPES OF MAGNET SUPERCONDUCTING MAGNET TYPES OF MAGNET IN TERMS OF FIELD STRENGTH Types of magnets in terms of field strengths Ultrahigh field (4-7 Tesla)- used for research High field (1.5-3 Tesla) Midfield (0.5-1.4 Tesla) Low field (0.2-0.4 Tesla) Ultra Low field (1500 ms Short TR: 80 ms Short TR: