Study Mri 2021

There are two types of motion exhibit by the electrons?

A) Spinning on its own axis B) Orbiting the nucleus Electrons will rotate over their axis (spin) and orbit around the atom's nucleus. (like the earth spin.

magnetization susceptibility classification of subtances;

Magnetic susceptibility refers to the degree of magnetization of a substance. Substances can be classified based on their magnetic susceptibility as: • Diamagnetic • Paramagnetic • Superparamagnetic • Ferromagnetic

What is the definition of; Vectors: Resonance:

Measure both a magnitude and force is a phenomenon that occurs when an object is exposed to an oscillating perturbation that has a frequency close to its natural frequency of oscillation.

Nuclear magnetic resonance; There are three basic requirements to produce an MR Image:

Nuclear magnetic resonance happens at the nucleus of the atom spin. Atomic nucleus that spin (odd mass number) can emit and absorb energy if it is transmitted at the same resonating frequency. An abundant atom with an odd mass number. External magnetic field (Magnet). External Radiofrequency Source (RF Pulse).

the right-hand rule

the right-hand rule establishes a relationship electric field and magnetic field electromagnetic. The thumb indicated the direction of the moving charge particle (electron in electricity). The other four fingers indicate the direction of the magnetic field (magnetic lines)

What is the definition for; (phase-coherent): spin interactions:

they get in-phase (phase-coherent),which means that they all get together at the same point on the precessional path. spin interactionstons, they will start to spread out in the transverse plane or lose phase-coherent (out of phase).

What is the definition of; Matter: Energy:

-Anything found in our surroundings composed of atoms and other energy phenomena such as sound or light. -the ability to do work. Energy never disappears, it can be transformed from one state to another.

Contrast agent: T1 agent:

-Gadolinium (Gd) is a rare earth metal (heavy metal) found in the periodic table's lanthanide series. behaves as a paramagnetic substance. Gadolinium-based contrast media is administered via intravenous (IV). When gadolinium is in the bloodstream, it reaches the body tissues via the blood. . When gadolinium gets into the tissues, it reduces their T1 relaxation time and makes them appear bright on the image. Gadolinium contrast agents are mainly used to help diagnose tumors, inflammatory conditions, and infection processes. -Contrast agents shorten the tissue relaxation times of both T1 and T2. Based on their combined with, they are classified as T1 agents or T2 agents. T1WI, water appears dark. When a T1WI is performed, both the lesion and the edema tend to appear dark on the image; this makes it very difficult to detect any tissue abnormality in T1WI.

Some property of magnets are; What is Magnetic flux's;

-Magnetism is a property of the more notorious characteristic to attract ferromagnetic material (iron). the magnets are having two poles, positive (+) and negative (-), and that they pose a magnetic field (magnetic flux). >Poles with different charges (polarity) will attack each other (positive and negative) >Poles with the same charge (polarity) will repel each other (positive and positive or negative and negative) -They are responsible for the magnet polarity. will always exit through the north pole of the magnet and enter by the south pole.

Motion in the Atom: the most abundant atom in the human body:

-Protons (+) will rotate (spin) over their axis -Neutrons (No charge) will rotate (spin) over their axis -Electrons will rotate over their axis (spin) and orbit around the atom's nucleus -"The most abundant atom in the human body is hydrogen, but there are other elements such as oxygen, carbon, and nitrogen"

What is the definition of; Motion: Electricity:

-Refers to the shifting, locomotion, or flow of one unit or object from one point to another. Motion is the result of applied force in a specific direction According to Newton's second law, an object's acceleration depends on its mass and force applied -the presence and flow (movement) of electric charge (electrons).Electricity permits the creation and reception of electromagnetic radiation, such as radio waves. (electricity charged particles that are electrical)

Spin Echo Contrast Summary Gradient Echo Contrast Summary FA AND T1

-Selecting the correct range of parameters is crucial to producing the desired image contrast in Spin Echo pulse sequences. (500-2500) Spin echo is TR Control contrast -In gradient echo, the scan times are drastically reduced, enabling high-speed pulse sequences.The use of partial FA reduces transverse magnetization, affecting the receiver coil's amount of signal collected. Very short TR (short) in combination with FA of 90 degree can result in tissue saturation. (Less then 50-100ms) For saturation to stop we need to use flip angles shorter then 90 Short flip angle in gradient echo is between 5 to 10 degree. And long flip angles between 70 to 100 degree. Echo TR and flip angle control the contrast. -the use of short FA minimizes differences based on T1 Saturation effects is "T1"

Discribe; Flip Angle (FA) The Flip Angle of the protons depends on:

-The flip of the hydrogen protons (vector M) away from the longitudinal axis -how long (time) the RF pulse is on. The longer the time, the longer the flip angle.In MRI, we use different flip angles for other purposes; some of the most common are 90° and 180°. If a 90° FA is used, protons will be in the transverse plane. If a 180° FA is used, protons will be in the longitudinal axis but antiparallel orientation. RF on for 1 second is 45 degree FA RF on for 2 second is 90degree FA RF on for 3 second is 135degree FA RF on for 4 seconds is 180degree FA

The spin net of; even mass number Proton and neutrons:term-40 odd number of Proton and neutrons:

-caused by an even number of protons and neutrons, half of the nucleons spin in one direction and half in the other. The forces of rotation cancel out, and the nucleus itself has no net spin. -odd number of both protons and neutrons, the spin directions are not equal and opposite, so the nucleus itself has a net spin or angular momentum."

What is the definition of; Electromagnetic radiation: Electromagnetic is is expressed in:

-happens when energy is emitted or absorbed in the form of a charged particle that exhibits wave- like behavior as it travels through space. two different waves: electric wave magnetic wave each of them if perpendicular 90degree from the other -Electromagnetic radiation is usually expressed in Hertz (Hz) units, where 1 Hz = 1 cycle per second. 1 Hz = 0.001 Kilohertz (KHz) 1 Hz = 0.000001 Megahertz (MHz) 1KHz=1,000Hz 1MHz = 1,000,000 Hz

Zeeman interaction is; For hydrogen nuclei, there are only two possible energy states;

-interaction of magnetic moment with external magnetic field and is "cause a discrete number of energy states" -Low-energy nuclei do not have enough energy to oppose the main B0 field "These are nuclei that align their magnetic moments parallel or spin-up to the main B0 field in the classical description. High-energy nuclei do have enough energy to oppose the main B0 field. These are nuclei that align their magnetic moments antiparallel or spin-down to the main B0 field in the classical description

T1 WEIGHTED T2 Weighted PD WEIGHTED IMAGES

-maximize T1, a short TR (500 ms) is required. minimize T2, a short TE (10 ms) is the choice. Tissue w/ high water will appear dark and tissues w/ lower water will be bright -To maximize T2, a long TE (100 ms or higher) is required. Bright • To minimize T1, a long TR (2500 ms or higher) is the choice. tissues with fat content appear dark or hypointense (subcutaneous fat) and Tissues with higher water content (Gray matter 86% water) bright. -Proton Density (PD), the goal is to minimize contrast differences based on T1 and T2. • To minimize T2, a short TE (10 ms) is required. • To minimize T1, a long TR (2500 ms or higher) is the choice. Every bright for both

What is the proton precessional frequency formula called? Describe the Larmor equation?

-this formula is called the Larmor Equation. -The Larmor equation establishes a relation between the magnetic field's strength (B0) and the gyromagnetic ratio of an MRI active Nuclei. All MRI active nuclei will have their own Gyromagnetic Ratio (constant for each element).

What is the structure of an Atoms; What is the atomic # and Mass #?

-three subatomic structures: protons(+) electrons(-) and neutrons(0) -The atomic number is the number of "protons" -The mass number is the number of "protons" plus the number of "neutrons" in the atom's nucleus.

The chemical shift between hydrogen in fat and hydrogen in water can be calculated by multiplying the precessional hydrogen frequency by 3.5 ppm. 1T Precessional Frequency 42.6 x 3.5 = 148 1.5T Precessional Frequency 63.8 x 3.5 = 224 3T Precessional Frequency 128 x 3.5 = 448

1T Precessional Frequency 42.6 x 3.5 = 148 1.5T Precessional Frequency 63.8 x 3.5 = 224 3T Precessional Frequency 128 x 3.5 = 448

Fat: Water:

>low inherent energy because they can absorb more energy efficiently >molecules are closely packed or more compact, making the transfer of power easier or faster between them. > the chemical shift, hydrogen in fat molecules (CH4) precesses at the same frequency as individual hydrogens (H). These similar precessional frequencies made the transfer of energy in fat molecules very efficient or fast. Water: >(H20) molecules have a high energy level, making transferring energy slow or less efficient >molecules are separate or spread; thus, energy needs to travel more spaces between the molecules, making the transfer of energy in water inefficient or slow. > water molecules (H20), hydrogen protons precess faster (chemical shift) than hydrogen alone (H). Thus, the transfer of energy in water molecules is slower or less efficient than in fat molecules.

Image Weighted

All tissues have their T1 and T2 relaxation times; these relaxation times directly impact the image's contrast. The term weighted comes from weight and establishes which relaxation time, T1, or T2 contributes the most to the image's difference

The primary source of magnetic field inhomogeneities is Eddy Currents.

An eddy current is a small electrical current caused when a moving magnetic field intersects a conductor, or vice-versa. This circulating flow of electrons (motion and charge), or current, will generate a secondary magnetic field. Some eddy currents in the magnetic field include the patient, the gradient magnetic field, and the RF coils.

T1 relaxation is a process characterized by releasing energy. (Intrinsic)

During T1 relaxation, tissues give up the energy received from the 90 RF pulse. Since T1 relaxation is characterized by removing energy, longitudinal or T1 relaxation happens faster in fat compared to water. the fat release energy faster and are said to have a SHORT T1 time. Tissues like water take more time to release energy and are said to have LONG T1 relaxation time. Fat= T1 short / T2 short Water=T1 Long /T2 long

The most important MR active nuclei are with their mass number: • Hydrogen •Nitrogen •Fluorine •Sodium • Oxygen • Carbon MRI Element (Atom) most common in the human body ISOTOPE: Oxygen Carbon Hydrogen

Example of mass number • Hydrogen (H2) •Nitrogen (N15) •Fluorine (F19) •Sodium (Na23) • Oxygen (O17) • Carbon (C13) The Oxygen atom has a mass number of 16 and spin 5/2 Two isotopes Oxygen 17 and Oxygen 18, most Oxygen found in the human body is Oxygen 16; this will put Oxygen out of the list of atoms we need. The Carbon atom has a 12-mass number AND spin 1/2 two isotopes, Carbon 13 and carbon 14; most of the Carbon found in the human body is Carbon 14. The Hydrogen atom mass 1 AND spin (1/2). Their is 3isotopes, Hydrogen 1 (protium) Hydrogen 2 (deuterium), and Hydrogen 3 (tritium). Protium or Hydrogen 1 (H1) is the hydrogen isotope found in the human body.

Lipids (fats)

Fat can be found in different forms in the body: • Phospholipids• Glycolipids• Cholesterol Fat or adipose tissue can be found in: Subcutaneous fat (More often in the abdominal and trunk area in general) Bone marrow (within the bone) Between the organs Inside the organs

Gradient Echo

Gradient Echo -essential type of pulse sequence. -The primary use of Gradient Echo pulse sequences is to scan faster (reduce scan time). - Gradient Echo is also known as Field Echo (FE) or Gradient Recall Echo (GRE).

MR-Active Nuclei. Another name for Hydrogen is;

MR-active nuclei have a net electrical charge (electric field) and are spinning (motion), and, therefore, automatically acquire a magnetic field. this magnetic field in the nucleus is known as magnetic moment. Proton or Spin

Magnetization To understand magnetization, we will break it into its two components: Longitudinal magnetization Transverse magnetization

If a 90° FA is used, protons will be in the transverse plane. - XY axe Transverse Relaxation is also known as T2-Relaxation, this is loosing of the phase- coherent or decay of transverse magnetization -the spin-spin interactions (protons crashing into each other and transferring energy). -T2-Relaxation is defined as the time required for transverse magnetization to decay to 37% of its original value. If a 180° FA is used, protons will be in the longitudinal axis -Z-axis -Longitudinal Relaxation is also known as T1-Relaxation, this is the 63% regrow in the longitudinal axis -Longitudinal Relaxation is also known as Spin-Lattice Relaxation because of loss of energy. T1-Relaxation is defined as the time required for longitudinal magnetization to regrow 63% of its original value.

Raymond Damadian

In the early 70's, Raymond Damadian (State University there are different T1 relaxation times between normal and abnormal tissues of the same type, as well as between different types of normal tissues.

T2 weighted image

Instead of using a 180 RF to rephrase proton in the transverse plane a gradient is used for this purpose GRE Images are under the effect of magnetic susceptibility, magnetic field inhomogeneities, and chemical shift Because of it there is no T2 in GRE the is only T2* T2* is also controlled by TE SE T2=BRIGHT FLUID AND DARK FAT SE T2*=BRIGHT FLUID AND DARK FAT Minimize T2* long TR and flip angle(5-10MS) Maximize T2* long TE (25ms)

Water in the body

Intracellular:(2/3 of body water) the water inside the cell membrane (cytoplasm) Extracellular fluid (1/3 of body water). It can be found in three areas:(blood) Transcellular fluid (Contained inside organs): ➢ Urine inside the bladder ➢ Bile inside the gall bladder ➢ The cerebrospinal fluid inside the ventricular system

Magnetic moments Vs. hydrogen nucleus Bo orientation is;

It is the magnetic movement of hydrogen is that align with Bo not hydrogen nucleus. the hydrogen nucleus only spins but don't change direction. the direction and strength of the magnetic field.

Describe how these protons flip

Once they start to receive the RF pulse, they begin to expand their precessional path and move towards the transverse plane; if the RF pulse is left on long enough (90°), protons will reach the transverse plane, but they keep on precessing through the XY axis (transverse plane). As they move to the transverse plane, they start to fan-out (spread the precessional path) until they reach it.

What is the precessional frequency of Hydrogen in a 1T Magnet? What is the precessional frequency of Hydrogen in a 1.5T Magnet? What is the precessional frequency of Hydrogen in a 3T Magnet?

Precessional Frequency = 1T x 42.57 MHz = 42.57 MHz/T Precessional Frequency = 1.5T x 42.57 MHz = 63.86 MHz/T Precessional Frequency = 3T x 42.57 MHz = 127.71 MHz/T

What is the equation and the different nuclide gyromagnetic radio? the Larmor equation

Precessional Frequency = Magnetic Field (B0 exp:1.5T,3T) x Gyromagnetic Ratio (γ) ω0 = γ X B0 Nuclide gyromagnetic radio(MHz) Hydrogen 1 =42.57MHz Fluoride 19 =40.05MHz Phosphorus 31 =17.24MHz Sodium 23 =11.26MHz

Proteins By mass number which one weights more? And by Atomic number weights more? Oxygen Carbon Hydrogen Other

Proteins' general functions include structural enzymes, hormones, antibodies, fluid balance, acid-base balance, transport, communication, etc. mass number Oxygen 65%, Atomic number Hydrogen 65%

PD weighted image

Proton Density (PD), the goal is to minimize contrast differences based on the T2 and minimize the contrast differences based on To minimize T2*, a short TE (5-10 ms) is required. • To minimize T1, a long TR (100 ms or higher) and a short FA (5-20) is the choice. the tissues' signal intensity depends on the number of protons (hydrogens) present on the tissues.

Relaxation Key Point

Relaxation Key Point T1 or longitudinal Relaxation occurs through an increase of the longitudinal magnetization, while transverse or T2 or Relaxation occurs through a decrease in transverse magnetization. On a subatomic level, T1 Relaxation occurs through the dissipation of energy (spin-lattice), while T2 Relaxation occurs through the loss of phase coherence (spin-spin interactions). T2 Relaxation happens at a faster rate compared to T1 Relaxation. As the magnetic field strength increases, T1 relaxation time increases, and T2 Relaxation remains the same.

What is Relaxation in MRI During Relaxation, two main events happen

Relaxation is the term used in MRI to refer to the return to thermal equilibrium after the RF-FA.After 90 RF pulse, protons are in phase in the transverse plane. When the RF pulse is off is known as Relaxation first, the protons will release energy, and second, they will lose phase coherent.

Net Magnetic Vector (NMV)

Represents the difference between the parallel and antiparallel protons. Vector M is always in the same direction as B0 because more protons are aligned in parallel orientation.

T1 and T2 image weighing are two of the most common contrasts in MRI.

T1 contrast is achieved by maximizing differences based on T1 relaxation. • T2 contrast is achieved by maximizing differences based on T2 relaxation. TR control= T1 TE control= T2 TR will control T1 relaxation=the amount regrow the in the longitudinal axis before the next flip angle FA. TE will control T2=the amount of decay 37% in the transverse plane The longer the TR, the more T1 relaxation before the next FA. Maxizes The shorter the TR, the less T1 relaxation before the next FA.minized

Short TR maximizes T1 differences* Long TR Minimizes T1 differences*

T1 differences can be maximized or minimized. Using short TE maximizes differences based on T1 or different between contrast. A short TR allows tissues with short T1 times (fat) to recover in the longitudinal axis. After the second 90 FA, fat has a strong component in the transverse plane while water has a week one. Since the signal is recorded in the transverse plane, strong signal intensity is collected from fat and almost no water signal. Short TR (500 ms) MAXIMIZING signal differences between fat (hyperintense or bright) and water (hypointense or dark). T1 time 200ms at TR of 500ms Fat is 90% T1 time 2200 ms at TR of 500ms water is 10% -The longer the TR, the more time the tissues with long T1 (Water) can catch up. A long TR is considered over 2500 ms. The T1 time of water is 2200 ms. After 2500 ms, water has also recovered its T1 are minimized. After the second 90 FA, fat has a strong component in the transverse plane, while water also has a strong part. Since the signal is recorded in the transverse plane, strong signal intensity is collected from fat and water, MINIMIZING differences. In this case, both fat and water will be bright or hyperintense on the image. -Fat is strong it will be components into bright or white.hyperintense -Water is weak the components are black. hypointense

T2 relaxation, After the 90 RF is shut off, protons start to defense in the transverse plane (T2 relaxation). (Intrinsic)

T2 dephase of spin spin interactions that causes exchange of energy or transfer of energy fat dephase FASTER than hydrogens in water. T2 relaxation in fat is FASTER or SHORTER than T2 relaxation in water. Tissues have T2 relaxation when they have decayed to 37% of its original value. Fat= T1 short 200ms/ T2 short 70ms Water=T1 Long 2200ms /T2 long 1000ms

T2 and TE

T2 weighted is manipulated by TE TE control the magnetization and T2 relaxation is the result of the protons dephasing in the transverse plane. Fat decay faster then water because they reach that 37% faster. The shorter the TE, the less T2 relaxation, the stronger the transverse magnetization and stronger tissue signal (bright) A short TE MINIMIZE signal differences between them, fat appears bright (hyperintense), and water is also bright (hyperintense).* A long TE is used, T2 differences are MAXIMIZE. The longer the TE, the more time for the tissues to dephase.* The longer the TE, the more T2 relaxation before reading the signal, resulting in less signal intensity coming from the tissues (dark).

the contrast on spin echo sequences, TR and TE ( extrinsic)

TR and TE can be manipulated by the MRI operator. SE pulse sequences always use a 90o FA and 180° rephrasing pulse and then we collect the signal. TR repetition time= between applications and is TR is measure in millisecond. Long TR:more than 2500 Short TR: 300-700ms TE echo time=time between applying in the 90 flip angle and collecting of echo to get MRI signal. TE short: 10 -25 ms TE long: 90-120

The two most essential time intervals in a spin-echo pulse sequence are the TR Repetition Time and TE Echo Time.

TR stands for Repetition Time, and it is the time between the application of the flip angles (90). TE is the Echo Time, and it is the time between the application of the 90 pulses (FA) and 180 the collection of the Echo (MR signal).

Remember that we are using only the protons in parallel orientation (low energy state). As they absorb the RF Pulse's energy, they start to gain energy and start flipping away from the longitudinal axis (away from parallel orientation). TRUE OR FALSE Discribe; Flip Angle (FA) How can protons resonate?

TRUE The flip of the hydrogen protons (vector M) away from the longitudinal axis 90 degree Radio Frequency (RF) pulse must be applied perpendicular to the protons (longitudinal axis) for protons to resonate.

What is definition and equivalent; Tesla (T) or Gauss (G)

Tesla (T) or Gauss (G)One Tesla is equivalent to ten thousand Gauss Testa is the Mri straight and gauss is the measurement of the strength of the magnetic field.

MRI signal

The MR signal depends on the amount of transverse magnetization; the more potent the transverse magnetization, the stronger the MR signal. As the transverse magnetization decays (T2 Relaxation), the signal becomes weaker. MFree Induction Decay (FID)

Describe the following terms; Net Magnetization Vector or Vector M.: MRI to produce the images:

The Net Magnetization Vector (NVM) or Vector (M) represents the difference between the parallel and antiparallel protons. Vector M is always in the same direction as B0 because more protons are aligned in parallel orientation."longitudinal plane or z-axis" The more parallel protons, the stronger the Vector M, and more information (Signal) is obtained from the patient tissues.

RF coil: There are two types of coils and their function:

The RF coil is nothing else than a solenoid placed perpendicular to the transverse plane.The RF coil captures the transverse magnetization while it passes through it (the MR signal). the one that collects the signal called the Receiver coil and another used to transmit the transmitter's the RF coil. The receiver coil's proximity to the signal's source (patient's tissues), the stronger the signal captured. It is imperative to always position the receiver coils as close as possible to the patient.

How to make the signal to last longer in the transverse plane?

The first technique invented to make the transverse magnetization last longer was sending a second RF pulse to the protons while in the transverse plane; this second RF would be 180 degrees. As we already know, protons start to dephase in the transverse plane after the 90 pulses are turned off; some begin to speed-up and others to slow-down; these will place the protons at different positions along the precessional path in the transverse plane. If we send a second RF pulse of 180o, protons will flip their magnetization 180 degrees. Still, they will continue to be in the transverse plane; after the 180 pulses, the protons that were ahead will be placed behind. The ones behind are now ahead; if we wait the same time between applying the 90 FA and the180 pulse, all protons will be in phase again.

Gradient

The gradient reduces the magnetic field over the area of the protons that are precessing faster; this will reduce their precessional frequency, making them slow down. The protons' rephasing happens much faster in gradient echo because the gradient has a mechanical effect over protons; right after applying, the gradient's protons is in-phase. In Spin Echo, after the application of the 180, we must wait a certain amount of time for the protons to regain phase-coherent, making the rephasing slower than GRE. GRE's Gradient application does not compensate for the dephasing mechanism (chemical shift, magnetic susceptibility, and magnetic field inhomogeneities); there is no T2, only T2* in GRE.

isocenter Parts Per Million (ppm) One ppm is equivalent to:

The isocenter is the center point of the magnetic field, located in the middle of the magnet's bore. As we move away from the magnet's isocenter, local magnetic field inhomogeneities start to increase. Parts Per Million (ppm) is the unit used to measure the magnetic field homogeneity; ppm is a way of expressing very dilute concentrations of a substance like(water or soil). Just as a percent (%) means out of a hundred, ppm means out of a million. One ppm is equivalent to 1 milligram of something per liter of water (mg/l) or 1 milligram of something per kilogram of soil (mg/kg).

What is the definition of; non-ionized ionization

The number of protons within the atom's nucleus is usually equal to the number of electrons; atoms with these characteristics are neutral atoms (non-ionized). Atoms can gain or lose electrons; this phenomenon is called ionization. Ionization results from the liberation of enough kinetic energy to liberate an electron from an atom, ionizing it.

Free Induction Decay (FID) T2* is the result of three factors called Dephasing Mechanism.

The quick fall-off of the MRI signal is known asFree Induction Decay (FID); the time that takes for the FID to happen is called T2 T2* is the result of three factors called Dephasing Mechanism. Local Magnetic Field Inhomogeneities Magnetic Susceptibility Chemical Shift is like T2, but it happens even faster; the start next to the T2* means that three other factors are accelerating the transverse magnetization(T2 relaxation)

There are two different types of magnets: Permanent magnets: Electromagnets:

There are two different types of magnets: Permanent magnets: This type of magnets is usually created by magnetizing ferromagnetic material such as iron, nickel, or cobalt .Electromagnets: They use electricity togenerate a magnetic field.

MRI is an external Radio Frequency (RF) Source.

This RF source is known as RF Pulse. The RF pulse used in MRI is a type of electromagnetic radiation.

A magnetic field (magnet), it will experience two forces: Torque, Rotational or Alignment force: Projectile or transactional foterm-52rce:

Torque, Rotational or Alignment force: is the first force experienced. It is characterized by an object's "tendency to be aligned with the external magnetic field, the poles' alignment (north with south). Projectile or transactional force: Second force, characterized by an "object's tendency to be attracted by the magnetic field" (moves towards the magnet).

T1 contrast in GRE

Variable flip angle will impact image contrast Variable FA are used to conjunction with the TR to increase or decrease the tissue saturation effects or T1 effects Maximize T1 in GRE means the same than maximize saturation effect Minimize T1 in GRE means the same than minimize saturation effect To maximize T1 contrast GRE SHORT TR (less than 50ms) Long FA (70-110) To minimize T1 contrast GRE Long TR (100ms) Short FA (less then 20)

The components of a wave are: What is the definition of; electromagnetic spectrum Radiation

Wavelength: The spatial period (distance) between two consecutive corresponding points of the wave (crest to crest). Amplitude: it is the height of the wave, and it is measured from the baseline to the crest. Frequency: how many waves complete their full cycle in one second (cycles per second). -The Electromagnetic Spectrum is the display of all types of electromagnetic radiation based on their frequency.

tissue saturation

When tissues appear dark (no signal) on the image, they are said to be saturated. The use of very short TRs in GRE produces saturation effects on the tissues. When a very short TR is used combined with a long flip angle (90), tissues can become saturated. Even tissues with very short T1 times (fat) can become partially saturated with the use of very short TRs. The shorter the TR, the more saturation effects, and less SNR on the image. IF very short TRs are used, all tissues can become saturated.

MRI High signal or hyperintense are translated; MRI low signal or hypointense are translated; The same signal;

White or bright Dark Isointense refers to tissue that have the same signs, intensity

Thermal Equilibrium

after the protons are placed under the effect of the external magnetic field, they align with it (longitudinal axis) and start to precess.This moment is known as Thermal Equilibrium.

What is the definition of; Molecules: Isotopes:

are the result of the union of two or more atoms by chemical and electromagnetic bonding. Variants of a particular chemical element which differ in neutron number or Isotopes are atoms that gain or loose neutron

MR, image contrast The factors that affect image contrast in diagnostic imaging are usually divided into two categories: Intrinsic and extrinsic contrast:

can be defined as the ratio of the transverse magnetization of one tissue to another tissue's transverse magnetization at a given moment in time. • Intrinsic contrast parameters= are inherent to the body's tissues and cannot be changed or manipulated by the MRI Technologist. T1 recovery or relaxation time, T2 decay or relaxation time, and the Proton Density or number of protons on the tissues. • Extrinsic contrast parameters=can be changed or manipulated by the MRI technologist to produce changes in the image. The extrinsic contrast parameters can be used to alter or manipulate the contrast of the picture. They include the Repetition Time (TR), Echo Time (TE), and Flip Angle (FA). By knowing the intrinsic contrast parameters' behavior and manipulating the extrinsic contrast parameters, the MRI technologist can produce various contrasts on the image.

T2 Contrast agent

combination with T2WI. They are based on a superparamagnetic molecule that also reduces the relaxation time of the tissues.the tissue relaxation times even more than the T1 agents. T2 agents are also known as negative contrast agents because of signal enhancement. T2WI is excellent in detecting tissue abnormalities. Since the pathology and edema are brilliant, it is difficult to determine the exact extent and location of the lesions themselves using T2WI. Most T2 agents used today are Oral and are classified as intraluminal agents

"What makes a proton spin and why is it charged?"

consist of quarks that are particles that make up protons and neutrons, each quarks "of alignment and spin" "The proton consists of three spinning quarks. Two quarks spin up and the other spins down. " Spin up +2/3 and down -1/3 +2/3+2/3-1/2=1

1973, Paul Lauterburp

described a new imaging technique that he termed Zeugmatography. the magnetic field, this By utilizing gradients in technique was able to produce a two- dimensional image (back-projection described a new imaging technique that he termed Zeugmatography. • the magnetic field, this By utilizing gradients in technique was able to produce a two- dimensional image (back-

Felix Bloch & Edward Purcell

developed Felix Bloch and Edward instruments, which could measure the magnetic resonance in bulk material such as liquids and solids. (Both honored with the Nobel Prize for Physics in 1952.NMR SPECTROSCOPY developed a complicated equation for predicting the MR signal intensity from a tissue subject to a spin-echo sequence.

Substances with these characteristics are classified as • Diamagnetic • Paramagnetic • Superparamagnetic • Ferromagnetic

diamagnetic substances. Diamagnetic substances are usually opposed or repelled by the external magnetic field. Examples of diamagnetic substances include Gold, Platinum, Silver, Titanium. These substances do not have a magnetic moment and are not affected by an external magnetic field. Paramagnetic substances are those that have an odd number of electrons on their electrons shell. If there are three electrons, two will be in one direction and one in the other; this generates a magnetic force in the two's direction. These substances will have a small magnetic moment, and they will experience a little attraction by an external magnetic field. Examples of these substances include Gadolinium, Magnesium, Oxygen and Lithium. Ferromagnetic Substances are usually the result of a larger number of electrons in one direction, and this can be the result of ionization and other factors. These substances will have a powerful magnetic moment, and they will respond very strongly (attraction) to the presence of an external magnetic field. Most of these substances will retain their magnetization once they are removed from the external magnetic field. Examples of these substances include Iron, Cobalt, and Nickel. Superparamagnetic substances have a more potent magnetic moment than paramagnetic substances but a weaker magnetic moment than ferromagnetic substances. They have a larger number of electrons in one direction compared to paramagnetic substances but less than ferromagnetic. They are mostly related to molecules that contain iron (not pure iron). These molecules usually are the result of a combination of paramagnetic and ferromagnetic substances. Examples of these substances include Iron Oxide, Ferritin, and Hemosiderin (these last two result from the breakdown of blood). Remember that blood contains hemoglobin, and there is lots of iron in the hemoglobin molecule; As hemoglobin breaks down, its magnetic susceptibility increases.

Sir Joseph Larmor (1857-1942)

equation demonstrating that the angular frequency of Sir Joseph Larmor (1857-1942) developed the precession of the nuclear spins if proportional to the strength of the magnetic field.

Basics of atom

hydrogen is the most abundant element in the human body Nuclei that are available for MRI are those that exhibit a net spin As all nuclei contain at least one positively charged proton, those that also spin have a magnetic field induced around them An arrow called a magnetic moment denotes the magnetic field of a nucleus in classical theory"

Faraday's law of induction

is a basic law of electromagnetism that predicts how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF), a phenomenon called electromagnetic induction this law is based on the interaction of three (3) physical phenomena:• Motion• Charge• Magnetism

Chemical Shift Spin Echo (SE) MRI signal is called the "Echo."

is the third dephasing mechanism that accelerates the decay of the transverse magnetization. Chemical shift is the result of hydrogen protons precessing at different precessional frequencies. basic pulse sequence that exists. The application of these RF pulses (90 and 180), combined with times intervals, is called "Pulse Sequence

What is precession, precessional path, angular momentum, precessional frequency ?

protons are parallel to B0, that is not entirely true; protons are laid at an angle with B0. After they align with B0, they start to rotate around B0 This rotation is called precession. This precession will form a path around B0(longitudinal) called the precessional path. precessional path will depend on the angle between the proton magnetization and B0 (Angular Momentum) The angular momentum depends on the strength of the magnetic field B0. The stronger the magnetic field, the smaller the angular momentum. the speed at which they precess around B0(longitudinal) is called the precessional frequency or Larmor frequency.

Local magnetic field inhomogeneities magnetic field inhomogeneities.

re the result of small changes in the magnetic field. The magnets are built to be homogeneous; this means to have the same strength all over the magnetic field (no variations) the most homogeneous magnetic fields will have some degree of variation called magnetic field inhomogeneities.

There are several reasons why protons are out of phase;

some include spin-spin interactions, chemical shift, magnetic susceptibility, and magnetic field inhomogeneities.

Hydrogen alignment; hydrogen protons align into two groups or populations;

the hydrogen protons are randomly oriented in the absence of an external magnetic field. When exposed to the external magnetic field, they align themselves with the external magnetic field (B0) (Alignment or torque force). When this alignment takes place, hydrogen protons align into two groups or populations -parallel direction: One group aligns itself with the magnetic field (same orientation). Parallel protons are the ones with a low energy state. This group is also known as Spin-Up Protons. opposite direction: second group of protons aligns themselves in opposite direction of B0; this group is called antiparallel protons; they are the protons in a high energy state. This group is also known as Spin- Down Protons. *They are always more protons that align in parallel than in antiparallel orientation.

Magnetic movement in hydrogen when is not in and out the magnetic field: What is the classification of alignments:

the magnetic moments of hydrogen nuclei are randomly orientated and produce no overall magnetic effect. however, when placed in a strong static external magnetic field the magnetic moments of hydrogen nuclei orientate with this magnetic field. This is called alignment. Parallel alignment: Alignment of magnetic moments in the same direction as the main B0 field (also referred to as spin-up) and have low energy state. Antiparallel alignment: Alignment of magnetic moments in the opposite direction to the main B0 field (also referred to as spin-down) and have high energy After alignment, there are always more spins with their magnetic moments aligned parallel than antiparallel.

These gradients are applied in such a way that they will produce an increase of the magnetic field over the area where the protons are precessing slower in the transverse plane;

this increase of the magnetic field will have an increase of the precessional frequency over those slow protons making them start precessing faster. The gradient reduces the magnetic field over the area of the protons that are precessing faster; this will reduce their precessional frequency, making them slow down. Since slow protons are accelerated and fast protons are slowed down, they eventually will catch up with each other, and the transverse magnetization will be recovered.

What is the definition of; transverse plane longitudinal axis.

transverse plane the X and Y axes are located perpendicular to the B0 or Z axis Z represents the longitudinal axisXY represents the transverse plane.The X-axis is in the Left to Right direction ,Bo Y-axis is in the magnet's inferior or superior longitudinal axis. patient in a horizontal magnet, Z-axis will be in the patient's head to foot direction.

When evaluating an MRI, there are four key influences on the image that are taken into consideration.

• Image Contrast= is the ability to see different shades of gray.can differentiate tissues and pathologic processes by their color or signal intensity on the MR image. Mri contrast is also known as weighted or contrast to noise ratio. • Signal to Noise Ratio (SNR)= is the amount of signal VS. how much noise is collect by the RF COIL. A signal from the patient or the background noise in the environment. The more signal and less noise collected by the receiver coils, the higher the SNR and the better the image quality. One of the significant advantages of high SNR images is that SNR can be traded for Spatial Resolution and scan time. • Spatial Resolution=the ability of seen detail on the images.High spatial resolution images offer the ability to appreciate sufficient anatomic detail and small pathologies on the image. In low spatial images Resolution is usually not well defined and is called blurry images. • Scan Time=is not part of the image but is a critical aspect to consider when producing it. Reducing scan time can reduce patient anxiety, discomfort, and chances of motion during image acquisition. Also, short scan times can improve patient throughput and productivity. technologist must be careful when trying to reduce scan time because it can compromise image quality by affecting Image Weighting and reducing SNR and Spatial Resolution.

relaxation happened at different rates because of several factors: The molecular disposition of the tissues refers to; The molecular tumbling rate refers to;

• The energy of the tissue • The molecular disposition of the tissues • Molecular tumbling rate of the tissue the distance between the molecules. to how close the precessional frequency of hydrogen atoms is in a molecule compared to hydrogen atoms alone (H).

The regrow of longitudinal magnetization (T1 relaxation), and the decay of transverse magnetization (T2 relaxation) happened at different rates of time depending on several factors:

• The energy of the tissue= all tissues have different energy level high and low. • The molecular disposition of the tissues=refers to the distance between the molecules. Molecules more closely packed or spread. • Molecular tumbling rate of the tissues= precessional frequency of hydrogen atoms is in a molecule.