1. MRI provides multi-planar, multi-contrast images to study organ structure, function, metabolism, physiology and pathology in a non-invasive manner.
2. When certain atomic nuclei such as hydrogen protons are placed in a strong, static magnetic field, they align with the field. A radiofrequency pulse can then excite the aligned protons, causing them to emit radiofrequency signals as they relax back to equilibrium.
3. T1 relaxation is the recovery of longitudinal magnetization along the magnetic field axis, while T2 relaxation is the loss of transverse magnetization in the plane perpendicular to the magnetic field. Differences in T1 and T2 values between tissues provide image contrast.
Quality Assurance Programme in Computed TomographyRamzee Small
Introduction to Computed Tomography
Basic description of the components of a CT System
Introduction to Quality Assurance
Quality Assurance and Quality Control Tests in Computed Tomography base on frequency
Objective of QA/QC Test
Basic physics of multidetector computed tomography ( CT Scan) - how ct scan works, different generations of ct, how image is generated and displayed and image artifacts related to CT Scan.
Quality Assurance Programme in Computed TomographyRamzee Small
Introduction to Computed Tomography
Basic description of the components of a CT System
Introduction to Quality Assurance
Quality Assurance and Quality Control Tests in Computed Tomography base on frequency
Objective of QA/QC Test
Basic physics of multidetector computed tomography ( CT Scan) - how ct scan works, different generations of ct, how image is generated and displayed and image artifacts related to CT Scan.
MRI uses a strong magnetic field and radio waves to create detailed images of the organs and tissues within the body.
Developed by the Lauterbur in 1972 at Stony brook in New York.
MRI does not involve radiation
MRI contrasting agent is less likely to produce an allergic reaction that may occur when iodine-based substances are used for x-rays and CT scans
MRI gives extremely clear, detailed images of soft-tissue structures that other imaging techniques cannot achieve
The MRI machine cannot just simply “see the hydrogen nuclei which lie “hidden” in the water molecules distributed in the patient.
It needs to do ‘something’ to the hydrogen nuclei to detect their presence.
NMR, principle, chemical shift , valu,13 C, applicationTripura University
Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong, constant magnetic field are perturbed by a weak oscillating magnetic field (in the near field [1]) and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at the nucleus. This process occurs near resonance, when the oscillation frequency matches the intrinsic frequency of the nuclei, which depends on the strength of the static magnetic field, the chemical environment, and the magnetic properties of the isotope involved; in practical applications with static magnetic fields up to ca. 20 tesla, the frequency is similar to VHF and UHF television broadcasts (60–1000 MHz). NMR results from the specific magnetic properties of certain atomic nuclei. Nuclear magnetic resonance spectroscopy is widely used to determine the structure of organic molecules in solution and study molecular physics and crystals as well as non-crystalline materials. NMR is also routinely used in advanced medical imaging techniques, such as magnetic resonance imaging (MRI). The original application of NMR to condensed matter physics is nowadays mostly devoted to strongly correlated electron systems. It reveals large many-body couplings by fast broadband detection, and it should not be confused with solid-state NMR, which aims at removing the effect of the same couplings by magic angle spinning techniques.
Ethanol (CH3CH2OH), or beverage alcohol, is a two-carbon alcohol
that is rapidly distributed in the body and brain. Ethanol alters many
neurochemical systems and has rewarding and addictive properties. It
is the oldest recreational drug and likely contributes to more morbidity,
mortality, and public health costs than all illicit drugs combined. The
5th edition of the Diagnostic and Statistical Manual of Mental Disorders
(DSM-5) integrates alcohol abuse and alcohol dependence into a single
disorder called alcohol use disorder (AUD), with mild, moderate,
and severe subclassifications (American Psychiatric Association, 2013).
In the DSM-5, all types of substance abuse and dependence have been
combined into a single substance use disorder (SUD) on a continuum
from mild to severe. A diagnosis of AUD requires that at least two of
the 11 DSM-5 behaviors be present within a 12-month period (mild
AUD: 2–3 criteria; moderate AUD: 4–5 criteria; severe AUD: 6–11 criteria).
The four main behavioral effects of AUD are impaired control over
drinking, negative social consequences, risky use, and altered physiological
effects (tolerance, withdrawal). This chapter presents an overview
of the prevalence and harmful consequences of AUD in the U.S.,
the systemic nature of the disease, neurocircuitry and stages of AUD,
comorbidities, fetal alcohol spectrum disorders, genetic risk factors, and
pharmacotherapies for AUD.
These simplified slides by Dr. Sidra Arshad present an overview of the non-respiratory functions of the respiratory tract.
Learning objectives:
1. Enlist the non-respiratory functions of the respiratory tract
2. Briefly explain how these functions are carried out
3. Discuss the significance of dead space
4. Differentiate between minute ventilation and alveolar ventilation
5. Describe the cough and sneeze reflexes
Study Resources:
1. Chapter 39, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 34, Ganong’s Review of Medical Physiology, 26th edition
3. Chapter 17, Human Physiology by Lauralee Sherwood, 9th edition
4. Non-respiratory functions of the lungs https://academic.oup.com/bjaed/article/13/3/98/278874
Knee anatomy and clinical tests 2024.pdfvimalpl1234
This includes all relevant anatomy and clinical tests compiled from standard textbooks, Campbell,netter etc..It is comprehensive and best suited for orthopaedicians and orthopaedic residents.
Explore natural remedies for syphilis treatment in Singapore. Discover alternative therapies, herbal remedies, and lifestyle changes that may complement conventional treatments. Learn about holistic approaches to managing syphilis symptoms and supporting overall health.
Recomendações da OMS sobre cuidados maternos e neonatais para uma experiência pós-natal positiva.
Em consonância com os ODS – Objetivos do Desenvolvimento Sustentável e a Estratégia Global para a Saúde das Mulheres, Crianças e Adolescentes, e aplicando uma abordagem baseada nos direitos humanos, os esforços de cuidados pós-natais devem expandir-se para além da cobertura e da simples sobrevivência, de modo a incluir cuidados de qualidade.
Estas diretrizes visam melhorar a qualidade dos cuidados pós-natais essenciais e de rotina prestados às mulheres e aos recém-nascidos, com o objetivo final de melhorar a saúde e o bem-estar materno e neonatal.
Uma “experiência pós-natal positiva” é um resultado importante para todas as mulheres que dão à luz e para os seus recém-nascidos, estabelecendo as bases para a melhoria da saúde e do bem-estar a curto e longo prazo. Uma experiência pós-natal positiva é definida como aquela em que as mulheres, pessoas que gestam, os recém-nascidos, os casais, os pais, os cuidadores e as famílias recebem informação consistente, garantia e apoio de profissionais de saúde motivados; e onde um sistema de saúde flexível e com recursos reconheça as necessidades das mulheres e dos bebês e respeite o seu contexto cultural.
Estas diretrizes consolidadas apresentam algumas recomendações novas e já bem fundamentadas sobre cuidados pós-natais de rotina para mulheres e neonatos que recebem cuidados no pós-parto em unidades de saúde ou na comunidade, independentemente dos recursos disponíveis.
É fornecido um conjunto abrangente de recomendações para cuidados durante o período puerperal, com ênfase nos cuidados essenciais que todas as mulheres e recém-nascidos devem receber, e com a devida atenção à qualidade dos cuidados; isto é, a entrega e a experiência do cuidado recebido. Estas diretrizes atualizam e ampliam as recomendações da OMS de 2014 sobre cuidados pós-natais da mãe e do recém-nascido e complementam as atuais diretrizes da OMS sobre a gestão de complicações pós-natais.
O estabelecimento da amamentação e o manejo das principais intercorrências é contemplada.
Recomendamos muito.
Vamos discutir essas recomendações no nosso curso de pós-graduação em Aleitamento no Instituto Ciclos.
Esta publicação só está disponível em inglês até o momento.
Prof. Marcus Renato de Carvalho
www.agostodourado.com
The prostate is an exocrine gland of the male mammalian reproductive system
It is a walnut-sized gland that forms part of the male reproductive system and is located in front of the rectum and just below the urinary bladder
Function is to store and secrete a clear, slightly alkaline fluid that constitutes 10-30% of the volume of the seminal fluid that along with the spermatozoa, constitutes semen
A healthy human prostate measures (4cm-vertical, by 3cm-horizontal, 2cm ant-post ).
It surrounds the urethra just below the urinary bladder. It has anterior, median, posterior and two lateral lobes
It’s work is regulated by androgens which are responsible for male sex characteristics
Generalised disease of the prostate due to hormonal derangement which leads to non malignant enlargement of the gland (increase in the number of epithelial cells and stromal tissue)to cause compression of the urethra leading to symptoms (LUTS
These lecture slides, by Dr Sidra Arshad, offer a quick overview of physiological basis of a normal electrocardiogram.
Learning objectives:
1. Define an electrocardiogram (ECG) and electrocardiography
2. Describe how dipoles generated by the heart produce the waveforms of the ECG
3. Describe the components of a normal electrocardiogram of a typical bipolar leads (limb II)
4. Differentiate between intervals and segments
5. Enlist some common indications for obtaining an ECG
Study Resources:
1. Chapter 11, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 9, Human Physiology - From Cells to Systems, Lauralee Sherwood, 9th edition
3. Chapter 29, Ganong’s Review of Medical Physiology, 26th edition
4. Electrocardiogram, StatPearls - https://www.ncbi.nlm.nih.gov/books/NBK549803/
5. ECG in Medical Practice by ABM Abdullah, 4th edition
6. ECG Basics, http://www.nataliescasebook.com/tag/e-c-g-basics
Tom Selleck Health: A Comprehensive Look at the Iconic Actor’s Wellness Journeygreendigital
Tom Selleck, an enduring figure in Hollywood. has captivated audiences for decades with his rugged charm, iconic moustache. and memorable roles in television and film. From his breakout role as Thomas Magnum in Magnum P.I. to his current portrayal of Frank Reagan in Blue Bloods. Selleck's career has spanned over 50 years. But beyond his professional achievements. fans have often been curious about Tom Selleck Health. especially as he has aged in the public eye.
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Introduction
Many have been interested in Tom Selleck health. not only because of his enduring presence on screen but also because of the challenges. and lifestyle choices he has faced and made over the years. This article delves into the various aspects of Tom Selleck health. exploring his fitness regimen, diet, mental health. and the challenges he has encountered as he ages. We'll look at how he maintains his well-being. the health issues he has faced, and his approach to ageing .
Early Life and Career
Childhood and Athletic Beginnings
Tom Selleck was born on January 29, 1945, in Detroit, Michigan, and grew up in Sherman Oaks, California. From an early age, he was involved in sports, particularly basketball. which played a significant role in his physical development. His athletic pursuits continued into college. where he attended the University of Southern California (USC) on a basketball scholarship. This early involvement in sports laid a strong foundation for his physical health and disciplined lifestyle.
Transition to Acting
Selleck's transition from an athlete to an actor came with its physical demands. His first significant role in "Magnum P.I." required him to perform various stunts and maintain a fit appearance. This role, which he played from 1980 to 1988. necessitated a rigorous fitness routine to meet the show's demands. setting the stage for his long-term commitment to health and wellness.
Fitness Regimen
Workout Routine
Tom Selleck health and fitness regimen has evolved. adapting to his changing roles and age. During his "Magnum, P.I." days. Selleck's workouts were intense and focused on building and maintaining muscle mass. His routine included weightlifting, cardiovascular exercises. and specific training for the stunts he performed on the show.
Selleck adjusted his fitness routine as he aged to suit his body's needs. Today, his workouts focus on maintaining flexibility, strength, and cardiovascular health. He incorporates low-impact exercises such as swimming, walking, and light weightlifting. This balanced approach helps him stay fit without putting undue strain on his joints and muscles.
Importance of Flexibility and Mobility
In recent years, Selleck has emphasized the importance of flexibility and mobility in his fitness regimen. Understanding the natural decline in muscle mass and joint flexibility with age. he includes stretching and yoga in his routine. These practices help prevent injuries, improve posture, and maintain mobilit
micro teaching on communication m.sc nursing.pdfAnurag Sharma
Microteaching is a unique model of practice teaching. It is a viable instrument for the. desired change in the teaching behavior or the behavior potential which, in specified types of real. classroom situations, tends to facilitate the achievement of specified types of objectives.
Title: Sense of Smell
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the primary categories of smells and the concept of odor blindness.
Explain the structure and location of the olfactory membrane and mucosa, including the types and roles of cells involved in olfaction.
Describe the pathway and mechanisms of olfactory signal transmission from the olfactory receptors to the brain.
Illustrate the biochemical cascade triggered by odorant binding to olfactory receptors, including the role of G-proteins and second messengers in generating an action potential.
Identify different types of olfactory disorders such as anosmia, hyposmia, hyperosmia, and dysosmia, including their potential causes.
Key Topics:
Olfactory Genes:
3% of the human genome accounts for olfactory genes.
400 genes for odorant receptors.
Olfactory Membrane:
Located in the superior part of the nasal cavity.
Medially: Folds downward along the superior septum.
Laterally: Folds over the superior turbinate and upper surface of the middle turbinate.
Total surface area: 5-10 square centimeters.
Olfactory Mucosa:
Olfactory Cells: Bipolar nerve cells derived from the CNS (100 million), with 4-25 olfactory cilia per cell.
Sustentacular Cells: Produce mucus and maintain ionic and molecular environment.
Basal Cells: Replace worn-out olfactory cells with an average lifespan of 1-2 months.
Bowman’s Gland: Secretes mucus.
Stimulation of Olfactory Cells:
Odorant dissolves in mucus and attaches to receptors on olfactory cilia.
Involves a cascade effect through G-proteins and second messengers, leading to depolarization and action potential generation in the olfactory nerve.
Quality of a Good Odorant:
Small (3-20 Carbon atoms), volatile, water-soluble, and lipid-soluble.
Facilitated by odorant-binding proteins in mucus.
Membrane Potential and Action Potential:
Resting membrane potential: -55mV.
Action potential frequency in the olfactory nerve increases with odorant strength.
Adaptation Towards the Sense of Smell:
Rapid adaptation within the first second, with further slow adaptation.
Psychological adaptation greater than receptor adaptation, involving feedback inhibition from the central nervous system.
Primary Sensations of Smell:
Camphoraceous, Musky, Floral, Pepperminty, Ethereal, Pungent, Putrid.
Odor Detection Threshold:
Examples: Hydrogen sulfide (0.0005 ppm), Methyl-mercaptan (0.002 ppm).
Some toxic substances are odorless at lethal concentrations.
Characteristics of Smell:
Odor blindness for single substances due to lack of appropriate receptor protein.
Behavioral and emotional influences of smell.
Transmission of Olfactory Signals:
From olfactory cells to glomeruli in the olfactory bulb, involving lateral inhibition.
Primitive, less old, and new olfactory systems with different path
2. 2
INTRODUCTION:
MRI is a non invasive, multi planar, multi
contrast, multimodal – not only used to depict
internal structure but also powerful tool for
studying organ function, metabolism, physiology
& pathology.
In 3 decades rapid technical advances has made
to improve the spatial resolution, types of
contrast & in particular speed of imaging.
Applications initially limited to neural axis, now
applicable to various organ systems & it has
become primary diagnostic investigation for
many clinical problems..
3. Magnetic properties of substances
1. Paramagnetic
(oxygen,melanin,gadolinium)
3
paramagnetic material is
attracted by externally
applied magnetic field
5. 3.Ferromagnetic substances
(Fe, Co, Ni)
5
Ferromagnetic materials- that can
be magnetized by an external magnetic
field and remain magnetized after the
external field is removed.
7. Basic Physics
Atom: nucleus (proton, neutron),
orbiting electrons
As a result of their nuclear spin and
charge distribution, protons and
neutrons have a magnetic field
called a magnetic dipole.
Magnetic moment is a vector that
represents the strength &
orientation of a magnetic dipole
7
8. 8
Nuclear Magnetic Resonance
Nuclear magnetic resonance (NMR) is a physical phenomenon that occurs
when certain elements interact with a magnetic field. NMR is the process
by which the signal detected in MRI is generated; it is the foundation on
which MRI is built. Some common elements that demonstrate NMR are
H = 1
P = 31
C= 13
Na=23
In order to qualify for this list, the element must have a nonzero magnetic moment.
It is not necessary for us to delve into what a nonzero magnetic moment
is, but it will be present when either the number of protons or neutrons in
an atom is odd.
9. MR ACTIVE NUCLEI
Atomic No.-no. of protons
Mass No.-no of protons and neutrons
Those nuclei with an odd mass no. possess the ability to align
themselves along the direction of applied magnetic field
and are called as
MR ACTIVE NUCLEI e.g. H = 1
P = 31
C= 13
Na=23
9
10. Hydrogen is used as the MR ACTIVE NUCLEUS
in clinical MRI because-
-it is very abundant in human body
-its solitary proton gives it a relatively large
magnetic moment(gyromagnetic ratio)
-it gives best and most intense signal among all
nucei.
11. Protons carry a positive charge
Protons are constantly spinning around a central axis
(the movement is akin to the movement of a spinning top when hit)
A spinning(moving) electrical charge is an electrical current which
generates a magnetic field around it
Thus the protons generate a magnetic field around themselves and
behave as small bar magnets
12. 12
Why we ignoring electrons in our discussion of
NMR?
Because of their much smaller mass, electrons
have a much higher gyromagnetic ratio and
precess at frequencies in the gigahertz range;
signals in this frequency range will not be
detected by our detection hardware
13. Spin is rotation of protons around its own axis
while
Precession is rotation of axis itself under the
influence of external magnetic field such that
it forms a cone.
and the frequency at which protons rotate
around the applied external magnetic field is
called as precessional frequency. Or Larmor
frequency
13
14. 14
This same phenomenon is responsible for the wobbling of a gyroscope.
Because such devices have "spin,“ when they interact with the earth's
gravitational field, they pursue the same conical trajectory.
18. Normally protons are aligned in a random
fashion. This, however, changes when
they are exposed to a strong external
magnetic field. Then they are aligned in
only two ways, either parallel or antiparallel
to the external magnetic field.
Naturally the preferred state of
alignment is the one that needs
less energy. So more protons
are on the lower energy level,
parallel to the external magnetic
Field.
19.
20. In the strong magnetic field more of these
nuclear magnetic dipoles align parallel to the
applied magnetic field this produces net
magnetisation in the direction of the field .
The direction of the strong magnetic field
conventionally defines the z axis which is
generally along the longitudinal axis of the
patient in a typical MRI machine.
20
21. Z
Y
X
SUM VECTOR
Thus we have a
NET MAGNETISATION VECTOR
(or Longitudinal Magnetisation)
the magnitude of which depends on the
strength of the external magnetic field
strength magnitude of NMV
22. But this NMV (Longitudinal
magnetization) is not measurable.
Because this NMV is along the external
magnetic field (Bo) and it is so small
relative to the static magnetic field Bo
(10 million times smaller)
So For measurement-
a magnetisation transrverse to external
magnetic field is necessary
This magnetisation should not be stationary
22
23. 23
At Rest (i.e when only Bo is applied), Signal
Is Not Detectable
Faraday's law of induction tells us that moving charge will induce a magnetic
field. It is conversely true that a moving magnet will induce an electric
field. In the presence of a conductor (a loop of wire-AKA antenna-that
we will call a receiver coil), a voltage will be induced by the moving magnet.
This is exactly how we measure the signal in NMR and MRI.
This is because we cannot measure the NMV of our sample,as it is stationary.
So it’s the only Transverse vector (rotating in the x-y
plain) which produces signal in the receiver. Longitudinal
vector can never produce a signal
24. Next step is to impart energy to this NMV so
as to get a transverse magnetization which is
measurable.
Energy exchange can only take place when protons and radio
frequency pulse have the Same frequency-*RESONANCE
25. 25
resonance is a process by which energy is transferred with great
efficiency from one system to another. This requires a source of energy
and a subject that receives the energy. In our case, the subject is the spin
sample (ie H atoms in patient body). Its natural frequency 0 , is
determined by the Larmor equation we discussed previously. The energy
source will be a second magnetic field that, while weaker than Bo and ,
will change its orientation over time at a frequency that matches 0 and
will always remain in a plain perpendicular to Bo.
This time -varying magnetic field is called B1 and it is described as a
"rotating magnetic field." Because B1 must rotate at 0 , which is in the
same range as the frequencies used in FM radio , it is also called the
radiofrequency (RF) field and is said to deliver a radiofrequency (RF)
pulse.
26. 26
The rotating magneticfield B1 (Dotted arrows) represent the two components
of B1• Each oscillates at the same frequency but 90° out of phase with the
other. The vector sum of these two components is represented by the solid arrow.
This net B1 rotates through a plane (xy in this example) that is perpendicular to
Bo,(parallel to the z axis in this example).
27. PHASE OF MAGNETIC MOMENTS
27
Due to spin around its own axis- there is net magnetisation in z axis
Due to precession – there is megnetisation in transverse plain. But without RF
pulse, these nuclei precess randomly i.e out of phase. So the net magnetisation in
transverse axis becomes zero.
But when RF pulse is applied(at a frequency equal to larmour frequency), these
nuclei come in phase and produce a magnetisation vector in transverse direction.
28. 2 things happen at Resonance (ie when we apply
RF pulse B1) due to energy absorption:
1- Increase number of High energy Spin Up nuclei ie nuclei in
antiparallel direction to Bo. Causing gradual decrease in
longitudinal magnetisation vector
2- increase in Phase Coherence- causing gradual inc in
transverse magnetisation vector.
With 90 deg RF pulse longitudinal vector becomes zero and
transverse vector becomes maximum. So the NMV
precesses only in transverse plain.
29. Application of 90 deg RF pulse
Longitudinal magnetisation
Transverse magnetisation
RF at Larmour frequency of H+
30. Effects of switching off the RF
pulse
NMV loses its energy Relaxation
Longitudinal magnetisation
gradually increases -Recovery
Transverse magnetisation
decreases -Decay
32. Excitation and Relaxation
(recovery)
Equilibrium is disturbed when a radio pulse rotates
net magnetization away from its initial longitudinal
plane .
This disturbance of equilibrium where by transverse
magnetisation is produced is termed as excitation.
The return of net magnetisation to equilibrium is
termed as relaxation.
32
34. Types of Relaxation
Longitudinal – precessing protons are pulled back
into parallel alignment with main magnetic field of
the scanner (Bo) increasing size of the magnetic
moment vector along z-axis
Transverse – precessing protons become out of
phase leading to a drop in the magnetic moment
vector along x-y plain
Transverse relaxation occurs much faster than
Longitudinal relaxation
Tissue contrast is determined by differences in
these two types of relaxation
35. T1 Relaxation
-Time taken by LM to recover to its original
value after RF Pulse is switched off
-relaxation is exponential in nature
-short T1 = rapid recovery
-long T1 = slow recovery
– longitudinal relaxation
– thermal relaxation
– spin-lattice relaxation
36. 36
•T1 relaxation rate is determined by
•Properties of the material
•Magnetic field strength
•T1 long in - small molecules-H20 and large
molecules – proteins.
•T1 short in fats & in intermediate sized molecules.
•Contrast agents Gd DTPA – T1 shortening.
•In general, T1 increases with increasing B0.
37. Causes of spin lattice relaxation i.e T1 relxn
Jostling by large molecules that are slow moving and near
to resonant frequency is most effective at removing energy
from excited dipoles. FAT(large molecules with low
inherent energy) can absorb energy easily and has short T1.
Jostling by small, light weight molecules with little inertia is
rapid and so relatively ineffective at removing energy from
excited dipoles, so free water, urine,amniotic fluid, csf and
other solution of salts have a long T1.Greater the proportion of
free water in tissue, longer is T1
Atoms in solid and rigid macromolecules are relatively
fixed and they are least effective at removing energy;
compact bones, teeth, calculi and metallic clips have very
long T1
38. 38
The time required for longitudinal magnetisation
to recover 63% of its original equilibrium level
after RF pulse is switched off is called as T1
relaxation time .
The curve showing gradual recovery of LM against
time is called T1 curve.
Longitudinal relaxation rate= 1/T1
39. T1 Recovery
T1 in WaterT1 in Fat
inefficient at receiving
energy
T1 is longer
i.e. nuclei take a lot
longer to dispose
energy to surrounding
water tissue
absorb energy quickly
T1 is very short
i.e. nuclei dispose
their energy to
surrounding fat tissue
and NMV return in
plain of B0 in very
short time
40. 40
Longitudinal relaxation. At t =0, a 90° RF pulse has just been delivered,
and all magnetization is in the transverse plane. Tl, the time at which 63% of Mz,
has recovered, describes the rate of recovery.
In this example, each line represents a different tissue: The dashed line represents
fat, which has a short Tl(Tla.) , the solid line represents CSF, which has a long TI
(T1c), and the dotted line represents brain , which has an intermediate Tl(Tlb) .
41. T2 DECAY
results from static or slowly fluctuating local magnetic
field variations resulting in loss of phase coherence among
groups of protons rotating in the transverse plane.
T2 is the time taken by TM to REDUCE TO 37% of its
original value.
IN PHASE OUT PHASE
transverse relaxation
–spin-spin relaxation
42. Causes of spin spin relaxation i.e T2 relxn
Dephasing occurs because a spinning proton experiences a tiny
additional magnetic field produced by each neighbouring
proton.Individual protons are affected slightly differently,so does
the rate of precession ,some precess faster and some slower,and
energy passes from one proton to another, or spin to spin.
Local variation of magnetic field is greatest in solid and rigid
macromolecules in which atoms are relatively fixed. Dipoles in
compact bone,teeth,calculi and metallic clips dephase quickly.they
have very short T2
The effect is least in free water, urine, amniotic fluid,csf and
other solutions of salt.
Lighter molecules are in rapid thermal motion,which smoothes
out the local field and result in Long T2.more free water longer
t2.spleen>liver renal medulla>cortex
43. T2 Decay
Fat much better at energy exchange than Water
Because T2 depends on:
- Proximity of other spins
So;
Fat's T2 time is very short compared to water
44. 44
Transverse relaxation. At t = 0, a 90° RF pulse has just been delivered,
and all magnetization is in the transverse plane. T2, the time at which 63% of Mt,
has dissipated and 37% remains, describes the exponential rate of signal loss. The
dashed line represents fat, which has a short T2(T2a.) , the solid line represents
CSF, which has a long T2(T2c), and the dotted line represents brain , which has an
intermediate T2(T2b)
45. T2* Relaxation
In addition to magnetic field inhomogeneity intrinsic to tissues
causing spin-spin relaxation, inhomogeneity of external magnetic
field also causes decay of TM, called T2 prime
The consequence of this spatial variation in Bo is that adjacent
spins will not experience the same field strength and,
consequently, will not precess at the same frequency. With time,
spins precessing at different frequencies will lose phase
coherence. The longer we observe a sample of spins exposed to a
heterogeneous Bo, the greater the loss of phase coherence and, of
course, the greater the resultant decline in the net M,of our
sample.
The combined decay of transverse magnetisation from t2
relaxation and heterogenous magnetic field is referred as t2*
relaxation
45
46. 46
T2 and T2*. The shapes of the T2 and T2* curves are similar, but their
time constants differ. T2* is essentially the T2 curve shifted to the left due to the
addition of relaxation due to T2'.
So T2’ causes faster signal loss
47. 47
The Spin Echo
The spin echo is a method for "recovering" Mt, lost due to heterogeneity of
the magnetic field, essentially neutralizing T2' effects.
This is achieved by giving an RF pulse that flips the magnetization 180° .
The RF pulse must deposit twice the amount of energy
as the 90° pulse in order to achieve a flip of exactly 180°.
48. 48
The spin echo. (A) Immediately after the 90°RF pulse has been applied,
spins are all phase coherent, represented by one large vector in the transverse plane .
(B) After a period of time, spins will dephase due to T2' effects. Note that the dotted
arrow is "ahead" of the solid arrow with respect to the direction of precession
(curved arrow) . (C) The 180° RF pulse rotates, spins out of and then back into the
transverse plane , effectively inverting their phase. Now, the dotted arrow is "behind"
the solid arrow . (D) After an additional period of time equal to that between
(A) and (B), the spins are back in phase , creating a spin echo .
49. 49
The spin echo corrects T2' effects. Initially, signal decays along the T2*
curve for a time x.
After the 180 pulse, signal begins to increase until at time 2x it
intersects the T2 curve. It is at this point that T2' effects have been
fully recovered , producing a spin echo.
52. TIME TO ECHO: Time
interval between start of RF
pulse and reception of signal
53. 53
FID
As the magnitude of transverse magnetisation
decreases , the magnitude of voltage induced in
receiver coil also decrease. The induction of
reduced signal is called FREE INDUCTION DECAY
SIGNAL.
The degree of rotation of magnetisation caused by an
excitation radio pulse is a product of strength and
duration of that pulse .
The amount of rotation that results from the radio
pulse is referred as FLIP ANGLE
With flip angle of 90, longitudinal magnetisation is
converted completely to transverse magnetisation
FLIP ANGLE
55. T1 WEIGHTED:
With short TR only the tissues with short T1 will show high signal
intensity.
T2 WEIGHTED:
At longer TE only those tissues with long T2 will have strong
signal.
PROTON DENSITY
With a long TR differences in LM are not important as all
the tissues have regained their Full LM.with short TE ,T2
has yet to become pronounced so the image is mostly
detremined by PD
56. 56
Each line represents a specific tissue( solid-water, dashed-fat). TR indicates the time at which
the second (and subsequent) RF pulse is applied .
Short TR alters initial Mz, Because Mz, has not fully recovered , only a portion of the
longitudinal magnetization Mz, is present when this next RF pulse is applied. The amount of
Mz, present at TR determines the amount of Mt, present in the lower graph of transverse
relaxation at t =O. If we sample Mt, immediately (at TE =0), the difference in signal between
tissues is due to differences in T1 that determined the amount of Mt recovered when the
RF pulse was applied at TR. if we sample Mt at longer TE, the difference in Signal is due to
difference in T2.
TR
TE
57. 57
T2 contrast is determined by TE.TE is indicated by the numbers.
As TE is varied (all other parameters are unchanged), tissue contrast changes
dramatically from one reflecting Tl differences to one reflectingT2 differences.When
using a short TE, signal is sampled before signal differences because of
T2 manifest. When using a long TE, however, such differences in signal manifest
substantially by T2. Notice also that signal to noise declines with inc in TE (because
at longer TE net Mt decreases).
58. 58
Tl contrast is modulated byTR. As TR (white numbers) is varied ( keeping all other
parameters are unchanged), tissue contrast changes from one reflecting Tl differences
(white matter with higher signal than gray matter and CSF very dark) to one
reflecting T2 differences .
When using a short TR, differences in Mz, are present when the RF pulse is applied ,
creating differences in signal immediately afterward. When using a long TR, however
such differences are eliminated as Mz, has fully recovered for all tissues by TR. Notice
also that signal to noise increases with TR because more Mz, recovers before each
Subsequent RF pulse. The more Mz the more Mt (signal) generated by the RF.
59. T1 WTED :
short TR 300 - 600 ms
short TE 20 - 30 ms
T2 WTED :
long TR 2500 - 6000 ms
long TE 80 - 100 ms
PD WTED :
long TR 2500 - 3500 ms
short TE 20 - 30 ms
64. Signal Intensities On T2 Weighted
High signal:CSF ,synovial fluid, hemangioma,
infection, inflammation, oedema, cysts,
slow flowing blood.
Low signal:
Cortical bone,bone islands, deoxy hb(P),hemosiderin
calcification,T2 paramagnetic agents.
No signal:
Air fast flowing blood, tendons, cortical bone, scar tissue
calcification
64
65. 65
T2 WEIGHTED IMAGE :
1.Fluid including CSF is bright.
2.White matter is dark and gray matter remains gray.
3.Due to increased water content lesions appear bright.
4.Useful for detection of pathology.
FLAIR images are similar but CSF is dark. Useful in ventricular &
periventricular lesions.
67. PROTON DENSITY IMAGE :
As the TR is prolonged more tissues fully
recover their longitudinal magnetisation
between repetitions and voxel intensity
becomes more independent of T1
At short TE values the effect of T2 decay is
minimised and one is left with an image with
little T1 or T2 dependence this can be called as
proton density image
67
69. 69
Contrast Agents and Their Effect on Tl
Paramagnetic contrast agents shorten the Tl of spins when unpaired
electrons of the paramagnetic element are within 3A(angstroms) of the
proton.
Currently, all paramagnetic contrast agents employ gadolinium (Gd),
which is highly paramagnetic, having nine unpaired electrons.
Shortening of Tl decreases the time required for longitudinal
relaxation to occur and can be viewed as shifting the Tl
curve to the left. This effect brings out differences in tissues (e.g., liver
and metastasis in our example below) due to differential shortening of
Tl; only tissues that take up the paramagnetic substance will "benefit"
from this effect.
70. 70
Tl shortening effect of contrast agents. In this case of a liver metastasis
(tumor), Mz, of the metastasis and liver tissue are very similar and would, therefore,
be difficult to distinguish. The Tl of the metastasis (Th) becomes shorter (Tla) when
gadolinium-containing contrast material accumulates due to tumor vascularity . The
change in Tl shifts the Tl curve of the meta stasis to the left. Thus, at TR, Mz, for the
tumor and normal tissue are very different. As a result, signal from the tumor will be
much higher and detection will be enhanced.
71. 71
Contrastenhancement. Both images of this meningioma were obtained
using identical parameters. (A) Before the contrast infusion, the tumor has signal
indistinguishable from normal brain tissue. (B) T1 shortening accomplished by
adding the contrast agent leads to a dramatic contrast between signal from the
tumor and normal tissue.
72. Gradients
gradients are coils of wire that, when a current is passed
through them ,alter the magnetic field strength in a
controlled and predictable way.
A gradient is simply a deliberate change in the
magnetic field
Gradients are used in MRI to linearly modify the
magnetic field from one point in space to
another
Gradients are applied along an axis (i.e. Gx
along the x-axis, Gy along the y-axis, Gz along
the z-axis)
On applying gradient the Bo changes,so the
larmour frequency of protons changes
accordingly at that location.
73. Effect of a Gradient
direction of the magnetic field remains the
same but strength changes acc to gradient
75. for axial images the gradient coil is applied
in cranio caudal direction
for sagital images right to left
for coronal section anterior to posterior
75
76. Localising the MR signal
We should know from which part of the body we
are receiving the MR signal
Possible by application of 3 types of gradients in
X, Y and Z planes.
Z axis - slice selection gradient
X axis - phase encoding gradient
Y axis - frequency encoding gradient
77. Slice Selection
When a gradient coil is switched on, B0 and
precessional frequency of nuclei is altered in a
linear fashion.
A specific point/nuclei situated within a slice
along the axis has specific precessional
frequency depending upon Bo at that point.
A slice can be selectively excited by
transmitting RF with a band of frequencies
coinciding with Larmor frequencies of spins in
a particular slice.
77
80. Z gradient selects axial slices
X gradient selects sagittal slices
Y gradient selects coronal slices
SLICE THICKNESS: depends on slope of gradient
and transmit bandwith.
TIMING OF SLICE SELECTION GRADIENT:
Applied during excitation 90· RF
80
81. Phase Encoding
After the selection of slide, phase encoding
gradiant is Applied perpendicular to the axis of
slide selection gradient and frequency encoding
gradient.
This brief gradient pulse causes precessional
frequencies to change along this axis , once the
phase encoding has ended the precessional
frequencies come to uniformity but the protons
spin will be in different phases.
The phase encoding gradient must be applied
repeatedly at different strengths to locate
different MR signals along the axis.
82
82. Phase Encoding
After the selection of slide, phase encoding
gradiant is Applied perpendicular to the axis
of slide selection gradient and frequency
encoding gradient.
Apply gradient in one direction briefly
and then turn off
Result:
Protons initially decrease or increase their
rate of precession
After the gradient is turned off all of the
protons will again precess at the same rate
Difference is that they will be out phase with
one another
86. The steepness of slope of the phase encoding
gradient determines the degree of phase shift
between two points along the gradient.
Strong phase encoding gradients accentuate
differences between two structures that are near
to each other.
So they are useful in resolving fine detail.
87
87. Timing Of Phase Encoding
The phase encoding gradient is switched on
after the RF excitation pulse has been
switched off and before 180’ rephasing
pulse.
The phase encoding gradient must be applied
repeatedly at different strengths to locate
different MR signals along the axis.
Its normally turned on for 4 ms and the
amplitude and polarity of the gradient is
altered for each phase encoding step.
88
90. 91
After PE Gradient turned off
All spins have same frequency again, but different phase
+90° 0° -90°
91. Frequency Encoding
Applied perpendicular to the axes of slide
selection gradient and phase encoding gradient
The gradient produces a frequency difference
along its axis.
The signal can now be located according to its
frequency.
92
92. Frequency Encoding
Apply gradient in one direction and
leave it on
Result:
Protons that experience a decrease in
the net magnetic field precess slower
Protons that experience an increase in
the net magnetic field precess faster
95. 96
•The frequency encoding gradient is switched
on when the signal is received , so it is called
Readout Gradient.
•With stronger frequency encoding gradient
small distances may be resolved better
because they correspond to greater
differences in frequency .
•So the spatial resolution improves as gradient
strength increases
96. 97
• The steepness of slope of frequency
encoding gradient determines the size of the
anatomy covered, so it determines- Field of
view.
99. By means of Fourier transformation ,a computer
analyzes the mixture of signals that come out Of a slice
and we get a MR IMAGE
100. Converting Received
Signal into an Image
• Signal produced using both
frequency and phase encoding can
be decomposed using a
mathematical technique called the
Fourier Transform
• Result is the signal (sinusoidal
squiggles) produced at each
individual pixel
101. From Signal to Image
Row 1,
Col 1
Row 2,
Col 2
Row 3,
Col 3
FFT
Pixels
102. Lauterbur’s Insight
• Use of gradients to provide spatial
encoding
• Frequency and Phase - was
Lauterbur’s contribution
• Awarded Nobel prize for this work
103. The K-space
Its an imaginary space where raw data is stored.
It is a spatial frequency domain
The unit of k space is radians /cm.
K space does not correspond to the image .
Its rectangular and has two axes :
Horizontal axis corresponds to the phase axis.
The vertical axis is frequency axis perpendicular to
phase axis.
The number of lines filled in k space determined by
number of different phase encoding steps.
104
104. What is K-space?
Space in which “raw” data is written
Complement to image space
= FT of
Image = Fourier Transform of k-space data
106. Appearance of K-space Data
Center of k-space contains
low spatial frequency info
(general shape; big things
that change little over
space)
Edge of k-space contains
high spatial frequency info
(details, edges)
107. Because k-space is symmetrical, one half of the space
can be determined from knowledge of the other half.
Imaging time can be reduced by a factor of 2
Most important information centered around the
middle of k-space
Half Fourier Imaging