Presentation on Magnetic resonance imaging

1. Synthesis, Characterization and
Evaluation of NiFe2O4/Cr2O3
Nano composite as T1-T2 Contrast
Agents for high-field MRI
Presented
By
Hamza Khalid
SP21-RPH-020/LHR
Supervised
By Dr Akbar Ali

2. Abstract
 Attractive Magnetic Resonance Imaging (MRI) is especially significant
in molecular-imaging and holds a great position.
 Attractive magnetic resonance imaging (MRI) is an intensely powerful
demonstrative technique in medical science.
 It offers different benefits, including remarkable imaging adaptability, non-
ionizing properties, patient security, and high-resolution pictures.
 It also secures high-goal pictures with extraordinary delicate tissue
contrast between tissues, as well as obtaining unmistakable clinical data.
 The different effects of MRI will strongly depend on the longitudinal and
transverse relaxation times of water protons in the human body.

3. Nickel Ferrite Nanoparticles and their contribution
in Medical Science
 Nickel ferrite is one of the most attractive nanostructure materials having
equal distribution of tetrahedral and octahedral sites and containing
inverse spinel show great properties as an electrode material.
 NiFe2O4 and its nanostructure is a good aspirant that exhibits large
thermal and chemical stability, shows excellent electrochemical behavior
and their application in different fields as energy storage devices, large
density recording value and biomedicine.
 The nanocomposites of NiFe2O4 as a cathode material are highly
effective and show great stability, selectivity, linearity and detect rapidly
dopamine, uric acid, and ascorbic acid in real samples

4. Apparatus used for Sample
preparation
 Weight balance for the measurement of samples Beakers of varied sizes
for the mixing of salts
 Magnetic bar
 Magnetic hot plate for stirring
 Autoclave
 Centrifuge machine for washing under magnetic force
 Oven for drying
 Pestle and mortar for grinding

5. Required steps for Sample preparation
 Required Materials
 Calculation of chemicals for sample preparation
 Preparation of solution
 Heating process of prepared solution using autoclave
 Washing
 Drying in the oven
 Grinding into fine powder

6. Preparation of
Solution

7. MRI principle with physical model
 Atoms are made of electrons, which hold a negative charge and rotate around a
nucleus. The nucleus can be divided into neutrons (not charged) and protons (charged
positively). It rotates around itself. MRI is based on this rotation motion. Some nuclei
have the property to align with a magnetic field if their mass number is odd, i.e., if the
sum of numbers of protons and neutrons is odd. This is called angular moment or spin.
Among others, 1H atoms, which represent 99.89% of naturally found hydrogens atoms
and are widely represented in biological systems, have a spin. MRI is thus particularly
relevant to study the structure of biological tissues such as the human brain. Spin nuclei
being positively charged, their motion induces a magnetic field. Conversely, the
resulting magnetic moment can be oriented by the application of a magnetic field. This
reciprocity is used in MRI. From a macroscopic point of view, no resulting field can be
observed directly since each spin has its own, independent, random orientation.
However, when placed in a powerful external magnetic field −→B0, the spin directions
align parallel to this field. More precisely, each spin rotates within a cone around −→B0.
This is called spin precession. The frequency of rotation, called the Larmor frequency, is
related to the magnetic field −→B0.

8. Excitation phase
 By applying an oscillating electromagnetic (radiofrequency)
pulse toward the area of the body to be examined, it is possible
to perturb the difference in the number of atoms between the
two energy states. The idea is to use a much weaker field than
−→B0 at the Larmor frequency of the targeted nuclei and to
apply it through a rotating reference frame orthogonal to −→B0.
It causes the particles in that area to absorb the energy required
to make them spin in a different direction and move from the
lower energy state towards the higher.
 The exposure to the radio-frequency pulse causes the net
magnetization to spiral away from −→B0. −→M rotates away
from the longitudinal position in an amount proportional to the
duration of the pulse.

9. Relaxation phase
 By removing the radio-frequency pulse, particles
begin to return to their initial energy state, aligned
with the external field, from higher to lower. This is
associated with a loss of stored excess energy to
surrounding particles which can be detected by the
coil of the MRI scanner. We can then observe two
different types of relaxation processes:
 • T1 weighted images follow the evolution of the
increasing longitudinal component of −→M
 • T2 weighted images follow the evolution of the
decreasing transversal component of −→M

10. Spin lattice relaxation (T1)
 The spin lattice relaxation is based on the energy
exchange between protons and surrounding
molecules. This energy dissipation is characterized
by the restoration of the longitudinal component to
its equilibrium value. This recovery process is
modeled by an exponential function characterized
by a time constant T1, the period for the
longitudinal magnetization to recover 63% of its
equilibrium value. For a 90-degree excitation pulse.
The recovery process is considered as finished
after 5 T1 periods.

11. Spin-spin relaxation (T2)
 Spin-spin relaxation refers to the loss of net
magnetization in the transverse plane related
to protons dephasing. Spins do not only give
up their energy to surrounding lattice
molecules but also to other neighboring
nonexcited spins. This process is also
modeled by an exponential function
characterized by another time constant T2,
which corresponds to the period for the
transversal component to lose 63% of its value
just after the RF pulse.

12. What is T1 relaxation?
 T1 relaxation is the process by which the net magnetization (M)
grows/returns to its initial maximum value (Mo) parallel to Bo.
Synonyms for T1 relaxation include longitudinal relaxation, thermal
relaxation and spin-lattice relaxation. The meanings and
implications of these synonyms will become apparent shortly.

13. What is T2 relaxation?
 T2 relaxation is the process by which the transverse components of magnetization
(Mxy) decay or dephase. As originally described by Felix Bloch (1946), T2
relaxation is considered to follow first order kinetics, resulting in a simple
exponential decay (like a radio-isotope) with time constant T2. Thus T2 is the time
required for the transverse magnetization to fall to approximately 37% (1/e) of its
initial value. Synonyms for T2 relaxation are transverse relaxation and spin-spin
relaxation. (I discourage using the second synonym because "spin-spin"
interactions are just one of several mechanisms by which T2 relaxation can occur.)

14. What is the difference between
relaxation rates and relaxation times?
 Relaxation times and relaxation rates are simple inverses of each other. The
values specified for T1 and T2 are relaxation times and typically measured in
milliseconds (ms). The corresponding relaxation rates are therefore
measured in units of [1/ms]. Relaxation rates corresponding to T1 and T2 are
typically designated by the symbols R1 and R2, where
 R1 = 1/T1 and R2 = 1/T2
 Although a simple concept I have found students to sometimes be confused
because a larger rate means a shorter time, and vice-versa. For example, if
Tissue A has a higher transverse relaxation rate than Tissue B, the T2 value
for A will be smaller than the T2 value for B.

15. Why is T1 longer than T2?
 T2 relaxation occurs whenever there is T1 relaxation. Some
additional processes also exist (such as static local fields and
spin "flip-flops") that cause T2 relaxation without affecting T1.
T2 relaxation always proceeds at a faster rate than T1
relaxation; thus the the T1 relaxation time is always longer
than or equal to T2.

17. What are the causes of T1 and T2
relaxation?
 In the approximately 70 years since Bloch's original description, considerable
progress has been made in explaining the physical mechanisms responsible for T1
and T2 relaxation. We now have reasonably comprehensive theories that explain
relaxation in water, simple solutions of salts and proteins, paramagnetic ions, and
relatively homogenous solid materials (such as collagen, lipids, and
macromolecules).Biological tissues, however, are infinitely more complex, with
internal microstructures containing water and larger molecules distributed
nonuniformly and within compartments. As such, no comprehensive quantitative
theory has yet been developed that easily explains, for example, why liver or brain
have the specific T1 and T2 values that they do. Nevertheless, much insight can
still be gained by understanding the six basic mechanisms responsible for
relaxation in simpler substances.

18. T1 Relaxation
Effect.
 When this molecular "tumbling" rate is close
to the Larmor frequency (fo), then the
fluctuating magnetic field from one spin is
optimal for inducing T1 relaxation in the
other. The relationship between T1 and
molecular tumbling rate is illustrated to the
right.
 In this figure we see that water, with its small
molecular size, tumbles much too rapidly in
its free state to be effective at T1
relaxation. T1 values are longer for free
water than for any other substance in the
body (approximately 4000 ms at
1.5T). When the water is in a partially bound
or in a restricted state, however, its tumbling
may be slowed to a rate much closer to the
Larmor frequency.

19. T2 Relaxation
Effect.  As the rate of molecular rotation falls below the
Larmor frequency, local fields created by each spin
fluctuate less and less and assume an increasingly
static character. The z-component of a slowly
fluctuating field (Bμz) from one dipole (μ) augments
or subtracts from the main field (Bo) at the site of the
other dipole. The second dipole then precesses at a
slightly lower or higher frequency, gaining or losing
phase in the process. This mechanism of dipolar
interaction results in T2 relaxation without T1
relaxation. As the solid state is attained, all molecular
rotations and translations largely cease and so the
static mechanism predominates, resulting in very
short T2 values.

20. Characterizations
 X-ray Diffraction (XRD)
 Raman
 Pl
 SEM
 MRI Application

21. Results and discussions
 XRD
 The XRD spectroscopy measurements of the
NiFe2O4 synthesized via hydrothermal method has
shown in the above figure.
 The results out from the XRD data using wavelength
λ = 0.15406 nm and radiation source of CuKα has
investigated the various structural parameters at
different peak values.
 The indexed pattern represent the crystal planes
(220), (311), (222), (400), (422) and (511) formed by
following Bragg’s law, βins = 0.573o matched with
the reference pattern: NiFe2O4, 96-591-0065 [96,
97].
 The prepared sample has cubic inverse spinel
structure and there are no impurity peaks found in
the boundary of X-Ray detection. The XRD analysis
of NiFe2O4 representing the single phase structure.

22. Raman spectra of nano-
material
 In the present study, the NiFe2O4 spectra exhibit number
of bands and intensity of the dehydrated material across
the applied wavelength
 The peak values-oriented at 213cm-1 and 279cm-1
represents the dispersion bands of NiFe2O4 powder and
the band (T2g) at 497cm-1 furnished due to the peaks
allotment around 490cm-1 and 522cm-1
 The difference in peaks around 200-400 cm-1 occur due to
varied ionic radii of Ni and Fe ions and A1g mode at 497cm-
1 formed the Fe2O3-hematite. All the bands at peak values
of 213, 279, 358, 497, 539, 522, and 699cm−1 represent
the symmetrical and anti-symmetrical stretching of an
oxygen atom at the octahedral and tetrahedral site.