3. Microscopy
1. Optical and electron microscopy involves
the diffraction, reflection, or refraction of
radiation incident upon the subject of study,
and the subsequent collection of this
scattered radiation in order to build up an
image.
2. Scanning probe microscopy involves the
interaction of a scanning probe with the
surface or object of interest.
4. Electron Microscopy - definition and types
• developed in the 1930s that use electron beams instead of light.
• because of the much lower wavelength of the electron beam
than of light, resolution is far higher.
TYPES
• Transmission electron microscopy (TEM) is principally
quite similar to the compound light microscope, by sending an
electron beam through a very thin slice of the specimen. The
resolution limit (in 2005) is around 0.05 nanometer.
• Scanning electron microscopy (SEM) visualizes details on
the surfaces of cells and particles and gives a very nice 3D
view. The magnification is in the lower range than that of the
transmission electron microscope.
5. Transmission Electron Microscopy (TEM)
• beam of electrons is transmitted through a specimen, then an
image is formed, magnified and directed to appear either on a
fluorescent screen or layer of photographic film or to be
detected by a sensor (e.g. charge-coupled device, CCD camera.
• involves a high voltage electron beam emitted by a cathode,
usually a tungsten filament and focused by electrostatic and
electromagnetic lenses.
• electron beam that has been transmitted through a specimen
that is in part transparent to electrons carries information about
the inner structure of the specimen in the electron beam that
reaches the imaging system of the microscope.
• spatial variation in this information (the "image") is then
magnified by a series of electromagnetic lenses until it is
recorded by hitting a fluorescent screen, photographic plate, or
CCD camera. The image detected by the CCD may be
displayed in real time on a monitor or computer.
6. Transmission Electron Microscopy (TEM)
Black Ant
House Fly
Human red blood cells
Human stem cells
Neurons CNS
Neuron growing on astroglia
House Fly
7. • type of electron microscope capable of producing high-
resolution images of a sample surface.
• due to the manner in which the image is created, SEM
images have a characteristic 3D appearance and are useful
for judging the surface structure of the sample.
Resolution
• depends on the size of the electron spot, which in turn
depends on the magnetic electron-optical system which
produces the scanning beam.
• is not high enough to image individual atoms, as is
possible in the TEM … so that, it is 1-20 nm
Scanning Electron Microscopy (SEM)
8. X-ray microscopy
• less common,
• developed since the late 1940s,
• resolution of X-ray microscopy lies between that of
light microscopy and the electron microscopy.
• X-rays are a form of electromagnetic radiation with
a wavelength in the range of 10 to 0.01 nanometers,
corresponding to frequencies in the range 30 PHz to
30 EHz.
9. History
Energy Source
The earliest medical images used light to create photographs,
either of gross anatomic structures, or if a microscope was used,
of histological specimens. Light is still an important source for
creation of images. However, visible light does not allow us to
see inside the body.
X-rays were first discovered in 1895 by Wilhelm Conrad
Roentgen, who was awarded the 1901 Nobel prize in physics for
this achievement. The discovery caused worldwide excitement,
especially in the field of medicine; by 1900, there already were
several medical radiological societies. Thus, the foundation was
laid for a new branch of medicine devoted to imaging the
structure and function of the body
10. X-Ray system
Principle of an X-ray system with image intensifier. X rays impinging on the image
intensifier are transformed into a distribution of electrons, which produces an amplified
light image on a smaller fluorescent screen after acceleration. The image is observed by
a television camera and a film camera and can be viewed on a computer screen and
stored on a CD-ROM or a PACS.
12. The X-rays are produced from electrons that have been accelerated from in vacuum
from the cathode to the anode.
Emission occurs when filament is heated by passing current through it.
When the filament is hot enough, the electrons obtain thermal energy sufficient to
overcome the energy binding the electron to the metal of the filament.
After accelerated they will be stopped at a short distance. Most of the electron energy
will produce heat at the anode. Some percentage will be converted to X-ray by two
main methods.
Deceleration of charged particle results in the emission of electromagnetic field
called Bremmstralung radiation.
These rays will have wide, continuous distribution of energies with the maximum
being the total energy the electron had when reaching the anode.
The number of X-rays will be small at higher energies and increased for lower energies.
14. Ultrasound (Sonography) - basics
It is used to visualize muscles, tendons, and many internal
organs, their size, structure and any pathological lesions
with real time tomographic images. They are also used to
visualize a fetus during routine and emergency prenatal care.
The technology is relatively inexpensive and portable,
especially when compared with modalities such as magnetic
resonance imaging(MRI) and computed tomography (CT).
It poses no known risks to the patient, it is generally described
as a "safe test" because it does not use ionizing radiation,
which imposes hazards (e.g. cancer production and
chromosome breakage).
However, it has two potential physiological effects: it enhances
inflammatory response; and it can heat soft tissue.
15. • the same principles involved in the sonar used by bats, ships
and fishermen.
• when a sound wave (frequency 2.0 to 10.0 megahertz )
strikes an object, it bounces backward or echoes.
• by measuring these echo waves it is possible to determine how
far away the object is and its size, shape, consistency (solid,
filled with fluid, or both) and uniformity.
• a transducer both sends the sound waves and records the
echoing waves. When the transducer is pressed against the
skin, it directs a stream of inaudible, high-frequency sound
waves into the body. As the sound waves bounce off of
internal organs, fluids and tissues, the sensitive microphone in
the transducer records tiny changes in the sound's pitch and
direction. These signature waves are instantly measured and
displayed by a computer, which in turn creates a real-time
picture on the monitor.
Ultrasound – how does it work?
16. Ultrasound - biomedical applications
• heart and blood vessels, incl. the abdominal aorta and its
major branches
• liver
• gallbladder
• spleen
• pancreas
• kidneys
• bladder
• uterus, ovaries, and unborn child (fetus) in pregnant patients
• eyes
• thyroid and parathyroid glands
• scrotum (testicles)
17. Ultrasound waves are reflected by air or gas; therefore ultrasound
is not an ideal imaging technique for the bowel.
Ultrasound waves do not pass through air; therefore an
evaluation of the stomach, small intestine and large intestine
may be limited. Intestinal gas may also prevent visualization of
deeper structures such as the pancreas and aorta.
Patients who are obese are more difficult to image because tissue
attenuates (weakens) the sound waves as they pass deeper into
the body.
Ultrasound has difficulty penetrating bone and therefore can only
see the outer surface of bony structures and not what lies within.
Ultrasound – limitations
19. SPECT
• Single Photon Emission Computed Tomography.
• gamma ray emissions are the source of information
(contrary to X-ray transmissions used in conventional CT)
• allows to visualize functional information about a patient's
specific organ or body system (similarly to X-ray Computed
Tomography (CT) or Magnetic Resonance Imaging (MRI)
20. • Internal radiation is administered by means of a pharmaceutical
which is labeled with a radioactive isotope / tracer /
radiopharmaceutical, is either injected, ingested, or inhaled.
• The radioactive isotope decays, resulting in the emission of
gamma rays. These gamma rays give us a picture of what's
happening inside the patient's body.
SPECT - how does it work?
21. • The Gamma camera collects gamma rays that are emitted
from within the patient, enabling us to reconstruct a picture of
where the gamma rays originated. From this, we can determine
how a particular organ or system is functioning.
• The gamma camera can be used in planar imaging to acquire 2-
dimensional images, or in SPECT imaging to acquire 3-
dimensional images.
SPECT /Gamma camera - how does it work?
22. Once a radiopharmaceutical has been administered, it is
necessary to detect the gamma ray emissions in order to attain
the functional information.
The instrument used in Nuclear Medicine for the detection of
gamma rays is known as the Gamma camera. The components
making up the gamma camera are the collimator, detector
crystal, photomultiplier tube array, position logic circuits,
and the data analysis computer.
Gamma Camera
23. Gamma Camera - Planar Dynamic Imaging
• Since the camera remains at a fixed position in a planar
study, it is possible to observe the motion of a radiotracer
through the body by acquiring a series of planar
images of the patient over time.
• Each image is a result of summing data over a short time
interval, typically 1-10 seconds.
24. SPECT - Imaging
• If one rotates the camera around the patient, the camera
will acquire views of the tracer distribution at a variety of
angles.
• After all these angles have been observed, it is possible to
reconstruct a three dimensional view of the radiotracer
distribution within the body.
25. SPECT - Applications
• Heart Imaging
• Brain Imaging
• Kidney/Renal Imaging
• Bone Scans
• …
Heart
A set of bone scan
projections
Kidney/Renal
Brain
27. CT - basics
• CT scans use a series of X-ray beams
• It creates cross-sectional images, e.g. of the brain and shows
the structure of the brain, but not its function.
• Digital geometry processing is used to generate a three-
dimensional image of the internals of an object from a large
series of two-dimensional X-ray images taken around a single
axis of rotation
28. CT - basics
• CT's primary benefit is the ability to separate anatomical
structures at different depths within the body.
• A form of tomography can be performed by moving the X-ray
source and detector during an exposure.
• Anatomy at the target level remains sharp, while structures at
different levels are blurred.
• By varying the extent and path of motion, a variety of effects
can be obtained, with variable depth of field and different
degrees of blurring of 'out of plane' structures.
29. CT - principle
• Because contemporary CT scanners offer isotropic, or near
isotropic, resolution, display of images does not need to be
restricted to the conventional axial images.
• Instead, it is possible for a software program to build a
volume by 'stacking' the individual slices one on top of the
other. The program may then display the volume in an
alternative manner.
30. CT - diagnostic use
Cranial
• diagnosis of cerebrovascular
accidents and intracranial
hemorrhage
• CT generally does not exclude
infarct in the acute stage of a
stroke. For detection of tumors,
CT scanning with IV contrast
is occasionally used but is less
sensitive than magnetic
resonance imaging (MRI).
31. CT - diagnostic use
Chest
•CT is excellent for detecting both acute and chronic changes in
the lung parenchyma.
•A variety of different techniques are used depending on the
suspected abnormality.
•For evaluation of chronic interstitial processes (emphysema,
fibrosis, and so forth), thin sections with high spatial frequency
reconstructions are used - often scans are performed both in
inspiration and expiration. This special technique is called High
resolution CT (HRCT).
•For detection of airspace disease (such as
pneumonia) or cancer, relatively thick
sections and general Purpose image
reconstruction techniques may be adequate.
32. CT - diagnostic use
Cardiac
• With the advent of subsecond rotation combined with
multi-slice CT (up to 64-slice), high resolution and high speed
can be obtained at the same time, allowing excellent imaging
of the coronary arteries (cardiac CT angiography).
• Images with an even higher temporal resolution can be formed
using retrospective ECG gating. In this technique, each portion
of the heart is imaged more than once while an ECG trace is
recorded. The ECG is then used to correlate the CT data with
their corresponding phases of cardiac contraction. Once this
correlation is complete, all data that were recorded while the
heart was in motion (systole) can be ignored and images can
be made from the remaining data that happened to be acquired
while the heart was at rest (diastole). In this way, individual
frames in a cardiac CT investigation have a better temporal
resolution than the shortest tube rotation time.
33. CT - diagnostic use
Abdominal and pelvic
• CT is a sensitive method for diagnosis of abdominal diseases.
It is used frequently to determine stage of cancer and to follow
progress. It is also a useful test to investigate acute abdominal
pain.
• Renal/urinary stones, appendicitis, pancreatitis, diverticulitis,
abdominal aortic aneurysm, and bowel obstruction are
conditions that are readily diagnosed and assessed with CT.
• CT is also the first line for detecting solid organ injury after
trauma.
39. MRI & fMRI - basics
• An MRI uses powerful magnets to excite hydrogen nuclei in
water molecules in human tissue, producing a detectable
signal. Like a CT scan, an MRI traditionally creates a 2D
image of a thin "slice" of the body.
• The difference between a CT image and an MRI image is in
the details. X-rays must be blocked by some form of dense
tissue to create an image, therefore the image quality when
looking at soft tissues will be poor.
• An MRI can ONLY "see" hydrogen based objects, so bone,
which is calcium based, will be a void in the image, and will
not affect soft tissue views. This makes it excellent for peering
into joints.
• As an MRI does not use ionizing radiation, it is the preferred
imaging method for children and pregnant women.
40. MRI & fMRI - basics
• Magnetic resonance imaging (MRI), formerly referred to as
magnetic resonance tomography (MRT) and, in scientific
circles and as originally marketed by companies such as
General Electric, nuclear magnetic resonance imaging
(NMRI) or NMR zeugmatography imaging, is a non-invasive
method using nuclear magnetic resonance to render images of
the inside of an object.
• It is primarily used in medical imaging to demonstrate
pathological or other physiological alterations of living tissues.
• MRI also has uses outside of the medical field, such as
detecting rock permeability to hydrocarbons and as a non-
destructive testing method to characterize the quality of
products such as produce and timber.
41.
42. MRI & fMRI - basics
• The scanners used in medicine have a typical magnetic field
strength of 0.2 to 3 Teslas. Construction costs
approximately US$ 1 million per Tesla and maintenance an
additional several hundred thousand dollars per year.
• Medical Imaging MRI, or "NMR" as it was originally known,
has only been in use since the 1980's. Effects from long
term, or repeated exposure, to the intense magnetic field
is not well documented.
• Functional MRI detects changes in blood flow to particular
areas of the brain. It provides both an anatomical and a
functional view of the brain.
• MRI uses the detection of radio frequency signals produced
by displaced radio waves in a magnetic field. It provides an
anatomical view of the brain.
43. Advantages:
• No X-rays or radioactive material is used.
• Provides detailed view of the brain in different dimensions.
• Safe, painless, non-invasive.
• No special preparation (except the removal of all metal objects)
is required from the patient. Patients can eat or drink anything
before the procedure.
Disadvantages:
• Expensive to use.
• Cannot be used in patients with metallic devices (pacemakers).
• Cannot be used with uncooperative patients because the patient
must lie still.
• Cannot be used with patients who are claustrophobic (unless
new MRI systems with a more open design are used).
MRI & fMRI – dis/advantages
44. MRI & fMRI
Functional MRI
• A fMRI scan showing regions of activation in
orange, including the primary visual cortex.
• Functional MRI (fMRI) measures signal
changes in the brain that are due to changing
neural activity. The brain is scanned at low
resolution but at a rapid rate (typically once
every 2-3 seconds). Increases in neural
activity cause changes in the MR signal; this
mechanism is referred to as the BOLD
(blood-oxygen-level dependent) effect.
45. Modern 3 Tesla clinical MRI scanner.
Medical MRI most frequently relies on the relaxation properties of
excited hydrogen nuclei in water and lipids. When the object
to be imaged is placed in a powerful, uniform magnetic field,
the spins of atomic nuclei with a resulting non-zero spin have
to arrange in a particular manner with the applied magnetic
field according to quantum mechanics. Nuclei of hydrogen
atoms (protons) have a simple spin 1/2 and therefore align
either parallel or antiparallel to the magnetic field.
MRI & fMRI - principle
46. The spin polarization determines the basic MRI signal strength.
For protons, it refers to the population difference of the two
energy states that are associated with the parallel and
antiparallel alignment of the proton spins in the magnetic
field. The bulk collection of nuclei can be partitioned into a
set whose sum spin are aligned parallel and a set whose sum
spin are anti-parallel.
MRI & fMRI - principle
47. The magnetic dipole moment of the nuclei then movies
around the axial field. While the proportion is nearly
equal, slightly more are oriented at the low energy
angle. The tissue is then briefly exposed to pulses of
electromagnetic energy (RF pulses) in a plane
perpendicular to the magnetic field, causing some of
the magnetically aligned hydrogen nuclei to assume
a temporary non-aligned high-energy state.
MRI & fMRI - principle
