imaging methods

8/2/2019 Imaging Methods

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Biomedical Imaging

Eugen Kvasnak, PhD.

Department of Medical Biophysics and Informatics3rd Medical Faculty of Charles University


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Content

Microscopy

Ultrasound & Sonography SPECT & Gamma Camera

CT

NMR & fMRI PET


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Microscopy

main branches: optical, electron and scanning probemicroscopy. (+ less used X-ray microscopy)

Optical and electron microscopy involves thediffraction, reflection, or refraction of radiationincident upon the subject of study, and thesubsequent collection of this scattered radiation inorder to build up an image.

Scanning probe microscopy involves the interactionof a scanning probe with the surface or object ofinterest.
http://en.wikipedia.org/wiki/Optical_microscopyhttp://en.wikipedia.org/wiki/Electron_microscopyhttp://en.wikipedia.org/wiki/Scanning_probe_microscopyhttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Reflection_%28physics%29http://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Scanning_probe_microscopyhttp://en.wikipedia.org/wiki/Scanning_probe_microscopyhttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Reflection_%28physics%29http://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Scanning_probe_microscopyhttp://en.wikipedia.org/wiki/Electron_microscopyhttp://en.wikipedia.org/wiki/Optical_microscopy


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Optical or light microscopy involves passing visible lighttransmitted through or reflected from the sample through asingle or multiple lenses to allow a magnified view of thesample.

The resulting image can be detected directly by the eye,imaged on a photographic plate or captured digitally.

The single lens with its attachments, or the system oflenses and imaging equipment, along with the appropriate

lighting equipment, sample stage and support, makes upthe basic light microscope.

Optical microscopy - definition
http://en.wikipedia.org/wiki/Visible_lighthttp://en.wikipedia.org/wiki/Lens_%28optics%29http://en.wikipedia.org/wiki/Photographic_platehttp://en.wikipedia.org/wiki/Digital_imaginghttp://en.wikipedia.org/wiki/Digital_imaginghttp://en.wikipedia.org/wiki/Photographic_platehttp://en.wikipedia.org/wiki/Lens_%28optics%29http://en.wikipedia.org/wiki/Visible_light


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Optical microscopy - scheme


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Optical microscopy - magnification


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Optical microscopy - limitations

OM can only image dark or strongly refracting objects effectively.Out of focus light from points outside the focal plane reduces

image clarity. Compound optical microscopes are limited intheir ability to resolve fine details by the properties of light andthe refractive materials used to manufacture lenses. A lensmagnifies by bending light. Optical microscopes are restrictedin their ability to resolve features by a phenomenon calleddiffraction which, based on the numerical aperture AN of theoptical system and the wavelengths oflightused (), sets adefinite limit (d) to the optical resolution. Assuming that opticalaberrations are negligible, the resolution (d) is given by:

In case of = 550 nm (green light), with air as medium, thehighest practicalANis 0.95, with oil, up to 1.5.

Due to diffraction, even the best optical microscope is limited to aresolution of around 0.2 micrometres.
http://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Numerical_aperturehttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Optical_resolutionhttp://en.wikipedia.org/wiki/Optical_aberrationhttp://en.wikipedia.org/wiki/Optical_aberrationhttp://en.wikipedia.org/wiki/1_E-7_mhttp://en.wikipedia.org/wiki/Greenhttp://en.wikipedia.org/wiki/Earth%27s_atmospherehttp://en.wikipedia.org/wiki/Micrometrehttp://en.wikipedia.org/wiki/Micrometrehttp://en.wikipedia.org/wiki/Earth%27s_atmospherehttp://en.wikipedia.org/wiki/Greenhttp://en.wikipedia.org/wiki/1_E-7_mhttp://en.wikipedia.org/wiki/Optical_aberrationhttp://en.wikipedia.org/wiki/Optical_aberrationhttp://en.wikipedia.org/wiki/Optical_resolutionhttp://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Numerical_aperturehttp://en.wikipedia.org/wiki/Diffractionhttp://en.wikipedia.org/wiki/Light


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Optical microscopy techniques

Bright field optical microscopy

Oblique illumination

Dark field optical microscopy Phase contrast optical microscopy

Differential interference contrast microscopy

Fluorescence microscopy

Confocal laser scanning microscopy

Deconvolution microscopy

Near-field Scanning OM

Optical microscopy - types


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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 beamthan of light, resolution is far higher.

TYPES Transmission electron microscopy (TEM) is principally

quite similar to the compound light microscope, by sending anelectron beam through a very thin slice of the specimen. Theresolution limit (in 2005) is around 0.05 nanometer.

Scanning electron microscopy (SEM) visualizes details onthe surfaces of cells and particles and gives a very nice 3Dview. The magnification is in the lower range than that of thetransmission electron microscope.
http://en.wikipedia.org/wiki/Transmission_electron_microscopyhttp://en.wikipedia.org/wiki/Scanning_electron_microscopehttp://en.wikipedia.org/wiki/Scanning_electron_microscopehttp://en.wikipedia.org/wiki/Transmission_electron_microscopy


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Transmission Electron Microscopy (TEM)

beam ofelectrons is transmitted through a specimen, then animage is formed, magnified and directed to appear either on afluorescent screen or layer ofphotographic film or to bedetected by a sensor (e.g. charge-coupled device, CCDcamera.

involves a high voltage electron beam emitted by a cathode,

usually a tungsten filament and focused by electrostatic andelectromagnetic lenses.

electron beam that has been transmitted through a specimenthat is in part transparent to electrons carries information aboutthe 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 isrecorded by hitting a fluorescent screen, photographic plate, orCCD camera. The image detected by the CCD may be

displayed in real time on a monitor or computer.
http://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Fluorescencehttp://en.wikipedia.org/wiki/Photographic_filmhttp://en.wikipedia.org/wiki/Charge-coupled_devicehttp://en.wikipedia.org/wiki/CCD_camerahttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Cathodehttp://en.wikipedia.org/wiki/Electromagnetichttp://en.wikipedia.org/wiki/Electromagnetichttp://en.wikipedia.org/wiki/Cathodehttp://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/CCD_camerahttp://en.wikipedia.org/wiki/Charge-coupled_devicehttp://en.wikipedia.org/wiki/Charge-coupled_devicehttp://en.wikipedia.org/wiki/Charge-coupled_devicehttp://en.wikipedia.org/wiki/Photographic_filmhttp://en.wikipedia.org/wiki/Fluorescencehttp://en.wikipedia.org/wiki/Electron


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Transmission Electron Microscopy (TEM)

Black Ant

House Fly

Human red blood cells

Human stem cells

Neurons CNS

Neuron growing on astroglia

House Fly


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type ofelectron microscope capable of producing high-resolution images of a sample surface.

due to the manner in which the image is created, SEMimages have a characteristic 3D appearance and are useful

forjudging 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 whichproduces the scanning beam.

is not high enough to image individual atoms, as ispossible in the TEM so that, it is 1-20 nm

Scanning Electron Microscopy (SEM)
http://en.wikipedia.org/wiki/Electron_microscopehttp://en.wikipedia.org/wiki/Electron_microscope


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X-ray microscopy

less common,

developed since the late 1940s,

resolution of X-ray microscopy lies between that oflight microscopy and the electron microscopy.

X-rays are a form ofelectromagnetic radiation witha wavelength in the range of 10 to 0.01 nanometers,corresponding to frequencies in the range 30 PHz to30 EHz.
http://en.wikipedia.org/wiki/Electromagnetic_radiationhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Nanometerhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Hertzhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Nanometerhttp://en.wikipedia.org/wiki/Wavelengthhttp://en.wikipedia.org/wiki/Electromagnetic_radiation


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Ultrasound


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Ultrasound (Sonography) - basics

It is used to visualize muscles, tendons, and many internalorgans, their size, structure and any pathological lesionswith real time tomographic images. They are also used tovisualize a fetus during routine and emergency prenatal care.

The technology is relatively inexpensive and portable,especially when compared with modalities such as magneticresonance 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 andchromosome breakage).

However, it has two potential physiological effects: it enhances

inflammatory response; and it can heat soft tissue.
http://en.wikipedia.org/wiki/Lesionhttp://en.wikipedia.org/wiki/Prenatal_carehttp://en.wikipedia.org/wiki/Magnetic_resonance_imaginghttp://en.wikipedia.org/wiki/Magnetic_resonance_imaginghttp://en.wikipedia.org/wiki/Computed_tomographyhttp://en.wikipedia.org/wiki/Computed_tomographyhttp://en.wikipedia.org/wiki/Magnetic_resonance_imaginghttp://en.wikipedia.org/wiki/Magnetic_resonance_imaginghttp://en.wikipedia.org/wiki/Prenatal_carehttp://en.wikipedia.org/wiki/Lesion


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the same principles involved in the sonar used by bats, shipsand 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 theechoing waves. When the transducer is pressed against theskin, it directs a stream of inaudible, high-frequency sound

waves into the body. As the sound waves bounce off ofinternal organs, fluids and tissues, the sensitive microphone inthe transducer recordstiny changes in the sound's pitch anddirection. These signature waves are instantly measured anddisplayed by a computer, which in turn creates a real-timepicture on the monitor.

Ultrasoundhow does it work?
http://en.wikipedia.org/wiki/Megahertzhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?term=transducerhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?term=transducerhttp://en.wikipedia.org/wiki/Megahertz


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Ultrasound - biomedical applications

heart and blood vessels, incl. the abdominal aorta and itsmajor branches

liver

gallbladder

spleen pancreas

kidneys

bladder

uterus, ovaries, and unborn child (fetus) in pregnant patients eyes

thyroid and parathyroid glands

scrotum (testicles)
http://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=aortahttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=liverhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=gallbladderhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=spleenhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=pancreashttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=kidneyhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=bladderhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=uterushttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=ovaryhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=fetushttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=thyroid_glandhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=parathyroid_glandshttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=scrotumhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=testishttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=testishttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=scrotumhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=parathyroid_glandshttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=thyroid_glandhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=fetushttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=ovaryhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=uterushttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=bladderhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=kidneyhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=pancreashttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=spleenhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=gallbladderhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=liverhttp://www.radiologyinfo.org/en/glossary/glossary1.cfm?Term=aorta


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Ultrasound waves are reflected by air or gas; therefore ultrasoundis not an ideal imaging technique for the bowel.

Ultrasound waves do not pass through air; therefore anevaluation of the stomach, small intestine and large intestinemay be limited. Intestinal gas may also prevent visualization ofdeeper 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 intothe body.

Ultrasound has difficulty penetrating bone and therefore can onlysee the outer surface of bony structures and not what lies within.

Ultrasoundlimitations


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Single Positron Emission Computed

Tomography (SPECT)


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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)


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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?


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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-

dimensionalimages.

SPECT /Gamma camera - how does it work?


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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 analysiscomputer.

Gamma Camera


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Gamma Camera - how does it work?


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Gamma Camera - Collimator

- the first object that an

emitted gamma photon

encounters after exiting the

body. The collimator is a

pattern of holes through

gamma ray absorbingmaterial, usually lead or

tungsten, that allows the

projection of the gamma ray

image onto the detectorcrystal. The collimator

achieves this by only allowing

those gamma rays traveling

along certain directions to

reach the detector.


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In order to detect the gamma photon we use scintillationdetectors. A Thallium-activated Sodium Iodide [NaI(Tl)]detector crystal is generally used in Gamma cameras. This isdue to this crystal's optimal detection efficiency for the gammaray energies of radionuclide emission common to NuclearMedicine.

A detector crystal may be circular or rectangular. It is typically3/8" thick and has dimensions of 30-50 cm.A gamma ray photon interacts with the detector by meansof the Photoelectric Effect or Compton Scattering with theiodide ions of the crystal. This interaction causes the releaseof electrons which in turn interact with the crystal lattice toproduce light, in a process known as scintillation.

Gamma Camera - Scintillation Detector


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Gamma CameraPhotoelectric effect


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Gamma CameraCompton Scattering


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Gamma Camera - Scintillation


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Gamma Camera - Photomultiplier

- instrument that detects andamplifies the electrons that

are produced by the

photocathode which, when

stimulated by light photons

ejects electrons. For every 7 to 10 photons

incident on the photocathode,

only one electron is

generated. This electron fromthe cathode is focused on a

dynode which absorbs this

electron and re-emits many

more electrons (6 to 10).


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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.


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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.


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SPECT - Applications

Heart Imaging

Brain Imaging

Kidney/Renal Imaging

Bone Scans

Heart

A set of bone scan

projections

Kidney/Renal

Brain


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Computed Tomography Scan (CT)


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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-dimensionalimage of the internals of an object from a large

series of two-dimensional X-ray images taken around a singleaxis of rotation
http://en.wikipedia.org/wiki/Geometry_Processinghttp://en.wikipedia.org/wiki/Dimensionhttp://en.wikipedia.org/wiki/Dimensionhttp://en.wikipedia.org/wiki/Imagehttp://en.wikipedia.org/wiki/X-rayhttp://en.wikipedia.org/wiki/X-rayhttp://en.wikipedia.org/wiki/X-rayhttp://en.wikipedia.org/wiki/X-rayhttp://en.wikipedia.org/wiki/Imagehttp://en.wikipedia.org/wiki/Dimensionhttp://en.wikipedia.org/wiki/Dimensionhttp://en.wikipedia.org/wiki/Dimensionhttp://en.wikipedia.org/wiki/Geometry_Processinghttp://en.wikipedia.org/wiki/Geometry_Processing


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CT - basics

CT's primary benefit is the ability to separate anatomicalstructures at different depths within the body.

A form of tomography can be performed by moving the X-raysource and detector during an exposure.

Anatomy at the target level remains sharp, while structures atdifferent levels are blurred.

By varying the extent and path of motion, a variety of effectscan be obtained, with variable depth of field and differentdegrees of blurring of 'out of plane' structures.
http://en.wikipedia.org/wiki/Depth_of_fieldhttp://en.wikipedia.org/wiki/Depth_of_field


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CT - principle

Because contemporary CT scanners offer isotropic, or nearisotropic, resolution, display of images does not need to berestricted to the conventional axial images.

Instead, it is possible for a software program to build avolume by 'stacking' the individual slices one on top of theother. The program may then display the volume in analternative manner.
http://en.wikipedia.org/wiki/Isotropyhttp://en.wikipedia.org/wiki/Isotropy


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CT - diagnostic use

Cranial

diagnosis ofcerebrovascular

accidents and intracranial

hemorrhage CT generally does not exclude

infarct in the acute stage of a

stroke. For detection oftumors,

CT scanning with IV contrastis occasionally used but is less

sensitive than magnetic

resonance imaging (MRI).
http://en.wikipedia.org/wiki/Cerebrovascular_accidenthttp://en.wikipedia.org/wiki/Cerebrovascular_accidenthttp://en.wikipedia.org/wiki/Intracranial_hemorrhagehttp://en.wikipedia.org/wiki/Intracranial_hemorrhagehttp://en.wikipedia.org/wiki/Infarcthttp://en.wikipedia.org/wiki/Strokehttp://en.wikipedia.org/wiki/Tumorhttp://en.wikipedia.org/wiki/Magnetic_resonance_imaginghttp://en.wikipedia.org/wiki/Magnetic_resonance_imaginghttp://en.wikipedia.org/wiki/Magnetic_resonance_imaginghttp://en.wikipedia.org/wiki/Magnetic_resonance_imaginghttp://en.wikipedia.org/wiki/Tumorhttp://en.wikipedia.org/wiki/Strokehttp://en.wikipedia.org/wiki/Infarcthttp://en.wikipedia.org/wiki/Intracranial_hemorrhagehttp://en.wikipedia.org/wiki/Intracranial_hemorrhagehttp://en.wikipedia.org/wiki/Cerebrovascular_accidenthttp://en.wikipedia.org/wiki/Cerebrovascular_accident


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CT - diagnostic use

Chest

CT is excellent for detecting both acute and chronic changes inthe 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.
http://en.wikipedia.org/wiki/Lunghttp://en.wikipedia.org/wiki/Emphysemahttp://en.wikipedia.org/wiki/Fibrosishttp://en.wikipedia.org/w/index.php?title=High_resolution_CT&action=edithttp://en.wikipedia.org/w/index.php?title=High_resolution_CT&action=edithttp://en.wikipedia.org/wiki/Pneumoniahttp://en.wikipedia.org/wiki/Lung_cancerhttp://en.wikipedia.org/wiki/Lung_cancerhttp://en.wikipedia.org/wiki/Pneumoniahttp://en.wikipedia.org/w/index.php?title=High_resolution_CT&action=edithttp://en.wikipedia.org/w/index.php?title=High_resolution_CT&action=edithttp://en.wikipedia.org/wiki/Fibrosishttp://en.wikipedia.org/wiki/Emphysemahttp://en.wikipedia.org/wiki/Lung


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CT - diagnostic use

Cardiac With the advent ofsubsecond rotation combined withmulti-slice CT (up to 64-slice), high resolution and high speedcan be obtained at the same time, allowing excellent imagingof the coronary arteries (cardiac CT angiography).

Images with an even higher temporal resolution can be formedusing retrospective ECG gating. In this technique, each portionof the heart is imaged more than once while an ECG trace isrecorded. The ECG is then used to correlate the CT data withtheir corresponding phases of cardiac contraction. Once thiscorrelation is complete, all data that were recorded while the

heart was in motion (systole) can be ignored and images canbe made from the remaining data that happened to be acquiredwhile the heart was at rest (diastole). In this way, individualframes in a cardiac CT investigation have a better temporalresolution than the shortest tube rotation time.


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CT - diagnostic use

Abdominal and pelvic

CT is a sensitive method for diagnosis ofabdominal diseases.It is used frequently to determine stage of cancer and to followprogress. It is also a useful test to investigate acute abdominal

pain. Renal/urinary stones, appendicitis, pancreatitis, diverticulitis,

abdominal aortic aneurysm, and bowel obstruction areconditions that are readily diagnosed and assessed with CT.

CT is also the first line for detecting solid organ injury after

trauma.
http://en.wikipedia.org/wiki/Human_abdomenhttp://en.wikipedia.org/wiki/Kidney_stonehttp://en.wikipedia.org/wiki/Appendicitishttp://en.wikipedia.org/wiki/Pancreatitishttp://en.wikipedia.org/wiki/Diverticulitishttp://en.wikipedia.org/wiki/Aortic_aneurysmhttp://en.wikipedia.org/wiki/Bowel_obstructionhttp://en.wikipedia.org/wiki/Bowel_obstructionhttp://en.wikipedia.org/wiki/Aortic_aneurysmhttp://en.wikipedia.org/wiki/Diverticulitishttp://en.wikipedia.org/wiki/Pancreatitishttp://en.wikipedia.org/wiki/Appendicitishttp://en.wikipedia.org/wiki/Kidney_stonehttp://en.wikipedia.org/wiki/Human_abdomen


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CTstep by step


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CTstep by step


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CTstep by step


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CTstep by step


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Magnetic Resonance Imaging (MRI)


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MRI & fMRI - basics

An MRI uses powerful magnets to excitehydrogennuclei inwater molecules in human tissue, producing a detectablesignal. Like a CT scan, an MRI traditionally creates a 2Dimage of a thin "slice" of the body.

The difference between a CT image and an MRI image is inthe details. X-rays must be blocked by some form of densetissue to create an image, therefore the image quality whenlooking 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 willnot affect soft tissue views. This makes it excellent for peeringinto joints.

As an MRI does not use ionizing radiation, it is the preferredimaging method for children and pregnant women.
http://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Hydrogen


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MRI & fMRI - basics

Magnetic resonance imaging (MRI), formerly referred to asmagnetic resonance tomography (MRT) and, in scientificcircles and as originally marketed by companies such asGeneral Electric, nuclear magnetic resonance imaging(NMRI) or NMR zeugmatography imaging, is a non-invasivemethod using nuclear magnetic resonance to render images ofthe inside of an object.

It is primarily used in medical imaging to demonstratepathological or other physiological alterations ofliving tissues.

MRI also has uses outside of the medical field, such asdetecting rock permeability to hydrocarbons and as a non-destructive testing method to characterize the quality ofproducts such as produce and timber.
http://en.wikipedia.org/wiki/General_Electrichttp://en.wikipedia.org/wiki/Non-invasive_%28medical%29http://en.wikipedia.org/wiki/Nuclear_magnetic_resonancehttp://en.wikipedia.org/wiki/Medical_imaginghttp://en.wikipedia.org/wiki/Pathologyhttp://en.wikipedia.org/wiki/Physiologyhttp://en.wikipedia.org/wiki/Tissue_%28biology%29http://en.wikipedia.org/wiki/Hydrocarbonshttp://en.wikipedia.org/wiki/Non-destructive_testinghttp://en.wikipedia.org/wiki/Non-destructive_testinghttp://en.wikipedia.org/wiki/Producehttp://en.wikipedia.org/wiki/Timberhttp://en.wikipedia.org/wiki/Timberhttp://en.wikipedia.org/wiki/Producehttp://en.wikipedia.org/wiki/Non-destructive_testinghttp://en.wikipedia.org/wiki/Non-destructive_testinghttp://en.wikipedia.org/wiki/Non-destructive_testinghttp://en.wikipedia.org/wiki/Hydrocarbonshttp://en.wikipedia.org/wiki/Tissue_%28biology%29http://en.wikipedia.org/wiki/Physiologyhttp://en.wikipedia.org/wiki/Pathologyhttp://en.wikipedia.org/wiki/Medical_imaginghttp://en.wikipedia.org/wiki/Nuclear_magnetic_resonancehttp://en.wikipedia.org/wiki/Non-invasive_%28medical%29http://en.wikipedia.org/wiki/Non-invasive_%28medical%29http://en.wikipedia.org/wiki/Non-invasive_%28medical%29http://en.wikipedia.org/wiki/General_Electric


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MRI & fMRI - basics

MRI should not be confused with the NMR spectroscopy

technique used in chemistry, although both are based on the

same principles ofnuclear magnetic resonance.

In fact MRI is a series of NMR experiments applied to the

signal from nuclei (typified by the hydrogen nuclei in water)

used to acquire spatial information in place of chemical

information about molecules.

The same equipment, provided suitable probes and magnetic

gradients are available, can be used for both imaging and

spectroscopy.
http://en.wikipedia.org/wiki/NMR_spectroscopyhttp://en.wikipedia.org/wiki/Chemistryhttp://en.wikipedia.org/wiki/Nuclear_magnetic_resonancehttp://en.wikipedia.org/wiki/Nuclear_magnetic_resonancehttp://en.wikipedia.org/wiki/Chemistryhttp://en.wikipedia.org/wiki/NMR_spectroscopy


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MRI & fMRI - basics

The scanners used in medicine have a typical magnetic fieldstrength of 0.2 to 3 Teslas. Construction costsapproximately US$ 1 million per Tesla and maintenance anadditional 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 longterm, or repeated exposure, to the intense magnetic fieldis not well documented.

Functional MRIdetects changes in blood flow to particularareas of the brain. It provides both an anatomical and afunctional view of the brain.

MRI uses the detection of radio frequency signals producedby displaced radio waves in a magnetic field. It provides ananatomical view of the brain.
http://en.wikipedia.org/wiki/Tesla_%28unit%29http://en.wikipedia.org/wiki/United_States_dollarhttp://www.functionalmri.org/http://www.functionalmri.org/http://en.wikipedia.org/wiki/United_States_dollarhttp://en.wikipedia.org/wiki/Tesla_%28unit%29


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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 anythingbefore the procedure.

Disadvantages:

Expensive to use.

Cannot be used in patients with metallic devices (pacemakers).

Cannot be used with uncooperative patients because the patientmust lie still.

Cannot be used with patients who are claustrophobic (unlessnew MRI systems with a more open design are used).

MRI & fMRIdis/advantages


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MRI & fMRI

Functional MRI A fMRI scan showing regions of activation in orange,including the primary visual cortex (V1, BA17).

Functional MRI (fMRI) measures signal changes in the brainthat are due to changing neural activity. The brain is scanned

at low resolution but at a rapid rate (typically once every 2-3seconds). Increases in neural activity cause changes in theMR signal via T2* changes; this mechanism is referred to asthe BOLD (blood-oxygen-level dependent) effect. Increasedneural activity causes an increased demand for oxygen, and

the vascular system actually overcompensates for this,increasing the amount of oxygenated hemoglobin(haemoglobin) relative to deoxygenated hemoglobin.
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MRI & fMRI

Because deoxygenated hemoglobin attenuates the MR signal,the vascular response leads to a signal increase that is relatedto the neural activity. The precise nature of the relationshipbetween neural activity and the BOLD signal is a subject ofcurrent research. The BOLD effect also allows for thegeneration of high resolution 3D maps of the venous

vasculature within neural tissue. While BOLD signal is the most common method employed

for neuroscience studies in human subjects, the flexible natureof MR imaging provides means to sensitize the signal to otheraspects of the blood supply. Alternative techniques employ

arterial spin labeling (ASL) or weight the MRI signal bycerebral blood flow (CBF) and cerebral blood volume

(CBV). The CBV method requires injection of a class

of MRI contrast agents that are now in human clinical

trials.


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Modern 3 Tesla clinical MRI scanner.

Medical MRI most frequently relies on the relaxation properties ofexcited hydrogennuclei in water and lipids. When the objectto be imaged is placed in a powerful, uniform magnetic field,

the spins ofatomic nuclei with a resulting non-zero spin haveto arrange in a particular manner with the applied magneticfield according to quantum mechanics. Nuclei of hydrogenatoms (protons) have a simple spin 1/2 and therefore aligneither parallel or antiparallel to the magnetic field.

MRI & fMRI - principle
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The spin polarization determines the basic MRI signal strength.For protons, it refers to the population difference of the twoenergy states that are associated with the parallel andantiparallel alignment of the proton spins in the magneticfield and governed by Boltzmann statistics. In a 1.5 T

magnetic field (at room temperature) this difference refers toonly about one in a million nuclei since the thermal energyfar exceeds the energy difference between the parallel andantiparallel states. Yet the vast quantity of nuclei in a smallvolume sum to produce a detectable change in field. Most

basic explanations of MRI will say that the nuclei alignparallel or anti-parallel with the static magnetic field;however, because ofquantum mechanical reasons, theindividual nuclei are actually set off at an angle from thedirection of the static magnetic field. The bulk collection ofnuclei can be partitioned into a set whose sum spin are

aligned parallel and a set whose sum spin are anti-parallel.

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The magnetic dipole moment of the nuclei then precesses aroundthe axial field. While the proportion is nearly equal, slightlymore are oriented at the low energy angle. The frequencywith which the dipole moments precess is called the Larmorfrequency. The tissue is then briefly exposed to pulses of

electromagnetic energy (RF pulses) in a plane perpendicularto the magnetic field, causing some of the magneticallyaligned hydrogen nuclei to assume a temporary non-alignedhigh-energy state. Or in other words, the steady-stateequilibrium established in the static magnetic field becomes

perturbed and the population difference of the two energylevels is altered. The frequency of the pulses is governed bythe Larmor equation to match the required energy differencebetween the two spin states.

http://en.wikipedia.org/wiki/Magnetic_dipole_momenthttp://en.wikipedia.org/wiki/Precessionhttp://en.wikipedia.org/wiki/Larmor_precessionhttp://en.wikipedia.org/wiki/Larmor_precessionhttp://en.wikipedia.org/wiki/Electromagnetichttp://en.wikipedia.org/wiki/Radiofrequencyhttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Larmor_equationhttp://en.wikipedia.org/wiki/Larmor_equationhttp://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Radiofrequencyhttp://en.wikipedia.org/wiki/Electromagnetichttp://en.wikipedia.org/wiki/Larmor_precessionhttp://en.wikipedia.org/wiki/Larmor_precessionhttp://en.wikipedia.org/wiki/Precessionhttp://en.wikipedia.org/wiki/Magnetic_dipole_moment


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Clinical practice, MRI is used to distinguish pathologic tissue (such as a brain tumor) from normal

tissue. One advantage of an MRI scan is that it is thought to be harmless to the patient. Ituses strong magnetic fields and non-ionizing radiation in the radio frequency range.Compare this to CT scans and traditional X-rays which involve doses ofionizing radiationand may increase the risk of malignancy, especially in a fetus.

While CT provides good spatial resolution (the ability to distinguish two structures an arbitrarilysmall distance from each other as separate), MRI provides comparable resolution with farbetter contrast resolution (the ability to distinguish the differences between two arbitrarilysimilar but not identical tissues). The basis of this ability is the complex library ofpulse

sequences that the modern medical MRI scanner includes, each of which is optimized toprovide image contrastbased on the chemical sensitivity of MRI.

For example, with particular values of the echo time (TE) and the repetition time (TR), which arebasic parameters of image acquisition, a sequence will take on the property of T2-weighting. On a T2-weighted scan, fat-, water- and fluid-containing tissues are bright (mostmodern T2 sequences are actuallyfast T2 sequences). Damaged tissue tends to developedema, which makes a T2-weighted sequence sensitive for pathology, and generally able todistinguish pathologic tissue from normal tissue. With the addition of an additional radio

frequency pulse and additional manipulation of the magnetic gradients, a T2-weightedsequence can be converted to a FLAIR sequence, in which free water is now dark, butedematous tissues remain bright. This sequence in particular is currently the most sensitiveway to evaluate the brain for demyelinating diseases, such as multiple sclerosis.

The typical MRI examination consists of 5-20 sequences, each of which are chosen to provide aparticular type of information about the subject tissues. This information is thensynthesized by the interpreting physician.

MRI & fMRI - applications
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Positron Emission Tomography (PET)


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A scanner detects radioactive material that is injected orinhaled to produce an image of the brain.

Commonly used radioactively-labeled material includesoxygen, fluorine, carbon and nitrogen.

When this material gets into the bloodstream, it goes to

areas of the brain that use it. So, oxygen and glucoseaccumulate in brain areas that are metabolically active.

When the radioactive material breaks down, it gives off aneutron and a positron.

When a positron hits an electron, both are destroyed and

two gamma rays are released. Gamma ray detectors record the brain area where the

gamma rays are emitted. This method provides a functionalview of the brain.


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Advantages:

Provides an image of brain activity.

Disadvantages:

Expensive to use.

Radioactive material used.



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For images thanks to:

http://www.sprawls.org/ppmi2/

http://www.sprawls.org/ppmi2/RADIOACT/

http://www.sprawls.org/resources/CTIMG/module.htm#31
http://www.sprawls.org/ppmi2/http://www.sprawls.org/ppmi2/


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DiagnosticMedicalImaging

MRI SPECTfMRI

X-Ray

CTUltrasound


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Thank you for your attention!

imaging methods

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