Download Medical Imaging - Engr. Ijlal Haider

Medical Imaging
Index
• Medical Imaging
• Evolution of Medical Imaging
• Types of Medical Imaging
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Medical Radiography
X-Ray Imaging
Nuclear Imaging
Bone Densitometry
Magnetic Resonance Imaging (MRI)
Ultrasound
Neuroprosthetics
Computed Tomography (CT)
Fluoroscopy
Echocardiography
▫ Digital Vascular Imaging
▫ Positron Emission Tomography (PET) and
Radionuclide Scanning
Medical Imaging
• Medical imaging is a discipline within the medical field which
involves the use of technology to take images of the inside of the
human body. These images are used in diagnostics, as teaching
tools, and in routine healthcare for a variety of conditions.
• Medical imaging is sometimes referred to as diagnostic imaging,
because it is frequently used to help doctors arrive at a diagnosis,
and there are a number of different types of technology used in
medical imaging.
The goal of medical imaging is to provide a picture of the inside
of the body in a way which is as non-invasive as possible.
An imaging study can be used to identify unusual things inside
the body, such as broken bones, tumors, leaking blood vessels,
and so forth. One of the most famous types of diagnostic
imaging is the x-ray, which uses radiation to take a static image
of a specific area of the body.
Evolution of Medical Imaging
• Medical imaging began with the discovery of XRays by Wilhelm Conrad Röntgen in 1895 and
his work showing that these rays could be used
to peer inside the body and visualize bony
structures.
From this Nobel Prize winning discovery to the modern
day, there are now many means by which the internal
structures of the body can be assessed without the need
for cutting it open.
Measurement and recording techniques which are
not primarily designed to produce images, such as
electroencephalography (EEG), magneto
encephalography (MEG), electrocardiography
(ECG) and others, but which produce data
susceptible to be represented as maps (i.e.
containing positional information), can be seen as
forms of medical imaging.
Types of Medical Imaging
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Medical Radiography
X-Ray Imaging
Nuclear Imaging
Bone Densitometry
Magnetic Resonance Imaging (MRI)
Ultrasound
Computed Tomography (CT)
Fluoroscopy
Echocardiography
▫ Digital Vascular Imaging
▫ Positron Emission Tomography
(PET) and Radionuclide Scanning
Medical Radiography
• During a radiographic procedure, an x-ray beam is passed
through the body.
• A portion of the x-rays are absorbed or scattered by the
internal structure and the remaining x-ray pattern is
transmitted to a detector so that an image may be recorded
for later evaluation.
• The recoding of the pattern may occur on film or through
electronic means
Medical Radiography is considered a noninvasive procedure, which
means that the process of acquiring a medical image does not
penetrate the skin.
Radiography is used in many types of examinations and
procedures where a record of a static image is desired. Some
examples include
▫ Dental examination
▫ Verification of correct placement of surgical
markers prior to invasive procedures
▫ Mammography
▫ Orthopedic evaluations
▫ Spot film or recording during fluoroscopy
▫ Chiropractic examinations
Digital Radiography
MATRIX
X-Ray Imaging
• X-rays are waves that have a relatively high
frequency along the electromagnetic spectrum.
They are absorbed or transmitted by different body
tissues in varying amounts, producing different
shades of black and white on an x-ray image.
The basic type of x-ray imaging is plain radiography. This involves
an x-ray machine aimed at the patient's body with a recording
plate positioned behind the region of interest. Once the machine
delivers its radiation, the image is captured on the plate. This
allows
a physician
to assess
the bones
for fractures,
abdomen
In general,
bone appears
white,
soft tissue
appears the
gray,
and
for
obstruction,
and the breasts for signs of cancer
airbowel
appears
black.
(mammography), among other applications.
Nuclear Imaging
• Nuclear imaging is unique in that the means of
visualization are not external waves delivered to the
body. Rather, electromagnetic waves are emitted
from within. In general, a radioactive marker is
introduced into the patient's bloodstream and
accumulates in the organ of interest. The marker
gives off gamma rays that are detected by a special
camera and processed into images by a computer.
This type of imaging is also unique in that nuclear medicine
physicians, not radiologists, are the ones who interpret
nuclear imaging studies. Applications of nuclear imaging
include perfusion of the heart, activity of the thyroid gland,
and late-stage cancer.
Nuclear medicine images
• Bone density scanning is a form of X-ray
technology used to measure a person’s bone loss.
Bone densitometry is most often used to diagnose
osteoporosis, a condition that causes a gradual
loss of calcium resulting in thinner and more
fragile bones.
Bone densitometry is also a preventative tool that
tracks the effect of treatment for various
conditions that cause bone loss.
Image Digitization
Transducer
Digitization with Matrix Arraying Scheme
Windowing
Inversion
Image Sharpening
MRI Scanners
• MRI scanners, like X-rays and CT scanners, are
basically machines doctors use to take pictures of
your insides so that they can figure out what’s ailing
you.
• But MRI doesn’t involve ionizing radiation, as do Xrays and CT scans. Rather, MRI takes advantage of
something you have plenty of in your body: water.
It is far more flexible than X-rays and CT scans, and can generate
three dimensional images in any orientation and at any depth in
the body.
MRI- SIGNAL FROM DETECTORS:
ANALOG
ANALOG
Residual Tumor Detection
1. Pre-opt MRI of tumor
2. Intraoperative MRI, residual tumor
3. Post-opt, no tumor
Ultrasound Imaging
• Ultrasound imaging uses high-frequency sound
waves to produce detailed images of internal
structures of the body.
• Ultrasound imaging is used by physicians to get
valuable information that will help them when it
comes to diagnosing certain types of illnesses.
• One such use is to determine the blood flow in a
patients blood vessels. One drawback of ultrasound
imaging is the fact that sound does not travel well
through bone.
• Ultrasound is produced and detected with a
transducer, composed of one or more ceramic
elements with electromechanical (piezoelectric)
properties.
The ceramic element converts electrical energy into
mechanical energy to produce ultrasound and
mechanical energy into electrical energy for
ultrasound detection.
• Over the past several decades, the transducer
assembly has evolved considerably in design,
function, and capability, from a single-element
resonance crystal to a broadband transducer
array of hundreds of individual elements.
▫ A simple single-element, plane-piston source
transducer has major components including the
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Piezoelectric material
Marching layer
Backing block
Acoustic absorber
Insulating cover
Sensor electrode
Transducer housing
Characteristics of Diagnostic Ultrasound
•Non-invasive
•Safe (under regulations)
•Real-time
•Reflection mode (similar to RADAR)
•Blood flow imaging
•Access
•Portable
•Body type dependent
Function Modes
•A-mode (A-scan, 1D).
•B-mode (Gray scale, 2D).
•3D ultrasound.
•M-mode (motion)
•Color Doppler (2D, blood flow).
•Spectral Doppler (localized, blood
flow).
•Audio Doppler.
Generic Ultrasonic Imaging System
Transmitter
–Arbitrary waveform.
–Programmable transmit voltage.
–Arbitrary firing sequence.
–Programmable apodization, delay
Receiver
–Programmable apodization, delay
control and frequency control.
–Arbitrary receive direction.
•Image processing:
–Pre-detection filtering.
–Post-detection filtering.
•Full gain correction: analog and digital.
•Scan converter: various scan format.
Image Data Acquisition
c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 501.
Ultrasound
• Heart and blood vessels, incl. the abdominal aorta and
its major branches
• Liver
• Gallbladder
• Spleen
• Pancreas
• Kidneys
• Bladder
• Eyes
• Thyroid and parathyroid glands
Image Digitization - ADC
Scanning
Sampling
Quantization
Ultrasound
• 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.
Image Manipulation
WINDOWING
INVERSION
IMAGE SHARPENING
Windowing
Image Inversion
Image Sharpening
Computed Tomography
Computed Tomography is a form of medical
imaging using tomography that is created by
computer processing. CT’s can be used to generate
three-dimensional images of the inside of the
human body. It does this by taking multiple twodimensional X-ray images around a single axis.
This data can then be manipulated to form an
image of different body structures.
Computed Tomography (CT) is a powerful
nondestructive evaluation (NDE) technique for
producing 2-D and 3-D cross-sectional images of
an object from flat X-ray images. Characteristics
of the internal structure of an object such as
dimensions, shape, internal defects, and density
are readily available from CT images.
• Unlike conventional radiography, in CT the patient lies on a couch
that moves through into the imaging gantry housing the x-ray tube
and an array of specially designed "detectors".
• Depending upon the system the gantry rotates for either one
revolution around the patient or continuously in order for the
detector array to record the intensity of the remnant x-ray beam.
These recordings are then computer processed to produce
images never before thought possible.
• CT on the other hand reconstructs images in a variety of body planes
the most usual being the axial or cross sectional plane.
• Because of the large range of the CT number scale and the fact that
the image is digital, it is possible to manipulate the display to show
the underlying soft tissues with enhanced contrast as well as the
bony structures.
Scanners today are capable of gathering even more data about
the body structure in a time span that is measured in seconds
thereby enhancing its clinical usefulness.
Why it is performed
CT rapidly creates detailed pictures of the body,
including the brain, chest, spine, and abdomen.
The test may be used to
Diagnose an infection
Guide a surgeon to the right area during a biopsy
Identify masses and tumors, including cancer
Study blood vessels
Risks
• Being exposed to radiation
• Allergic reaction to contrast dye
• CT scans do expose you to more radiation than
regular x-rays. Having many x-rays or CT scans
over time may increase your risk for cancer
BASIC DATA AQUSITION SCHEME IN CT
ANALOG
ADC
Fluoroscopy
• If a doctor needs real-time moving images of
internal bodily structures, then they will use an
imaging technique called fluoroscopy.
• The process of fluoroscopy consists of using a
radiation and a fluorescent screen.
This form of imaging exposes the patient to extremely high
forms of ionized radiation.
Echocardiography
• An echocardiography is a medical imaging procedure
that uses sound waves to create a moving picture of an
organ, usually the heart.
• Doctors use it because it gives a detailed picture and
exposes the patient to zero radiation.
• An echocardiogram enables the doctor to see the heart
beating, rather than just looking at a picture of the heart.
It also provides a detailed moving image of the heart
valves that provide even more useful information to the
doctor when attempting to diagnose an illness.
Types
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Transthoracic Echocardiography
Stress Echocardiography
Trans-esophageal Echocardiography
Fetal Echocardiography
Three-Dimensional Echocardiography
Digital Vascular Imaging
• This is an imaging modality that utilizes the
technology of digital fluoroscopy and additional
equipment and computer systems to image the
blood vessels (arteries and veins) of the human
body.
Positron Emission Tomography(PET)
and Radionuclide Scanning
• Another means of imaging the inside of the human body is to
inject chemicals such as glucose, which are routinely used by
cells, and to label them with short-lived radioactive elements.
• In positron emission tomography, a radiopharmaceutical
compound is injected which can be “seen” by specialized
detectors built into the scanner.
• As the radiopharmaceutical undergoes radioactive decay it
emits positrons which lead to molecular actions that can be
detected by the scanner.
This method can measure the metabolic activity of specific
tissues or regions of tissues as well as to assess the metabolic
activity and spread of cancers, especially when coupled with
coincident CT scanning as is the most common approach used
today.
Innovations in medical imaging continue to revolutionize
the field of medicine. The advances that have been made
are allowing physicians to not only see inside the body
with greater clarity, but it is also providing them with the
ability to see how certain organs are functioning.
References
• http://www.med.monash.edu.au/radiography/geninfo/index.html
• http://www.wisegeek.com/what-is-medical-imaging.htm
• http://www.vumc.com/afdelingen/imagingcenter/economic_impact/medi
cal_imaging/
• http://anthony-lee.suite101.com/types-of-medical-imaging-a85622
• http://www.onlinenursingprograms.com/resources/a-guide-on-the-typesof-medical-imaging/