Transcript X-RAY IMAGING

Introduction to medical
imaging
Li SHAO DONG
Department of Radiology, Affiliated Hospital of Xuzhou Medical College
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CONVENTIONAL RADIOGRAPHY (X-RAYS;
PLAIN FILMS)
X-rays are a form of electromagnetic radiation.
The frequency and energy of X-rays are much
greater than visible light.
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They are produced in an X-ray tube by focusing
a beam of high-energy electrons on to a
tungsten target.
They are able to pass through the human body
and on to X-ray film thus producing an image.
X-ray film are held in cassettes of varying size
depending on the part of the body to be
examined.
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After an X-ray exposure is made the films are processed
in a darkroom or more commonly in free-standing
daylight processors.
The resulting image is commonly known as an ‘X-ray’.
The common terms ‘chest X-ray’ and ‘abdomen X-ray’
are widely accepted and commonly abbreviated to CXR
and AXR, respectively. More correct terms for an X-ray
image are ‘radiograph’ or ‘plain film’.
锁骨
肩胛骨
肋骨
椎体
diaphysis
medullary
cavity
compact
bone
metaphysis
Epiphysis
epiphyseal
plate
periosteum
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As a beam of X-rays passes through the human body
some of the X-rays are absorbed or scattered producing
reduction or attenuation of the beam.
The degree of X-ray beam attenuation is largely
dependent on the density and atomic number of the
various tissues. Tissues of high density cause more X-
ray beam attenuation.
X-rays turn X-ray film black.
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Therefore, less-dense tissues and structures
appear darker than tissues of highter density.
Similarly, materials of high atomic number cause
more X-ray beam attenuation than those of low
atomic number.
Five principal densities are recognized on plain
radiographs.
They are listed here in order of increasing
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1. Air/gas: black, e.g. lungs, bowel and stomach.
2. Fat: dark grey, e.g. subcutaneous tissue layer,
retroperitoneal fat.
3. Soft tissues/water: light grey, e.g. solid organs, heart,
blood vessels, muscle and fluid-filled organs such as
bladder.
4. Bone: off-white.
5. Contrast material/metal: bright white.
锁骨
肩胛骨
肋骨
椎体
正常后前位胸片
（图）
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An object will be seen with conventional
radiography if its borders lie beside tissue of
different density.
For example, the heart border is seen because it
lies against aerated lung, which is less dense.
When lung consolidation occurs, such as in
pneumonia, the lung density approaches that of
soft tissue.
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Consolidated lung lying against the heart border
will therefore obscure that border. A good
example is consolidation or collapse of the right
middle lobe causing loss of definition of the right
heart boder.
These comments apply to all radiographically
visible anatomical interfaces in the body.
Right upper lobe consolidation
Density in the projection of right upper lung field
Upper lobe distribution
No significant loss of lung volume
Air bronchogram
大叶性肺炎
（图）
右下肺密度增高
影，水平叶间裂
显示清楚
Note forward movement of left oblique fissure in the lateral
view.
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FLUOROSCOPY
Fluoroscopy refers to the technique of
examination of the anatomy and motion of
internal structures by a constant stream of Xrays.
The term ‘fluoroscopy’ is derived from the ability
of X-ray to cause fluorescenc.
人工对比
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The original fluoroscopes were rather primitive and
consisted of an X-ray tube, fluorescent screen and X-ray
table.
The radiologist directly viewed the image on the
fluorescent screen.
The images were very faint; examinations were
performed in a darkened room by a radiologist with darkadapted vision.
Dark-adaptation was achieved by wearing red goggles for
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Fluoroscopy was revolutionized in the 1950s by the
development of the image intensifier.
The image intensifier converts X-ray into images that are
usually viewed via a closed circuit television chain.
Images may be recorded as X-ray spot films performed
during screening or electronically from television
cameras in digital format.
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Uses of fluoroscopy include:
1.
Barium studies of the gastrointestinal tract.
2.
Angiography and interventional radiology.
3.
General surgery (operative cholangiography,
colonoscopy, etc.)
4.
Orthopaedic surgery: reduction and fixation of
fractures, joint replacements, etc.
5.
Airway screening in children for tracheomalacia, and
diaphragm screening.
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DIGITAL SUBTRACTION IMAGING
Digital subtraction imaging (DSI) is a process whereby a
computer removes unwanted information from a
radiographic image.
It is particularly useful for angiography, referred to as
DSA.
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COMPUTED AND DIGITAL RADIOGRAPHY
Diagnostic imaging is currently undergoing a digital
revolution.
Radiographic images may now be produced digitally
using one of two processes, computed radiography (CR)
and digital radiography (DR).
Both methods use an X-ray tube, as described above.
Instead of using X-ray film, CR employs cassettes that
contain a photostimulable phosphor.
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After the X-ray exposure is performed the
cassette is inserted into a laser reader.
A fine laser beam passes across the phosphor in
the cassette dislodging light photons.
The number of photons dislodged is in proportion
to the amount of X-rays that have hit the
phosphor.
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An analogue-digital converter (ADC) produces a digital
image.
Digital radiography uses a detector screen containing
silicon detectors.
There detectors produce an electrical signal when
exposed to X-rays.
This signal is analysed to produce a digital image.
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Computed radiography is generally more portable and
versatile than DR.
The latter is most widely used in mammography and
dental radiography.
Both methods remove the need for the chemicals used in
processing X-ray films.
More important are the many inherent advantages of
digital imaging.
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There include the ability to perform various manipulations
on the images after they have been taken, including
magnification of areas of interest, alteration of density
and accurate measurements of distances and angles.
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PICTURE ARCHIVING AND COMMUNICATION SYSTEMS
Many hospital X-ray departments now employ large computer storage
facilities and networks known as picture archiving and
communication systems (PACS).
Images obtained by CR and DR may be stored digitally, removing the
need for bulky X-ray packets and large X-ray storage rooms in
hospital.
The PACS also allow instant recall and display of a patient’s
radiographs and scans.
These can be displayed on monitors in the wards or theatre as
required.
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CONTRAST MATERIALS
The ability of conventional radiography and fluoroscopy to
display a range of organs and structures may be
enhanced by the use of various contrast materials.
The most common contrast materials are based on
barium or iodine.
Barium and iodine are high atomic number materials that
strongly absorb X-rays and are therefore seen as dense
white on radiography.
人工对比
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GASTROINTESTINAL CONTRAST MATERIALS
Contrast materials may be swallowed or injected via
nasogastric tube to outline the upper gastrointestinal
tract and small bowel, or may be introduced via an
enema tube to demonstrate the large bowel.
Gastrointestinal contrast materials are usually based on
barium, which is non-water-soluble.
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Occasionally a water-soluble contrast material based on iodine is
used for imaging of the gastrointestinal tract.
A single contrast barium study is one where a hollow viscus such as
the stomach or bowel is filled with barium.
The outline of the organ can be appreciated, although not its mucosal
surfaces.
If gas is then used to dilate the organ, the mucosal surfaces can be
seen coated with barium.
This is ‘double contrast’.
胃
• 分部(胃底fundus、胃体body、胃窦antrum、大弯
greater curvature、小弯lesser curvature)
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The majority of barium meals and enemas are performed
in double contrast as it provides much better mucosal
detail than single contrast.
For double contrast barium meals gas-forming
compounds are swallowed along with the barium.
In double contrast barium enemas air is pumped into the
bowel after coating of the mucosal surfaces with barium.
Single contrast studies using barium only may be
performed in children, and occasionally in the very
elderly.
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IODINATED CONTRAST MATERIALS
Water-soluble contrast materials may be injected into
veins, arteries, and various body cavities and systems.
The radiographic contrast of these water-soluble contrast
materials is based on the high atomic number of iodine.
These compounds are therefore known as iodinated
contrast materials.
Iodinated contrast materials are used in radiography to
visualize various body systems and organs as follows:
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1.
Arteries: injection into arterial system – arteriography or
angiography.
2.
Kidneys, ureters and bladder: intravenous injection followd
by renal excretion – intravenous pyelography (IVP).
3.
Joints: injection into various joints including shoulder, hip
and knee - arthrography.
4.
Outline of nerve roots and spinal cord: injection into thecal
sac – myelography.
5.
Salivary glands: injection into salivary gland duct –
sialography.
IVP