Far Eastern University – Nicanor Reyes Medical Foundation
GROSS RADIO – B: INTRODUCTION-DIAGNOSTIC IMAGING
AUGUST 2020
Dr. Chito
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FILM RADIOGRAPHY
Utilizes a screen-film system within a film cassette (x-ray detector)
OVERVIEW
Diagnostic Imaging Methods
Naming Radiographic Views
Basic Radiography Densities
Cross-sectional Imaging
DIAGNOSTIC IMAGING METHODS
CONVENTIONAL RADIOLOGY HISTORY
1895 – Wilhelm Conrad Roentgen produced the 1st x-ray image
PROCEDURE
(1) Patient is positioned
(4) X-RAY film is read thru a
negatoscope
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(2) X-RAY is taken
(3) Film cassette is taken to the
dark room for developing
X-RAY
Form of radiant energy similar to visible light
Has very short wavelength
Penetrates many substances that are opaque to light
Produced by bombarding a tungsten target with an electron beam
within an x-ray tube
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COMPUTED RADIOGRAPHY (CR)
Filmless system
No processing
Produces digital radiographic images
Substitutes a phosphor imaging plate for the film screen cassette
How is an x-ray film produced in conventional radiography?
X-rays pass through the body (a) à x-rays are attenuated by interaction
with body tissue (a) à transmitted x-rays through the patient bombard a
fluorescent particle-coated screen (b) in the film cassette à produces
photochemical interaction à light rays are emitted, which exposes the film
(c) in the cassette à film is developed
How is an x-ray film produced in computed radiography?
X-rays pass through the body à phosphor-coated imaging plate interacts
with x-rays transmitted through the patient à phosphor plate is placed
within a reading device à data is captured and processed into a digital
image
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PROCEDURE
(1) Patient is positioned
(2) X-RAY is taken
(4) Digital image developed is read thru
a monitor
(3) Film cassette is placed in
a computed radiography
processing machine
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NAMING RADIOGRAPHIC VIEWS
Most x-ray views are named on the basis of the way that an x-ray
beam passes through the patient
Views are also named by the position of the patient
Naming on the basis of the way that an x-ray beam passes through the
patient:
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DIGITAL RADIOGRAPHY (DR)
Also a filmless system
Substitutes a fixed electronic detector on charge-coupled device for
the film screen cassette or phosphor imaging plate à NO CASSETTE
NEEDED
Immediate images are produced through direct readout
PROCEDURE
(1) Patient is positioned
(2) X-RAY is taken
Chest posteroanterior (PA)
Chest anteroposterior (AP)
Naming on the basis of the position of the patient:
(3) Digital image is read thru a monitor
Abdomen left lateral decubitus
Abdomen upright
5 BASIC RADIOGRAPHY DENSITIES
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FLUOROSCOPY
Real time radiographic visualization of moving anatomic structures
Continuous x-ray beam passes through the patient and falls on a
fluorescing screen à produces a light pattern which is amplified
electronically à amplified real time images are displayed on a
monitor
Useful in evaluating motion such as gastrointestinal peristalsis,
movement of diaphragm during respiration, and cardiac action.
Also used to monitor continuously radiographic procedures such as
Barium studies and catheter placements
Air density
- Lungs
Fat density
- Subcutaneous tissue
Soft tissue density
- Heart
Bone density
- Ribs
Metal/contrast density
- Pacemaker
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Air density
- Bowel gas
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Fat density
- Flank stripe
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Soft tissue density
- Liver
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Bone density
- Pelvis
MAMMOGRAPHY
Makes use of low-energy x-rays (30 kVp) to examine the human
breast
Indication:
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Screening
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Diagnostic
Two views:
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Craniocaudal view
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Mediolateral view
Metal/contrast density
- Barium
What is attenuation?
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Process by which a beam of radiation is reduced in intensity when
passing through material
If a tissue has low attenuation it would suggest that it is relatively
transparent and appears dark (Example: air/gas)
High attenuation is a denser material and (bone) objects appear
brighter
In general, the denser the material, the better its ability to attenuate
x-ray beam, the brighter/whiter it would appear on x-ray images
AIR DENSITY
Air attenuates very little of the xray beam – most are transmitted
à black on radiograph
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BONE AND METAL DENSITY
Bone, metal and contrast agents
attenuate a large proportion of xray beam à white on
radiograph
FAT AND SOFT TISSUE DENSITY
Fat and soft tissue attenuate
intermediate amounts of x-ray
beam à shades of gray on
radiograph
CROSS-SECTIONAL IMAGING TECHNIQUES
CT, MR, and Ultrasound – techniques that produce cross-sectional
images of the body
Produces slices of patient tissue to produce a two-dimensional image
To analyze optimally all of the anatomic information of any particular
slice, the image is viewed at different window-width and windowlevel settings, which are optimized for bone, air-filled lung, soft
tissue, etc.
COMPUTED TOMOGRAPHY (CT)
Uses a computer to mathematically reconstruct a cross-sectional
image of the body from measurements of x-ray transmission through
thin slices of patient tissue
Displays each imaged slice separately
No superimposed blurred structures seen in conventional
tomography
The patient is placed on an examination. An x-ray tube rotates 360° around
the patient, producing pulses of radiation that pass through the patient.
Transmitted x-rays are detected by a circumferential bank of radiation
detectors.
Types of CT scan:
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Conventional CT (nonhelical)
Obtains image data one slice at a time – one slice per breath
hold
Requires at least two to three times the total scanning time of
helical CT
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Helical CT (spiral CT)
Performed by moving the patient table through the gantry
while scanning continuously with an x-ray tube rotating
around the patient
Continuous volume of image data is acquired during a single
breath-hold
Improved speed of image acquisition
Improved visualization of small lesions
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Multidetector helical CT (MDCT)
Latest technical advance in CT imaging
Like helical scanner but with multiple rows of detector rings
Obtains multiple slices per tube rotation à increases the area
of the patient that can be covered in a given time
5-8 times faster than single-slice helical CT
Allows for high-detail CT angiography and virtual CT
colonoscopy and bronchoscopy
Disadvantage: radiation dose, 3-5 times higher than with
single-slice CT
Advantages of CT compared with MR:
Rapid scan acquisition
Superior bone detail, and demonstration of calcifications
PRINCIPLES OF INTERPRETATION
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Like radiography, images are dependent on the degree of
attenuation by different materials
Hounsfield Units (HU) – Units of x-ray attenuation used in CT
scanning
the brighter the tissue, the higher the HU
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HOUNSFIELD UNIT (HU) SCALE
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Air: -1,000 H
Lung tissue: -400 to -600 H
Fat: -60 to -100 H
Water: value of 0 H
Soft tissue: +40 to +80 H
Bone: +400 to +1,000 H
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Gray scale: in the
left edge
Centimeter scale:
along the right side
of the image
R: patient's right
side
L: patient's left side
Cross-sectional images in the transverse plane are
routinely viewed from “below,” as if standing at the
patient's feet
Optimal bone detail is viewed at bone windows
Window width of 2,000 H, window level of 400 to 600 H
Lungs are viewed at lung windows
Window width of 1,000 to 2,000H, window levels of about 500 to
600H
Soft tissues
Window width of 400 to 500 H, window level 20 to 40H
LUNG WINDOW
PLANES
a to c: AXIAL/ TRANSVERSE d: CORONAL e: SAGGITAL
SOFT TISSUE WINDOW
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CONTRAST ADMINISTRATION IN CT
Intravenous iodine-based contrast agents are administered in CT to:
Enhance density differences between lesions and surrounding
parenchyma
To demonstrate vascular anatomy and vessel patency
To characterize lesions by their patterns of contrast
enhancement
Oral or rectal contrast is generally required to opacify the bowel for
CT scans of the abdomen and pelvis.
Bowel without intraluminal contrast may be difficult to
differentiate from tumors, lymph nodes, and hematomas.
CONTRAST ADMINISTRATION IN MR:
Gadolinium chelates
Given to:
Identify regions of disruption of the blood-brain barrier
Enhance organs to accentuate pathology
Document patterns of lesion enhancement
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SAFETY CONSIDERATIONS IN MRI
Contraindicated in patients who have electrically, magnetically, or
mechanically activated implants
Cardiac pacemakers, insulin pumps, cochlear implants,
neurostimulators, bone-growth stimulators, and implantable
drug infusion pumps
Intracardiac pacing wires or Swan-Ganz catheters
Ferromagnetic implants, such as cerebral aneurysm clips,
vascular clips, and skin staples
Bullets, shrapnel, and metallic fragments
Safe for MR
Nonferromagnetic vascular clips and staples and orthopaedic
devices
Prosthetic heart valves with metal components
Pregnant patients can be scanned, provided the study is medically
indicated
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A – PLAIN
B – WITH CONTRAST
PRINCIPLES OF INTERPRETATION
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MAGNETIC RESONANCE IMAGING (MRI)
Produces tomographic images by means of magnetic fields and radio
waves
Based on the ability of a small number of protons within the body to
absorb and emit radio wave energy when the body is placed within a
strong magnetic field
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Soft tissue contrast is obtained through imaging sequences that
accentuate differences in T1 and T2 tissue relaxation times
Water is the major source of the MR signal in tissues other than
fat
Mineral-rich structures, such as bone and calculi, and
collagenous tissues, such as ligaments, tendons, fibrocartilage,
and tissue fibrosis, are low in water content and lack mobile
protons to produce an MR signal
low in signal intensity on all MR sequence
FREE WATER in MRI
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Most tissues can be differentiated by differences in their T1 and T2
relaxation times
T1 is a measure of a proton's ability to exchange energy with
its surrounding chemical matrix
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It is a measure of how quickly a tissue can become
magnetized
T2 conveys how quickly a given tissue loses its magnetization
ADVANTAGES OF MR:
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Outstanding soft tissue contrast resolution
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Provides images in any anatomic plane
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Absence of ionizing radiation
DISADVANTAGES OF MR:
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Limited in its ability to demonstrate dense bone detail or
calcifications
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Involves long imaging times for many pulse sequences
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Possesses limited spatial resolution compared with CT
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Limited availability in some geographic areas
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Expensive
Found mainly as extracellular fluid, also as intracellular free water
Organs with abundant extracellular fluid:
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Kidneys (urine)
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Ovaries and thyroid (fluid-filled follicles)
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Spleen and penis (stagnant blood)
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Prostate, testes, and seminal vesicles (fluid in tubules)
Edema (increase in extracellular fluid)
Most neoplastic tissues have increase in extracellular fluid as well as
an increase in the proportion of intracellular free water à bright
signal intensity on T2WIs
Ventricles and
sulci contain
CSF à black
on T1 , white on
T2
PROTEINACEOUS FLUIDS IN MRI
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Addition of protein to free water shortens T1 relaxation time – bright
T2 relaxation is also shortened, but the T1 shortening effect is
dominant even on T2WIs -- remain bright on T2Wis
Synovial fluid, complicated cysts, abscesses, many pathologic fluid
collections, and necrotic areas within tumors
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ULTRASONOGRAPHY
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T1W
T2W
A complicated rectal cyst showing hyperintensity on both T1 and T2 images
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SOFT TISSUES ON MRI
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Soft tissues that have a predominance of intracellular bound water
have shorter T1 and T2 times than do tissues with large amounts of
extracellular water
Liver, pancreas, adrenal glands, and muscle -- intermediate signal
intensities on both T1WIs and T2WIs
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ULTRASOUND
Utilizes pulse-echo technique
Transducer converts electrical energy to a brief pulse of highfrequency sound energy transmitted into patient à transducer
becomes a receiver, detecting echoes of sound energy reflected from
tissue à composite image is produced
Produces nearly real-time images of moving patient tissue
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Enables assessment of respiratory and cardiac movement,
vascular pulsations, peristalsis, and moving fetus
Images may be produced in any anatomic plane by adjusting the
orientation and angulation of the transducer and the position of the
patient.
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Standard orthogonal planes: axial, sagittal, and coronal
Visualization of structures by US is limited by bone and gascontaining structures (e.g. bowel and lung)
ULTRASOUND PROBE – transducer and a
receiver.
T1W
T2W
FAT ON MRI
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T1 relaxation time is short = bright signal
T2 of fat is shorter than T2 of water = lower signal intensity for fat,
relative to water
On images with lesser degrees of T2 weighting, T1 effect
predominates and fat appears isointense or slightly hyperintense
compared with water.
STIR sequences suppress signals from all tissues with short T1 times,
including fat
Subcutaneous fats are bright on both
T1 and T2
PLANES
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Sagittal/longitudinal
Transverse/axial
Coronal
AXIAL/TRANSVERSE
FLOWING BLOOD ON MRI
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Higher-velocity blood flow alters the MR signal in complex ways,
depending on multiple factors.
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High-velocity signal loss predominates in spin-echo imaging,
resulting in signal void “black blood” in areas of flowing blood.
SAGGITAL/LONGITUDINAL
Patent Blood Vessels
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LIMITATION OF ULTRASOUND
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Bone: Sound energy is nearly
completely absorbed at interfaces
between soft tissue and bone (rib,
R), causing an acoustic shadow
limiting visualization of structures
deep to the bone surface
ULTRASOUND ARTIFACTS
ACOUSTIC SHADOWING
Gallbladder stone
Bone (rib)
ACOUSTIC ENHANCEMENT
Cyst
Gallbladder
COMET-TAIL ARTIFACT
Arises from normal pleura (*)
reflecting sound waves
Adenomyomatitis
on th bladder
Air:
Soft
tissue-gas
interfaces (bowel loop)
cause nearly complete
reflection of the sound
beam,
preventing
visualization of deeper
structures Bowel wall
DOPPLER ULTRASOUND
Adjunct to real-time gray-scale imaging
Detects reflection of the sound wave from a moving object – RBC in
flowing blood
Can detect presence of blood flow and its direction and velocity
DOPPLER ULTRASOUND OF THE CAROTID ARTERY
PRINCIPLES OF ULTRASOUND INTERPRETATION
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FLUID-CONTAINING STRUCTURES
HYPERECHOIC
Dilated renal calyces & pelvis
ANECHOIC
SOLID TISSUE (FATTY TISSUE)
Fatty liver
Lipoma
SOLID ORGANS
(P) Pancreas
Kidney
HYPOECHOIC
Liver
Focal nodular hyperplasia
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Terminology
RADIOGRAPH
ULTRASOUND
CT SCAN
Density
• Radiolucent: black
• Radiopaque
/Radiodense: white
Echogenicity
• Anechoic: black
• Hypoechoic:
darker
than parenchyma
• Hyperechoic:
whiter
than parenchyma
• Isoechoic: same as
parenchyma
Density
• Hypodense: darker
• Hyperdense: whiter than
parenchyma
• Isodense:
same
as
parenchyma
MRI
Echogenicity
• Hypointense: darker than parenchyma
• Hyperintense: whiter than parenchyma
• Isointense: same as parenchyma
T1
T2
how quickly a tissue
can become
magnetized
how quickly a given
tissue loses its
magnetization
Hyperintense
Lower intensity than
water
Hyperintense
Intermediate intensity
Air
Fat
Radiolucent
Moderately radiolucent
Not visualized
Hyperechoic
Black
Hypodense
Hypointense
Hypointense
Water/Fluids
Soft Tissue
Moderately radiopaque
Moderately radiopaque
Anechoic
Varying echogenicity
Hyperdense
Varying hyperdensity
Bone/Metal
Very radiopaque
Not visualized
Very hyperdense
Hypointense
Intermediate
intensity
Hypointense
Hypointense
SOURCES:
1. PPT 2020
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