11. Modality Exploration and Radiation Therapy Flashcards
A radiologic examination that involves the use of strong magnets, radiofrequency waves, and computer to create an image of the internal structures of the body
Magnetic Resonance Imaging
Magnetic Resonance Imaging discovered simultaneously in ____ by :
1947
o Felix Bloch
o Edward Mills Purcell
In \_\_\_\_, provided an impetus to the development of actual clinical imaging using strong magnetic fields by suggesting that radio wave signal relaxation times of different tissues might be indicative of tumour malignancy
Raymond Damadian (1971)
Provided the first 2D MR image of
chemical sample in ____
Paul Lauterbur (1973)
MRI Components
o Primary magnets
o Gradient magnets
o Radiofrequency (RF) Coils
o Computer system
MRI Image Formation
o Large magnet produces a strong
magnetic field around the body
o Nuclei in the body precess at the larmor
frequency
o Gradient coils vary the magnetic field
across the body
o A slice of the body is specified by the
magnetic field variation along the Z-axis
The slow movement of the axis of a
spinning body around another axis due
to a torque acting to change the
direction of the first axis
Precession
refers to the rate of precession of
the magnetic moment of the proton
around the external magnetic field
Larmor or precessional frequency in
MRI
MRI Image Formation (1)
o Gradient coils also vary magnetic field along the x and y directions to select a tiny volume o The magnetic field in that volume is set so that only the nuclei in that volume are at resonant Larmor frequency o The procedure that follows will identify the tissue type in that volume o This small volume will form one pixel of the final image o During the scan, many small volumes will be scanned o Nuclei in the volume precess at the specified Larmor frequency
MRI Image Formation (2)
o A pulse of radio photons is transmitted into the body o Nuclei absorb energy and resonate, they flip into higher energy state o After a period of time the nuclei relax: flip back to their normal energy state o When they relax, they emit a radio photon o The emitted photons form the signal received by the RF coils o The mean time that elapses between switching off the transmitted RF pulses and receiving a signal from relaxing nuclei is the relaxation time o The tissue type at the specified volume is identified from the relaxation time
is a mathematical technique that allows an MR signal to be decomposed into a sum of sine waves of different frequencies, phases, and amplitudes
Fourier Transform
is a specialized are of radiology that uses very small amounts of radioactive amounts, or radiopharmaceuticals, to examine organ function and structure
Nuclear Medicine
Three-stage process of radionuclide imaging
o Introduction of suitable radionuclide into the patient o Concentration of radionuclide in the specific organ o Scanning of organ using appropriate scanner
Common ways in How to Produce Artificial
Radionuclide
o Irradiating materials in a nuclear
reactor
o Using technetium generator
o Using a medical cyclotron
Gamma Camera first developed by _____ in
___
Hal Oscar Anger,
1958
Specialized type of scintillation counter where the position as well as the count of the scintillations within a thin Nal Crystal (or multiple crystals) are obtained using a number of photomultipliers
Gamma Camera
is a diagnostic medical procedure that uses sound waves to produce images on a screen which allows medical providers to view internal structures of the body
Ultrasonography
Approximate speed of sound in Air
340 m/s
Approximate speed of sound in Lung
650 m/s
Approximate speed of sound in Fat
1460 m/s
Approximate speed of sound in Pure water
1500 m/s
Approximate speed of sound in Salt water
1530 m/s
Approximate speed of sound in Kidney
1560 m/s
Approximate speed of sound in Blood
1570 m/s
Approximate speed of sound in Muscle
1580 m/s
Approximate speed of sound in Bone
3000 m/s
is the
ability to bounce an echo
Echogenicity or echogeneity
Echogenicity or echogeneity
o Hypoechoic
o Hyperechoic
o Anechoic
A device that produces sound waves that bounce off body tissues and make echoes. It also receives the echoes and sends them to a computer that uses them to create a picture called a \_\_\_\_\_
Transducer,
sonogram
is the ability of
certain materials to generate an electric
charge in response to applied
mechanical stress
Piezoelectric Effect
The word Piezoelectric is derived from
the Greek _____, which means to
squeeze or press, and ___, which is
Greek for push.
piezein,
piezo
Piezoelectric Effect
Strengths
o Inexpensive o Quick o Mobile o Non-invasive o Can depict free fluid and aneurysms, e.g. in acute aneurysms o Can differentiate between solid and fluid structures o Can depict flow and motion o Good for shallow structures
Piezoelectric Effect
Weaknesses
o Operator dependent o Images may be hard to interpret o Suffers from image artifacts o May be prone to giving “false positives” o Not good for deep structures o Cannot penetrate through bone or air
Began in 1930s with angiography
Interventional radiology
pionerred
transbrachial selective coronary
angiography
Mason Jones (Early 1960s)
introduced coronary
angiography
Melvin Judkins
introduced visceral
angiography
Charles Dotter
Refers to the opacification of vessels
through injection of contrast media
Angiography
Imaging Procedures
- Angiography
- Aortography
- Arteriography
- Cardiac catheterization
- Myelography
- Venography
Interventional Procedures
- Stent Placement
- Embolization
- Intravascular stent
- Thrombolysis
- Balloon angioplasty
- Atherectomy
- Electrophysiology
Embolization
- Narrow neck aneurysms
- Aneurysm catheterization
- Coil development
- Microcatheter removal
described
a method of arterial access in which
catheter was used
Sven Ivar Seldinger (in 1953)
18 gauge hollow
needle with stylet
Seldinger needle
Allows safe introduction of the catheter
into the vessel
Guidewires
Fabricated of stainless steel and contain
an inner core that is tapered at the end
to a soft flexible tip
Guidewires
are 145 cm
long
Conventional guidewires
Catheters - categorized in French (Fr) sizes; __ Fr
equal to __ mm in diameter
3,
1
used for femoral
approach to the brachiocephalic vessels
H1 or headhunter tip- (designed by
Vincent Hinck)
highly curved
designed for cerebral angiography
Simmons catheter
has angled tip for
celiac, renal, and mesenteric arteries
C2 or Cobra Catheter
have side holes for ejecting
contrast media into a compact bolus
Pigtail
Procedure room should not be less than
20 feet along any wall and not less than
500 ft^2
Interventional Radiology Suite
Control room must be large, perhaps
100 ft^2
Interventional Radiology Suite
2 or 3 radiographers, interventional
radiologist, radiology nurse
Interventional Radiology Suite
More massive, flexible and expensive
than conventional; radiographic and
fluoroscopic imaging
X-ray Apparatus
Small target angle
X-ray Tube
Large diameter massive anode disc
X-ray Tube
designed for magnification
and serial radiography
Cathodes (X-ray Tube)
X-ray Tube Small focal spot size
not greater than
0.3 mm
X-ray Tube SID
100 cm
X-ray Tube OID
40 cm
The use of high-energy radiation from xrays, gamma rays, neutrons, protons,
and other sources to kill cancer cells
and shrink tumors
Radiation therapy
Teletherapy other name
External beam radiation therapy (EBRT)
EBRT
External beam radiation therapy
Radiation delivered from a distant
source, from outside the body and
directed at the patient’s cancer site
Teletherapy
involves placing radiation sources as close as possible to the tumor site. Sometimes, they may be inserted directly into the tumor
Brachytherapy
Sometimes, they may be inserted
directly into the tumor
Brachytherapy
The use of high-energy radiation
from x-rays, gamma rays, neutrons,
protons, and other sources to kill
cancer cells and shrink tumors
Radiation therapy
Energies up to 150 Kv with beam
filtration of 1-8 mm al at an FSD
(focal skin distance) of 10-30 cm
Superficial units
with energies of
150-500 kV with 0.5-3 copper
filtration at a 50 cm FSD
Orthovoltage unit or “deep therapy”
Accelerate electrons in a straight
path
Linear Accelerator (LINAC)
Energies up to 5 MeV
Linear Accelerator (LINAC)
LINAC
Linear Accelerator
Linear Accelerator (LINAC) - Divided into two large structures
o Floor-mounted stand
o Motor-driven gantry
An evacuated cylindrical structure, consisting of hollow, indirectly heated, oxide-coated cathode surrounded by a copper anode containing equidistant cavities that communicate with the space surrounding the cathode
Magnetron
Anode and cathode are supplied by
pulse direct current supply from the
modulator
Magnetron
AFC
Automatic Frequency Control
Maintains the frequency with
an accuracy of +- kHz
AFC- Automatic Frequency Control
AFC- Automatic Frequency Control
Magnetron
Simple hollow tubes that carry the RF
waves from the magnetron to the
accelerator section waveguides
Waveguides
are sealed at both ends by ceramic discs that are transparent to
microwave radiation
Waveguides
Waveguides are filled with ______ to
improve its power-handling capabilities
sulphur hexafluoride
Situated between the magnetron and
the waveguide
RF Circulator
Act as a one-way valve permitting the
RF radiation to pass into the waveguide,
but preventing any from passing back
into the magnetron
RF Circulator
Situated in the gantry of LINAC
Accelerating Waveguide and Accelerator
Uses RF to accelerate electrons to
very high velocities
Accelerating Waveguide and Accelerator
Electron gun injects electron into
the guide impulses under the
control of modulator, in
synchronization with the RF waves
Accelerating Waveguide and Accelerator
at the entrance and
exit of the waveguide ensure that
the electron beam is centered to
the center of the guide and target
Focusing coils
Deflects the electron beam through a
270 degree angle
Bending Magnet and Treatment Head
is an evacuated
structure situated externally to the
accelerator structure
Bending magnet
Attached to an external
opening on the treatment
head
Electron applicator
Designed to produce a
“flat” electron beam
Scattering foil
