Midterms | Medical Image, Image Quality, and Data Formats Flashcards
have unique performance requirements, safety restrictions, characteristic attributes, and technical limitations that often make them more difficult to create, acquire, manipulate, manage, and interpret.
MEDICAL IMAGE
MEDICAL IMAGE have unique (1), (2), (3), and (4) that often make them more difficult to create, acquire, manipulate, manage, and interpret.
- performance requirements
- safety restrictions
- characteristic attributes
- technical limitations
Imaging for medical purposes involves a team which includes the service of
- Radiologists
- radiographers (X-ray technologists)
- sonographers (ultrasound technologists)
- medical physicists
- nurses
- biomedical engineers
- and other support staff working together to optimize the wellbeing of patients, one at a time.
IMPORTANCE OF MEDICAL IMAGING
Medical imaging encompasses different (1) and (2) to image the human body for (3) and (4) purposes and therefore plays an important role in initiatives to improve (5) for all population groups. Furthermore, medical imaging is frequently justified in the (6) of a disease already diagnosed and/or treated.
- imaging modalities
- processes
- diagnostic
- treatment
- public health
- follow-up
It is determined by the imaging method, the characteristics of the equipment, and the imaging variables selected by the operator.
QUALITY OF A MEDICAL IMAGE
QUALITY OF A MEDICAL IMAGE is determined by
- imaging method
- characteristics of the equipment
- imaging variables selected by the operator
Image quality is not a single factor but is a composite of at least five factors:
- contrast
- blur
- noise
- artifacts
- distortion
Difference in OD
Radiographic contrast
Define kVp
Penetrating ability of XRs
Contrast controlling factor
KVP
SOURCE of Conventional Radiography
X-rays
X-rays are (1) radiation; part of the electromagnetic spectrum emitted as a result of bombardment of a (2) by (3) from a cathode.
- ionizing
- tungsten anode
- free electrons
DETECTORS OF DIGITAL RADIOGRAPHY
ANALOG DETECTOR
DIGITAL DETECTOR
fluorescent screen and radiographic film
ANALOG DETECTOR
computed radiography (CR) uses a photostimulable or storage phosphor imaging plate
DIGITAL DETECTOR
DIGITAL DETECTOR subprocesses
DIRECT DR
INDIRECT DR
Direct DR devices convert X-ray energy to (1) in a/n (2) photoconductor, which are read out by a/n (3) array of (4).
- electron–hole pairs
- amorphous selenium
- thin-film transistor (TFT)
- amorphous silicon (Am-Si)
(YT) The DR image receptor is made up of a matrix of very small detector elements or —
DELs
(YT) Each DEL contains this three components
- capture element
- storage capacitor
- TFT switch.
(YT) Recall direct DR conversion
- Voltage is applied to top of detector just before the exposure is made
- The X-ray beam interacts directly with the amorphous selenium, causing the selenium atoms to release electrons, creating an electronic charge.
- Storage capacitors collect the charge.
- After the exposure, the TFT switches release the electrical charges from the individual DELs to the analog-to-digital converter, which converts them to a digital signal used to produce the digital image.
(YT) What system produces higher image quality than other systems? Why?
Direct conversion DR system. Because it skips the step of converting X-rays to visible light
(YT) Direct conversion DR systems are mostly used in —
Why?
Mammography
- higher image quality allows for better visualization of microcalcifications
- amorphous selenium detectors cannot be produced large enough for use in general radiography
(YT) Essential difference between direct and indirect conversion DR systems
Indirect systems first convert the X-ray photons into visible light photons, which are then converted to an electrical signal.
INDIRECT DR DEVICES. Light is generated using a/n (1) and converted to a proportional charge in a/n (2) (e.g., cesium iodide scintillator) and read out by a/n (3) or (4).
- X-ray sensitive phosphor
- photodiode
- charge-coupled device (CCD)
- flat panel Am-Si TFT array
(YT) In both types of indirect conversion DR systems, there is a scintillation layer made up of either (1) or (2)
- cesium iodide
- gadolinium
(YT) In the CCD system, the scintillation layer is coupled to each CCD sensor chip either by (1) or (2).
- lenses
- fiber optics
(YT) Because light is emitted (1), light photons are spread out in all directions, which causes (2) and reduces (3).
- isotropically
- blur
- spatial resolution
(YT) What is the preferred material for scintillation layers? Why?
Cesium iodide. It can be formed into very small needles or columns which helps to focus the light photons, improving spatial resolution
(YT) Recall CCD system under indirect DR conversion
- Scintillation layer is coupled to each CCD sensor chip either by lenses or fiber optics
- X-ray photons strike the scintillation layer, which are then converted into light photons.
- CCD sensor chips convert the light photons into electrical signals.
- Electrical signals are then sent through ADC which sends the converted digital signal to a computer for processing
(YT) Recall TFT system under indirect DR conversion
- X-ray photons strike the scintillation layer and are converted into light photons
- Photodiode layer converts the light photons into an electrical signal that is transferred to the TFT array.
- TFT array sends the electrical signal to ADC to produce a digital signal which is then sent to a computer for processing
(YT) Both CCD and TFT indirect conversion DR systems are used in (1),
and TFT indirect conversion DR systems are typically used in (2) and (3).
- general-purpose radiography
- angiography
- fluoroscopy
IMAGE ATTRIBUTES of prijection radiography
variations in the gray scale of the image represent
the (1) or (2)
- X-ray attenuation
- density of tissues
IMAGE ATTRIBUTES of prijection radiography
absorbs large amounts of radiation allowing less signal to reach the detector, resulting in white or bright areas of the image
Bone
IMAGE ATTRIBUTES of prijection radiography
has the least attenuation causing maximum signal to reach the detector, resulting in black or dark areas of the image.
Air
Advantages of digital raiography
○ fast and easy to perform
○ equipment is relatively inexpensive and widely available; low amounts of radiation
○ high spatial resolution capability. Particularly useful for assessing the parts of the body that have inherently high contrast resolution but require fine detail such as for imaging the chest or skeletal system
Disadvantages of digital raiography
○ poor differentiation of low contrast objects
○ superposition of structures makes image interpretation difficult
○ uses ionizing radiation.
SOURCE of Fluoroscopy
○ continuous low-power X-ray beam
○ ionizing radiation
FLOUROSCOPY IMAGE ATTRIBUTES
○ continuous acquisition of a sequence of (1) over time results in a (2) X-ray movie.
○ May use (3) (white
for air; black for bones).
- X-ray images
- real-time
- inverted grayscale
FLOUROSCOPY DETECTOR
X-ray image intensifier amplifies the output image
FLOUROSCOPY ADVANTAGES
○ Can image (1) and provide (2) during procedures.
- anatomic motion
- real-time image feedback
FLOUROSCOPY ADVANTAGES
○ Useful for monitoring and carrying out (1) of the (2), (3), and (4) such as (5).
- barium studies
- gastrointestinal tract
- arteriography
- interventional procedures
- positioning catheters
FLOUROSCOPY DISADVANTAGES
Lower quality moving projection radiograph.
COMPUTED TOMOGRAPHY SOURCE
○ collimated X- ray beam; X-ray tube rotates around the patient.
COMPUTED TOMOGRAPHY DETECTOR
○ early sensors: (1)
○ modern detectors: (2)
○ An image is obtained by computer processing of the (3) of the detectors.
- scintillation detectors with photomultiplier tubes excited by sodium iodide (NaI) crystals
- solid state scintillators coupled to photodiodes (indirect) or are filled with low- pressure xenon gas (direct)
- digital readings
COMPUTED TOMOGRAPHY IMAGE ATTRIBUTES
○ thin transverse sections of the body are acquired representing a/n (1)
of each tissue.
○ Absorption values are
expressed as (2).
- absorption pattern or X-ray attenuation
- Hounsfield Units
Dense bone CT Number
3000
Muscle CT Number
50
White Matter CT Number
45
Gray Matter CT Number
40
Blood CT Number
20
CSF CT Number
15
Water CT Number
0
Fat CT Number
-100
Lungs CT Number
-200
Air CT Number
-1000
○ good contrast resolution allowing differentiation of tissues with similar physical densities
CT
○ tomographic acquisition eliminates the superposition of images of overlapping structures
CT
○ advanced scanners can produce images that can be viewed in multiple planes or as volumes. Any region of the body can be scanned
CT
○ has become diagnostic modality of choice for a large number of disease entities
CT
○ useful for tumor staging
CT
CT DISADVANTAGES
○ high cost of equipment and procedure;
○ high dose of ionizing radiation per examination
○ artifacts from high contrast objects in the body such as bone or devices.
MRI SOURCE
○ high-intensity magnetic field and radiofrequency
MRI SOURCE
What are magnets are typically used in MRI today?
○ typically, helium-cooled superconducting magnets are used today
MRI SOURCE
What turn pulses on/off?
○ gradient coils turn radiofrequency (RF) pulses on/off.
MRI DETECTOR
○ phased array receiver coils capable of acquiring multiple channels of data in parallel.
MRI Image Attributes
produces images of the body by utilizing the (1) properties of certain nuclei, predominately (2) and (3)
- magnetic
- hydrogen (H+) in water
- fat molecules
MRI Image Attributes
the response of magnetized tissue when perturbed by an RF pulse (1) and is (2) as compared to normal.
- varies between tissues
- different for pathological tissue
MRI Advantages
○ non-ionizing radiation, originally called (1) but because the word ‘‘(2)’’ was associated with ionizing radiation, the name was changed to emphasize the modality’s safety
- nuclear magnetic resonance (NMR)
- nuclear
○ can image in any plane
○ has excellent soft tissue contrast detail
MRI
○ visualizes blood vessels without contrast; no bony artifact since no signal from bone
MRI
MRI is particularly useful in (1), (2), (3), and (4) imaging.
- neurological
- cardiovascular
- musculoskeletal
- oncological
(MONC)
MRI Disadvatages
○ high purchase and operating costs
○ lengthy scan time
○ more difficult for some patients to tolerate
○ poor images of lung fields
○ inability to show calcification
○ contraindicated in patients with pacemakers or metallic foreign bodies.
NUCLEAR MEDICINE SOURCE
X-ray or g-ray emitting radioisotopes are injected, inhaled, or ingested
most common isotopes in NUCLEAR MEDICINE
are
technetium-99
thallium- 201
iodine-131
(TIT)
NUCMED DETECTOR
○ (1) measures the radioactive decay of the active agent
○ emitted light is read by (2)
○ (3) measures number and height of pulses.
● Further, these pulses are converted to (4) that is subsequently processed into a (5) image.
- gamma camera with NaI scintillation crystal
- photomultiplier tubes
- pulse arithmetic circuitry
- electrical signal
- gray scale
gamma camera with NaI scintillation crystal measures —
radioactive decay of the active agent
photomultiplier tubes reads —
emitted light
pulse arithmetic circuitry measures —
number and height of pulses
○ measures targeted specific chemical-physiologic tissue function
NUCLEAR MEDICINE
NUCLEAR MEDICINE is a valuable diagnostic tool particularly for imaging (1) in the cardiovascular system, (2) of the respiratory tract for (3), imaging uptake at sites of (4) as in arthritis and tumors, assessing (5), and in (6)assessment.
- infarcts
- perfusion, and ventilation scanning
- pulmonary embolus
- increased bone turnover
- focal nodules
- oncologic
NUCLEAR MEDICINE IMAGE ATTRIBUTES
(1), (2), or (3) interactions of the radioisotope are measured.
- metabolic
- chemical
- physiological
NUCLEAR MEDICINE IMAGE ATTRIBUTES
The radioisotope chemical is distributed according to (1) so the image primarily represents (2)
however since function is distributed in the physical structures, recognizable (3) are produced.
- physiological function
- functional information
- anatomical images
NUCLEAR MEDICINE DISADVANTAGES
○ high cost
○ PET isotopes require a cyclotron for production
ULTRASOUND SOURCE
high-frequency sound waves produced by a transducer made of a piezoelectric crystal.
Active component of transducer
piezoelectric crystal
ULTRASOUND DETECTOR
○ the source (1) also functions as a receiver of (2) and converts the signal into a/n (3), which is subsequently processed into a/n (4) image.
- transducer
- reflected sound
- electric current
- grayscale
ULTRASOUND IMAGE ATTRIBUTES
○ (1) travel through the body, are affected by the different types of tissues (2) and (3)
○ a/n (4) is obtained as the transducer is passed across the body.
- sound waves
- encountered
- reflected back
- moving image
○ relatively low cost
○ non-ionizing energy source and safe; can scan in any plane
ULTRASOUND
○ equipment is portable and can be used for bedside imaging
ULTRASOUND
ULTRASOUND is particularly useful for
- monitoring pregnancy
- imaging the neonatal brain
- visualizing the uterus, ovaries, liver, gallbladder, pancreas, and kidneys
- confirming pleural effusions and masses
- assessing the thyroid, testes, and soft-tissue lesions
(UPKLOG, PM, PN, SoLe TeThy)
ULTRASOUND DISADVANTAGES
○ operator-dependent
○ poor visualization of structures underlying bone or air
○ scattering of sound through fat yields poor images in obese patients.
It is non-invasive but has limited ability to penetrate tissues deeply like the energies used in radiological imaging.
VISIBLE LIGHT
Visible light imaging is used in (1), (2), (3), (4), (5), and during (6).
- light microscopy for pathological diagnosis
- hematology
- dermatology to photograph the skin
- gastroenterology
(colonoscopy/ endoscopy) - ophthalmology to image the retina
- surgical procedures
(LOG HDS)
Subtopic under radiographic contrast
IR contrast
Subject contrast
High contrast : (1)
High CR: (2)
Low contrast: (3)
- large difference in OD
- Low noise
- Small difference in OD resulting in shades of gray
IR contrast is affected by the (1);
Contrast inherent in (2), influenced by (1)
- processing film
- screen-film combination
Size, shape, attenuating characteristics of anatomy energy (kVp)
Subject contrast
Ways to acquire optimum image on
- Properly positioning pt
- Proper measuring of pt thickness
(YT) A form of digital imaging that uses a cassette based system similar in many ways to conventional film based radiography
CR
(YT) The CR cassettes have protective outer cases and a PSP plate made up of five key components
- Protective layer
- Phosphor layer
- Conductive or anti-static layer
- Support layer or base
- Reflective or light shielding layer
(YT) CR CXTs can come in different sizes and are typically constructed of?
- hard plastics
- light metals
- carbon fibers
(YT) Serves to ground the imaging plate and reduce electrostatic charge.
Conductive/ Antistatic layer
(YT) Serves to direct the emitted light in the imaging plate reader.
Reflective/ Light shielding layer
(YT) Most common phosphors
Barium fluorohalide bromides and iodides with europium activators
(YT) X-ray photon energy is captured in the (1) by energy transfer through a process called (2).
- phosphor layer
- photoelectric absorption
(YT) During the photoelectric absorption, the number of (1) produced in the phosphor layer is proportional to the number of (2) that interact with it.
- photoelectrons
- X-ray photons
CR takes advantage of the PSP which is —
barium fluorohalide doped with europium
Where latent image is actually formed in the form of light photons
Europium
Europium is a/n (1); without it, no (2) is produced
- activator
- latent image
Active component of CR
Photostimulable Phosphor (PSP)
Emission of light upon the interaction of laser light to the phosphor
PSL/P?
