Theory Flashcards
Ultrasound definition
- Mechanical oscillation
- Higher freq (pitch) than 20000 Hz (upper limit human ear)
- Longitudinal in liquid and gas
- Both (longit.& transv.) in solids
Direct piezoelectric effect
US -> electric energy
- Detection of ultrasound
- Piezoelectric insulators accumulate electric charge and gets polarized when mechanical strain (pressure, tension) is applied on them.
This results in measurable potential difference between electrodes on opposite sides of crystals.
Inverse piezoelectric effect
Electric energy -> US
- In the transducer
- Electric voltage applied on electrodes of piezoelectric material -> becomes deformed
Transducer
Device that converts electric energy into mechanical and vice versa
Damping (US)
Parameter that characterises attenuation of US
- J0: initial intensity
- J: intensity after passing theough layer
- Energy lost as heat
Acoustic impedance
Characterizes acoustic properties of medium
- Z = density*velocity
- Boundary surface/interface: acoustic impedance changes
(Higher difference=higher reflection)
Reflexivity
Ratio of reflected:incident intensity
R=0: no reflection
R=1: total reflection
Pulse echo method
d=(c*t)/2
Calculate distance between transducer and reflecting boundary surface
c: sound velocity (known for medium)
t: elapsed time from emission to arrival of sound
Doppler effect
Frequency (and wavelength change as a result of relative motion and source of the observer
- Towards you: shorter wavelength - higher pitch
- Away: longer wavelength - lower pitch
Use of US
1) Diagnostic (ultrasonography, medical sonography)
- Non-invadive
2) Therapy
- Rheumatology
- Musculoskeletal disorders (arthrosis)
- Removal of dental calculus
Source of US
Sine wave oscillator conduct electric pulse (MHz) to trancducer containing the piezoelectric crystals (converts electric->US “Inverse piezoelectric effect”)
Ultrasound pulse…
Should be short - only a couple of time periods (sine waves)
Eigen-frequency
Frequency of largest amplitude vibration of a solid material (own resonance frequency)
*For best US - electric signal should match Eigen-frequency of the piezoelectric material
Detection of US
- US -> transducer (polarizes) -> electric signal (direct piezoelectric effect) -> conducted through cable to electronic amplifier
Diagnostic US imaging methods
1) One dimentional A-image (amplitude modulation)
2) One dimentional B-image (brightness modulation)
3) Two-dimentional B-image (2D, brightness modulated)
- Series of one dimentional B-images at diff. angles
4) M image (motion)
- Info: position of the given surface as function of time
5) Reconstructed 3D image (tomography)
6) Reconstructed 4D image
- Time is 4th dimention - US movie created
7) Doppler methods
Brightness
Pixels - proportional to amplitude of reflected US signal
Doppler shift
= f - f0
Proportional to the relative velocity (v/c) and to the incident frequency
Doppler methods
1) Doppler time-velocity image:
- Doppler-frequency-shift plotted as a function of time - corresponds to velocity of observed surface
2) Color-coded Doppler image:
- Color coded velocity information
3) Doppler flow meter
- Can measure velocity of blood flow in larger blood vessels
Digital image
Information displayed at different discrete spatial points in the form of color
- 2 or 3 dimentional array or matrix of picture elements
Characteristics of the digital image
1) Picture element (pixel)
2) Information associated with the pixel
- XY location: coordinates related to spatial resolution
- Color depth: intensities related to color/gray-scale resolution
3) Spatial resolution
- Number of resolved pixels in the X and Y directions
4) Grayscale/color depth
- Number of resolved colors/grayscale intensities (bit)
Color histogram
- Resolved intensities may be displayed as a function
- Relative frequency of colors or grayscale intensities in the image
Image enhancement techniques
1) Contrast manipulation
- Color transfer function: assigns color to pixel densities (expressed in numerical values)
2) Convolution
- Kernel operation - se eget kort
- Blurry vs skarpt
3) Rank operations
- The pixel is exchanged for another from its ranked neighborhood (e.g noise removal - prikker)
- Min, max, median, mean(?)
Convolution
Image enhancement technique
- Kernel operation -> smoothing, sharpening, edge detect.
- Convolution is the process of adding each element of the image to its local neighbors, weighted by the kernel
Fourier transformation + principle
Fourier principle: any function may be generated as the sum of sine function and its harmonics
Fourier transform: decomposes a function of time (a signal) into the frequencies that make it up (FFT, inverse FFT, masked FFT)
Smoothie analogy:
- What does the Fourier Transform do? Given a smoothie, it finds the recipe.
- How? Run the smoothie through filters to extract each ingredient.
- Why? Recipes are easier to analyze, compare, and modify than the smoothie itself.
- How do we get the smoothie back? Blend the ingredients.
Binary transformation
The image is partitioned according to certain parameters
- Tresholding, segmentation
- Excecution:
1: Select a certain grayscale range of the image
2: The selected pixels form the “foreground”
3: The rest of the pixels form the “background” - Bildet blir svart og hvitt i stedet for gråskala
Binary operations
1) Boolean functions (of image a and b):
- a OR b (union)
- a AND b (intersection)
- a NOR b (union+intersection?)
- NOT a (complement of a)
* Boolean operation: separation of touching objects
2) Erosion, Dilatation, Opening, Closing
- Moving pixels from the foreground to the background and vice versa
- Erosion: svarte prikkene blir mindre og mindre
- Dilatation: svarte prikkene blir større og større
DICOM
Digital imaging and communications in medicine
- En standard for håndtering, lagring, utskrift og overføring av medisinske digitale bilder og informasjon relatert til disse bildene
X-rays (characteristic, wavel, freq, energy)
- Electromagnetic wave
- Wavelength: 10 - 0.01 nm (10nm: soft x-r, 0,01: hard)
- Frequency: 30 * 10^15 - 30 * 10^18 Hz (petaHz-exaHz)
- Energy: 120 eV - 120keV
Generation of X-ray - rotating anode tube
- X-rays are emitted when a high-speed electron hits a metal target - is decelerated (1 % of electron beam converted to protons, rest to heat)
- Rotating anode to deal with heating problem
- Hot-wire cathode (heated by DC circuit)
- Anode at 45 degrees angle to direct toward window
2 mechanisms of X-ray generation + spectrum
1) Bremsstrahlung
- Breaking/deceleration radiation
- Continous energy spectrum
2) Characteristic radiation
- X-ray fluorescence
- Electron collides w/K-shell electron -> K-shell electron ejected -> higher shell electron jumps down -> emission of a single X-ray photon
- Linear energy spectrum
μm
Mass attenuation coefficient (cm^2/g)
= the sum of mass attenuation coefficients of the different absorption mechanisms
Attenuation mechanisms
1) Photoeffect (=> 1 photoelectron)
2) Compton scatter (=> compton photon+compton elec.)
3) Pair production, annihilation (=> electron + positron and the positron gives 2 photons)
* Energy colliding electron must be > 1022 keV
Se bilde ipad!!!
Diagnostic X-ray contrast mechanism
1) between soft tissue and bone: photoeffect (~Z^3)
2) within soft tissue: compton scatter (~density)
X-ray image is a…
…summation image
- Contrast arises due to spatially varying attenuation
Spatial resolution x-ray
Bidirectional x-ray imaging
CT
aka CAT scan
= tomographic digital imaging method that uses x-rays
- Objective: to determine the atten. coeff. of the individual volume elements (voxels)
- Rotation of source and detector
Types of CT techniques
- Conventional (outdated) technique
- Spiral CT technique
- Multidetector spiral CT (MSCT - multi slice…)
CT image reconstruction
1) Algebraic reconstruction techniques
2) Direct Fourier reconstruction
3) Filtered back projection (current method)
CT image and contrast manipulation
- Density: Hounsfield units
- water = 0 HU, fat ~ -200, bone ~ 1000
- Windowing = contrast manipulation
Dual source CT
- Use 2 diff. X-ray sources and detectors simultaneously
- Placed perpendicular to each other
- Dual-energy mode: different accelerating voltages
CT contrast agents
Water-soluble, iodine-containing macromolecule causing enhanced absorbance at the sites of accumulation
- Ionic contrast agents are outdated, must be non-ionic
- Monomeric or dimeric, low osmolality
- Filtration through kidney (nephrotropic)
Imaging blood vessels
CT angiography
- With iv contrast+conventional tech: vessels>1 cm (aorta)
- Spiral CT angiography:
a. Single detector array spiral CT: aorta br.s (>2-3mm)
b. Multidetector array spiral CT: periph vs (>1mm)
HRCT
High resolution CT
- Very thin slices (1-2 mm)
- Very high contrast resolution
Limitations of CAT scanning
- Ionizing radiation (x-ray)
- Irradiation dose 50-100x conventional x-ray
- Direct exposure to radiation
- scattered radiation
Hybrid technologies
- NanoSPECT/CT
MRI fundamentals
Nuclear magnetic resonance imaging
1) Atomic nuclei with nuclear spin are elementary magnets
- Atomic nuclei have mass, angular momentum, charge and magnetic moment
2) Nuclear spin orient in a magnetic field
3) Oriented nuclear spins display precessional motion
- “Precession is a change in the orientation of the rotational axis of a rotating body”
- Net magnetization - se eget kort
4) The system may be excited with radio frequency radiation
- Resonance condition: Larmor frequency
Proton (aka nuclei) mass and charge
Mass: 1.6710^(-24) g
Charge: 1.610^(-19) C
Useful nuclei in MRI
H, C, F, N, P
Net magnetization
Due to spin access in different energy states
- Ratio of magnetic spins in high-energy (antiparallel) and low energy (parallel) states
- Boltzmann distribution
Electromagnetic radiation in MRI
Radio waves
T1 and T2 (MRI)
The approach to thermal equilibrium is known as relaxation. T1 and T2 are relaxation times.
T1: “Spin-lattice relaxation”
- Depends on interaction between elementary magnet (proton) and environment
- Longitudinal relaxation
- Larmor frequency
T2: “Spin-spin relaxation”
- Depends on interaction between elementary magnets (protons)
- Transverse relaxation
- FID: see free induction decay
Spin-echo sequence
Repetitive pulses of excitation and subsequent relaxation
- T2 or transverse relaxation
Contrast in MRI
Determined by interaction of spin systems
- Free water have high mobility
- Solid have low mobility
Spatial encoding in MRI
3D (voxels)
- Magnetic field gradient
- Gradient coils: y-, x- and z-coil (of machine)
- Magnetic field is always in z-direction
Magnetic field direction MRI
Always Z-direction
Image reconstruction MRI
1) Backprojection
2) 2D Fourier transformation
Color contrast MRI is based on…
- Spin density
- Relaxation times
Contrast agents MRI
Positive
- Paramagnetic elements (T1 contrast): Gd, Mn
Negative
- Superparamagnetic, ferromagnetic (T2 contrast): FeIII, MnII
Artifacts and dangers MRI
Artifacts: motion, metals
Dangers/contraindications:
- Metals
- Gradient field - induced current
- Radio frequency field (thermal effects - lens, testis)
MRI angiography
- Saturated spins moves out of the image due to flow of blood
- Non-invasive
MR spectroscopy uses
- Chemical shift
- Identification of metabolites
- Tumor diagnostics
Tractography
Imaging of neural tracts
MRI - Diffusion imaging
Functional MRI
High time resolution images recorded synchronously with physiological processes
MRI and PET
Can be superimposed
Molecular imaging definition
Molecular imaging is the visualization, characterisation and measurement of biological processes at the molecular and cellular levels in humans and other living systems
Molecular imaging ideals
Visualization
- Signal to noise ratio
- Accuracy of information (where?)
- Spatial resolution (yes or no?)
Characterization
- Time resolution (when? How?)
- Magnitude and density of information (how?)
Measurement
- Robustness, repeatability
- Quantitation, accuracy (how much?)
Molecular sensitivity
This quality of any given imaging modality is to be used upon decision of its application. Considers:
- Cell conc
- No. of targeted molecules
- How much contrast reach target vs injected
- Activity
++
Examples molecular imaging
- SPECT
- Immunochemistr, immunofluorescence (microscopy)
- Dual photon microscopy
General structure of molecular probe
- Therapeutic part (?)
- Targeting part - binds to specific molecules (small molecules, peptides, proteins/subunits, Ab’s/subunits)
- Signalling/contrasting element
Molecular probe examples
Chemical
- PET/SPECT: isotopes (radioactivity)
- Optical/acoustic: fluorescent dyes
- MRI: Gd, Fe
- CT: iodine, barium sulphate
Nano/microparticles
- Optical: quantum dot, carbon nanotubes, Au particles
- MRI: iron and Mn-oxide particles
- CT: golden particles
Advantages CT
- Any imaging depth (also disadvantage)
- Good resolution (also disadvantage)
- Simple
- Medium-priced
- Sub-minute scan times
Disadvantages CT
- Radiation
- Just anatomical and functional images
- Semi-expensive
- Soft tissue contrast
- WB imaging
- Minute-scanning time
Contrast materials CT
Ba, I, Kr, Xe, Au
Clinical use CT
- Tumor perfusion
- Ca-score
- Ventillation
US advantages
- No ionizing radiation
- Fast/RT imaging
- High sensitivity
- High resolution
- Cheap
US disadvantages
- No WB imaging
- Only vascular contrast materials
- Operator dependency
Contrast material US
Microbubbles
Clinical use US
- Focal liver lesions
- ECG
- Blood perfusion
- Prostate cancer VEGF expression (phase III BR55)
MRI advantages
- Any imaging depth and plane
- WB imaging
- No ionizing radiation
- High soft tissue contrast
MRI disadvantages
- Expensive
- Low sensitivity
- Long imaging time
MRI contrast materials
Gd3+,iron-oxide particles (SPIO, USPIO)
MRI clinical use
- Liver
- Brain lesions
- Cardio-MRI
MRS advantages
- No ionizing radiation
- WB imaging
MRS disadvantages
- Expensive
- Very low sensitivity
- External calibration/special knowledge
MRS contrast materials
- Cholin
- Lactate
- Creatine
- Lipids
- N-Ac-Aspartate
MRS clinical use
- Brain tumor stratification
- Stroke
Optical methods advantages
- No ionizing radiation
- Short/RT imaging
- High spatial resolution
- Very sensitive
- Semi-quantitative
- Multiplex
Optical methods disadvantages
- Limited transparency
- No WB imaging
Optical methods contrast materials
- Fluorescent molecules
- Light-emitting reactions
- Dyes
- QD-s
- NP-s
Optical methods clinical use
- Experimental
- Sentinel LN
- Image-guided surgery
- Retinopathies (OCT)
- Mammary screening (LumaGem)
SPECT advantages
- Any imaging depth
- WB imaging
- Quantitative
- Good resolution
- Multiplexing
- Theragnostics
- Combination w/CT
SPECT disadvantages
- Radiation
- Sub-mm resolution
- Long imaging times
SPECT contrast materials
- Tc-99m
- Tl-201
- I-123
- In-111
- Ga-67
- Lu-177
- Ho-166
SPECT clinical use
- Nuclear cardiology
- Brain perfusion
- Oncology (Ab, peptides)
- Receptor T
PET advantages
- Any imaging depth
- WB imaging
- Quantitative
- Anatomical co-registration CT, MRI
PET disadvantages
- Radiation
- PRICE
- Resolution
- Longer imaging times
PET contrast materials
- C-11
- F-18
- Ga-68
- Cu-64
- Zr-89
PET clinical use
- FDG patient staging + follow-up
Confocal laser endomicroscopy
Mucosa examined at cell level using fiber optic confocal microscope at autofluorescence emission/excitation
- Esophagus
- Stomach
- Bile ducts
- Ileal/colonic mucosa
Bioluminescence
Energy-dependent multi-event reporter imaging
- Firefly, jellyfish
Tumor targeting
Fluorescence (?)
- Can be passive (in tissue around tumor)
- or active (targeting tumor cells)
Personalized targeted therapy
- SPECT
- MRI
- RNT
OCT
Optical coherence tomography
- Retina
- Mucosae
- Cartilage
- Blood flow
- Mm penetration
- Micron resolution
- Real time imaging
Isotope
Same number of protons
- (Bio)chemically same element
2 types:
- Plus protons
- Plus neutrons
Production isotopes
- Plus protons: in cyclotron
- Plus neutrons: in reactor
Types of radiation isotopes
Plus protons
- Positron emission (pos. beta) => annihilation
- EC (K, L, M…) - avalanche (X-ray, gamma)
- Alpha particle + gamma
Plus neutrons
- Beta
- Gamma
Most important isotopes in nuclear medicine
Diagnostic (electromagnetic radiation)
- Plus neutron: Tc-99m (gamma, metastable)
- Plus proton: Ga-67 (x-r, gamma), C-11 (annihil.)
Therapeutic (particle - absorption)
- Plus neutron: Y-90 (beta)
- Plus proton: At-211 (alpha)
- Se mer bilde ipad
Advantages of Tc-99m
m = metastable (energy slowly)
Used in 80 % of SPECT examinations
- Physical: 140 keV (ideal for gamma camera) and monoenergetic (easy for imaging)
- Biologic: low radiation dose, half-life 6 hrs
- Practical: from Mo-99 generator, elution by phys saline
Theranostic concept
Function-specific molecules
- Diagnostic testing employed for selecting targeted therapy
- Theranostic concept: The same molecule
Detection: imaging in nuclear medicine
1) Gamma camera (SPECT, scintigraphy)
2) Positron camera (PET)
* * Shows function of body!
Detection: non-imaging in nuclear medicine
1) Ex-vivo measurements
- Biological samples: blood, urine (Schilling test)
2) Small dedicated instruments
- Thyroid uptake test
- Intraoperative gamma-probes for localization (ex: LNs)
SPECT
Single-photon* emission computed tomography
- Is a nuclear medicine tomographic imaging technique using gamma rays. Provides 3D info (2D: scintigraphy = gamma camera)
- Double-photon emission = PET
PET vs SPECT
PET: double-photon
- More sensitive
- Better spatial resolution
- Quantitation is easier
- Biomolecules! (“Slice of life”)
Hybrid systems imaging
Function+morphology
1) PET/CT (PET always in hybrid today)
2) SPECT/CT
3) PET/MRI
PET/MRI advantages
- Soft-tissue contrast ins excellent
- No ionizing radiation
Nuclear molecular imaging advantages and disadvantages
Advantages:
- Functions!!
- Non-invasive (not toxic, few allergies)
Disadvantages:
- Geometric resolution limited
- Anatomy, morphology, details, localization (but hybrid)
- Radiation (Gamma: 1-7 mSv, annihil.: 5-10 mSv, EC: 15 mSv)
Molecular nuclear imaging selection of targets
- Enzymes-subst
- Receptor-ligands
- Ag’s-Ab’s
- Transport proteins-subst
- Deposits-binding molecules
FDG
Fluor-deoxy-glucose
- Most important radiopharmaceutical (PET)
- Mainly in oncology - tumors need sugar for energy
- Not tumor-specific
Radionuclide therapy general characteristics
SELLER:
- Specific
- Effective
- Low dose rate (but high dose)
- Low side-effects
- Excellent palliation (reduce sympt./partially treat)
- Repeatable
Wave types in diff media
Gas+liquid: only longitudinal
Solid: transverse
Timbre
Tone color
- Relative strengths of overtones/harmonics (spectrum)
Acoustic impedance formula
Z=cρ (speed velocitydensity)
Human ear audible range
20 Hz - 20 000 Hz
- Below: infrasound
- Above: ultrasound
Phenomena at boundery of different media US
Perpendiclar incidence: reflection + transmission
Skew incidence: Snellius-Descartes (refraction)
Wavelength piezoelectric crystal vs couplant layer
Piezoelectric crystal: λ/2
Couplant layer: λ/4
Time sharing mode US
Pulses instead of continous wave US (gives band spectrum)
Zones US beam
Near field: Fresnel zone (straight)
Far field: Fraunhofer zone (fan-shaped)
Resolving limit and resolution
Resolving limit: Distance between to object detais which can just be resolved as disting objects
- Smaller is better
- Axial RL: depend on pulse length
- Lateral RL: depends on beam width
Resolution: Reciprocal of resolving limit
- Larger is better
Focusing US beam
Increases the divergence of the beam in the far field and reduces depth sharpness
Huygens’ principle
Any wave propagates so that each point of a wave serves as a source of a secondary wave with speed and freq equal to the primary wave
Electronic focusing
Delay units alter the time of emission
Color coding US
BART
“Blue away red toward”
Beating phenomenon
Beating frequency equals the difference of the two interfering frequencies
- Addition and deletion
Time domain correlation method (CVI)
CVI = color velocity imaging
- If the reflecting surface and/or the scatterer are moving then the US signal at a fixed position depends on time.
Sono-CT
Image reconstruction from several multidirectional B-images
Sonoelastography
Sonoelastography is an ultrasound imaging technique where low amplitude, low-frequency shear waves are propagated through internal organs, while real-time Doppler techniques are used to image the resulting vibration pattern. When a discrete hard inhomogeneity, such as a tumour, is present within a region of soft tissue, a decrease in the vibration amplitude will occur at its location
- Check softness/elasticity of tissues
- Intravascular sonoelastography also exist
CHI
THI
Contrast harmonic imaging: behaviour of microbubbles
Tissue harmonic imaging
*Se bilde ipad
IVUS
Intravascular US
Image pixel size and distance in analogue vs digital image
Analogue: random
Digital: uniform
PPI and DPI
PPI: pixel per inch - display
DPI: dots per inch - printer
Zoom, bitmap, vector
Increase pixel size
- Bitmap: no more information - gets unsharp eventually
- Vector graphics: unlimited zoom - must be described as curves
DSA
Digital subtraction angiography
Most common source of noise
Detector (semiconductor detectors are heat-sensitive - cooling may decrease noise)
Fourier transformation and reconstruction
FT: spatial domain => frequency domain
FR: frequency domain => spatial domain
Application of Fourier transformation
- Noise filtering
- To find edges
Aliasing
Sampling problem
- Sampling must be the double of the signal frequency at least
Filetypes
1) Uncompressed: BMP (bitmap)
2) Compressed:
- Lossless: TIFF, GIF
- Lossy: JPG (small storage, loss of info)
3) DICOM: uniform file type + network communication protocol in medicine)
DEXA
Dual energy x-ray absoptiometry
Photoacoustic tomography
To diagnose tissue alteration without the application of any harmful radiation
- Photoacoustic tomography combines the advantages of US with the non-ionizing selective laser excitation
Radiopharmacons composition
Two parts
- Radioactive isotope as radioactive source
- Pharmacon responsible for selective delivery
Most common isotopes PET and SPECT
PET: F-18, C-11, Ga-68
SPECT: Tc99m, I-123, I-125, I-131, Tl-201 and Ga-67
Benefits of Tc-99m
1) Emit only gamma-radiation
2) Optimal gamma-energy
3) Optimal half-life time
4) Easy to create and bind to different pharmacons
5) Cheap
The 2 criteria radiological images must fulfill
1) Appropriate spatial resolution
2) Contrast
The 2 criteria radiological images must fulfill
1) Appropriate spatial resolution
2) Contrast difference
Radiopharmacons CNS
Catagorized by ability to cross BBB:
1) Hydrophilic and anionic molecules cannot cross BBB unless altered permeability
- DTPA (normally cannot cross - used to detect endothel dysfunction in the brain)
2) Lipophilic - can cross BBB
- Tc-HMPAO - measure organ perfusion (ex: brain)
- F-18-FDG - show speed of brain glucose metabolism
Is it possible to detect the distribution of two or more isotopes at the same time?
SPECT: Yes, because we can distinguish between two differen radiopharmacons with different isotope, because they have different gamma energy
PET: No! Same gamma energy after annihilation
CB1-R
Target receptor in diagnosis of epilepsy and alzheimer disease
Designing PET ligands
Easiest: Change one H of ligand analogue with F18 or a C with C-11
CNS imaging
Multimodal imaging: can see CNS distribution of a SPECT (not PET!) in front of MRI and CT
Brain blood flow: multi-isotope signaling (Tc-HMPAO)
BBB injury: dual labeling techiques
Thyroid imaging
Iodine isotopes (I-125, I-131)
99mTc
*Substrates of Na/I symporter
Nuclear cardiology examinations + isotope
1) Myocardial perfusion (Tc-MIBI - or: Tl-201)
2) Help diagnose AMI
3) Measure myocardial metabolism (FDG or C11 marked glucose)
Bone scintigraphy diagnoses
1) Oncologic diseases
2) Bone metabolism
3) Fracture
* Show if increased osteoblast and osteoclast activity + pathological hyperaemia
* Phosphate compounds marked with Tc bind to free hydroxyappatite crystals of bones
* *Most frequently used: MDP (methyl-diphosphate)
Why is bone scintigraphy preferred over x-ray in pediatrics?
- Higher sensitivity
- Lower dose
Liver nuclear molecular imaging
- Liver function
- Bile-excretion, -flow and -ducts
- Use derivatives of IDA marked by Tc
- Kupffer cells: HSA nanobodies
PEG
Polyethylene glycol
- On a nanobody
- Disguise against the immune system
Dose requirement
ALARA: as low as reasonably achievable
High sensitivity
Nuclear imaging
