Nobel Prize in Medical Imaging Quiz
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What significant invention did Wilhelm Roentgen receive the Nobel Prize for in 1901?

The discovery of X-rays.

In what year did George de Hevesy win the Nobel Prize, and what was the focus of his work?

1943; his work focused on the use of isotopes as tracers in chemical processes.

Who were the recipients of the Nobel Prize in 1979 for their work on X-ray computerized tomography (CT)?

Hounsfield and Cormack.

What imaging technique is associated with the 2003 Nobel Prize awarded to Lauterbur and Mansfield?

<p>Magnetic Resonance Imaging (MRI).</p> Signup and view all the answers

How is Nuclear Medicine different from Radiology according to the content?

<p>Nuclear Medicine is to physiology as Radiology is to anatomy.</p> Signup and view all the answers

What characteristic is associated with Radiology imaging modalities like X-ray and CT?

<p>Electron density.</p> Signup and view all the answers

What type of radiation does SPECT and PET utilize for imaging?

<p>Gamma rays.</p> Signup and view all the answers

Which imaging modality uses radiofrequency (RF) to determine its characteristic?

<p>MRI.</p> Signup and view all the answers

What is the maximum count rate allowed for data acquisition in nuclear medicine imaging?

<p>The maximum count rate allowed is less than 20000 counts per second.</p> Signup and view all the answers

How does pixel size relate to spatial resolution in nuclear medicine imaging?

<p>The pixel size should be 1/3 to 1/2 of the spatial resolution.</p> Signup and view all the answers

What matrix sizes are commonly used in nuclear medicine imaging?

<p>Common matrix sizes are 64×64, 128×128, or 256×256.</p> Signup and view all the answers

What is the purpose of a bar phantom in nuclear medicine imaging?

<p>A bar phantom is used to measure extrinsic and intrinsic linearity and spatial resolution.</p> Signup and view all the answers

What are the primary advantages of SPECT imaging over traditional planar imaging?

<p>SPECT provides 3-D images, better contrast, and more accurate lesion localization.</p> Signup and view all the answers

How does intrinsic linearity testing differ from extrinsic testing in nuclear medicine?

<p>Intrinsic testing uses a Tc-99m point source with the collimator removed, while extrinsic testing involves a Co-57 sheet source placed over the bar phantom on the collimator.</p> Signup and view all the answers

What is the typical rotation range for SPECT data acquisition?

<p>The typical rotation range is 180º with two perpendicular detectors or 360º with two opposite detectors.</p> Signup and view all the answers

What is the effect of collimator defects on imaging uniformity?

<p>Collimator defects cause a decrease in imaging uniformity and can shift the energy peak.</p> Signup and view all the answers

In SPECT, what is the significance of using two detectors mounted at specific angles?

<p>Using two detectors at 180° or 90° allows for effective data collection and improved image accuracy.</p> Signup and view all the answers

What two sources are used in bar phantom testing for extrinsic and intrinsic evaluation?

<p>For extrinsic evaluation, a Co-57 sheet source is used, and for intrinsic evaluation, a Tc-99m point source is used.</p> Signup and view all the answers

What are the typical patient preparation steps required before a PET scan?

<p>Patients must fast and manage their medications appropriately.</p> Signup and view all the answers

What is the significance of SUVmax and SUVmean in defining regions of interest in PET scans?

<p>SUVmax indicates the highest radiotracer uptake, whereas SUVmean represents the average uptake within a defined region.</p> Signup and view all the answers

State the effective dose to a patient from a 10 mCi FDG injection during a PET scan.

<p>The effective dose is approximately 7 mSv.</p> Signup and view all the answers

How does PET scanning improve sensitivity compared to SPECT?

<p>PET achieves higher sensitivity due to coincidence detection and electronic collimation.</p> Signup and view all the answers

What is a limitation of functional imaging in medical diagnostics?

<p>Functional imaging suffers from limited spatial resolution and poor signal-to-noise ratio.</p> Signup and view all the answers

Who was responsible for fusing anatomical and functional imaging techniques in 1968?

<p>H.N. Wagner is credited with this advancement.</p> Signup and view all the answers

What distinguishes the first commercial SPECT/CT system from its prototype?

<p>The first commercial SPECT/CT was installed in 1999, whereas the prototype was built in 1990.</p> Signup and view all the answers

What is the primary function of attenuation correction in PET systems?

<p>To improve image quality by compensating for the loss of signal during photon transmission.</p> Signup and view all the answers

Name two detector materials used in PET systems and identify their respective manufacturers.

<p>BGO by GE and LSO by Siemens.</p> Signup and view all the answers

What is the stopping power of NaI at 511 keV?

<p>0.32/cm.</p> Signup and view all the answers

How does the pile-up effect influence count rates in scintillation detectors?

<p>It reduces the count rate and introduces artifacts due to the inability to distinguish between two closely timed γ photon detections.</p> Signup and view all the answers

What is the significance of correction in analyzing lesions in SPECT imaging?

<p>Correction is important for accurately judging the activity of lesions, ensuring that the assessment reflects true physiological conditions.</p> Signup and view all the answers

Describe one advantage and one disadvantage of SPECT/CT imaging.

<p>An advantage of SPECT/CT imaging is the ability to provide 3D lesion locations without overlapping structures. A disadvantage is that the images can be noisy, which may affect diagnostic accuracy.</p> Signup and view all the answers

What parameters define the spatial resolution in a PET system?

<p>The dimensions of individual detector elements and their optical isolation.</p> Signup and view all the answers

What advantages do ring detectors offer in PET imaging?

<p>Higher detection efficiency and improved spatial resolution.</p> Signup and view all the answers

What role do positron emitters play in Positron Emission Tomography (PET)?

<p>Positron emitters are crucial as they release positrons, which subsequently annihilate with electrons to produce gamma rays used for image formation in PET.</p> Signup and view all the answers

Explain the concept of Lines of Response (LOR) in PET imaging.

<p>Lines of Response (LOR) refer to the path between detected gamma rays that indicate the position of annihilation events in PET imaging.</p> Signup and view all the answers

What is the scintillation decay time of LSO?

<p>40 ns.</p> Signup and view all the answers

Describe the significance of the transverse field of view (FOV) in PET systems.

<p>It determines the width of the section being imaged, influencing the overall coverage and detail of the scan.</p> Signup and view all the answers

What is the result of scatter and random coincidences in PET imaging?

<p>Scatter and random coincidences introduce noise and degrade the quality of the images, complicating the interpretation of the radioactivity distribution.</p> Signup and view all the answers

Why are collimators absent in PET scanners, and what advantage does this provide?

<p>Collimators are absent in PET scanners, which enhances detection efficiency and spatial resolution by allowing more gamma rays to be detected.</p> Signup and view all the answers

How are detector blocks in PET systems designed to enhance count rate?

<p>They are configured to acquire data simultaneously from all blocks, significantly increasing the overall count rate.</p> Signup and view all the answers

What is the energy resolution range for GSO detectors in PET systems?

<p>10% to 18%.</p> Signup and view all the answers

Discuss the purpose of attenuation correction in PET imaging.

<p>Attenuation correction in PET imaging is used to account for the loss of signal due to absorption of gamma rays in body tissues, which can distort images.</p> Signup and view all the answers

What materials are commonly used in PET detectors, and why are they important?

<p>Common materials used in PET detectors include BGO, LSO, GSO, and LYSO, which are important for their efficiency in detecting gamma rays.</p> Signup and view all the answers

Contrast the types of radionuclides used in PET versus SPECT imaging.

<p>PET imaging typically uses radionuclides such as $^{18}F$, $^{82}Rb$, and $^{13}N$, while SPECT imaging commonly employs $^{99m}Tc$, $^{67}Ga$, and $^{111}In$.</p> Signup and view all the answers

How is the CT number calculated in CT imaging, and what does it represent?

<p>The CT number is calculated using the formula CT number $(x,y) = 1000 ( rac{ u(x,y) - u_{water}}{ u_{water}})$, representing the relative attenuation of a substance compared to water.</p> Signup and view all the answers

Study Notes

Medical Physics: Introduction to Nuclear Medicine

  • Course provided by Peyman Sheikhzadeh, PhD
  • Department of Nuclear Medicine and Medical Physics, Tehran University of Medical Sciences

Medical Imaging Techniques

  • Discovery of X-rays: Wilhelm Roentgen received the Nobel Prize in 1901 for discovering X-rays.
  • Radiopharmaceuticals: George de Hevesy received the Nobel Prize in 1943 for his work on using isotopes as tracers to study chemical processes.
  • Development of X-ray CT: Hounsfield & Cormack received the Nobel Prize in 1979 for developing X-ray computerized tomography (CT).
  • Development of MRI: Lauterbur & Mansfield received the Nobel Prize in 2003 for developing Magnetic Resonance Imaging (MRI).

Structural & Functional Imaging

  • Nuclear Medicine is to physiology as Radiology is to anatomy.

What does Probe Mean in Imaging?

  • Radiology: X-ray - Electron Density
  • Mammography: X-ray - Electron Density
  • CT: X-ray - Electron Density
  • Angiography: X-ray - Electron Density
  • MRI: RF - Proton Density
  • SPECT: Gamma Ray - Radionuclide Distribution
  • PET: Gamma Ray - Radionuclide Distribution
  • Sonography: Ultrasound - Acoustic Impedance

History

  • Wilhelm Conrad Roentgen, a German physicist, discovered X-rays in 1901.

NM and PET Process

  • Diagrams depict the process of Nuclear Medicine (NM) and Positron Emission Tomography (PET).
  • Information about elements involved in process is also shown.

Radioisotopes and Radiopharmaceuticals

  • Radioisotope: the radioactive atom source of radiation
  • Radiopharmaceutical: the vector molecule targeting organs
  • Radiopharmaceutical (radiotracer): Radioisotope + pharmaceutical

Why is Nuclear Medicine Different?

  • Emission source is the organ
  • Functional imaging is the method
  • Nuclear Medicine complements, not replaces other modalities
  • Contrast between nuclear medicine and other modalities is highlighted

NM Activity Poles

  • Radiopharmacy: Radiopharmaceuticals; nuclear and biochemical industry
  • Functional Imaging: clinical use (imaging); physicians
  • Instrumentation: camera, PET; manufacturers/physicist

A Review: Nuclear Decay Rules

  • β⁻ decay: AX₂ → AYz+¹ + e⁻ + ν
  • β⁺ decay: AX₂ → AYz⁻¹ + e⁺ + ν
  • e⁻ capture: AX₂ + e⁻ → AYz⁻¹ + ν
  • γ decay and internal conversion: no changes for A & Z

Radioactivity

  • A(t): disintegration rate at time t (decays/sec)

  • N(t): number of nuclei at time t

  • λ: decay constant (1/sec or 1/hr)

  • λ = ln2 / T½ = 0.693/T½

  • T½: half-life

  • 1 Bq = 1 disintegration/second (Becquerel)

  • 1 Ci = 3.7 x 10¹⁰ dps (Curie)

  • 1 mCi = 37 MBq

  • NM imaging: ~1 to 30 mCi (30 – 1100 MBq)

Physical Half-life (Tp)

  • Tp: time for radioactive atoms to reduce by one-half
  • N₁ = N₀ e-λt or A₁ = A₀ e-λt
  • Tp = 0.693 / λ λ = 0.693 / Tp
  • Where N₀ = Initial number of radioactive atoms, and N₁ = number of radioactive atoms at time t.

Effective Half-life (Te)

  • Time to reduce radiopharmaceutical in the body by one-half
  • Due to functional clearance and radioactive decay
  • Te = (1 / Tp) + (1 / Tb)
  • Tp >> Tb --> Te ≈ Tb
  • Tp << Tb --> Te ≈ Tp

Radionuclides used in Nuclear Medicine

  • Table (Radionuclide, Decay Mode, Principal Photon Emissions, Half-Life, Primary Use) provides examples of radionuclides and their properties
  • Table details radionuclides, decay mode, emissions, half-life and use.
  • The table includes both imaging and therapeutic purposes.

Radiation Detectors in NM

  • Survey meters (ionization chambers, Geiger-Müller)
  • Dose calibrators (ionization chambers)
  • Well counters (scintillation detectors)
  • Thyroid probes (scintillation detectors)

Ionization Chamber

  • Signal strength is proportional to energy deposited
  • Used to measure radiation (exposure, air kerma)

Dose calibrator quality control

  • Constancy
  • Linearity
  • Accuracy
  • Geometry

Geiger-Müller Region

  • Signal strength independent of energy deposited
  • Used to measure radiation presence

Scintillation Detectors

  • Scintillator: converts radiation energy into light flashes (fluorescence)
  • Photomultiplier tube (PMT): detects and amplifies the light signals

Gamma Camera, Scintillation Camera

  • Obtaining a Nuclear Medicine (NM) image involves administering a radiopharmaceutical, concentrating it in target areas, and detecting emitted gamma photons using a gamma camera.

How to Obtain a NM Image?

  • Administer radiopharmaceutical (radionuclide-labeled pharmaceutical)
  • Radiopharmaceutical concentrates in target areas.
  • Detect emitted gamma photons using a gamma camera (scintillation camera).

Steps for obtaining PET Images

  • The diagrams depict the steps involved in acquiring a PET (Positron Emission Tomography) image.
  • The steps include the injection of radiopharmaceutical into the patient, its absorption by the organ, generation of gamma rays by the organ, focusing of gamma rays by collimator, conversion of signals from PMTs, identification of positions by localization electronics and final display of the image.

Basic Principle of Gamma Camera

  • Gamma rays directed to a scintillation crystal (e.g., NaI(Tl))
  • Multiple photomultiplier tubes (PMTs) detect light flashes
  • Signals are converted to electrical pulses and analyzed
  • Image of radionuclide distribution is formed and displayed.

Nuclear Medicine is Emission Imaging

  • Gamma photons emitted from inside the patient
  • Gamma energies: 70 to 511 keV
  • Relatively poor image quality due to limited photon number and spatial resolution.
  • Image noise is a limitation.
  • CT imaging is a transmission method.

Nuclear Medicine is Molecular Imaging

  • Radiopharmaceutical interaction with cells/molecules.
  • Binding directly to target molecules (e.g., monoclonal antibody)
  • Accumulation by molecular/cellular activities (e.g., FDG, Tc-sestamibi)
  • Improved diagnosis from earlier detection of molecular or cellular activities (e.g., heart perfusion, brain, kidney, lungs, cancers).

Major Components of Gamma Camera

  • Pre-amp, PMT, Nal(Tl) crystal, collimator, Pulse Height Analysis, Position Analysis
  • X, Y, Z axes for Localization, Computer, Display
  • Details are displayed in diagrams.

Collimator

  • Establishes geometric relationship between y photon source and detector
  • Affects gamma camera count rate and spatial resolution.

Different Parallel-Hole Collimators

  • Descriptions of various collimator types (low-energy all-purpose [LEAP], low-energy high-resolution [LEHR], medium-energy all-purpose [MEAP], high-energy all-purpose [HEAP])

Collimators

  • Descriptions of various collimator types (parallel-hole, pin-hole, converging)

Scintillation Process in Detector

  • Converts y photons to blue photons.
  • Blue photon number proportional to energy deposited.
  • Electron liberation in PMT photocathodes proportional to the number of blue photons.
  • Electrical pulse height is proportional to the energy deposited by the y photon in the crystal.

Desirable Scintillator Properties

  • Absorption efficiency (High p, Z)
  • High light output (conversion efficiency)
  • Energy discrimination (Spatial Resolution)

Photomultiplier Tube (PMT)

  • Create and amplify electrical pulses
  • Photocathode (CsSb) converts blue light to electrons.
  • 12 Dynodes: each multiplies electrons by 3-6 times.
  • Anode collects electrons (6 x 10⁷ gain).

Photomultiplier Tube (PMT)

  • Optical coupling to crystal assembly via silicone compound.
  • Light emissions detected by PMTs, converted to electrical pulses, then voltage pulses before amplification.

Photomultiplier Tube (PMT)

  • 40 to 100 PMTs in a modern gamma camera.
  • Photocathode directly coupled to detector or via plastic light guides.
  • Anode connected to electronics within tube base.
  • Sensitive to magnetic fields.

PMT Function

  • PMT arrangement on crystal surface.
  • Tubes nearest scintillation produce strongest signals.
  • Weaker signals produced by farther tubes.
  • Signals used to determine photon origination location within the body.

Localization Electronics

  • PMT signals fed to localization electronics.
  • Analyzed into X, Y, Z pulses:
  • Z pulse: Proportional to energy deposited in the crystal.
  • X and Y pulses: Provide positional information from the resistors.

System Layout in Nuclear Systems

  • Major components (Gantry, Table, Head Electronics, PMT, Crystal, Collimator)
  • Diagram providing system layout

Image Formation (Photopeak)

  • Gamma photons detected by the crystal.
  • Stops >99.95% of y’s.
  • Efficiency of a LEHR collimator ~ 0.02%.

Scatter

  • Main source of image degradation in nuclear medicine.
  • Increases image noise & reduces lesion contrast.
  • Photopeak windowing suppresses scatter, not completely eliminating it.

Scatter in Patient

  • Diagrams depict scatter in patient, including energy selection for scatter rejection.

Image Degradation: Septal Penetration

  • Collimator septal penetration causes degraded images.

Image Degradation: Simultaneous Detections

  • Coincidental interactions lead to image degradation.

System Spatial Resolution

  • Rsys = √(Rint² + Rcol²)
  • Intrinsic (detector) resolution (Rint)
  • Collimator resolution (Rcol)
  • System resolution (Rsys)

Collimator Resolution

  • Spatial resolution degrades with increasing pt-collimator distance.

Data Acquisition

  • Collimator matching to radioisotope energy window.
  • Pixel size (1/3 to ½ of spatial resolution).
  • Matrix size = detector size / pixel size
  • Usually, 64 x 64, 128 x 128 or 256 x 256 matrix sizes are used.
  • 2 bytes per pixel depth
  • Count rate < 20,000/sec.
  • Patient proximity to the detector.

Effect of Matrix Size

  • Larger matrix size (e.g., 128 x 128) provides finer details compared to a smaller size (e.g., 64 x 64)

Planar NM Imaging

  • Image of a medical equipment used for planar NM imaging.

Uniformity

  • Examples of images showing various uniformity defects, including collimator imperfections, PMT problems, and energy peak shifts.

Bar Phantom

  • Made of lead stripes with varied orientations and spacing in 4 quadrants.
  • Used to evaluate, measure, and analyze extrinsic and intrinsic linearity and spatial resolution.

Tomographic NM Imaging (SPECT)

  • Acquires data at several angles around the patient.
  • Similar to CT imaging.

Tomographic Imaging (SPECT)

  • Produces tomographic images using conventional gamma camera projection data at multiple angles around the patient

SPECT

  • 3D images eliminate overlaying/underlying activity.
  • Characteristics: better contrast, more accurate lesion localization, increased time and demand, greater noise.

SPECT Data Acquisition

  • Generally, two detectors mounted at 180° or 90° on a rotating gantry.
  • Sequence of 2D static images at various angular positions.
  • Detector rotation range: 180° with 2 perpendicular detectors or 360° with 2 opposite detectors.
  • Circular or elliptical orbit of detectors closer to the patient for better spatial resolution.

SPECT Image Acquisition

  • Typically, two camera heads rotate around the patient.
  • Projection images taken every 3-6 degrees.
  • Scan time is ~15 minutes.
  • Matrix sizes: 64 x 64 or 128 x 128.

Data Collection: Angular Stops

  • 3 to 6 degrees common.
  • Fewer angular stops cause streaking if causing problems with image quality.

View Number for 360˚ SPECT

  • Number of views = matrix size (128 or 64).

An image with 128 x 128 Matrix

  • Contains 128 projections.
  • Each projection has 128 data points.
  • Equivalent to 128 slice CT images per rotation.

Sinogram (for one of many slices)

  • Mapping of 1D projection profiles into 2D sinogram space.

Back Projection

  • Blurring in image due to streaks and star-like artifacts.

Filtered Back Projection

  • Suppresses blurring via filtering of projections.
  • High-pass filter (ramp filter) used to reduce blurring.

Filtered Back Projection (of noiseless data)

  • Diagrams show filtered backprojection with 2, 4,and 256 angles

Filter

  • Applied filter is produced through ramp or user-selected filter (e.g., Shepp-Logan, Hahn, Butterworth, Weiner, Hamming).
  • Other filters (e.g., Hanning in MCG Philips) frequently turned off.

Selection of Filters for SPECT

  • Filters trade noise for resolution.
  • No single method is universally better for optimization.
  • Patient variation, physician preference, and vendor recommendations apply to filter choice.

Iterative Reconstruction (IR)

  • Filtered Back Projection (FBP) has limitations.
  • Corrections required (e.g., attenuation, Compton scatter).
  • Iterative reconstruction methods like Ordered Subsets Expectation Maximization (OSEM) address these.

Iterative Reconstruction

  • Slower than Filtered Back Projection (FBP).
  • Common reconstruction for PET.
  • Increasing use in SPECT.

Image Recon - Iterative

  • Process of iterative reconstruction is displayed step by step, including the comparison of projections and the iterative estimates

Iterative Reconstruction Algorithms

  • Diagram displays the iterations of images for iterative reconstruction algorithms.

Brain Phantom (FBP vs IR OSEM)

  • Iterative reconstruction method (e.g., OSEM) compared to filtered back projection (FBP).

Non-filter Noise Factors

  • Collimator, Matrix (64 x 64 or 128 x 128), Slice Thickness, Time per Stop, Number of Stops, Administered Dose

Data Collection: Counts

  • Determination of image counts.
  • Activity in patient.
  • Time per stop.
  • Number of stops.

Attenuation Correction

  • Attenuation in radionuclide imaging
  • Important for judging lesion activity.

Uniform Phantom with Evenly Distributed 99m Tc

  • Diagrams demonstrate the impact of attenuation correction on image quality with respect to low counts in the center

SPECT/CT

  • Combination of SPECT and CT imaging systems

Patient Studies

  • Advantages: no overlapping structures, 3D lesion locations.
  • Disadvantages: image noise, increased time due to motion, decreased patient comfort.
  • Fusion techniques combining CT/MRI and NM images improves visualization/diagnosis

Introduction to the Physics of Positron Emission Tomography

  • Principles of Positron Emission Tomography (PET) are introduced.

Biograph Vision Quadra™

  • The features related to medical equipment are highlighted.

Gamma Camera Components

  • Components of gamma camera and its functionalities: stationary and rotating gantry, detectors, and patient table
  • Transmission acquisition system

PET Scanner Components

  • Diagram illustrating gantry, detector ring, acquisition/processing station, and patient table

PET/CT Scanner

  • Schematic depiction of combined PET and CT scanner, including gantry, PET detector, CT module, acquisition/processing station and patient table

The PET/CT Power..!

  • CT images depicting skeletal structure, lesions and other anatomic features.

Anatomic and Functional Imaging

  • Diagrams depict anatomical imaging (CT), functional imaging (NM) and fusion (CT + NM) images.

Effective Dose of NM Procedures

  • Table depicting various NM procedures and their effective doses.

Dose Limits

  • Table presenting occupational and general public exposure limits & guidelines for radiation doses.

SPECT & PET

  • SPECT uses 2 views, resolution is affected by distance from the collimator face and detector size.
  • PET is simultaneous; resolution related to the detector width and maximal in the center of the ring.
  • SPECT sensitivity is ~0.02%; PET ~2-3% or high

Advantages of PET over SPECT

  • Superior spatial resolution
  • Higher sensitivity
  • Attenuation correction

Limitation of Functional Imaging

  • Limited spatial resolution
  • Poor signal-to-noise ratio
  • Poor uptake of the radiotracer by certain diseased conditions.
  • Images registration with anatomical imaging can improve visualization

Medical Imaging Techniques

  • Examples of anatomic imaging (CT), functional imaging (NM), and hybrid imaging (PET/CT) are illustrated.

Fusing Anatomy and Function

  • Hand-Drawn, Visual Fusion methods, and Hardware Fusion techniques.

History of Dual-modality Imaging (SPECT/CT, PET/CT)

  • Historical context & development of combined imaging procedures
  • Detailed details regarding the systems involved are highlighted.

Gamma Camera Components

  • Components of a gamma camera including a stationary gantry, rotating gantry, detectors, and a patient table.
  • Describes transmission acquisition system
  • Includes a clear image

PET Scanner Components

  • Main components of a PET scanner: gantry, detector ring, and patient table.
  • The acquisition/processing station is also shown.

PET/CT Scanner

  • Diagram depicting a PET scanner with connected CT components; gantry, PET detector module, CT module, acquisition/processing station and a patient table.

PET/CT Power!

  • CT image showing a lesion/anatomic feature

Anatomic and Functional Imaging

  • CT (anatomic) and NM (functional) images are displayed.
  • Fusion of imaging modalities is visually demonstrated.

Effective Dose of NM procedures

  • Table listing various nuclear medicine procedures, their administered activity (MBq), effective dose (mSv), and dose per MBq.

Dose Limits

  • Table outlining occupational and public radiation dose limits.

Time-of-Flight PET

  • Use of Time-of-Flight (TOF) technique to increase image quality and reduce scan time in PET imaging.

Time of Flight PET Image of a Big Patient

  • Comparison using images with normal image and time of flight imaging.

Discovery PET/CT 710 (GE), Ingenuity TF PET/CT (Philips) and Biograph TruePoint PET/CT (Siemens)

  • Medical Image modalities

Attenuation Correction in PET/CT

  • Scout image and CT image are displayed.

Attenuation Correction

  • Attenuation corrected and uncorrected PET images are illustrated.

Photon Attenuation in PET

  • Diagram depicts photon attenuation in different parts of the body, including high uptake in lungs, low uptake in others, and high uptake in skin, showing differences with/without attenuation compensation

Typical PET/CT Imaging

  • Shows the procedure of reconstructing CT and PET images, pre-correcting, and displaying them.

Role of FDG

  • FDG is not cancer specific; accumulates in metabolically active tissues like tumors, hyperactive (muscular/nervous) tissues, and areas of active inflammation

Hyperactivity

  • Demonstration shows FDG uptake in pectoralis major after strenuous exercise.
  • Images illustrate regions of high activity post-exercise.

Inadequate Fasting

  • Comparison of PET images from patients with 45-minute and overnight fasting illustrating differences in uptake in various organs due to fasting time.

Semiquantitative PET: Standard Uptake Value (SUV)

  • Defined as the ratio of activity concentrations in a tissue region-of-interest and the whole body average.
  • SUV often used as a cut-off to distinguish malignant and non-malignant pathology.

SUV in Clinical Studies

  • The numerator is the highest pixel value (SUVmax) or mean pixel value (SUVmean) from a region-of-interest (ROI).
  • The denominator is the activity administered divided by the patient's body mass, lean body mass, or body surface area.
  • SUV depends on physiologic conditions (uptake time, fasting state), image quality (noise, resolution), and ROI definition.

Requirement for Reproducible SUV

  • FDG uptake period, scan length, scanning range, and direction.
  • Patient preparation (fasting, medication).
  • Reconstruction parameters (slice thickness, filters).
  • Region-of-interest (ROI) definition, consistency in body mass/lean body mass/surface area.

Clinical Use of PET

  • Oncology accounts for ~90% use case.
  • 10% for cardiac and neuro applications.

Typical Oncology Protocol

  • Administered FDG dose (10-20 mCi).
  • 60 minutes in a quiet room for FDG uptake and blood clearance.
  • Scanning (eyes-to-thighs), 6-7 bed positions, 30 minute scan time.
  • SUV tumor typically increases with time and SUV background typically decreases with time.

Patient Dose (FDG)

  • Effective dose to the patient: ~7 mSv for 10 mCi (370 MBq) FDG injection
  • Organ with maximum dose: bladder
  • Equivalent dose for 10 mCi (370 MBq) FDG injection is ~63 mGy
  • CT dose for attenuation correction (~5 mSv)
  • Diagnostic/contrast CT dose (~15–18 mSv)

SPECT & PET

  • SPECT uses 2 views, resolution is affected by distance from collimator face and detector size.
  • PET is simultaneous; resolution related to the detector width and maximal in the center of the ring.
  • SPECT sensitivity is ~0.02%; PET ~2-3% or high

Advantages of PET over SPECT

  • Superior spatial resolution
  • Higher sensitivity
  • Attenuation correction

Limitations of Functional Imaging

  • Limited spatial resolution
  • Poor signal-to-noise ratio
  • Poor radiotracer uptake in diseased tissues.
  • Registration with anatomical images is helpful.

Medical Imaging Techniques

  • Graphical representations of medical images illustrating anatomical and functional imaging techniques, hybrid imaging (fusion) techniques

Fusing Anatomy and Function

  • Different techniques (hand-drawn, visual, and hardware fusion) for combining anatomical (e.g., CT) and functional (e.g., PET or SPECT) images are highlighted.

History of Dual-Modality Imaging (SPECT/CT, PET/CT)

  • Historical context of dual-modality imaging, including the first prototype SPECT/CT by Hassegawa in 1990 and the development of PET/CT by Townsend in 1998.

Gamma Camera Components

  • Diagram illustrating a gamma camera with its stationary gantry, rotating gantry, detectors, and patient table, and also showing the transmission acquisition system

PET Scanner Components

  • Diagram illustrating a PET scanner with its gantry, detector ring, patient table, and acquisition/processing station.

PET/CT Scanner

  • Diagram illustrating a PET/CT scanner with its gantry, PET detectors, CT module, patient table and acquisition/processing station

PET/CT Power!

  • CT image displaying a lesion/anatomic feature on a human body

Anatomic and Functional Imaging

  • CT (anatomical) and NM (functional) images are displayed
  • Fusion of imaging modalities is highlighted

Effective Dose of NM Procedures

  • Table of various nuclear medicine procedures, administered activity (MBq), effective dose (mSv), and dose per MBq

Dose Limits

  • Table highlighting occupational and public exposure limits and guidelines for radiation doses

Detector Materials

  • Materials for detectors: BGO (GE), LSO (Siemens), GSO (Philips) and LYSO (used by others).

Stopping Power (Attenuation Coefficients)

  • Table presenting stopping power values for NaI(Tl), BGO, LSO, GSO, and LYSO scintillators.

Scintillation Decay Time

  • Scintillation decay times (ns) for various scintillators (NaI(Tl), BGO, LSO, GSO, and LYSO) are provided.

Energy Resolution

  • Energy resolution percentages for various scintillators (NaI(Tl), BGO, LSO, GSO, LYSO).

Detector Blocks PET

  • Detector elements (width ~ 4-6 mm) are typically used in a PET system. They are optically isolated via reflective material.
  • A PMT array within a crystal cuts determines the detector element which absorbs the 511 keV photon.

Detector Blocks

  • Each detection element (4 mm x 4 mm x 30 mm)
  • Small tangential and axial sizes provide good spatial resolution.
  • Large radial size offers high stopping power for high count rate.
  • Simultaneous data acquisition by all blocks significantly raises the count rate.

Advantages of PET Imaging

  • Higher detection efficiency and improved spatial resolution compared to SPECT.
  • Ring and block detectors improve detection efficiency.

2014 PET Image of the ACR Phantom

  • Image of various sphere sizes in a PET system

2014 SPECT Image of the ACR Phantom

  • Images of ACR phantom spheres with different diameters in a SPECT system

Time-of-Flight PET

  • TOF is used to strengthen signal-to-noise ratio and reduce image scan time
  • Computationally intensive algorithm

Time of Flight PET Image of a Big Patient

  • Comparison of PET images with and without time-of-flight (TOF) imaging

Discovery PET/CT 710 (GE), Ingenuity TF PET/CT (Philips) and Biograph TruePoint PET/CT (Siemens)

  • Medical image modalities

Attenuation Correction in PET/CT

  • Showing how CT data is used for attenuation correction in a PET/CT system

Attenuation Correction

  • Demonstrating how attenuation correction improves image quality in PET imaging (the application with attenuation (AC) gives better image detail/contrast)

Photon Attenuation in PET

  • High uptake in lungs, low uptake in others, and high uptake in skin.

Typical PET/CT Imaging

  • Typical steps to construct and display PET/CT (Positron Emission Tomography/Computed Tomography) images are illustrated in a flow chart

Role of FDG

  • FDG is not specific to cancer. It accumulates in regions of high metabolism & glycolysis.
  • Increased uptake is seen in hyperactive tissues, sites of active inflammation and tissue repairs.

Hyperactivity

  • High FDG uptake in the pectoralis major after strenuous exercise

Inadequate Fasting

  • Showing images of patients with inadequate fasting time.

Semiquantitative PET: Standard Uptake Value (SUV)

  • The ratio of activity concentrations in-tissue versus whole body.
  • Threshold (SUV ~ 2.5) to differentiate malignant and benign pathology.

SUV in Clinical Studies

  • Numerator: highest SUVmax (pixel value) from region-of-interest (ROI), or mean SUVmean
  • Denominator: Activity administered / patient body mass or surface area
  • SUV depends on physiologic conditions (fasting state, uptake time), image quality (noise/resolution), ROI definition, and scanning parameters.

Requirement for Reproducible SUV

  • FDG uptake period, scan length, scanning range, and direction.
  • Patient preparation (fasting, medication).
  • Reconstruction parameters (slice thickness, filters).
  • Region of interest (ROI) definition, consistency in body mass / lean body mass / surface area.
  • Consistency is the foremost factor.

Clinical Use of PET

  • Oncology (~90%): Detection, staging, treatment response assessment, restaging.
  • Cardiac & neuro (~10%): Perfusion, etc.

Typical Oncology Protocol

  • Administering FDG (~10–20 mCi) over 60 minutes in a quiet room.
  • Scanning from eyes to thighs over 6–7 bed positions.
  • Total scan time ~ 30 minutes (3 minutes per bed position) to allow uptake and clearance.

Patient Dose (FDG)

  • Effective dose of a 10mCi FDG injection: ~7 mSv
  • Maximum dose to the bladder
  • Equivalent dose: ~63 mGy for a 10mCi injection
  • CT dose from attenuation correction: ~5 mSv
  • CT diagnostic/contrast: ~15–18 mSv

SPECT & PET

  • SPECT: Two views from opposite sides, resolution proportional to collimator resolution and degrades with increasing distance from the collimator face.
  • PET: Simultaneous acquisition (no collimation). Resolution proportional to detector width, highest in the center of the ring.
  • SPECT sensitivity 0.02%; PET sensitivity2-3% due to coincidence detection (electronic collimation)
  • Significant losses in SPECT due to absorptive collimators

Advantages of PET over SPECT

  • Superior spatial resolution
  • Higher sensitivity
  • Amenable to attenuation correction

Limitations of Functional Imaging

  • Limited spatial resolution
  • Poor signal-to-noise ratio
  • Low tracer uptake in some diseased areas
  • Registration with anatomic images important to improve accuracy

Medical Imaging Techniques

  • Combining anatomical (CT) and functional (PET/SPECT) imaging data for improved insights into patient conditions.

Fusing Anatomy and Function

  • Demonstrating techniques like hand-drawn, visual, and hardware fusion for combined anatomical and functional image information.

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Test your knowledge on the significant contributions and inventions in medical imaging that earned various scientists Nobel Prizes. This quiz covers key figures, inventions, and techniques associated with radiology and nuclear medicine. Dive into the world of imaging and see how well you understand its history and technology.

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