Nuclear Medicine Imaging Systems

3y ago
16 Views
2 Downloads
5.28 MB
37 Pages
Last View : 16d ago
Last Download : 2m ago
Upload by : Genevieve Webb
Transcription

Nuclear Medicine Imaging Systems Position estimationPMT signal– based on 2-D centroid calculation– called Anger logic or Anger cameraPosi/onop/cal photonsScin/lla/onCollimatorgamma-ray

Analogies with X-ray ImagingX-rays– photon formation bremsstrahlung characteristic x-rays– attenuation by tissues photoelectric absorption Compton scatter– detection systems scintillators– 2-D projection imaging radiographs– tomographic imaging CT collect projections from aroundthe patientNuclear medicine– photon formation positron emission isomeric transition– attenuation by tissues photoelectric absorption Compton scatter– detection systems scintillators– 2-D projection imaging scintigraphs– tomographic imaging SPECT and PET collect projections from aroundthe patient

Gamma Camera Imaging (SPECT)Siemens Healthcare, SymbiaPhilips Medical, Brightview XCTGE Healthcare, MG

Single Photon Emission Computed Tomography SPECT is to scin/graphy as CT is to radiographyWe collect projec/on views all the way around the pa/entWe use tomographic principles (e.g. FBP) to reconstruct an imageOne difference is that we are using emission rather than transmissionAnother difference is that aGenua/on is a headache rather than what we want(as for CT)– ScaGered photons, however, remain a nuisance––––

SPECT Imaging Equa/on Using parallel-hole collimators, and ignoring depth-dependentcollimator burring etc., we haveR A(x, y, z)Rφ (z, l) exp µ (x, y", z, E)dy" dy2y4π (y R){} Our inverse problem is: given φ(z,l) for all angles θ, what is A(x,y,z)?- Like poly-energe/c CT problem this is hard- Complicated by aGenua/on- Solu/on discovered in 2000integra/ongeometry

SPECT Image Reconstruc/on For the approximate solu/on used in prac/ce, we make severalassump/ons– ignore collimator effects– parameterize x and y as func/ons of distance along linex(s) l cosθ s sin θy(s) l sin θ s cosθintegra/ongeometry This changes the imaging equa/on to:RA(x(s), y(s))φ (l,θ ) exp µ (x( s% ), y( s% ); E)ds% ds 4π (s R)2sR{}

SPECT Image Reconstruc/on Addi/onal assump/ons– ignore inverse-square dependence of fluence– assume we can correct for aGenua/on effects later This changes the imaging equa/on to φ (l,θ ) A(x(s), y(s))ds A(x, y)δ (x cosθ ysin θ l)dx dywhich is the 2-D x-ray or Radon transform that we can solve with FBPA(x, y) π0where( ρ Φ( ρ,θ )e j 2 πρl d ρ dθ*) -,Φ( ρ, θ ) F1D {φ (l, θ )}

Angular asymmetry p)

Comparison of Imaging Equa/ons

Image reconstruction

Image reconstructionPoint source reconstrction byFiltered back projection (FBP)Filtering the projection data with aramp filter creates the negativevalues in back-projected profilenecessary for cancelling thecontributions from other angles in theregion about the reconstructed point.The back projections from differentangles are added together to form thereconstructed imageCullom SJ, In: Cardiac SPECT Imaging, 2001

Image reconstructionStar (or streak) artifact of FBP reconstruction A objectB through G {1, 3, 4, 16, 32, 64} number of projectionsStar artifact decreases with number of projectionsBruyant PP, J Nucl Med 2002; 43:1343–58

Reconstruction Filtersused to reduce image noise A ramp filter of the form “ r ” used to correct for “1/r” tomographic blurring ar/fact Ohen, the “ramp” filter is further modified by addi/onal frequency filters, such as:the “Hann,” “Shepp-Logan” or “BuGerworth” filters. In filtering, we see a tradoff of image noise vs. spa/al resolu/on Higher cutoff frequencies maintain spa/al resolu/on at the expense of more noise Filtered FBP is a very rapid technique for reconstruc/ng SPECT data Itera/ve reconstruc/on techniques, such as ordered subset will be covered in laterlectureModified Frequency FiltersEffect of BuGerworth-filter cutoffKoch W. J Nucl Med 2005; 46:1804–11

Iterative reconstruction – a generic examplef (0 )ini/al imagees/matef (k)systemmodelp(k) Hfnoise(k) nEs/mate of projec/onpmeasureddatapp( k)f ( k ) f ( k 1)Compare measured to Update image basedes/mated projec/on on ra/o or difference– Model the system (and the noise) used in projector– Image update is typically based on differences orratio of measured and estimated projection data– Must decide when to stop iterating

Projector can account for Signal probability modelPhysics model of SPECT imagingSystem (intrinsic collimator) spa/al resolu/onPa/ent aGenua/onCompton ScaGer (in pa/ent, collimator, crystal)Collimator septal penetra/on

Various Itera/ve Recon. Methods Algebraic reconstruc/on technique (ART) Mul/plica/ve ART (MART) Weighted least-squares conjugate gradient (WLS-CG) Expecta/on maximiza/on (EM)

Expecta/on Maximiza/on (EM) Es/mates parameters of the sta/s/cal distribu/onsunderlying the measured data Maximize marginal likelihood by itera/ng two steps:Expecta/on: Marginalize log likelihood with respect to the missing data givenobserved data for the current es/mate of parametersMaximiza/on: Find set of parameters that maximizes this quan/ty In the case of SPECT– Observed data, F {fj , j 1, ,J) are the projec/ons onto detector elements– Parameters, A {Ai , i 1, ,I) are the true count rate in a voxel at {xi, yi, zi}– The parameters {Ai} are independent and Poisson distributedIJφ j AiiA e argmax{pr(φ A)} Aφj !i 1 j 1

Ordered subset EM (OS-EM) Performs EM sequen/ally on non-overlapping subsets ofthe projec/on data un/l all projec/ons are considered Must decide # of subsets (n) and # of itera/ons (m) m n EM itera/ons, but only m projec/ons of data Time for 1 OSEM itera/on (all subsets) 1 EM itera/on However, OSEM increases convergence rate

Image Acquisition

Number of detectors and orbits Single head- 180 vs 360 acquisition: speed vs. uniformity tradeoff- Conjugate views- Non-circular orbits: improved resolution Two headed- Smaller rotation needed: 360!180 or 180!90- H vs. L modes: region of interest and attenuation Circular vs. contouring orbits

Number of detectors and orbits Single head- 180 vs 360 acquisition: speed vs. uniformity tradeoff- Conjugate views- Non-circular orbits: improved resolution Two headed- Smaller rotation needed: 360!180 or 180!90- H vs. L modes: region of interest and attenuation Circular vs. contouring orbits

Image Acquisition Modes Frame mode (data stored as an image)-static- single image acquisition- can have multiple energy windows-dynamic- series of images acquired sequentially-gated- repetitive, dynamic imaging- used for cardiac imaging List-mode (data stored event by event)-time stamps are included within data streamallows for flexible post-acquisition binningcan result in very large data files

Dynamic acquisitionRegions of interests(ROIs)Time-ac/vity curves(TACs)From: The Essen/al Physics of Medical Imaging (Bushberg, et al)

Cardiac Gated AcquisitionFrom: The Essential Physics of Medical Imaging (Bushberg, et al)

Gated cardiac SPECTImages obtained during individualphases of cardiac cycle Gating based on EKG 8-16 frames per cycle Assessment of global and regional(apex, mid, base) left ventricular(LV) function vs. phase (i.e. systolicand diastolic)

Attenuation EffectsEnergy dependanceObject sizeCherry SR, In: Physics in Nuclear Medicine, 2003, p 308 & 311

Methods of Attenuation Correction Transmission measurement- Scanned line source- Moving energy window: different energy fortransmission & emission photons- Low signal-to-noise due to practical transmissionactivity- Direct measure of attenuation coefficient

Methods of Attenuation Correction Conjugate views- Arithmetic mean: (L1 L2)/2- Geometric mean: (L12 L22)L21

Methods of Attenuation Correction Chang correction-Assumes constant μ within anatomical boundaryRequires accurate anatomical boundary definitionEmpirically adjusted for out-of-plane scatterAccurate boundaries difficult to obtainWhere will this work well?Brain SPECTWhere is this problematic?Variable μ values (esp. in thorax)

Methods of Attenuation Correction X-ray CT- Co-located and co-registered- Lower energy than transmission delivers lowerdose- Conversion from CT Hounsfield units to equivalentlinear attenuation coefficient

Converting Hounsfield Units to attenuation coefficients

Examples of SPECT imaging

Thyroid ImagingSample nuclear medicine thyroidimages. The main characteristicsused for interpretation of theimages are size of the thyroids andwhether there is uniform uptakebetween the left and right thyroids.

SPECT/CT Thyroid Image ExampleA 37 YOF with elevated Ca, decreased phosphorus and increased parathyroid hormone(a), (b) early and delayed Tc99m-sestamibi scin/graphs showing uptake near thyroid(c) CT, SPECT, and fused SPECT/CT images localize increased tracer uptake to the posterior aspectof right lobe of the thyroid confirming a right superior parathyroid adenoma

Renal ImagingA renogram provides a timeactivity curve of the uptakeand excretion of a radiotracerby the kidneys. It is used toboth evaluate renal functionand if there are any bilateraldifferences between thekidneys.There is often aperfusion phase and afunctional phase of the exam.A standard protocol is 80 onesecond frames to visualizekidney perfusion and 120twenty second frames toevaluate function.Robert Miyaoka, PhD., BioEng 420, Spring 2013

Brain ScanIn this example, an imaging agent called DaTscan is used to differentiate betweenParkinsonian syndromes (PS) and essential tremor. The “comma” image is for apatient without PS (upper panel), while the abnormal “period” scan is for a patientwith PS (lower panel). DaTscan is a radiopharmaceutical indicated for striataldopamine transporter visualization.

SPECT/CT Lung Perfusion ImagingTc-99 MAA lung perfusion with planar perfusion (upper left) and SPECT/CT with attenuation correction (upperright). The estimated perfusion contribution of each lung obtained by both methods is nearly identical (lowerleft). However, the SPECT/CT method provides more anatomically accurate lobar perfusion quantitation.

Nuclear medicine – photon formation positron emission isomeric transition – attenuation by tissues photoelectric absorption Compton scatter – detection systems scintillators – 2-D projection imaging scintigraphs – tomographic imaging SPECT and PET collect projections from around the patient . Gamma Camera Imaging (SPECT) Siemens Healthcare, Symbia GE .

Related Documents:

Guide for Nuclear Medicine NUCLEAR REGULATORY COMMISSION REGULATION OF NUCLEAR MEDICINE. Jeffry A. Siegel, PhD Society of Nuclear Medicine 1850 Samuel Morse Drive Reston, Virginia 20190 www.snm.org Diagnostic Nuclear Medicine Guide for NUCLEAR REGULATORY COMMISSION REGULATION OF NUCLEAR MEDICINE. Abstract This reference manual is designed to assist nuclear medicine professionals in .

in nuclear medicine. This year the topic is hybrid imaging in conventional nuclear medicine. When choosing the theme for the Tech Guide, the Technologists’ Committee had in mind the impact of non-PET hybrid imaging on nuclear medicine practice. Moreover, SPECT-CT and the Tech Guide are of similar age, so we wanted to

1. Medical imaging coordinate naming 2. X-ray medical imaging Projected X-ray imaging Computed tomography (CT) with X-rays 3. Nuclear medical imaging 4. Magnetic resonance imaging (MRI) 5. (Ultrasound imaging covered in previous lecture) Slide 3: Medical imaging coordinates The anatomical terms of location Superior / inferior, left .

Nuclear Chemistry What we will learn: Nature of nuclear reactions Nuclear stability Nuclear radioactivity Nuclear transmutation Nuclear fission Nuclear fusion Uses of isotopes Biological effects of radiation. GCh23-2 Nuclear Reactions Reactions involving changes in nucleus Particle Symbol Mass Charge

Nuclear Medicine Technology 7 August 2022 . PROGRAM OF STUDY - NUCLEAR MEDICINE TECHNOLOGY (SUBJECT TO CHANGE) Program follows specified cohort . Fall 1 . Course # Course Title Credits . 15 NUC101 Essentials of Nuclear Medicine Technology 1 NUC110 Introduction to Radiation Physics and Biology for Nuclear Medicine 3

BIBLIOGRAPHY Physics for Medical Imaging P. Allisy-Roberts, J. Williams – Farr’s Physics for Medical Imaging Radiological Physics P. Dendy, B. Heaton – Physics for Radiologists Medical Imaging J. Bushberg et al – The Essential Physics of Medical Imaging S. Webb – The Physics of Medical Imaging Nuclear Medicine

nuclear imaging. PET/CT scanners perform a significant role in contemporary nuclear imaging as an outcome of their hybrid existence. A Hybrid PET/CT scanner can show the information of the image by merging metabolic imaging (PET) and morphological imaging with computed tomography (CT).1 Phantom is commonly used as a PET/CT scanner validation

Machine learning (ML) and artificial intelligence (AI) have been around for many years. However, in the last 5 years, remarkable progress has been made using multilayered neural networks in diverse areas such as image recognition, speech recognition, and machine translation. AI is a general purpose technology that is likely to impact many industries. In this chapter I consider how machine .