Advances in Imaging: Echo, CT, CMR

transcript

Advances in Imaging:Advances in Imaging:

Echo, CT, CMREcho, CT, CMR

Justin D Pearlman MD ME PhDJustin D Pearlman MD ME PhD

Director, Dartmouth Advanced Imaging CenterDirector, Dartmouth Advanced Imaging Center

DisclosuresDisclosures

• Consultant for:Consultant for:–General ElectricGeneral Electric–Picker/Marconi/PhillipsPicker/Marconi/Phillips–ChironChiron–Boehringer-IngelheimBoehringer-Ingelheim–MagnaLabMagnaLab–Perfusion=off-label use of contrastPerfusion=off-label use of contrast

Dartmouth Advanced Imaging Dartmouth Advanced Imaging Center - AimsCenter - Aims

•1. Realtime 1. Realtime CMRCMR

•2. 4D Cardiac 2. 4D Cardiac CTCT

•3. 3D Echo, PET3. 3D Echo, PET

High-end imaging capabilities; Bench->BedsideHigh-end imaging capabilities; Bench->Bedside

•ViabilityViability

•MyopathyMyopathy

•MicrocirculatiMicrocirculationon

•DxDx

•RxRx

EquipmentEquipment

MREcho

Images: CMR vs. EchoImages: CMR vs. Echo

Echo short axisEcho short axisCMR short axisCMR short axis

Cost: $400-800Cost: $500-$1500

SimilaritiesSimilaritiesEchoEcho

• Inject packets of energy Inject packets of energy waves, pulsed,waves, pulsed,

Receive echoesReceive echoes• Scan to collect data to Scan to collect data to

convert to imageconvert to image• TomographicTomographic• DynamicDynamic• Flow signal from phase Flow signal from phase

shiftshift

CMRCMR• Insert packets of energy Insert packets of energy

waves, pulsed,waves, pulsed,Receive echoesReceive echoes

• Scan to collect data to Scan to collect data to convert to imageconvert to image

• TomographicTomographic• DynamicDynamic• Flow signal from phase Flow signal from phase

shiftshift

DifferencesDifferences• Sound SpeedSound Speed

– 1540 m/s1540 m/s• Echo=A-mode (amp-time)Echo=A-mode (amp-time)• Stopped byStopped by

– MetalMetal– BoneBone– Air-tissueAir-tissue

• Views limited by rib window, Views limited by rib window, contact, anglecontact, angle

• Resolution depends on Resolution depends on frequency, beamwidthfrequency, beamwidth

• Bright blood requires contrastBright blood requires contrast

• Radiowave SpeedRadiowave Speed– 299,792,258 m/s299,792,258 m/s

• Echo=K-mode (amp-spatial freq)Echo=K-mode (amp-spatial freq)• Distorted byDistorted by

– MetalMetal– (No problems with bone, (No problems with bone,

air/tissue)air/tissue)• Any viewAny view• Resolution is adjustable down to Resolution is adjustable down to

10 microns, limited by noise and 10 microns, limited by noise and acquisition timeacquisition time

• Bright blood many waysBright blood many ways

Echo CMR

Basis for MRIBasis for MRI

B0 B1 Mz Mxy+ + Gx,y,z

MagnetismMagnetism

Change in MagnetizationChange in Magnetization

-1 0 1 2 3 4 5

Time (seconds)L

-5 5 15 25 35 45

Time (milliseconds)

-1 0 1 2 3 4 5

Time (seconds)Lo

1-e(-TR/T1)

1-2e(-TI/T1)

e(-TE/T2)

K-SpaceK-Space

0.5 (3,2) + (2,5)

K-space sumsK-space sums

(3,2) + (2,5) (3,2) + 0.5 (2,5)

3,2 Sum

Fourier TransformFourier Transform

Pulse SequencePulse SequenceGradient Echo (FLASH)Gradient Echo (FLASH)

Pulse SequencePulse SequenceInversion Recovery (STIR)Inversion Recovery (STIR)

MethodsMethods

• Magnetization PreparationMagnetization Preparation

• ExcitationExcitation

• Spatial Encoding, EchoesSpatial Encoding, Echoes

• Image ReconstructionImage Reconstruction

Bright Blood TurboGradient Echo, Dark Blood FSEDIR, Fat-suppresive TIR, … (100’s)

Corresponding notionsCorresponding notions

• Echo IntenseEcho Intense • Short T1 (if T1-Short T1 (if T1-weighted image)weighted image)

• Short T2 (if T2-Short T2 (if T2-weighted image)weighted image)

• Water (if fat Water (if fat suppressed)suppressed)

• Fat (if not fat Fat (if not fat suppressed)suppressed)

Fat vs. Fat Suppression: RVDFat vs. Fat Suppression: RVD

JDP 2/02

FatFat++ vs. Fat- vs. Fat-

SMART functionSMART function

Motion Thickening

bFGF-2

Saline

Pearlman JD et al Serial motion assessment by reference tracking (SMART): application to detection of local functional impact of chronic myocardial ischemia. J Comput Assist Tomogr, 2001. 25(4): p. 558-62

Self-Triggered MRASelf-Triggered MRA

Coronary ImagingCoronary Imaging

Calcium ScoringCalcium ScoringClaims:•Negative score may indicate non-cardiac sources of chest pain•Scores over 1,000 predict coronary event within the next 2-3 years•Positive scores referred for catheterization or stress test•BUT significant disease may have negative score•Positive score may be stable plaque

Current Use: Current Use: Aberrant Coronary OriginsAberrant Coronary Origins

Dynamic CTDynamic CT

Elastic Match of CoronariesElastic Match of Coronaries

• Fast CT of mom

• Elastic match contrast

• Simulated holography as background, for context

Coronary Sinus RxCoronary Sinus Rx

4D CMR4D CMR

Perfusion-Sensitive ImagingPerfusion-Sensitive Imaging

Resting delayed blood arrival predicts ischemiaResting delayed blood arrival predicts ischemia

Rest Delayed Blood ArrivalRest Delayed Blood ArrivalDark Late Zone Arrived

Space-Time MapSpace-Time Map

We introduced Space-

Time Maps to see delay

in blood arrival in a

single derived image

Perfusion EquitimePerfusion Equitime

Rest MRI vs. Rest MRI vs. rest Thallium / stress MIBIrest Thallium / stress MIBI

Blood Distribution Defects

2.97 3.13

MRI Stress Rest

P<0.001P=0.35

Coverage of Defects

mri/str str/mri res/mri mri/res res/str str/res

Target/Reference

P=0.43P<0.001

P=0.01

Total number

Disease vessel 105 38 97 2.69 0.10

CABG 42 10 26 1.08 0.13

Angioplasty 36 22 56 0.92 0.14

Table 1: Clinical Characteristics of Study Population

Patients

N % Prevalence SE

Stent 15 11 28 0.38 0.11

1 2 3 4 5 6 7 8

Location

stress

Agreement between Rest MRI and Rest / Stress Nuclear

ViabilityViability

Delayed EnhancementDelayed Enhancement62 year old patient with 3-vessel CAD c/o angina at rest.Hx MI 1992, PTCA LAD 1992, CABG 1995.Scintigraphy, MRI : lateral + anteroseptal wall defects

LAlateral

septum

Delayed Enhancement vs. Delayed Enhancement vs. Delayed ArrivalDelayed Arrival

Molecular ImagingMolecular ImagingbFGF2

Microvascular MRIMicrovascular MRI

• Tissue bright• Major vessels visible• Dynamic physiology

• Small vessels hidden

Angiogenesis-Sensitive MRIAngiogenesis-Sensitive MRI

No contrast Dark Flash 3D CT Validation

Acad Rad 4:680 ’97 Nat Med 1:1085 ‘95Radiology 214:801 ‘00

Dark Flare Dark Flare PredictsPredicts ImprovedImproved Blood Blood Arrival From AngiogenesisArrival From Angiogenesis

Baseline 1 Month 2 Months

Dark Flare/Delayed Arrival CombinedDark Flare/Delayed Arrival Combined

First Dose-Response for Angiogenesis RxDA=Demand, CX=Response

Angiogenesis imaging may also Angiogenesis imaging may also help diagnose and treat cancerhelp diagnose and treat cancer

34 y.o. woman with apalpable breast mass.

Ultrasound negativeMammography negative

Collateral Sensitive MRI: fat black, collateral neovascular development flashes; cancer found.

MRI Microscopy in Large TargetMRI Microscopy in Large Target

Fold-over problem Limit signal to 1 cm2

Avoid fold-over

Response-

Modulated

ExcitationFold-over No fold-over

Look at bowl of kiwi40 micron resolution

Intravascular ImagingIntravascular Imaging

What to knowWhat to know• VocabularyVocabulary

–BB00, B, B11, M, Mzz, M, Mxyxy, T, T11, T, T22, T, T22*,*,, , , , , , –TI, TR, TE, TI, TR, TE, , Matrix, FOV, , Matrix, FOV, , TD, TW, TD, TW

–GE, SE, FISP, HASTE, …GE, SE, FISP, HASTE, …

• Tilted Tomographic AnatomyTilted Tomographic Anatomy

• Pathophysiology, Clinical DecisionsPathophysiology, Clinical Decisions

• Physics, Image ProcessingPhysics, Image Processing

Echo vs. CMREcho vs. CMR

“Both are watching out for the CAT skinner”

Clinical ExampleClinical Example 42 y.o. man with large 42 y.o. man with large

cell lymphomacell lymphoma Radiation to chestRadiation to chest Paroxysmal atrial Paroxysmal atrial

fibrillationfibrillation CT: Mediastinal CT: Mediastinal

mass ? LA mass ? LA compressioncompression

Long Axis 4 Chamber ViewLong Axis 4 Chamber View

Echo MRI: mass, effusion

Echo: ? NL fxn MRI:effusion,mass

Long Axis 3 Chamber ViewLong Axis 3 Chamber ViewEcho MRI

Long Axis 5 Chamber ViewLong Axis 5 Chamber ViewEcho: WNL MRI: Effusion,Mass

Short Axis Cine (Stack) ViewShort Axis Cine (Stack) ViewMRI: Effusion, MassEcho: WNL

Short Axis Stack Short Axis Stack CineCine

Clinical ExampleClinical Example

• 63 y.o. 63 y.o. WomanWoman

• Paroxysmal Paroxysmal Atrial FibAtrial Fib

Long Axis 2 Chamber ViewLong Axis 2 Chamber ViewEcho: LVH MRI: LVH

Long Axis 3 Chamber ViewLong Axis 3 Chamber ViewEcho: ASH MRI:LVH+RVH

Long Axis 4 Chamber ViewLong Axis 4 Chamber ViewEcho: ASH; lung/RV MRI: LVH+RVH

Long Axis 5 Chamber ViewLong Axis 5 Chamber ViewEcho: “ASH” MRI: LVH+RVH

Cine Stacks: RPA stenosisCine Stacks: RPA stenosis

Short Grid Base Cine ViewShort Grid Base Cine ViewEcho: hyperkinetic MRI: Rt septum hypo, order

• 61 y.o. woman61 y.o. woman• Tamoxiphen Tamoxiphen

RxRx• Idiopathic Idiopathic

CHFCHF

Echo MRI

Long Axis 4 Chamber ViewLong Axis 4 Chamber ViewEcho MRI

Long Axis 5 Chamber ViewLong Axis 5 Chamber ViewEcho: ?Good EF MRI: EF 11%

Long Axis Rotating ViewsLong Axis Rotating ViewsMRI: DCM, CS, IVC

Short Axis ( Grid Tag Stack) ViewShort Axis ( Grid Tag Stack) ViewEcho: Low EF ?Constriction MRI:DCM, No constriction

• 60 y.o. Woman 60 y.o. Woman s/p L s/p L Mastectomy, XRTMastectomy, XRT

• CO=1.0CO=1.0• TR=4+TR=4+

4L Chamber View4L Chamber ViewEcho MRI

Grid Cine vs. DobutamineGrid Cine vs. Dobutamine

10ug/kg0 ug/kg 20 ug/kg

RV Strain vs Dobutamine RxRV Strain vs Dobutamine Rx

0.09 0.17 0.26 0.34 0.43 0.52 0.60 0.69 0.77 0.10

Seconds

0 ug/kg10 ug/kg20 ug/kg

Apical RV Strain vs. RxApical RV Strain vs. Rx

0.09 0.17 0.26 0.34 0.43 0.52 0.60 0.69 0.77 0.10

Seconds

0 ug/kg10 ug/kg20 ug/kg

AV ProsthesisAV Prosthesis

Suture DehiscenceSuture Dehiscence

Aortic Cusp AneurysmAortic Cusp Aneurysm

MR ArtifactsMR Artifacts• Chemical Shift ArtifactsChemical Shift Artifacts : Fat, water yield sum of two shifted images 3.5 PPM : Fat, water yield sum of two shifted images 3.5 PPM• AliasingAliasing : : Field of view divides all of space – sine wave is infinite pattern, so copies sumField of view divides all of space – sine wave is infinite pattern, so copies sum• Black Boundary ArtifactsBlack Boundary Artifacts : : At 1.5 T, 3.5 PPM water - fat shift cancels at 4.5 ms multiples from 2.3 At 1.5 T, 3.5 PPM water - fat shift cancels at 4.5 ms multiples from 2.3

ms, eg 6.8, 11.3, and 15.9 ms. Avoid with TE's close to 4.5, 9, 13.6,....ms, eg 6.8, 11.3, and 15.9 ms. Avoid with TE's close to 4.5, 9, 13.6,....

• Gibbs or Truncation ArtifactsGibbs or Truncation Artifacts : Ringing : Ringing• Zipper ArtifactsZipper Artifacts : Door open : Door open• Phase-encoded Motion ArtifactsPhase-encoded Motion Artifacts : Ghosts : Ghosts• Entry Slice PhenomenonEntry Slice Phenomenon : Artery/Vein dark or bright by slice order; false “clot” : Artery/Vein dark or bright by slice order; false “clot”• Slice-overlap ArtifactsSlice-overlap Artifacts : Faded : Faded• Magic Angle EffectsMagic Angle Effects : Tendon gets T2 increased 100x at 55 angulation : Tendon gets T2 increased 100x at 55 angulation• MoireMoire Fringes Fringes : Aliasing + Phase differences R/L : Aliasing + Phase differences R/L• RF Overflow Artifacts : Washed outRF Overflow Artifacts : Washed out• Central Point Artifact : SpikeCentral Point Artifact : Spike• Susceptibility Artifacts : Microscopic gradients -> Bright/Dark spotsSusceptibility Artifacts : Microscopic gradients -> Bright/Dark spots• Zero-fill Artifact : DC offset -> Gibbs ringing -> Zebra stripesZero-fill Artifact : DC offset -> Gibbs ringing -> Zebra stripes

Thank you for your Thank you for your attentionattention

Key TermsKey Terms• Resonance = Specific matching frequencyResonance = Specific matching frequency• Excitation = Sending in a pulsed radiowaveExcitation = Sending in a pulsed radiowave• K-space trajectory = Data collection patternK-space trajectory = Data collection pattern• Magnetic Field Gradients = Magnetic Field Gradients =

– Spatial encoding toolSpatial encoding tool• MR Echo is not from tissue interface – it is externally produced from all locations in slice byMR Echo is not from tissue interface – it is externally produced from all locations in slice by

– Refocusing Radiowave PulseRefocusing Radiowave Pulse– and/or Gradient Reversaland/or Gradient Reversal

• Image is produced by “Fourier Transform”Image is produced by “Fourier Transform”– Converts “K-space” data to “X-space” imageConverts “K-space” data to “X-space” image

• Pulse Sequence = Sequence of pulses, gradients Pulse Sequence = Sequence of pulses, gradients and steps to get an image or series of imagesand steps to get an image or series of images

Key TermsKey Terms• T1 = Time to develop magnetizationT1 = Time to develop magnetization• Gradient = Magnetic Field Slope low-high in X, Y, or ZGradient = Magnetic Field Slope low-high in X, Y, or Z• Gradient-echo = echo caused by reversing X gradientGradient-echo = echo caused by reversing X gradient• Spin-echo = echo caused by addition of a radiowave refocusing pulseSpin-echo = echo caused by addition of a radiowave refocusing pulse• T2 = Time constant for loss in transverse magnetization with spin-echoT2 = Time constant for loss in transverse magnetization with spin-echo• T2*= Time constant for loss in transverse magnetization with gradient-echo; T2*= Time constant for loss in transverse magnetization with gradient-echo;

susceptibilitysusceptibility• TR = “Repetition time” = T1 contrast weightTR = “Repetition time” = T1 contrast weight• TE = “Echo time” = T2 or T2* contrast weightTE = “Echo time” = T2 or T2* contrast weight• T1 Weighted = method emphasizing T1 differencesT1 Weighted = method emphasizing T1 differences• T2 Weighted = method emphasizing T2 differencesT2 Weighted = method emphasizing T2 differences

Advances in Imaging: Echo, CT, CMR

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