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Advances in Imaging: Echo, CT, CMR Justin D Pearlman MD ME PhD Director, Dartmouth Advanced Imaging Center Disclosures • Consultant for: –General Electric –Picker/Marconi/Phillips –Chiron –Boehringer-Ingelheim –MagnaLab –Perfusion=off-label use of contrast Dartmouth Advanced Imaging Center - Aims High-end imaging capabilities; Bench->Bedside •1. Realtime CMR •Viability •Dx •2. 4D Cardiac CT •Myopathy •Rx •3. 3D Echo, PET •Microcirculation Equipment Echo MR CT Images: CMR vs. Echo CMR short axis Cost: $500-$1500 Echo short axis Cost: $400-800 Similarities Echo • Inject packets of energy waves, pulsed, Receive echoes • Scan to collect data to convert to image • Tomographic • Dynamic • Flow signal from CMR • Insert packets of energy waves, pulsed, Receive echoes • Scan to collect data to convert to image • Tomographic • Dynamic • Flow signal from phase shift Differences • • • • • • Echo Sound Speed – 1540 m/s Echo=A-mode (amp-time) Stopped by – Metal – Bone – Air-tissue Views limited by rib window, contact, angle Resolution depends on frequency, beamwidth Bright blood requires contrast • • • • • • CMR Radiowave Speed – 299,792,258 m/s Echo=K-mode (amp-spatial freq) Distorted by – Metal – (No problems with bone, air/tissue) Any view Resolution is adjustable down to 10 microns, limited by noise and acquisition time Bright blood many ways Basis for MRI B0 + Gx,y,z + B1 + Mz Mxy Magnetism Magnetism Longitudinal Magnetization Change in Magnetization 1 0.8 T1/TR 1-e(-TR/T1) 0.6 0.4 0.2 0 -1 0 1 2 3 4 5 Time (seconds) Longitudinal Magnetization 1 1-2e(-TI/T1) 0.5 T1/TI 0 -1 0 1 2 3 -0.5 4 5 Time (seconds) Transverse Magnetization -1 1 T2/TE e(-TE/T2) 0.5 0 -5 5 15 25 Time (milliseconds) 35 45 K-Space K-space sums 3,2 (3,2) + (2,5) + 2,5 (3,2) + 0.5 (2,5) = Sum 0.5 (3,2) + (2,5) Fourier Transform Pulse Sequence Gradient Echo (FLASH) Pulse Sequence Inversion Recovery (STIR) Methods • Magnetization Preparation • Excitation • Spatial Encoding, Echoes • Image Reconstruction Bright Blood TurboGradient Echo, Dark Blood FSEDIR, Fat-suppresive TIR, … (100’s) Corresponding notions • Echo Intense • Short T1 (if T1weighted image) • Short T2 (if T2weighted image) • Water (if fat suppressed) • Fat (if not fat suppressed) Fat vs. Fat Suppression: RVD Fat+ RV vs. Fat- RV JDP 2/02 SMART function 40% 40% SMART bFGF-2 Fixed 30% 30% Saline 20% 20% 10% 10% 0% 0% Motion Motion Thickening Thickening 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 MRA Coronary Imaging Coronary Imaging Calcium Scoring Claims: •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: Aberrant Coronary Origins Dynamic CT Elastic Match of Coronaries • Fast CT of mom • Elastic match contrast • Simulated holography as background, for context Coronary Sinus Rx 4D CMR Perfusion-Sensitive Imaging Resting delayed blood arrival predicts ischemia Rest Delayed Blood Arrival Dark Late Zone Arrived Space-Time Map We introduced SpaceTime Maps to see delay in blood arrival in a single derived image Perfusion Equitime Rest MRI vs. rest Thallium / stress MIBI Table 1: Clinical Characteristics of Study Population Patients N Disease vessel 105 % 38 P=0.35 Prevalence 97 2.69 0.10 CABG 42 10 26 1.08 0.13 Angioplasty 36 22 56 0.92 0.14 Stent 15 11 28 0.38 2.10 2 1 0 MRI 0.11 20 15 10 5 20 17 12 10 12 10 4 99 100 17 9 8 3 25 23 rest P=0.01 30 stress 25 Rest P<0.001 P=0.43 3 3 4 5 2 2 2 Coverage (%) Number of Defects MRI 30 Stress Coverage of Defects 33 33 32 3.13 2.97 3 Agreement between Rest MRI and Rest / Stress Nuclear 35 P<0.001 4 SE # Segments (of 8) Total number Blood Distribution Defects 80 75 83 81 61 62 str/mri res/mri mri/res res/str 60 40 20 0 0 1 2 3 4 5 Location 6 7 8 mri/str Target/Reference str/res Viability Delayed Enhancement 62 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 Scar RV TV septum RA LVOT LV lateral LA MV Delayed Enhancement vs. Delayed Arrival Molecular Imaging bFGF2 Microvascular MRI • Tissue bright • Major vessels visible • Dynamic physiology • Small vessels hidden Angiogenesis-Sensitive MRI r=.95 No contrast Nat Med 1:1085 ‘95 Dark Flash 3D CT Validation Radiology 214:801 ‘00 Acad Rad 4:680 ’97 Dark Flare Predicts Improved Blood Arrival From Angiogenesis Baseline 1 Month 2 Months Dark Flare/Delayed Arrival Combined First Dose-Response for Angiogenesis Rx DA=Demand, CX=Response Angiogenesis imaging may also help diagnose and treat cancer 34 y.o. woman with a palpable breast mass. Ultrasound negative Mammography negative Collateral Sensitive MRI: fat black, collateral neovascular development flashes; cancer found. MRI Microscopy in Large Target Limit signal to 1 cm2 Fold-over problem Avoid fold-over Look at bowl of kiwi 40 micron resolution Fold-over RME = ResponseModulated Excitation No fold-over Intravascular Imaging What to know • Vocabulary –B0, B1, Mz, Mxy, T1, T2, T2*,, , , –TI, TR, TE, , Matrix, FOV, , TD, TW –GE, SE, FISP, HASTE, … • Tilted Tomographic Anatomy • Pathophysiology, Clinical Decisions • Physics, Image Processing Echo vs. CMR CMR Echo “Both are watching out for the CAT skinner” Clinical Example 42 y.o. man with large cell lymphoma Radiation to chest Paroxysmal atrial fibrillation CT: Mediastinal mass ? LA compression Long Axis 4 Chamber View Echo MRI: mass, effusion Long Axis 2 Chamber View Echo: ? NL fxn MRI:effusion,mass Long Axis 3 Chamber View Echo MRI Long Axis 5 Chamber View Echo: WNL MRI: Effusion,Mass Short Axis Cine (Stack) View Echo: WNL MRI: Effusion, Mass Short Axis Stack Cine Clinical Example • 63 y.o. Woman • Paroxysmal Atrial Fib Long Axis 2 Chamber View Echo: LVH MRI: LVH Long Axis 3 Chamber View Echo: ASH MRI:LVH+RVH Long Axis 4 Chamber View Echo: ASH; lung/RV MRI: LVH+RVH Long Axis 5 Chamber View Echo: “ASH” MRI: LVH+RVH Cine Stacks: RPA stenosis Short Grid Base Cine View Echo: hyperkinetic MRI: Rt septum hypo, order Clinical Example • 61 y.o. woman • Tamoxiphen Rx • Idiopathic CHF Long Axis 2 Chamber View Echo MRI Long Axis 4 Chamber View Echo MRI Long Axis 5 Chamber View Echo: ?Good EF MRI: EF 11% Long Axis Rotating Views MRI: DCM, CS, IVC Short Axis ( Grid Tag Stack) View Echo: Low EF ?Constriction MRI:DCM, No constriction Clinical Example • 60 y.o. Woman s/p L Mastectomy, XRT • CO=1.0 • TR=4+ 4L Chamber View Echo MRI Grid Cine vs. Dobutamine 0 ug/kg 10ug/kg 20 ug/kg RV Strain vs Dobutamine Rx 14.00 13.00 0 ug/kg 10 ug/kg 20 ug/kg 12.00 Strain 11.00 10.00 9.00 8.00 7.00 6.00 0.09 0.17 0.26 0.34 0.43 0.52 Seconds 0.60 0.69 0.77 0.10 Apical RV Strain vs. Rx 14.00 13.00 0 ug/kg 10 ug/kg 20 ug/kg Strain 12.00 11.00 10.00 9.00 8.00 7.00 6.00 0.09 0.17 0.26 0.34 0.43 0.52 0.60 0.69 0.77 0.10 Seconds AV Prosthesis Suture Dehiscence Aortic Cusp Aneurysm MR Artifacts • Chemical Shift Artifacts : Fat, water yield sum of two shifted images 3.5 PPM • Aliasing : Field of view divides all of space – sine wave is infinite pattern, so copies sum • Black Boundary Artifacts : 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,.... • • • • • • • • • • Gibbs or Truncation Artifacts : Ringing Zipper Artifacts : Door open Phase-encoded Motion Artifacts : Ghosts Entry Slice Phenomenon : Artery/Vein dark or bright by slice order; false “clot” Slice-overlap Artifacts : Faded Magic Angle Effects : Tendon gets T2 increased 100x at 55 angulation Moire Fringes : Aliasing + Phase differences R/L RF Overflow Artifacts : Washed out Central Point Artifact : Spike Susceptibility Artifacts : Microscopic gradients -> Bright/Dark spots Thank you for your attention ! Key Terms • • • • Resonance = Specific matching frequency Excitation = Sending in a pulsed radiowave K-space trajectory = Data collection pattern Magnetic Field Gradients = – Spatial encoding tool • MR Echo is not from tissue interface – it is externally produced from all locations in slice by – Refocusing Radiowave Pulse – and/or Gradient Reversal • Image is produced by “Fourier Transform” – Converts “K-space” data to “X-space” image • Pulse Sequence = Sequence of pulses, gradients and steps to get an image or series of images Key Terms • T1 = Time to develop magnetization • Gradient = Magnetic Field Slope low-high in X, Y, or Z • Gradient-echo = echo caused by reversing X gradient • Spin-echo = echo caused by addition of a radiowave refocusing pulse • T2 = Time constant for loss in transverse magnetization with spin-echo • T2*= Time constant for loss in transverse magnetization with gradient-echo; susceptibility • TR = “Repetition time” = T1 contrast weight • TE = “Echo time” = T2 or T2* contrast weight • T1 Weighted = method emphasizing T1 differences