Presentation on theme: "Cardiac CT and CT Angiography: Techniques & Clinical Applications"— Presentation transcript:
1 Cardiac CT and CT Angiography: Techniques & Clinical Applications Ethan J Halpern, MDDirector, Cardiac CTThomas Jefferson University
2 Cardiac Imaging Technique Patient PreparationContrast InjectionScan PositioningmAs and kVpECG GatingMulticycle ReconstructionEditing of ECG GatingECG Gated Dose ModulationImage reconstruction
3 Patient Preparation Prior to CT Ask patient to refrain from stimulants (i.e. coffee) on the day of the scanNo solid food for 4 hours prior to the studyPremedicate for asthma & allergic historyMedrol 32mg po 12hrs and 2 hrs prior to studyPatient should have good IV access (18G antecubital)Adequate EKG tracing – good contactPatient prep guidelines.Bullet 1 – Increase heart rate with coffee, the funny story from Wake Forest and the free cappuccinoBullet 3 – MotivationBullet 4 – Decrease the chance of miscommunicationBullet 5 – Use the right basilic vein is preferred
4 Patient Preparation - Heart Rate IV Beta Blockade (preferred)2.5 – 30 mg MetoprololTitrate to heart rate of 55-60Monitor BP while giving metoprololIf asthmatic, consult physicianNo more than 10mg metoprololConsider calcium channel blockersDiltiazem (bolus 0.25mg/kg)Oral Beta Blocker50 – 100 mg Metoprolol1 hour prior to examinationWho will monitor the patient ?
5 Objective of the Contrast Injection Uniform enhancement of the left heart to greater than 300 HUMinimize streaking due to contrast in SVC and RV
6 Impact of Iodine Concentration 140cc injectionHU in aortaCademartiri F et al. Intravenous Contrast Material Administration at Helical 16–Detector Row CT Coronary Angiography: Effect of Iodine Concentration on Vascular Attenuation. Radiology 236: , 2005
7 Contrast Injection Use high iodine density contrast 350 mgI/mL We use Optiray 350 (Mallinckrodt Inc.)16 detector system (25-30 second scan)cc 4 cc/s40 4 cc/s40 detector system (15-20 second scan)100 cc cc/s40 cc 5 cc/s64 detector system (15 second scan)75 cc cc/sStart scan 5 seconds after the contrast reaches the left heartContrast volume = scan duration * injection rateWant sufficient contrast to enhance PDA at end of scan
8 Scan Start Position Native coronary arteries Bypass Grafts Begin above carinaTortuous aorta or prominent upper left heart border – begin scan 1-2cm higherBypass GraftsVeins: top of archLIMA: above clavicles
9 Scan Ending Position Need to image PDA Note overlap of heart & diaphragmObserve contour of heartExtend scan ~2cm below the caudal extent of the heartPosition of heart will change with inspiratory effort
10 Center the Scan on the Heart Maximize spatial resolution for coronariesCT resolution is greatest in the center of scan fieldSet left-right position on AP scout viewMove table up-down to center on aortic root and Left ventricle
11 Voltage kV 90 kV, 120 kV, 140 kV Cardiac protocols These values determine the Peak value of X-ray photons.The effective energy is about half of these valuesA higher voltage means:Lower contrastLess noiseHigher Patient dose: dose proportional to ~ kV 2.7Longer recovery time between scans (shorter life)
12 Tube Current: mA/mAs Axial: mAs = mA x Rotation-time/slice Helix: mAs = mA x (Rotation-time/360°)/ PitchFor most scanners: tube provides mAA higher mAs means:Less noise: noise proportional to 1/(mAs)0.5Higher Patient dose: dose proportional to mAsLarger X-ray tube damage/scanLonger recovery time between scans
13 Scan Parameters kVp mAs Pitch Generally set at 120kVp For heavy patients (>200lbs) use 140kVpFor patients with calcified arteries and stents also use 140kVpmAsEffective mAs = mA x (rotation time / pitch)Effective mAs in the range ofIncrease for heavy patients to minimize noisePitchGenerally , but adjust for heart rate
14 EKG Gating Coronary CTA requires EKG gating to overcome cardiac motion Heart is most quiescent in mid-diastole and end-systoleBest time for reconstruction70-80% of R-R interval for LAD, CRX70-80 or 40% for RCASingle cycle vs. multicycle
15 EKG Based Techniques Fixed time offset Percentage of R-R interval Example: 500 ms after R peakWindow centered at 500 msPercentage of R-R intervalExample: 60% of R-R intervalFor 60 bpm, R-R interval = 1000 msWindow centered at 600 ms500600
17 Consistent Phase Selection Beat-to-Beat Variable Delay Algorithm 58 bpmr-r interval = 1021 msecr-t interval = 258 msec70%Fixed time and percent of R-R may not pick a consistent phaseBeat-to-Beat variable delay algorithmAlways pick same percentage delay in diastoleImproves image quality79 bpmr-r interval = 757 msecr-t interval = 230 msec104 bpmr-r interval = 576 msecr-t interval = 204 msec
18 Single Cycle Reconstruction Single Heart beatUses 180o per heart beatTemporal Res = (rot time)/2
19 Multi-Cycle Reconstruction Combine a portion of projections from one heart cycle with a portion of projections from another to make the full 1800.Improves temporal resolution, because each segment of data covers the same (smaller) region in time.
20 Single Cycle vs. Multicycle Stenosis= 50%Single CycleMulticycleNonassessable21% (28/136)2% (3/136)Sensitivity74% (31/42)88% (37/42)Specificity71% (67/94)91% (86/94)PPV84% (31/37)NPV94% (67/71)95% (86/91)Accuracy72% (98/136)90% (123/136)Toshiba Aquilion 16-slice: 27/34 patients with HR>65Dewey et al. Investigative Radiol 39: , 2004
24 EKG Dose Modulation Best images obtained at mid-diastole RCA sometimes is best at end-systoleDose modulation can achieve dose reduction of 40-50%Use only with stable heart rateLimitationsCannot review coronary anatomy at end-systoleCannot correct for errors in gating
25 Image Reconstruction Reconstruction slice thickness 3mm for functionmm for coronary arteriesmm for photon limited scansReconstruction kernelSharper kernel: noisier image, but may be required to visualize coronary lumen with stents and calcified vessels
26 Slice thickness vs. noise A thicker slice from 0.8mm to 1.0mm decreases noise and makes the images less grainy.0.8mm1.0mm
27 Reconstruction filter vs. noise Filters vs. noise: CA is the smoothest.CB gives you the higher standard deviation and noise. This filter is usually the best choice.Girth is size of the patient in diameter.Girth 0 = 32cmGirth 1 = 37cmGirth 2 = 42 cm20 – 25 or below looks better visually with less noise for slice thickness and mAs..
28 Reconstructions Choose appropriate filter Sharper filter for patients with heavy coronary calcium or stentsPerform targeted reconstructions3mm reconstruction of contiguous slices @ 10 phases for cardiac function analysis0.8mm reconstruction of overlapping 40%, 70%, 75% and 80% for coronary anatomy. 1.0mm recons for heavy patients.
29 Clinical Application of Coronary CTA IndicationsRendering & display modesCharacterization of PlaqueGrading of stenosis
30 Cardiac IndicationsThe MDCT angiography of the chest for cardiac assessment (0146T-0149T) is indicated for the following signs or symptoms of disease:Emergency evaluation of acute chest painCardiac evaluation of a patient with chest pain syndrome (e.g. anginal equivalent, angina), who is not a candidate for cardiac catheterizationManagement of a symptomatic patient with known coronary artery disease (e.g., post-stent, post CABG) when the results of the MDCT may guide the decision for repeat invasive interventionAssessment of suspected congenital anomalies of coronary circulation
32 Plaque Characterization Calcified vs. SoftPositive remodelingIrregularityUlceration
33 Grading of StenosisLeber AW et al. Quantification of Obstructive and Nonobstructive Coronary Lesions by 64-Slice Computed Tomography: A Comparative Study With Quantitative Coronary Angiography and Intravascular Ultrasound JACC 46(1):147-54, 2005
35 Impact of Calcified Vessels on detection of stenosis >50% Calcium scoreCutpoint = 55CTA: 1310 segsLow CS ptsSens = 90%Spec = 92%High CS ptsSens = 97%Spec = 91%Low CSHigh CSAge57 +/-1058 +/-11Male/female55/5Heart rate57 +/-758 +/-7Calcium score14 +/-16578 +/-716Weight (kg)70 +/-672 +/-8Cademartiri F et al. Impact of coronary calcium score on diagnostic accuracy for the detection of significant coronary stenosis with multislice computed tomography angiography. American Journal of Cardiology. 95(10):1225-7, 2005
36 Impact of Coronary Calcium All segmentsCa Score < 1000Patients6046Segments780598True positive5439False positive2110Sensitivity72%98%Specificity97%PPV80%NPV100%Kuettner A et al. Noninvasive detection of coronary lesions using 16-detector multislice spiral computed tomography technology: initial clinical results. JACC 44(6):1230-7, 2004.
37 Proximal versus Distal Segments All segmentsProximal segsPatients33Segments530438True positive3427False positive1913Sensitivity63%82%Specificity96%93%PPV64%68%NPV97%Hoffmann F et al., Predictive value of 16-slice multidetector spiral computed tomography to detect significant obstructive coronary artery disease in patients at high risk for coronary artery disease patient-versus segment-based analysis. Circulation 110: 2638–2643.