Cardiac CT and CT Angiography: Techniques & Clinical Applications Ethan J Halpern, MD Director, Cardiac CT Thomas Jefferson University

Cardiac Imaging Technique Patient Preparation Contrast Injection Scan Positioning mAs and kVp ECG Gating Multicycle Reconstruction Editing of ECG Gating ECG Gated Dose Modulation Image reconstruction

Patient Preparation Prior to CT Ask patient to refrain from stimulants (i.e. coffee) on the day of the scan No solid food for 4 hours prior to the study Premedicate for asthma & allergic history Medrol 32mg po 12hrs and 2 hrs prior to study Patient should have good IV access (18G antecubital) Adequate EKG tracing – good contact Patient prep guidelines. Bullet 1 – Increase heart rate with coffee, the funny story from Wake Forest and the free cappuccino Bullet 3 – Motivation Bullet 4 – Decrease the chance of miscommunication Bullet 5 – Use the right basilic vein is preferred

Patient Preparation - Heart Rate IV Beta Blockade (preferred) 2.5 – 30 mg Metoprolol Titrate to heart rate of 55-60 Monitor BP while giving metoprolol If asthmatic, consult physician No more than 10mg metoprolol Consider calcium channel blockers Diltiazem (bolus 0.25mg/kg) Oral Beta Blocker 50 – 100 mg Metoprolol 1 hour prior to examination Who will monitor the patient ?

Objective of the Contrast Injection Uniform enhancement of the left heart to greater than 300 HU Minimize streaking due to contrast in SVC and RV

Impact of Iodine Concentration 140cc injection HU in aorta Cademartiri F et al. Intravenous Contrast Material Administration at Helical 16–Detector Row CT Coronary Angiography: Effect of Iodine Concentration on Vascular Attenuation. Radiology 236:661-665, 2005

Contrast Injection Use high iodine density contrast  350 mgI/mL We use Optiray 350 (Mallinckrodt Inc.) 16 detector system (25-30 second scan) 100-150 cc contrast @ 4 cc/s 40 cc @ 4 cc/s 40 detector system (15-20 second scan) 100 cc contrast @ 5-5.5 cc/s 40 cc saline @ 5 cc/s 64 detector system (15 second scan) 75 cc contrast @ 5-5.5 cc/s Start scan 5 seconds after the contrast reaches the left heart Contrast volume = scan duration * injection rate Want sufficient contrast to enhance PDA at end of scan

Scan Start Position Native coronary arteries Bypass Grafts Begin above carina Tortuous aorta or prominent upper left heart border – begin scan 1-2cm higher Bypass Grafts Veins: top of arch LIMA: above clavicles

Scan Ending Position Need to image PDA Note overlap of heart & diaphragm Observe contour of heart Extend scan ~2cm below the caudal extent of the heart Position of heart will change with inspiratory effort

Center the Scan on the Heart Maximize spatial resolution for coronaries CT resolution is greatest in the center of scan field Set left-right position on AP scout view Move table up-down to center on aortic root and Left ventricle

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 values A higher voltage means: Lower contrast Less noise Higher Patient dose: dose proportional to ~ kV 2.7 Longer recovery time between scans (shorter life)

Tube Current: mA/mAs Axial: mAs = mA x Rotation-time/slice Helix: mAs = mA x (Rotation-time/360°)/ Pitch For most scanners: tube provides 300-500mA A higher mAs means: Less noise: noise proportional to 1/(mAs)0.5 Higher Patient dose: dose proportional to mAs Larger X-ray tube damage/scan Longer recovery time between scans

Scan Parameters kVp mAs Pitch Generally set at 120kVp For heavy patients (>200lbs) use 140kVp For patients with calcified arteries and stents also use 140kVp mAs Effective mAs = mA x (rotation time / pitch) Effective mAs in the range of 700-900 Increase for heavy patients to minimize noise Pitch Generally 0.2-0.3, but adjust for heart rate

EKG Gating Coronary CTA requires EKG gating to overcome cardiac motion Heart is most quiescent in mid-diastole and end-systole Best time for reconstruction 70-80% of R-R interval for LAD, CRX 70-80 or 40% for RCA Single cycle vs. multicycle

EKG Based Techniques Fixed time offset Percentage of R-R interval Example: 500 ms after R peak Window centered at 500 ms Percentage of R-R interval Example: 60% of R-R interval For 60 bpm, R-R interval = 1000 ms Window centered at 600 ms 500 600

Heart rate variation during CTA Diastole varies in length 58 bpm r-r interval = 1021 msec r-t interval = 258 msec 70% 79 bpm r-r interval = 757 msec r-t interval = 230 msec Timing of Intervals in Different Heart Rates Systole remains stable Changes in heart rate primarily effect diastole 104 bpm r-r interval = 576 msec r-t interval = 204 msec

Consistent Phase Selection Beat-to-Beat Variable Delay Algorithm 58 bpm r-r interval = 1021 msec r-t interval = 258 msec 70% Fixed time and percent of R-R may not pick a consistent phase Beat-to-Beat variable delay algorithm Always pick same percentage delay in diastole Improves image quality 79 bpm r-r interval = 757 msec r-t interval = 230 msec 104 bpm r-r interval = 576 msec r-t interval = 204 msec

Single Cycle Reconstruction Single Heart beat Uses 180o per heart beat Temporal Res = (rot time)/2

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.

Single Cycle vs. Multicycle Stenosis= 50% Single Cycle Multicycle Nonassessable 21% (28/136) 2% (3/136) Sensitivity 74% (31/42) 88% (37/42) Specificity 71% (67/94) 91% (86/94) PPV 84% (31/37) NPV 94% (67/71) 95% (86/91) Accuracy 72% (98/136) 90% (123/136) Toshiba Aquilion 16-slice: 27/34 patients with HR>65 Dewey et al. Investigative Radiol 39:223-229, 2004

Temporal Window & Heart Rate ---- 50% phase ____ 80% phase +__+ multicycle reconstruction Hoffmann MHK: Radiology 234:86-97, 2005

Image Quality & Heart Rate Hoffmann MHK: Radiology 234:86-97, 2005

Correction of Gating Errors

EKG Dose Modulation Best images obtained at mid-diastole RCA sometimes is best at end-systole Dose modulation can achieve dose reduction of 40-50% Use only with stable heart rate Limitations Cannot review coronary anatomy at end-systole Cannot correct for errors in gating

Image Reconstruction Reconstruction slice thickness 3mm for function 0.5-0.8mm for coronary arteries 1.0-1.2mm for photon limited scans Reconstruction kernel Sharper kernel: noisier image, but may be required to visualize coronary lumen with stents and calcified vessels

Slice thickness vs. noise A thicker slice from 0.8mm to 1.0mm decreases noise and makes the images less grainy. 0.8mm 1.0mm

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 = 32cm Girth 1 = 37cm Girth 2 = 42 cm 20 – 25 or below looks better visually with less noise for slice thickness and mAs. .

Reconstructions Choose appropriate filter Sharper filter for patients with heavy coronary calcium or stents Perform targeted reconstructions 3mm reconstruction of contiguous slices @ 10 phases for cardiac function analysis 0.8mm reconstruction of overlapping slices @ 40%, 70%, 75% and 80% for coronary anatomy. 1.0mm recons for heavy patients.

Clinical Application of Coronary CTA Indications Rendering & display modes Characterization of Plaque Grading of stenosis

Cardiac Indications The 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 pain Cardiac evaluation of a patient with chest pain syndrome (e.g. anginal equivalent, angina), who is not a candidate for cardiac catheterization Management 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 intervention Assessment of suspected congenital anomalies of coronary circulation

Rendering Modes MIP & slab MIP Surface Display Vessel tracking Curved MIP Globe view

Plaque Characterization Calcified vs. Soft Positive remodeling Irregularity Ulceration

Grading of Stenosis Leber 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

Bland-Altman Analysis of Stenosis Grading Dashed lines --- 95% CI Hoffmann: JAMA, Volume 293(20).May 25, 2005.2471–2478

Impact of Calcified Vessels on detection of stenosis >50% Calcium score Cutpoint = 55 CTA: 1310 segs Low CS pts Sens = 90% Spec = 92% High CS pts Sens = 97% Spec = 91% Low CS High CS Age 57 +/-10 58 +/-11 Male/female 55/5 Heart rate 57 +/-7 58 +/-7 Calcium score 14 +/-16 578 +/-716 Weight (kg) 70 +/-6 72 +/-8 Cademartiri 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

Impact of Coronary Calcium All segments Ca Score < 1000 Patients 60 46 Segments 780 598 True positive 54 39 False positive 21 10 Sensitivity 72% 98% Specificity 97% PPV 80% NPV 100% 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.

Proximal versus Distal Segments All segments Proximal segs Patients 33 Segments 530 438 True positive 34 27 False positive 19 13 Sensitivity 63% 82% Specificity 96% 93% PPV 64% 68% NPV 97% 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.

Non-coronary Assessment Valvular assessment Cardiac morphology Cardiac function EP planning