Cardiac and CT angiography

techniques
Cardiovascular Boot Camp 1

NASCI 40th Annual Meeting

October 13, 2011
 Financial disclosures

  Research funding from GE and Medrad for work

that is not related to this presentation.

  Consultant for Medrad , Inc.

 Overview

  Basic Technical Concepts

  CT angiography
•  Contrast administration – arterial
opacification
•  Time scan acquisition during the arterial
phase

  Cardiac CT
•  ECG synchronization
•  Parameter selection

  Protocol examples
CT angiography
contrast administration

basic concepts
 Achieve arterial enhancement
  CT angiography
•  Need intravenous contrast to achieve arterial enhancement

  Proportional to the iodine administration rate

•  iodine concentration of contrast medium
•  injection flow rate (mL/s)
•  Amount of iodinated contrast delivered per unit time
•  injection duration (larger volume of contrast)

Fleischmann, D. Radiol Clin N Am, 2010; 48: 237

 Higher concentration of Iodine

0.1 1.0 10 100

mg/ml mg/ml mg/ml mg/ml

14 HU 24 HU 305 HU 2679 HU

Higher Iodine concentration

Bae KT. Radiology 2010;256:32

increased arterial enhancement Simulated contrast enhancement curves

of the abdominal aorta

25 – 30 HU per mg/mL Iodine 125 mL of contrast at 4 mL/s

Three CM concentrations
 Flow rate
  Higher rate
•  Enhancement increases   Routine injections rates 4-5
•  Duration decreases mL/sec
•  Needle sizes
•  Vein size

  Flow rates > 8 mL/s

•  Don’t result in greater
enhancement
•  Pooling in central venous
system, reflux into IVC

Bae KT. Radiology 2010;256:32

Simulated contrast enhancement curves of
the abdominal aorta Higher flow rate of CM
125 mL of 350 mg/mL contrast
Injected at three different rates increased arterial enhancement
 Injection duration = contrast volume
350

Simulated aortic enhancement

curves (adult male, 70kg,
170cm).
250
Aortic attenuation (HU)

Varying injection durations of

350 mg/ml contrast at 3 cc/s.

5 sec = 15 cc
150

20 sec = 60 cc
40 sec = 120 cc
60 sec = 180 cc
50

20 40 60 80

Time in seconds
Longer injection duration

increased peak arterial enhancement

Bae KT. Radiology 2010;256:32

 Saline chaser

  Pushes contrast in tubing

and peripheral veins into
central veins
•  20 – 30 cc
•  Allows reduction in
contrast volume
•  Increases peak attenuation

  Reduced streak artifacts

from veins and right heart

  Simpler to implement with

dual head injectors
CT Angiography
Timing scan acquisition to the
arterial phase

Basic concepts
 Arterial phase of contrast bolus
  After contrast injection
•  Time-to-peak enhancement differs for different target
arteries (PA – coronary – aorta – foot)
•  Distance from venous access site
•  individual cardiac output

Bae KT. Radiology 2010;256:32

 Arterial phase of contrast bolus
  After contrast injection
•  Time-to-peak enhancement differs for different target
vessels (PA – coronary – aorta – foot)
•  Distance from venous access site
•  individual cardiac output
•  Differ due to local vascular pathology
•  Stenosis
•  aneurysm
Enhancement (HU)

time
Bae KT. Radiology 2010;256:32
 Arterial phase of contrast bolus
  Contrast media arrival time (tarr)
•  Time for the bolus to reach target vessel

  Can be determined for each individual and desired

target vessel
•  Timing bolus
•  Bolus tracking

tarr
Enhancement (HU)

time
Bae KT. Radiology 2010;256:32
 Scan timing methods

Timing bolus
  Select target location from
scout topogram
  Inject small test-bolus
•  15 – 20 mL contrast

  Acquire low-dose dynamic

scan at specified location
during injection

  ROI in target structure

  Measure time-attenuation
curve
•  Contrast material arrival time
in aortic root
 Scan timing methods

Bolus triggering
  Select trigger location

  Acquire reference image

•  Place ROI in vascular
structure of interest

  Inject diagnostic contrast

bolus (80 – 150 cc)

  Acquire low-dose dynamic

scans

  Monitor attenuation in ROI

  Start scan when desired

threshold reached

Fleischmann, D. Radiol Clin N Am, 2010; 48: 237

 Scan timing methods

Timing bolus
  Advantages
•  Test adequacy of contrast
path
•  Multiple ROIs
•  art and veins – tro, chd
•  replace if error
•  Avoid artifacts
•  Can be repeated
•  Test patient response
•  Heart rate
•  More controlled breath hold
instructions

  Disadvantages
•  Two contrast injections
•  time
 Scan timing methods

Bolus triggering
  Advantages
•  Time efficient
•  less contrast

  Disadvantages
•  Different scan delay times
•  Single shot
•  Unable to trouble shoot
•  Adjust to problems
•  Streak artifacts,
misplaced ROI,
occluded vein,
connector leak
•  Difficult breath holding
instructions

Fleischmann, D. Radiol Clin N Am, 2010; 48: 237

 CT angiography: basic strategy

  Use a bolus of iodinated

Enhancement
contrast to produce arterial

(HU)
enhancement

  determine the contrast

arrival time time

•  Timing bolus

350
•  Bolus tracking

Aortic attenuation (HU)

250
scan

  Perform diagnostic scan

150
near peak enhancement
achieved with the contrast 50

bolus in the target vessel

10 20 30 40
Time in seconds
 Basic strategy with timing bolus
  Select bolus to achieve tarr td

350
sufficient vascular attenuation
•  Vol: 150 cc (350 mgI/mL)
•  Rate: 5 cc/s

Aortic attenuation (HU)

250
  Determine contrast media
arrival time (tarr) scan
•  Timing bolus
•  15 cc @ 5 cc/s + saline flush

150
  Specify diagnostic delay (td)

50
•  Account for larger volume of
primary bolus
•  Achieve greater enhancement
10 20 30 40

•  Start scan = tarr + td Time in seconds

•  Scan delay = tarr + 8 sec

Fleischmann, D. Radiol Clin N Am, 2010; 48: 237

 Basic strategy with timing bolus
  Select bolus to achieve tarr td

350
sufficient vascular attenuation
•  Vol: 150 cc (350 mgI/mL)
•  Rate: 5 cc/s

Aortic attenuation (HU)

250
  Determine contrast media
arrival time (tarr)
•  Timing bolus
•  15 cc @ 5 cc/s + saline flush

150
scan

  Shorter diagnostic delay (td)

50
•  Lower arterial enhancement
150 vs 200 HU
10 20 30 40
•  Start scan = tarr + td
Time in seconds
•  Scan delay = tarr + 4 sec

Fleischmann, D. Radiol Clin N Am, 2010; 48: 237

 Basic strategy with bolus tracking
tarr td
  Select bolus to achieve

350
sufficient vascular
attenuation

Aortic attenuation (HU)

250
  Determine contrast media
scan
arrival time (tarr)
•  Inject primary bolus

150
•  Bolus tracking
•  100 HU threshold (50 HU)

50
  Specify diagnostic delay (td)
•  Scan delay = tarr + td 10 20 30 40

•  tarr + 8 sec Time in seconds

Fleischmann, D. Radiol Clin N Am, 2010; 48: 237

 CTA summary points
  Higher contrast concentrations
•  Higher arterial enhancement for the same volume of contrast

  Flow rate 4 – 5 mL/s

  Timing bolus or bolus tracking

•  Location
•  Size of target vessel
•  Expected complexity of anatomy
•  Importance of breath hold

  Saline chaser

  Lower kVp when possible

CTA protocols examples

Putting it all together

 Imaging protocol: pulmonary embolism

Timing bolus
  AP and lateral scouts

  Timing bolus below carina. ROI in

PA.
•  Short arrival time
•  Better control of breath hold
•  Central venous catheters

  helical acquisition at timing bolus

peak + 5 sec

  contrast
Omnipaque 350

  caudal-cranial scan direction from

diaphragm to lung apices

Timing bolus: 15 cc contrast (5 cc/s) + 15 cc saline (5cc/s)

Primary bolus: 85 cc contrast (5 cc/s) + 30 cc saline (5 cc/s)
CTA pulmonary embolism
 Imaging protocol: CTA abdominal aorta
Bolus tracking

  AP and lateral scouts

  Bolus tracking at L1. ROI in

abdominal aorta.
•  Large target
•  Retroperitoneal, minimal motion

  Helical acquisition at threshold of

70 HU

  Contrast bolus
Omnipaque 350

  Cranial-caudal scan direction from

diaphragm to lesser trochanter

< 55 kg: 120 cc contrast (4 cc/s) + 30 cc saline (4 cc/s)

55-74 kg: 125 cc contrast (4 cc/s) + flush
75-84 kg: 130 cc contrast (4.5 cc/s) + flush
85-94 kg: 145 cc contrast (4.5 cc/s) + flush
> 95 kg: 150 cc contrast (5 cc/s) + flush
CTA abdominal aorta
Autologous breast reconstruction
 Example 3d Images
Volume rendered skin view for Sagittal and axial oblique views
Location map of where of point where perforator exits
perforator exits fascia fascia and IM course
CTA for DIEP flap breast reconstruction
Alternate delay for veins

  AP and lateral scouts

  Timing bolus at level of

acetabulum. ROI in right
external iliac artery.
•  Small iliac arteries, near
veins

  Helical acquisition at timing

bolus peak + 10 sec
  Caudal-cranial scan
direction from lesser femoral
trochanters to 4 cm above
umbilicus

Primary bolus: 100 cc contrast (5 cc/s) + 30 cc saline (5 cc/s)

 Imaging protocol: upper extremity CTA

Distal timing bolus

  AP and lateral scouts

  contralateral arm IV placement

  Timing bolus near area of

concern. ROI in target artery.
•  Complex anatomy
•  Assure patency

  helical acquisition at timing bolus

peak + 4 sec

  scan through extremity from hand

to chest.
•  Decrease venous contamination

Bolus > 20 sec, 100 cc (5 cc/s)

Anderson S, Radiology 2008;249:1064

upper extremity
Cardiac CT

Basic concepts
 Objectives
  Cardiac CT for Coronary artery disease
•  ECG synchronization
•  Retrospective
•  Prospective
•  Contrast bolus types and timing

  Protocol application examples

•  Triple-rule out for chest pain
•  Non-ischemic cardiovascular applications
•  PV mapping
•  Masses
•  Central venous thrombosis
•  pericardium
 ECG gated MDCT
  Basic concept = time image acquisition to cardiac
cycle
•  ECG synchronization
•  use data at same point in cardiac cycle to create image
•  Motion free periods – motion free images

R R

Q
S
Coronary rest period = low coronary motion
mid-late diastole

Lau GT, Radiology, 2005;235:415

ECG synchronization
ECG synchronization

•  two main types

1.  Retrospective
2.  Prospective
 Retrospective ECG gating
  Helical acquisition

  Low pitch (0.2 – 0.4)

  Record with ECG

  Retrospectively gate data

into phases
Retrospective ECG gating

•  beam continuously on

•  data from entire R – R

•  high radiation exposure !!

Retrospective ECG gating – ECG dose
modulation
•  beam modulated
•  max mA
•  min mA

•  data from entire R – R

•  overall dose less (40%)

 prospective ECG triggerring
  Axial step-and-shoot,
half-scan acquisition

  Trigger from ECG

Prospective ECG triggering – beam on time

•  ECG trigger
•  half scan
•  beam on
•  beam off
Prospective ECG triggering – beam on time

•  beam completely off

•  trigger – completely on
•  max mA
•  beam on time

•  60 – 80% less dose

 ECG synchronization

Retrospective Gating Prospective Triggering

  Less susceptible to
  60 – 80% less radiation
irregular heart beats
exposure
•  Data editing
  Higher pitch (coverage)
  Functional data
•  Whole chest
•  Valves
•  Thoracoabdominal aorta
•  LV and RV function
  Axial acquisition
  Full helix (photons)
•  Table position fixed
•  Larger patients
•  Less partial volume
averaging
 Retrospective ECG Gating

parameters range

  ECG dose modulation

Min mA (20%) 200 – 400 mA
•  Min – max mA
200
•  Body size
Max mA 200 – 800 mA
•  Functional information ? 750
Max mA 0 – 90%
•  Phase duration of max mA duration 70 – 80%
•  Heart rate variability
•  Functional information ? 70% 80%

min max min

 ECG synchronization

Retrospective Gating Prospective Triggering

  More tolerant to irregular   60 – 80% less radiation

heart beats exposure
•  Data editing
  Step-shoot (inc. coverage)
  Functional data •  Whole chest
•  Valves •  Thoracoabdominal aorta
•  LV and RV function
  Axial acquisition
  Full helix (photons) •  Table position fixed
•  Larger patients •  Less partial volume
averaging
 Prospective ECG Triggering
parameters ranges and values

mA 200 – 800 mA
  Step-and-shoot technique
Center 0 – 100 %
•  Manual mA value
frequency 75%
  Body size
Beam on time 0 – 200 mS
100 mS
•  Center frequency
  Heart rate
70% 80%
•  Beam on time
  HR variability

on
 64 channel CTA

  Timing bolus at aortic root mA selection

  Triphasic contrast injection   No AEC (chest)

with dual syringe injector
  Weight based
  Scan acquisition at timing
bolus peak + 5 sec

< 60 kg 400-450 mA
60 – 90 kg 500-550 mA
90 – 120 kg 600-650 mA
> 120 kg 700-750 mA
 topogram attenuation estimates
  region specific patient attenuation differences !
•  not reflected by weight
•  men vs women
•  short vs tall

  Prescribe scan with ATCM, review mA look-up table and DLP

(NI 30)

206 lbs 199 lbs 207 lbs 200 lbs

topo -44.4 hu topo -27.1 hu topo 15.1 hu topo 42.5 hu

Mitsumori LM, ARRS 2008

 Topogram vs weight based mA selection
weight vs image noise

4/30 = 13% 15/46 = 33%

Topogram based mA selection Weight based mA selection

median 27.2 median 25.2
IQ 75 = 29.3 IQ 75 = 28.9
IQ 25 = 24.7 IQ 25 = 21.6

Mitsumori LM, ARRS 2008

RG vs PT gating

Earls JP, Int J Cardiovasc Im, 2008

 Contrast Administration
  Timing bolus at aortic root

  Triphasic contrast injection with dual syringe

injector

  Scan acquisition at timing bolus peak + 5 sec

 Scan timing methods

Timing bolus Bolus triggering

  Advantages   Advantages
•  Test adequacy of contrast •  Time efficient
path
•  less contrast
•  Multiple ROIs
•  (art and veins)   Disadvantages
•  replace if error •  Different scan delay times
•  Avoid artifacts •  Single shot
•  Test patient response •  Unable to trouble shoot
•  Heart rate •  Adjust to problems
•  More controlled breath hold
•  Streak artifacts,
misplaced ROI,
  Disadvantages occluded vein,
•  Two contrast injections connector leak
•  time
 Contrast Administration
  Timing bolus at aortic root

  Triphasic contrast injection with dual syringe

injector
•  phase 1 — 50 mL 100% iodixanol at 5 cc/s
•  phase 2 — 50 mL blend 60% iodixanol with
40% saline at 5 cc/s
•  phase 3 — 50 mL saline at 5 cc/s.

  Scan acquisition at timing bolus peak + 5

sec

contrast 50 cc 30 cc
5 cc/s 5 cc/s 50 cc
5 cc/s

saline 20 cc
5 cc/s
 contrast bolus types
  Intermediate attenuation in right heart to minimize
contrast related streak artifacts but allow
visualization of right heart structures

High right heart attn Low right heart attn Intermed right heart attn
Streak artifacts No streak artifacts No streak artifacts
RH structures not seen RH structures visible

Kerl JM, Radiology 2008;247(2):356

 Scan acquisition

  Timing bolus at aortic root

  Triphasic contrast injection

with dual syringe injector

  Scan acquisition at timing

bolus peak + 5 sec
•  Cranial – caudal
•  2 cm above root through
heart
Cardiac CT protocol examples
Triple rule out CTA

Technique
what needs to be changed ?
Triple rule out CTA : contrast bolus

  Greater longitudinal coverage

  simultaneously opacify three separate vascular

territories
•  PA – CA – Thoracic aorta
•  Reflect both right and left heart circulations

Pulmonary Coronary Thoracic

arteries arteries aorta
Triple rule out CTA : contrast bolus

  Reduce attenuation in right heart to minimize

contrast related streak artifacts
 Contrast Administration
  Modified coronary triphasic contrast
injection with dual syringe injector

•  phase 1 — 70 mL 100% iodixanol at 5

cc/s
•  phase 2 — 50 mL blend 70% iodixanol
with 30% saline at 5 cc/s
•  phase 3 — 50 mL saline at 5 cc/s.

contrast 70 cc 35 cc
5 cc/s 5 cc/s 50 cc
5 cc/s

saline 15 cc
5 cc/s
Mitsumori LM, AJR 2010
 Example clinical TRO case: diagnostic opacification of PA,
Coronary arteries, and Aorta with relative clearing of the Right
heart.

Mitsumori LM, AJR 2010

 TRO exam
  Scouts

  Timing bolus at aortic root

  Triphasic contrast injection with dual syringe

injector

  Scan acquisition at timing bolus peak + 4 sec

Pulmonary Vein Anatomy for AFIB ablation
 Scan timing methods

Bolus triggering
  ROI mid left atrium

  Triphasic bolus @ 5 cc/s

•  coronary

  Threshold at 75 HU
Constrictive pericarditis – 60 sec delay
Pericardial Calcifications
RA mass, r/o PE -- delayed venous

PE – arterial phase 2 minute delayed

ECG gating and central venous catheters
 In closing
  Basic concepts of Cardiac CT and CT
angiography
•  Contrast administration
•  Scan timing
•  ECG synchronization

  Protocol examples
•  Modifications based on the anatomy and
pathology imaged

  Foundation for use with other platforms

•  Larger detector arrays (128-320)
•  Dual source - high pitch (3)
•  Dual energy and spectral imaging
Thank you !