1 Protocol and Assessment of CT Perfusion

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• Patient preparation and scan protocol

– Patients are advised to avoid caffeine, a nonselective

competitive adenosine receptor antagonist, 24 h before

examination.

– Intravenous access is performed in both antecubital

veins: one for adenosine or other vasodilator infusion

and one for the contrast administration.

– Using beta-blockers for CT perfusion study such as

oral metoprolol are optional for heart rate control.

Although using beta-blockers can mask the ischemia

in vasodilator stress perfusion study, recent studies

have reported no observed effect on coronary flow

reserve in the study.

– The scan protocol comprises a stress- and a restphase acquisition. Stress-first-and-rest-second protocol has the advantage of increased sensitivity to

myocardial ischemia in stress-phase scan, and it

allows administration of nitrates for subsequent rest

scan, which may be contraindicated if the rest scan

was performed first. Rest first and stress second protocol has the advantage that second-stress scan can

be avoided and subsequently reduce radiation exposure; stress scan will be only performed when moderate to severe coronary artery stenosis is identified on

the rest scan.

– More than 10 min time interval between two acquisitions is necessary, and 20 min or more time interval is

recommended. When the time interval is short, the

contrast used in the first phase may still remain in the

myocardium at the time of the second acquisition,

which may decrease the sensitivity for detecting myocardial ischemia and infarction.



10.1.1 Snapshot or Helical CT Perfusion

• Scout images are acquired for scan positioning. Generally,

scan range is from the carina to the heart base.

• ECG pulsing is used according to the heart rate of the

patient. In the subject with a heart rate <65 bpm, middiastolic acquisition between 60 and 80 % of R-R interval

is possible. In the subject with a heart rate >65 bpm,

which is frequently seen during the stress scan, multisegmental reconstruction or ECG pulsing targeting

20–80 % of R-R interval must be considered.

• For the stress perfusion imaging, intravenous adenosine

infusion at the rate of 140 μg/kg/min is performed, and intravenous contrast media of 60–70 mL is delivered at the rate

of 4–5 mL/s after 4–5 min from start of adenosine infusion.

• For the rest scan, intravenous contrast media of 60–70 mL

is delivered at the rate of 4–5 mL/s without adenosine

infusion. Nitrate can be administered before the rest scan

when the stress scan is performed before the rest scan.

• Start of scan is timed to occur 2–4 s after peak contrast

enhancement of the ascending aorta determined by test

bolus of 10–15 mL of contrast media at the rate of 4–5 mL/s

followed by a 20 mL saline flush at the same rate (test bolus

method) or 8–10 s after the CT number of the ascending

aorta reaches 100–150 HU (bolus tracking method).

• Image reconstruction of both stress and rest scan is performed by reconstruction of multiple phases: best systolic

and diastolic phases for the “least” cardiac motion are

recommended, or every 3–5 % intervals of cardiac phases

are recommended. A reconstruction algorithm that can

reduce beam-hardening artifact is recommended (FC03 in

320-detector CT by Toshiba, B10f by Siemens, smooth

kernel by GE) (Fig. 10.1).



a



10 to 20 min interval

Calcium

scoring



Scan range



Adenosine infusion



Stress scan



4 to 5 min

(until the end of stress

scan)



Retrospective ECGgating



Sublingual NTG

(Optional)



2 min before

Rest scan



Rest scan

(CTA)



Retrospective ECG-gating



Option



Option



1. Static perfusion



1. Retrospective mode



2. Dynamic perfusion



2. Prospective mode

3. High-pitch mode



Fig. 10.1 CT imaging protocol. (a) “Stress-first” protocol is the stress

scan that is acquired followed by the rest scan, and the nitrate can be

administered before the rest scan. (b) “Rest-first” protocol is the rest



scan that is acquired followed by the stress scan; the nitrate must not be

administered before the stress scan



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Evaluation of Myocardial Ischemia Using Perfusion Study



137



b



10 to 20 min interval

Calcium scoring



Rest scan

(CTA)



Define scan range



Retrospective ECG-gating



Adenosine infusion



4 to 5min

(until the end of stress scan)



Stress scan



Retrospective ECG-gating



Option



Option



1. Retrospective mode



1. Static perfusion



2. Prospective mode



2. Dynamic perfusion



3. High-pitch mode



Fig. 10.1 (continued)



10.1.2 Dynamic CT Perfusion

• Dynamic perfusion scan can be performed by serially

recording the kinetics of iodinated contrast media in the

blood pool and myocardium for stress and/or rest scan.

• Approximately 30–40 serial scans from the injection of

the iodinated contrast media are performed in every or

every other heart beats.

• Until now, two different scan modes are developed. One is

that the scan table is stationary during the dynamic study

using 320-detector CT, and the other is that the scan table is

in shuttle mode during the study using the dual-source CT.

• Time-attenuation curves (TACs) of the myocardium, the

left ventricular cavity, and the aorta can be acquired.

Thus, myocardial blood flow (MBF) and volume (MBV)

can be derived from TACs using the mathematical model

(Figs. 10.2 and 10.5).



10.1.3 Dual-Energy CT (DECT) Perfusion

• DECT is based on the principle that tissues in the body

and intravascular iodinated contrast media have unique

spectral characteristics to the x-rays of different energy

levels.

• After processing of high-energy and low-energy data

(usually 140 kVp for high-energy and 80 kVp for lowenergy data), iodine content in the myocardium is detected

using color-coded maps, which can provide additional

information beyond the usual CT attenuation.

• The temporal resolution of DECT is increased to 165 ms

(using the dual-source CT) and 250 ms (using the fast



tube-power switch mode CT) until now, and thus, DECT

is susceptible to motion artifact (Fig. 10.3).



10.1.4 Assessment of CT Perfusion

10.1.4.1 Qualitative Analysis

• Visual assessment of CT perfusion study has been used in

most clinical studies.

• Simultaneous visualization of both rest and stress images

for regions with hypo-attenuated myocardium compared

with normal myocardium is necessary (see Sect. 10.3).

• Narrow setting of window width and level (window width,

200–300; window level, 100–150) and the slice thickness of

5–10-mm is recommended for the detection of subtle contrast

difference of the myocardium of CT perfusion (Fig. 10.4).

• Short-axis images are widely used for the detection of the

perfusion defect; additional long-axis images can provide

information.

• Standard 17-segmental model of the left ventricular myocardium suggested by the American Heart Association is

used for the location and scoring of the myocardial perfusion status.

• Each myocardial segment is scored for the presence or

absence of the perfusion defect and graded as transmural

if the perfusion defect involves ≥50 % of thickness or

non-transmural. Reversibility is also graded as reversible,

partially reversible, and irreversible or fixed.

• To ensure the perfusion defect is detected, images from

multiple phases must be reviewed. Motion artifacts and

beam-hardening artifacts can mimic perfusion defect (see

Sect. 10.4.1 of this chapter).



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Time attenuation curve (TAC)



300



Enhancement (HU)



Dynamic



Snapshot

or helical

150



Artery

Myocardium



20



40



60



80

Scan time (s)



Snapshot or helical

Dynamic



Fig. 10.2 Comparison of dynamic and snapshot or helical study. In

dynamic study, serial scans are performed approximately 30 s. In the

snapshot or helical study, scan was only performed during the peak



a



Fig. 10.3 Color-coded maps using DECT perfusion. Color-coded

maps using DECT perfusion show defect of the anteroseptal, anterior



enhancement of the myocardium (http://extras.springer.com/2015/9783-642-36396-2 – cine image of the myocardium)



b



wall, and anterolateral wall. (a) Coronary angiography shows severe

stenosis of mid-LAD (b) (arrow)



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Evaluation of Myocardial Ischemia Using Perfusion Study



a



139



b



c



Fig. 10.4 Setting of window width/level. (a) Window width 350/level

35. (b) Window width 240/level 150. Perfusion defect on the apical

inferior wall is well detected on the narrowed window and width images



(arrow). (c) Severe stenosis at the proximal end of stent of left circumflex artery is seen in the patient (arrow)



• Finally, correlation with the coronary artery lesions on the

rest scan is mandatory to match the coronary artery stenosis and the perfusion defect (Fig. 10.5).



10.2



10.1.4.2 Quantitative Analysis

• Myocardial blood flow and myocardial blood volume can

be derived by the time-attenuation curves (TACs) of the

myocardium, the left ventricular cavity, and the aorta

using the dynamic CT perfusion study.

• Various mathematical models may be used for quantitative analysis, and more validation and clinical evidences

are required (Fig. 10.6).



Protocol and Assessment of MR

Perfusion



• Backgrounds

– MRI has the advantage of no radiation exposure; thus,

dynamic scan is possible that can be easily used for

quantitative assessment.

– One of the important principles in perfusion study

must be performed during the early portion of first-pass

circulation, as the contrast media is predominantly

located intravascularly.



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Step 1



Step 2



Step 3



Rest scan

interpretation



Image processing



Quality assess



• Coronary artery

stenosis and plaque

analysis



• Best phases of

motionless

myocardium

• Epi-and

endocardialcontour

(for dynamic study)



• Motion artifact

• Beam hardening

• Cone-beam

• Stair-step

• Image noise



Step 4



Image interpretation



• Transmurality (≥50 % or

<50 %)

• Reversibility

• Myocardial thinning

• Simultaneous vision of

both stress and rest scans



Fig. 10.5 Diagram of the flow chart of qualitative assessment of CT perfusion study



a



c



Fig. 10.6 (a) Dynamic perfusion

scan [(a) and QR code at

Fig. 10.2] and the derived

myocardial blood flow (MBF)

map show the impaired MBF of

the inferior wall of the left

ventricle (arrow) (b). CT

coronary angiography also shows

the severe stenosis of the right

coronary artery (arrow) (c)



b



Step 5

Correlation with rest

scan



Match perfusion defect

and coronary artery

lesion