CTP: Time for Patient-Tailored Acquisition Protocols

J. Molad

doi:10.3174/ajnr.A7457

The use of perfusion imaging has greatly increased during the recent decade, becoming an integral part of the acute stroke imaging protocol,¹ and it is now included in recent acute stroke guidelines, recommending perfusion imaging in the late (6- to 24-hour) timeframe for intervention.² Because the role of perfusion imaging in patient selection is increasingly widespread, obtaining high-quality and accurate acquisitions and analysis becomes of critical importance.

Most stroke centers worldwide use CTP rather than MR perfusion due to its wider availability, rapid imaging, superior vascular imaging of extracranial and distal intracranial vessels, and fewer absolute contraindications.^1-3 However, CTP still has several limitations and pitfalls, precluding it from being the criterion standard for the assessment of salvageable brain tissue. These limitations include lack of standardized acquisition protocols, heterogeneity of postprocessing techniques and thresholds, inaccurate estimation of white matter lesions, and low sensitivity for the detection of lacunar infarcts.^4-6

Delayed arrival of the contrast bolus or truncation (early termination) is the main cause of inadequate acquisition of CTP and is reported to occur in up to 67% of CTP scans.^7,8 Truncation may result in incomplete capture of the tissue time-attenuation curves and thus precludes accurate estimation of the infarct core and penumbra. Previous studies have found truncation to falsely repartition the ROI into a larger ischemic core and smaller penumbra volumes.⁸ Delayed contrast arrival and early termination frequently result from the susceptibility of CTP to the influence of impaired cardiac output or flow-limiting carotid artery stenosis.^4,9 Because the 2 leading etiologies for large-vessel occlusion (LVO) are large-vessel atherosclerosis and atrial fibrillation, inadequate contrast-injection timing becomes a main pitfall of CTP. Truncation rates vary in accordance with the duration of CTP scan times. Although a longer scan duration of 90 seconds may reduce truncation rates many centers use 40- to 60-second protocols to reduce the radiation load and risk of patient movement.¹⁰

In this issue of the American Journal of Neuroradiology, Hartman et al¹¹ examined the use of patient-tailored CTP acquisition protocols, a standard acquisition versus specific low cardiac output (LCO) protocol, to achieve better timing of the contrast bolus and avoid truncation.¹¹ This novel approach is in contrast to previous studies¹⁰ that tried to define a unified optimal scan duration. In the current trial, the LCO protocol had a prolonged image-acquisition time of 75 seconds and an expanded scan delay of 7 seconds after contrast bolus injection, compared with an acquisition time of 65 seconds and a delay of 2 seconds in the standard protocol. Protocol selection was determined using test dose enhancement rise timing, routinely performed on CTA. A cutoff value of 15 seconds from contrast injection to a measure of 100 HU in the aortic arch was used. Among 157 scans obtained, truncation was demonstrated in only 2.5% versus 9.8% among 153 patients who underwent routine CTP using the standard protocol exclusively. The use of this semiautomated model allowed substantial improvement in the CTP acquisition without exposing patients to unneeded excess radiation. Most important, among patients who were found suitable for the standard acquisition duration, no cases of truncation were documented. Therefore, it seems that the proposed algorithm for protocol selection has very good sensitivity and may imply that the extension of the scan duration in the LCO protocol may reduce truncation rates even further.

The authors further examined factors that distinguish patients with high-versus-low risk for early termination. Age, a low left-ventricular ejection fraction, and the absence of hypertension were found to be independent risk factors for truncation. These factors and other previously mentioned parameters are directly associated with contrast arrival time to the intracranial vessels.^4,9,11 Such clinical characteristics may also be used to detect patients with a high risk of truncation. However, the use of test dose enhancement rise timing is preferable, due to the semiautomated nature of the described protocol, which requires no preliminary clinical data nor any action from the stroke physician and thus would not lead to any delay in imaging or intervention times.

The limitations of the current study are mainly because all scans were performed in a single center with the use of a single CTP postprocessing software package. The suggested protocols should be examined using various scanners and software programs to assess the generalizability of the results. Second, a relatively high exclusion rate was observed, with 16% of patients excluded due to a lack of an echocardiogram or severe technical problems. The authors discuss these limitations, including the possibility of selection bias.

The current study emphasizes the importance of case-specific CTP acquisition protocols and brings us one step closer to improved CTP diagnostic accuracy. Further studies are needed to optimize CTP acquisition and processing protocols, examine possible needed adjustments for other specific cases including carotid occlusion, and improve CTP resolution for the detection of small, lacunar infarcts.

References

1.↵
1. Campbell BC,
2. Majoie CBL,
3. Albers GW, et al
; HERMES collaborators. Penumbral imaging and functional outcome in patients with anterior circulation ischaemic stroke treated with endovascular thrombectomy versus medical therapy: a meta-analysis of individual patient-level data. Lancet Neurol 2019;18:46–55 doi:10.1016/S1474-4422(18)30314-4 pmid:30413385
CrossRef PubMed
2.↵
1. Powers WJ,
2. Rabinstein AA,
3. Ackerson T, et al
; American Heart Association Stroke Council. 2018 Guidelines for the Early Management of Patients with Acute Ischemic Stroke: A Guideline for Healthcare Professionals from the American Heart Association/American Stroke Association. Stroke 2018;49:e46–110 doi:10.1161/STR.0000000000000158 pmid:29367334
Abstract/FREE Full Text
3.↵
1. Biesbroek JM,
2. Niesten JM,
3. Dankbaar JW, et al
. Diagnostic accuracy of CT perfusion imaging for detecting acute ischemic stroke: a systematic review and meta-analysis. Cerebrovasc Dis 2013;35:493–501 doi:10.1159/000350200 pmid:23736122
CrossRef PubMed
4.↵
1. Vagal A,
2. Wintermark M,
3. Nael K, et al
. Automated CT perfusion imaging for acute ischemic stroke: Pearls and pitfalls for real-world use. Neurology 2019;93:888–98 doi:10.1212/WNL.0000000000008481 pmid:31636160
Abstract/FREE Full Text
5.
1. Heit JJ,
2. Wintermark M
. Perfusion computed tomography for the evaluation of acute ischemic stroke: strengths and pitfalls. Stroke 2016;47:1153–58 doi:10.1161/STROKEAHA.116.011873 pmid:26965849
FREE Full Text
6.↵
1. Sotoudeh H,
2. Bag AK,
3. Brooks MD
. “Code-stroke” CT perfusion; challenges and pitfalls. Acad Radiology 2019;26:1565–79 doi:10.1016/j.acra.2018.12.013 pmid:30655051
CrossRef PubMed
7.↵
1. Copen WA,
2. Deipolyi AR,
3. Schaefer PW, et al
. Exposing hidden truncation-related errors in acute stroke perfusion imaging. AJNR Am J Neuroradiol 2015;36:638–45 doi:10.3174/ajnr.A4186 pmid:25500309
Abstract/FREE Full Text
8.↵
1. Borst J,
2. Marquering HA,
3. Beenen LF, et al
; MR CLEAN investigators. Effect of extended CT perfusion acquisition time on ischemic core and penumbra volume estimation in patients with acute ischemic stroke due to a large vessel occlusion. PLoS One 2015;10:e0119409 doi:10.1371/journal.pone.0119409 pmid:25789631
CrossRef PubMed
9.↵
1. Mangla R,
2. Ekhom S,
3. Jahromi BS, et al
. CT perfusion in acute stroke: know the mimics, potential pitfalls, artifacts, and technical errors. Emerg Radiol 2014;21:49–65 doi:10.1007/s10140-013-1125-9 pmid:23771605
CrossRef PubMed
10.↵
1. Kasasbeh AS,
2. Christensen S,
3. Straka M, et al
. Optimal computed tomographic perfusion scan duration for assessment of acute stroke lesion volumes. Stroke 2016;47:2966–71 doi:10.1161/STROKEAHA.116.014177 pmid:27895299
Abstract/FREE Full Text
11.↵
1. Hartman JB,
2. Morran S,
3. Zhu C, et al
. Use of CTA test dose to trigger a low cardiac output protocol improves acute stroke CTP data analyzed with RAPID software. AJNR Am J Neuroradiol 2022;43:388–93 doi:10.3174/ajnr.A7428 pmid:35177549
Abstract/FREE Full Text

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[1] 1.↵
Campbell BC,
Majoie CBL,
Albers GW, et al
; HERMES collaborators. Penumbral imaging and functional outcome in patients with anterior circulation ischaemic stroke treated with endovascular thrombectomy versus medical therapy: a meta-analysis of individual patient-level data. Lancet Neurol 2019;18:46–55 doi:10.1016/S1474-4422(18)30314-4 pmid:30413385
CrossRef PubMed

[2] Campbell BC,

[3] Majoie CBL,

[4] Albers GW, et al

[5] 2.↵
Powers WJ,
Rabinstein AA,
Ackerson T, et al
; American Heart Association Stroke Council. 2018 Guidelines for the Early Management of Patients with Acute Ischemic Stroke: A Guideline for Healthcare Professionals from the American Heart Association/American Stroke Association. Stroke 2018;49:e46–110 doi:10.1161/STR.0000000000000158 pmid:29367334
Abstract/FREE Full Text

[6] Powers WJ,

[7] Rabinstein AA,

[8] Ackerson T, et al

[9] 3.↵
Biesbroek JM,
Niesten JM,
Dankbaar JW, et al
. Diagnostic accuracy of CT perfusion imaging for detecting acute ischemic stroke: a systematic review and meta-analysis. Cerebrovasc Dis 2013;35:493–501 doi:10.1159/000350200 pmid:23736122
CrossRef PubMed

[10] Biesbroek JM,

[11] Niesten JM,

[12] Dankbaar JW, et al

[13] 4.↵
Vagal A,
Wintermark M,
Nael K, et al
. Automated CT perfusion imaging for acute ischemic stroke: Pearls and pitfalls for real-world use. Neurology 2019;93:888–98 doi:10.1212/WNL.0000000000008481 pmid:31636160
Abstract/FREE Full Text

[14] Vagal A,

[15] Wintermark M,

[16] Nael K, et al

[17] 5.
Heit JJ,
Wintermark M
. Perfusion computed tomography for the evaluation of acute ischemic stroke: strengths and pitfalls. Stroke 2016;47:1153–58 doi:10.1161/STROKEAHA.116.011873 pmid:26965849
FREE Full Text

[18] Heit JJ,

[19] Wintermark M

[20] 6.↵
Sotoudeh H,
Bag AK,
Brooks MD
. “Code-stroke” CT perfusion; challenges and pitfalls. Acad Radiology 2019;26:1565–79 doi:10.1016/j.acra.2018.12.013 pmid:30655051
CrossRef PubMed

[21] Sotoudeh H,

[22] Bag AK,

[23] Brooks MD

[24] 7.↵
Copen WA,
Deipolyi AR,
Schaefer PW, et al
. Exposing hidden truncation-related errors in acute stroke perfusion imaging. AJNR Am J Neuroradiol 2015;36:638–45 doi:10.3174/ajnr.A4186 pmid:25500309
Abstract/FREE Full Text

[25] Copen WA,

[26] Deipolyi AR,

[27] Schaefer PW, et al

[28] 8.↵
Borst J,
Marquering HA,
Beenen LF, et al
; MR CLEAN investigators. Effect of extended CT perfusion acquisition time on ischemic core and penumbra volume estimation in patients with acute ischemic stroke due to a large vessel occlusion. PLoS One 2015;10:e0119409 doi:10.1371/journal.pone.0119409 pmid:25789631
CrossRef PubMed

[29] Borst J,

[30] Marquering HA,

[31] Beenen LF, et al

[32] 9.↵
Mangla R,
Ekhom S,
Jahromi BS, et al
. CT perfusion in acute stroke: know the mimics, potential pitfalls, artifacts, and technical errors. Emerg Radiol 2014;21:49–65 doi:10.1007/s10140-013-1125-9 pmid:23771605
CrossRef PubMed

[33] Mangla R,

[34] Ekhom S,

[35] Jahromi BS, et al

[36] 10.↵
Kasasbeh AS,
Christensen S,
Straka M, et al
. Optimal computed tomographic perfusion scan duration for assessment of acute stroke lesion volumes. Stroke 2016;47:2966–71 doi:10.1161/STROKEAHA.116.014177 pmid:27895299
Abstract/FREE Full Text

[37] Kasasbeh AS,

[38] Christensen S,

[39] Straka M, et al

[40] 11.↵
Hartman JB,
Morran S,
Zhu C, et al
. Use of CTA test dose to trigger a low cardiac output protocol improves acute stroke CTP data analyzed with RAPID software. AJNR Am J Neuroradiol 2022;43:388–93 doi:10.3174/ajnr.A7428 pmid:35177549
Abstract/FREE Full Text

[41] Hartman JB,

[42] Morran S,

[43] Zhu C, et al

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