Optimizing Photon-Counting Detector CT for Imaging Intracranial Aneurysms

Kishore Rajendran; Ajay A. Madhavan

doi:10.3174/ajnr.A8400

Computed tomography offers superior visualization of small vessels, such as the intracranial arteries encountered in neuroradiologic imaging. CT is an excellent technique for the initial work-up of intracranial aneurysms (IAs). In this setting, it is also the preferred technique for detection of spontaneous SAH with high predictive value.^1,2 With traditional treatment options such as microsurgical clipping and endovascular coiling³ and recent advances such as flow-diverting devices⁴ and intrasaccular flow disruptors^5,6 to treat unruptured IAs, diagnostic imaging plays a vital role in the initial diagnosis and treatment-planning. After endovascular treatment, longitudinal follow-up and monitoring via imaging were proved valuable as shown in the International Subarachnoid Aneurysm Trial (ISAT).⁷ Aneurysm morphology, device integrity, and stent apposition/malapposition are useful indicators for assessing IA recurrence and identifying de novo aneurysms.^8,9 Currently, cerebral angiography is widely used for comprehensive characterization of IAs and treatment-planning.^2,10 This is an invasive procedure that may lead to clinical complications such as puncture-site hematoma, arteriovenous fistula, nerve injury, and pulmonary embolism.¹¹ Therefore, MRI and CTA have received substantial attention as safe noninvasive alternatives to conventional angiography for IA detection and management.³

The American Stroke Association/American Heart Association recommends routine follow-up of unruptured aneurysms using MRI or CTA to monitor morphologic changes for assessing the risk of rupture.¹² Furthermore, CT is commonly used in the acute setting for critically ill patients with a pooled sensitivity for IA detection of 98%.¹³ However, detecting small aneurysms (<2 mm) has remained a challenge for CT technologies.² With the introduction of photon-counting detector (PCD) CT in clinical practice, unprecedented spatial resolution (up to 110 µm, in-plane) and multienergy “spectral” imaging are made possible,¹⁴ further advancing the clinical utility of CT for neuroimaging tasks. Several studies involving prototype PCD-CT systems and the recent clinical PCD-CT system have explored the benefits of PCD-CT for neuroimaging applications. However, comprehensive reader studies focusing on neurovascular imaging, specifically ultra-high-resolution (UHR) neurovascular imaging, have been scarce. Symons et al¹⁵ demonstrated superior image quality from PCD-CT compared with energy-integrating detector (EID) CT for carotid and intracranial CTA in 16 asymptomatic human subjects using a prototype PCD-CT system equipped with a 0.25-mm detector pixel (at the isocenter).

Since PCD-CT became clinically available in 2021, additional evidence demonstrating the benefits of UHR and multienergy PCD-CT for head and neck imaging has been reported. For instance, UHR PCD-CT can clearly depict infundibulum versus aneurysm,¹⁶ often ambiguous on EID-CT. UHR PCD-CT may also be superior for the detection of tiny recurrent or remnant aneurysms after surgical or other treatment (Figure). Spampinato et al,¹⁷ using virtual monoenergetic images from clinical PCD-CT (standard collimation at 144 × 0.4 mm) reconstructed at 50 and 60 keV, showed a superior contrast-to-noise ratio (CNR) compared with EID-CT images acquired at 90−100 kV. However, a study by Michael et al¹⁸ revealed that the polychromatic images from PCD-CT outperform monoenergetic reconstructions for diagnostic head and neck CTA. Due to the use of new detector technology and different image types on the first commercial PCD-CT system (NAEOTOM Alpha; Siemens Healthineers), a systematic optimization of imaging and image reconstruction parameters is imperative to take full advantage of the unique technical features of PCDs for neurovascular imaging.

FIGURE

Example of a remnant anterior communicating artery aneurysm missed on EID CTA (A) and evident on PCD CTA (B) in a patient imaged during follow-up after aneurysm clipping. Coronal oblique reconstruction from the EID CTA examination, reconstructed at 0.75-mm section thickness (Qr54 kernel), demonstrates no clear evidence of recurrent aneurysm (A, arrow) due to relatively lower spatial resolution and blooming artifacts from the aneurysm clip. Coronal oblique image from follow-up PCD-CTA (0.2-mm section, Qr89 kernel) of the same patient clearly shows a small remnant aneurysm (B, arrow), better depicted due to higher spatial resolution and reduced blooming artifacts.

In this study, Tóth et al²² present results from their preliminary assessment of PCD-CT image quality for visualization of intracranial aneurysms in a small cohort of patients (n = 10). PCD-CT scans were acquired at a single tube potential (140 kV) using the UHR collimation (120 × 0.2 mm) and polychromatic images (T3D with x-ray energies between the low-energy threshold and the maximum x-ray energy defined by the tube potential) were reconstructed. EID-CT scans were obtained using varying tube potentials (100–140 kV) and different scanner platforms. The authors measured quantitative parameters such as noise, SNR, CNR, and sharpness by means of the full width at half maximum of line profiles to objectively characterize image quality. Furthermore, 3 radiologists rated PCD-CT and EID CT images for subjective assessment of image quality.

Quantitative results showed that image noise increased with increasing kernel strength (Bv36 to Bv48) on PCD-CT as anticipated. This trend consequently resulted in decreased SNR and CNR at the sharpest kernel and the highest SNR and CNR for the smooth kernel (Bv36). Similarly, vessel sharpness was higher with the sharpest kernel (Bv48) compared with Bv44, Bv40, and Bv36. While comparisons within the PCD-CT group provide objective information across the different kernels, PCD-CT versus EID-CT comparisons for signal, SNR, and CNR pooled across patients are likely confounded due to the use of single tube potential (140 kV) on PCD-CT and variable tube potentials (100–140 kV) on the EID-CT. In addition to the image-reconstruction parameters discussed by Tóth et al, future studies should be aimed at assessing the optimal tube potential that plays an important role in overall image quality for contrast-enhanced examinations.

Qualitative results from this study showed that the readers preferred PCD-CT images reconstructed using Bv44 and Bv48 over EID-CT images, despite having higher noise and lower CNR and SNR compared with the PCD-CT Bv36 kernel. Furthermore, PCD-CT Bv48 images had statistically lower image noise (P = .012) in small intracranial arteries and no significant difference in image noise for extracranial and large intracranial locations compared with EID-CT images. Readers preferred Bv48 over Bv36 for aneurysm visualization despite a higher image noise in the former, resulting in a noise-resolution trade-off. However, the iterative reconstruction (quantum iterative reconstruction [QIR]) strength was set to the minimum value of 1 in this study, and further reduction in image noise, if desired, could be achieved by using higher QIR strengths without altering the image texture (noise power spectrum) or spatial resolution as shown in prior studies.^14,19

This study has a few limitations owing to its pilot nature. First, the sharpest kernel evaluated in this study was Bv48, which is a body-vascular kernel with a 50% modulation transfer function of 5.4 line-pairs per centimeter.²⁰ This kernel does not leverage the full intrinsic spatial resolution of UHR PCD-CT. Also, dedicated head kernels (eg, head vascular) may be more relevant for imaging IAs. While through-plane resolution was maximized by means of thin 0.2-mm sections, dedicated UHR kernels beyond Bv48 will yield improved in-plane resolution. The average maximum diameter of IAs detected in this study was 3.3 mm. Investigations focusing on smaller aneurysms are warranted to determine the detection limits for IAs using UHR PCD-CT as a reliable and safer alternative to invasive cerebral angiography. Second, to translate the proposed approach to post-IA treatment scenarios where devices such as stents and flow diverters are present, dedicated metal artifact reduction techniques²¹ should be investigated to address device-related artifacts. This suggestion is particularly important in the assessment of residual IAs or recurrence using UHR PCD-CT. The study by Tóth et al provides initial insights regarding the potential of UHR PCD-CT for imaging IAs and serves as a foundation for future PCD-CT investigations in neurovascular imaging.

References

1.↵
1. Boers AM,
2. Zijlstra IA,
3. Gathier CS, et al
. Automatic quantification of subarachnoid hemorrhage on noncontrast CT. AJNR Am J Neuroradiol 2014;35:2279–86 doi:10.3174/ajnr.A4042 pmid:25104292
Abstract/FREE Full Text
2.↵
1. Chung CY,
2. Peterson RB,
3. Howard BM, et al
. Imaging intracranial aneurysms in the endovascular era: surveillance and posttreatment follow-up. Radiographics 2022;42:789–805 doi:10.1148/rg.210131 pmid:35333634
CrossRef PubMed
3.↵
1. Darsaut TE,
2. Findlay JM,
3. Bojanowski MW, et al
. A pragmatic randomized trial comparing surgical clipping and endovascular treatment of unruptured intracranial aneurysms. AJNR Am J Neuroradiol 2023;44:634–40 doi:10.3174/ajnr.A7865 pmid:37169541
Abstract/FREE Full Text
4.↵
1. Raymond J,
2. Iancu D,
3. Boisseau W, et al
. Flow diversion in the treatment of intracranial aneurysms: a pragmatic randomized care trial. AJNR Am J Neuroradiol 2022;43:1244–51 doi:10.3174/ajnr.A7597 pmid:35926886
Abstract/FREE Full Text
5.↵
1. Pierot L,
2. Liebig T,
3. Sychra V, et al
. Intrasaccular flow-disruption treatment of intracranial aneurysms: preliminary results of a multicenter clinical study. AJNR Am J Neuroradiol 2012;33:1232–38 doi:10.3174/ajnr.A3191 pmid:22678844
Abstract/FREE Full Text
6.↵
1. Papagiannaki C,
2. Spelle L,
3. Januel AC, et al
. WEB intrasaccular flow disruptor-prospective, multicenter experience in 83 patients with 85 aneurysms. AJNR Am J Neuroradiol 2014;35:2106–11 doi:10.3174/ajnr.A4028 pmid:24994823
Abstract/FREE Full Text
7.↵
1. Campi A,
2. Ramzi N,
3. Molyneux AJ, et al
. Retreatment of ruptured cerebral aneurysms in patients randomized by coiling or clipping in the International Subarachnoid Aneurysm Trial (ISAT). Stroke 2007;38:1538–44 doi:10.1161/STROKEAHA.106.466987 pmid:17395870
Abstract/FREE Full Text
8.↵
1. Soize S,
2. Gawlitza M,
3. Raoult H, et al
. Imaging follow-up of intracranial aneurysms treated by endovascular means: why, when, and how? Stroke 2016;47:1407–12 doi:10.1161/STROKEAHA.115.011414 pmid:27026629
FREE Full Text
9.↵
1. Zaeske C,
2. Hickethier T,
3. Borggrefe J, et al
. Postinterventional assessment after stent and flow-diverter implantation using CT: influence of spectral image reconstructions and different device types. AJNR Am J Neuroradiol 2021;42:516–23 doi:10.3174/ajnr.A6952 pmid:33384288
Abstract/FREE Full Text
10.↵
1. Howard BM,
2. Hu R,
3. Barrow JW, et al
. Comprehensive review of imaging of intracranial aneurysms and angiographically negative subarachnoid hemorrhage. Neurosurg Focus 2019;47:E20 doi:10.3171/2019.9.FOCUS19653 pmid:31786554
CrossRef PubMed
11.↵
1. Wang Z,
2. Xia J,
3. Wang W, et al
. Transradial versus transfemoral approach for cerebral angiography: a prospective comparison. J Interv Med 2019;2:31–34 doi:10.1016/j.jimed.2019.05.008 pmid:34805867
CrossRef PubMed
12.↵
1. Thompson BG,
2. Brown RD Jr.,
3. Amin-Hanjani S, et al
; American Stroke Association. Guidelines for the Management of Patients with Unruptured Intracranial Aneurysms: A Guideline for Healthcare Professionals From the American Heart Association/American Stroke Association. Stroke 2015;46:2368–400 doi:10.1161/STR.0000000000000070 pmid:26089327
Abstract/FREE Full Text
13.↵
1. Westerlaan HE,
2. van Dijk JM,
3. Jansen-van der Weide MC, et al
. Intracranial aneurysms in patients with subarachnoid hemorrhage: CT angiography as a primary examination tool for diagnosis: systematic review and meta-analysis. Radiology 2011;258:134–45 doi:10.1148/radiol.10092373 pmid:20935079
CrossRef PubMed
14.↵
1. Rajendran K,
2. Petersilka M,
3. Henning A, et al
. First clinical photon-counting detector CT system: technical evaluation. Radiology 2022;303:130–38 doi:10.1148/radiol.212579 pmid:34904876
CrossRef PubMed
15.↵
1. Symons R,
2. Reich DS,
3. Bagheri M, et al
. Photon-counting computed tomography for vascular imaging of the head and neck: first in vivo human results. Invest Radiol 2018;53:135–42 doi:10.1097/RLI.0000000000000418 pmid:28926370
CrossRef PubMed
16.↵
1. Madhavan AA,
2. Bathla G,
3. Benson JC, et al
. High yield clinical applications for photon counting CT in neurovascular imaging. Br J Radiol 2024;97:894–901 doi:10.1093/bjr/tqae058 pmid:38460543
CrossRef PubMed
17.↵
1. Spampinato MV,
2. Rodgers J,
3. McGill LJ, et al
. Image quality of photon-counting detector CT virtual monoenergetic and polyenergetic reconstructions for head and neck CT angiography. Clin Imaging 2024;108:110081 doi:10.1016/j.clinimag.2024.110081 pmid:38340435
CrossRef PubMed
18.↵
1. Michael AE,
2. Boriesosdick J,
3. Schoenbeck D, et al
. Photon counting CT angiography of the head and neck: image quality assessment of polyenergetic and virtual monoenergetic reconstructions. Diagnostics (Basel) 2022;12:12 doi:10.3390/diagnostics12061306 pmid:35741116
CrossRef PubMed
19.↵
1. Sartoretti T,
2. Landsmann A,
3. Nakhostin D, et al
. Quantum iterative reconstruction for abdominal photon-counting detector CT improves image quality. Radiology 2022;303:339–48 doi:10.1148/radiol.211931 pmid:35103540
CrossRef PubMed
20.↵
1. Gruschwitz P,
2. Hartung V,
3. Ergun S, et al
. Comparison of ultrahigh and standard resolution photon-counting CT angiography of the femoral arteries in a continuously perfused in vitro model. Eur Radiol Exp 2023;7:83 doi:10.1186/s41747-023-00398-x pmid:38110729
CrossRef PubMed
21.↵
1. Anhaus JA,
2. Schmidt S,
3. Killermann P, et al
. Iterative metal artifact reduction on a clinical photon counting system-technical possibilities and reconstruction selection for optimal results dependent on the metal scenario. Phys Med Biol 2022;67 doi:10.1088/1361-6560/ac71f0 pmid:35594851
CrossRef PubMed
22.↵
1. Tóth A,
2. Chetta JA,
3. Milad Yazdani M, et al
. Neurovascular imaging with ultra-high-resolution photon-counting CT: preliminary findings on image quality evaluation. AJNR Am J Neuroradiol 2024;45:1450–57 doi:doi: 10.3174/ajnr.A8350 pmid:38760079
Abstract/FREE Full Text

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Show more NEUROVASCULAR/STROKE IMAGING

[1] 1.↵
Boers AM,
Zijlstra IA,
Gathier CS, et al
. Automatic quantification of subarachnoid hemorrhage on noncontrast CT. AJNR Am J Neuroradiol 2014;35:2279–86 doi:10.3174/ajnr.A4042 pmid:25104292
Abstract/FREE Full Text

[2] Boers AM,

[3] Zijlstra IA,

[4] Gathier CS, et al

[5] 2.↵
Chung CY,
Peterson RB,
Howard BM, et al
. Imaging intracranial aneurysms in the endovascular era: surveillance and posttreatment follow-up. Radiographics 2022;42:789–805 doi:10.1148/rg.210131 pmid:35333634
CrossRef PubMed

[6] Chung CY,

[7] Peterson RB,

[8] Howard BM, et al

[9] 3.↵
Darsaut TE,
Findlay JM,
Bojanowski MW, et al
. A pragmatic randomized trial comparing surgical clipping and endovascular treatment of unruptured intracranial aneurysms. AJNR Am J Neuroradiol 2023;44:634–40 doi:10.3174/ajnr.A7865 pmid:37169541
Abstract/FREE Full Text

[10] Darsaut TE,

[11] Findlay JM,

[12] Bojanowski MW, et al

[13] 4.↵
Raymond J,
Iancu D,
Boisseau W, et al
. Flow diversion in the treatment of intracranial aneurysms: a pragmatic randomized care trial. AJNR Am J Neuroradiol 2022;43:1244–51 doi:10.3174/ajnr.A7597 pmid:35926886
Abstract/FREE Full Text

[14] Raymond J,

[15] Iancu D,

[16] Boisseau W, et al

[17] 5.↵
Pierot L,
Liebig T,
Sychra V, et al
. Intrasaccular flow-disruption treatment of intracranial aneurysms: preliminary results of a multicenter clinical study. AJNR Am J Neuroradiol 2012;33:1232–38 doi:10.3174/ajnr.A3191 pmid:22678844
Abstract/FREE Full Text

[18] Pierot L,

[19] Liebig T,

[20] Sychra V, et al

[21] 6.↵
Papagiannaki C,
Spelle L,
Januel AC, et al
. WEB intrasaccular flow disruptor-prospective, multicenter experience in 83 patients with 85 aneurysms. AJNR Am J Neuroradiol 2014;35:2106–11 doi:10.3174/ajnr.A4028 pmid:24994823
Abstract/FREE Full Text

[22] Papagiannaki C,

[23] Spelle L,

[24] Januel AC, et al

[25] 7.↵
Campi A,
Ramzi N,
Molyneux AJ, et al
. Retreatment of ruptured cerebral aneurysms in patients randomized by coiling or clipping in the International Subarachnoid Aneurysm Trial (ISAT). Stroke 2007;38:1538–44 doi:10.1161/STROKEAHA.106.466987 pmid:17395870
Abstract/FREE Full Text

[26] Campi A,

[27] Ramzi N,

[28] Molyneux AJ, et al

[29] 8.↵
Soize S,
Gawlitza M,
Raoult H, et al
. Imaging follow-up of intracranial aneurysms treated by endovascular means: why, when, and how? Stroke 2016;47:1407–12 doi:10.1161/STROKEAHA.115.011414 pmid:27026629
FREE Full Text

[30] Soize S,

[31] Gawlitza M,

[32] Raoult H, et al

[33] 9.↵
Zaeske C,
Hickethier T,
Borggrefe J, et al
. Postinterventional assessment after stent and flow-diverter implantation using CT: influence of spectral image reconstructions and different device types. AJNR Am J Neuroradiol 2021;42:516–23 doi:10.3174/ajnr.A6952 pmid:33384288
Abstract/FREE Full Text

[34] Zaeske C,

[35] Hickethier T,

[36] Borggrefe J, et al

[37] 10.↵
Howard BM,
Hu R,
Barrow JW, et al
. Comprehensive review of imaging of intracranial aneurysms and angiographically negative subarachnoid hemorrhage. Neurosurg Focus 2019;47:E20 doi:10.3171/2019.9.FOCUS19653 pmid:31786554
CrossRef PubMed

[38] Howard BM,

[39] Hu R,

[40] Barrow JW, et al

[41] 11.↵
Wang Z,
Xia J,
Wang W, et al
. Transradial versus transfemoral approach for cerebral angiography: a prospective comparison. J Interv Med 2019;2:31–34 doi:10.1016/j.jimed.2019.05.008 pmid:34805867
CrossRef PubMed

[42] Wang Z,

[43] Xia J,

[44] Wang W, et al

[45] 12.↵
Thompson BG,
Brown RD Jr.,
Amin-Hanjani S, et al
; American Stroke Association. Guidelines for the Management of Patients with Unruptured Intracranial Aneurysms: A Guideline for Healthcare Professionals From the American Heart Association/American Stroke Association. Stroke 2015;46:2368–400 doi:10.1161/STR.0000000000000070 pmid:26089327
Abstract/FREE Full Text

[46] Thompson BG,

[47] Brown RD Jr.,

[48] Amin-Hanjani S, et al

[49] 13.↵
Westerlaan HE,
van Dijk JM,
Jansen-van der Weide MC, et al
. Intracranial aneurysms in patients with subarachnoid hemorrhage: CT angiography as a primary examination tool for diagnosis: systematic review and meta-analysis. Radiology 2011;258:134–45 doi:10.1148/radiol.10092373 pmid:20935079
CrossRef PubMed

[50] Westerlaan HE,

[51] van Dijk JM,

[52] Jansen-van der Weide MC, et al

[53] 14.↵
Rajendran K,
Petersilka M,
Henning A, et al
. First clinical photon-counting detector CT system: technical evaluation. Radiology 2022;303:130–38 doi:10.1148/radiol.212579 pmid:34904876
CrossRef PubMed

[54] Rajendran K,

[55] Petersilka M,

[56] Henning A, et al

[57] 15.↵
Symons R,
Reich DS,
Bagheri M, et al
. Photon-counting computed tomography for vascular imaging of the head and neck: first in vivo human results. Invest Radiol 2018;53:135–42 doi:10.1097/RLI.0000000000000418 pmid:28926370
CrossRef PubMed

[58] Symons R,

[59] Reich DS,

[60] Bagheri M, et al

[61] 16.↵
Madhavan AA,
Bathla G,
Benson JC, et al
. High yield clinical applications for photon counting CT in neurovascular imaging. Br J Radiol 2024;97:894–901 doi:10.1093/bjr/tqae058 pmid:38460543
CrossRef PubMed

[62] Madhavan AA,

[63] Bathla G,

[64] Benson JC, et al

[65] 17.↵
Spampinato MV,
Rodgers J,
McGill LJ, et al
. Image quality of photon-counting detector CT virtual monoenergetic and polyenergetic reconstructions for head and neck CT angiography. Clin Imaging 2024;108:110081 doi:10.1016/j.clinimag.2024.110081 pmid:38340435
CrossRef PubMed

[66] Spampinato MV,

[67] Rodgers J,

[68] McGill LJ, et al

[69] 18.↵
Michael AE,
Boriesosdick J,
Schoenbeck D, et al
. Photon counting CT angiography of the head and neck: image quality assessment of polyenergetic and virtual monoenergetic reconstructions. Diagnostics (Basel) 2022;12:12 doi:10.3390/diagnostics12061306 pmid:35741116
CrossRef PubMed

[70] Michael AE,

[71] Boriesosdick J,

[72] Schoenbeck D, et al

[73] 19.↵
Sartoretti T,
Landsmann A,
Nakhostin D, et al
. Quantum iterative reconstruction for abdominal photon-counting detector CT improves image quality. Radiology 2022;303:339–48 doi:10.1148/radiol.211931 pmid:35103540
CrossRef PubMed

[74] Sartoretti T,

[75] Landsmann A,

[76] Nakhostin D, et al

[77] 20.↵
Gruschwitz P,
Hartung V,
Ergun S, et al
. Comparison of ultrahigh and standard resolution photon-counting CT angiography of the femoral arteries in a continuously perfused in vitro model. Eur Radiol Exp 2023;7:83 doi:10.1186/s41747-023-00398-x pmid:38110729
CrossRef PubMed

[78] Gruschwitz P,

[79] Hartung V,

[80] Ergun S, et al

[81] 21.↵
Anhaus JA,
Schmidt S,
Killermann P, et al
. Iterative metal artifact reduction on a clinical photon counting system-technical possibilities and reconstruction selection for optimal results dependent on the metal scenario. Phys Med Biol 2022;67 doi:10.1088/1361-6560/ac71f0 pmid:35594851
CrossRef PubMed

[82] Anhaus JA,

[83] Schmidt S,

[84] Killermann P, et al

[85] 22.↵
Tóth A,
Chetta JA,
Milad Yazdani M, et al
. Neurovascular imaging with ultra-high-resolution photon-counting CT: preliminary findings on image quality evaluation. AJNR Am J Neuroradiol 2024;45:1450–57 doi:doi: 10.3174/ajnr.A8350 pmid:38760079
Abstract/FREE Full Text

[86] Tóth A,

[87] Chetta JA,

[88] Milad Yazdani M, et al

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