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Predicting Lesion-Crossability Using a Novel Magnetic Resonance Histology Score to Improve Planning of Percutaneous Vascular Interventions in Chronic-Limb Threatening Ischemia Patients
Madeline Drake, Judit Csore, Bright Benfor, Peter Osztrogonacz, Christof Karmonik, Trisha Roy
Houston Methodist Hospital, Houston, TX

BACKGROUND: The use of endovascular therapies for treatment of chronic limb-threatening ischemia (CLTI) continues to rise.1 Despite significant advances in endovascular technologies, the recent BEST-CLI trial reports an initial technical failure rate of 15% for endovascular interventions2, which is a significant burden on patients, interventionalists and facilities. The success of endovascular peripheral vascular interventions (PVIs) is often limited by plaque composition.3 Severely calcified plaques or those composed of dense collagen are hard and thus more difficult to cross with routine guidewires and catheters. Preoperative imaging is routinely obtained for planning PVIs, however current vascular imaging techniques lack the ability to differentiate hard lesions from soft. Ultrasound and computed tomography angiography (CTA) are limited in cases of severely calcified vessels due to acoustic shadowing and blooming artifact, particularly in infrapopliteal regions.4 Two major anatomic scoring systems have been created to quantify burden of disease in peripheral arterial disease (PAD), the Trans-Atlantic Inter-Society Consensus Document (TASC) and the Global Anatomic Staging System (GLASS).5,6 Based on angiographic imaging, the TASC and GLASS scoring systems use a combination of lesion quantity and lengths to provide a classification suggestive of disease extent and subsequently intervention complexity. These scoring systems, however, do not provide information about plaque composition or morphology and are based on invasive imaging techniques. Thus, they have limited use in preoperative planning of PVI. The purpose of this study was to assess the effectiveness of a novel magnetic resonance (MR) histology technique in identifying lesions that are high risk of PVI failure. METHODS:Patients underwent MRI within 14 days of scheduled PVI for chronic limb-threatening ischemia (CLTI). A novel MR histology protocol including balanced steady-state free precession (bSSFP) and ultrashort echo time (UTE) sequences was used to locate and characterize hard lesion components, including calcium and dense collagen. Target lesions for intervention were scored as ‘hard’ if ≥50% of the lumen was occluded with hard components (calcium or dense collagen) as determined by MR image characteristics in the hardest cross-section within the lesion. Two readers (a vascular surgeon and a radiologist with 2 and 5 years of expertise, respectively) evaluated the MR datasets independently, and the treating physician was blinded to their results. The primary endpoint of the study was defined as initial crossing failure, which referred to either the inability to penetrate the target lesion using a guidewire or the requirement of wire/device escalation to successfully treat the lesion. Per lesion image quality was graded on a three-point grading scale: (1= non-diagnostic quality; 2= sufficient image quality for diagnosis but limited by suboptimal image contrast, noise, or subtle blurring; and 3= good contrast conditions without relevant image noise). Lesions with grade >1 were considered to be of sufficient diagnostic quality for further analysis. Final values for MR histology score and image quality were decided by consensus of the two readers. Fisher’s exact test was performed to study the relationship between MRI lesion characterization and procedure outcomes. Inter-observer reliability of qualitative image quality and crossability evaluation was calculated using intraclass correlation coefficient (ICC). TASC and GLASS scoring was performed based upon angiographic imaging obtained during PVI. The TASC system classifies lesions into grades A-D (in either the femoropopliteal region (FP) or infrapopliteal (IP)), while the GLASS scoring combines a grade from the FP and IP regions to derive a stage I-III. TASC A and GLASS stage I scoring are defined as the lowest severity of disease and most amenable to endovascular intervention, while TASC D and GLASS stage III are the most severe and least amenable to endovascular intervention. The relationship between MR histology scoring, TASC/GLASS scoring and lesion crossability were investigated using univariate analysis. RESULTS: MRI scans were obtained in 20 patients (12 females, average age 66±9 years), yielding 35 target lesions (3 SFA, 9 popliteal, 9 AT, 3 TP, 5 PT, 6 peroneal). Per lesion image quality was rated 1 (non-diagnostic) for 2 lesions belonging to the same patient and were excluded from MR histology scoring. For the remaining 33 lesions, image quality was sufficient in 23 cases and good in 10 cases. Recanalization was attempted in 31/33 lesions. Among these, 8 lesions (24.2%) were scored as hard, 2 were diagnostic only, 3 were immediate technical failures, and 3 necessitated the use of adjunctive devices. 100% of the lesions with initial crossing failure were scored as hard. The number of lesions requiring complex intervention (n=11) were significantly higher in MRI-defined hard lesions compared to soft lesions (0% vs. 13%; p<0.01). ICC showed good reliability for per lesion image quality (0.77) and almost excellent reliability for crossability assessment (0.86). MRI-defined hard lesions trended according to more advanced TASC and GLASS scoring, however these findings were not statistically significant (p=0.74 and p=0.97, respectively). In comparison to high TASC/GLASS scoring (TASC C/D, GLASS stage III), MRI-defined hard lesions were the only factor significantly associated with crossability in our cohort (p<0.001, compared to TASC p=0.28, GLASS p=0.26, or prior ipsilateral revascularization p=0.57).
CONCLUSIONS:Our novel MRI histology protocol demonstrated the ability to reliably identify PVIs with initial crossing failures and complex intervention. As a result, this protocol holds promising potential for aiding in the selection of patients more suitable for either endovascular or surgical revascularization and in identifying those who may benefit from the use of adjunctive endovascular devices. These findings suggest that the MRI histology technique could be a valuable tool for the preoperative and noninvasive treatment optimization in challenging CLTI patients.REFERENCES:

    Cull DL, Langan EM, Gray BH, et al. Open versus endovascular intervention for critical limb ischemia: a population-based study. J Am Coll Surg2010;210:555-61.
    Farber A, Menard MT, Conte MS, et al. BEST-CLI Investigators. Surgery or Endovascular Therapy for Chronic Limb-Threatening Ischemia. N Engl J Med. 2022 Dec 22;387(25):2305-2316. doi: 10.1056/NEJMoa2207899. Epub 2022 Nov 7. PMID: 36342173.
    Roy TL, Chen HJ, Dueck AD, Wright GA. Magnetic resonance imaging characteristics of lesions relate to the difficulty of peripheral arterial endovascular procedures. J Vasc Surg. 2018 Jun;67(6):1844-1854.e2. doi: 10.1016/j.jvs.2017.09.034. Epub 2017 Dec 13. PMID: 29248239.
    Werncke T, Ringe KI, von Falck C, Kruschewski M, Wacker F, Meyer BC. Diagnostic Confidence of Run-Off CT-Angiography as the Primary Diagnostic Imaging Modality in Patients Presenting with Acute or Chronic Peripheral Arterial Disease. Zhang H, editor. PLOS ONE. 2015 Apr 2;10(4):e0119900.
    Norgren L, Hiatt WR, Dormandy JA, Nehler MR, et al.; TASC II Working Group. Inter-Society Consensus for the Management of Peripheral Arterial Disease (TASC II). J Vasc Surg. 2007 Jan;45 Suppl S:S5-67. doi: 10.1016/j.jvs.2006.12.037. PMID: 17223489.
    Conte MS, Bradbury AW, Kolh P, et al.; GVG Writing Group for the Joint Guidelines of the Society for Vascular Surgery (SVS), European Society for Vascular Surgery (ESVS), and World Federation of Vascular Societies (WFVS). Global Vascular Guidelines on the Management of Chronic Limb-Threatening Ischemia. Eur J Vasc Endovasc Surg. 2019 Jul;58(1S):S1-S109.e33. doi: 10.1016/j.ejvs.2019.05.006. Epub 2019 Jun 8. Erratum in: Eur J Vasc Endovasc Surg. 2020 Mar;59(3):492-493. Erratum in: Eur J Vasc Endovasc Surg. 2020 Jul;60(1):158-159. PMID: 31182334; PMCID: PMC8369495.
    Koo TK, Li MY. A Guideline of Selecting and Reporting Intraclass Correlation Coefficients for Reliability Research. J Chiropr Med. 2016 Jun;15(2):155-63. doi: 10.1016/j.jcm.2016.02.012. Epub 2016 Mar 31. Erratum in: J Chiropr Med. 2017 Dec;16(4):346. PMID: 27330520; PMCID: PMC4913118.

Table 1. MR histology vs. anatomic scoring in predicting technical failure in PVIs.
VariableOR [CI-95%]P-value
MRI score (hard)5 [2.3-11.0]<0.001*
TASC (C/D)2.3 [0.4-18]0.28
GLASS (Stage III)0.7 [ 0.1-4.1]0.47
Prior ipsilateral revascularization0.8 [0.1 - 5.3]0.57

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