Progress in the identification of unstable carotid artery plaque.

We aimed to quantitatively compare different computed tomography (CT)-based bone volume fraction (BV/TV) measurements. We hypothesize that phantom-less measurement using virtual monochromatic images (VMI) reconstructed form dual-energy CT (DECT) or photon counting CT (PCT) is less affected by tissue variations in trabecular bone than quantitative CT (QCT) and that PCT allows measurements with a lower radiation dose. The BV/TV of bovine trabecular bone samples were measured using four CT scanning methods. Eight different measurements were compared using three soft tissue substitutes (air, saline solution, and fat) to investigate its effect on BV/TV estimation. For this purpose, the samples' bone marrow was removed and replaced with one of the three substitutes in succession for CT scanning. For QCT, a standard bone phantom was used to derive BV/TV form CT values. While DECT- and PCT-based measurements were based on a system of energy-dependent equations established by reconstructing VMIs for specific photon energies. T-test, ANOVA tests and pairwise comparison were performed using the micro-CT (µCT) measurements as reference standard. QCT showed a significant difference between the fat, saline solution, and air. DECT and especially PCT showed no differences between the substitutes. PCT showed no significant differences between radiation doses. Our results highlight the complexity of BV/TV measurements and emphasize the impact of the trabecular bone components on measurement accuracy. Despite these challenges, VMIs from "low" dose PCT provide a reliable alternative to standard QCT. They have the potential to improve the estimation of bone conditions, as well offering valuable insights for clinical, and forensic applications.

Purpose: Fibrous cap rupture from atherosclerotic plaque can send distal emboli and lead to stroke in patients with carotid disease. The NADPH oxidases (Nox) family play an important role in the pathophysiology of atherosclerosis. However, the relationship of Nox expression with atherosclerotic plaque vulnerability remain elusive. We aim to assess the association of Nox4 and Nox5 expression with carotid plaque vulnerability in a swine model. Methods: Carotid atherosclerosis was induced in miniswines using partial ligation and high cholesterol diet, and a minimum 70% stenosis was confirmed by Doppler ultrasonography. Carotid artery sections were obtained for histologic examination and immunohistochemical study for Nox4 and Nox5 at 3 months. The atherosclerotic lesions of AHA type IV to VI were defined as advanced plaques. The association of Nox4 and Nox5 expression in the plaque with the feature of plaque vulnerability was analyzed. Results: Seventy-five carotid segments from ten carotid artery models had fibrous cap plaques with AHA type IV to VI. Distal embolism with the presence of atheroemboli was found in all rete mirabilis, and deemed to be from the ipsilateral carotid plaques. Positive staining of Nox4 and Nox5 were mostly distributed in the surrounding of lipid core, endothelium and plaque shoulder. Increased expression of Nox4 in the plaque was associated with the features of a large lipid core, marked foam cell and thin fibrous cap (p<0.01). Overexpression of Nox5 in the plaque was associated with marked foam cell and cap rupture (p<0.05). Co-overexpression of Nox4 and Nox 5 in the plaque was associated with thin cap (p<0.05). Low expression of both Nox4 and Nox5 in the plaque was associated with less thin cap and less cap rupture (p<0.01). There was a higher frequency of thin cap and cap rupture in 27 plaques with co-overexpression of Nox4 and Nox 5 than in 26 plaques with low expression of both Nox4 and Nox5. Conclusion: Nox4 and Nox5 are both expressed in carotid atherosclerotic plaques in a swine model, and their overexpression in carotid plaques are associated with thin fibrous cap and cap rupture. Upregulated Nox4 and Nox5 may participate in the process of vulnerable atherosclerotic plaque and may be used as a target for reducing the risk of distal embolism.

Clear representation of anatomy is essential in the assessment of pathology in computed tomography (CT). With the introduction of photon-counting CT (PCCT) and more advanced iterative reconstruction (IR) algorithms into clinical practice, there is potential to improve low-contrast detectability in CT protocols. As such, it is necessary to perform task-based assessments to optimize protocols and compare image quality between PCCT and energy-integrating CT, like dual-energy CT (DECT) and single-energy CT (SECT). This work aimed to assess low-contrast detectability in abdominal protocols used in clinical PCCT, DECT, and SECT, using both model and humanobservers. Data were acquired with the standard resolution scan mode on a PCCT (NAEOTOM Alpha, Siemens Healthineers, Forchheim, Germany) and a DECT/SECT (SOMATOM Force, Siemens Healthineers, Forchheim, Germany). Detectability was investigated in the CTP 515 low-contrast module of the Catphan 600 phantom, which was surrounded by a fat annulus to simulate an abdomen and resulted in a water equivalent diameter of 298 mm. Supra-slice contrast rods with a nominal 1.0% contrast and diameters of 4, 6, 9, and 15 mm were used. Factory abdominal protocols were adjusted to acquire images with various tube potentials (70, 90, 120, and 140 kV in PCCT; 70/150Sn and 80/150Sn kV in DECT; 100 and 120 kV in SECT), virtual monoenergetic image (VMI) energy levels (40 to 140 keV in PCCT and DECT), doses (5, 10 mGy in PCCT; 10 mGy in DECT and SECT), and IR settings (Br40 kernel, no quantum IR (QIR) and QIR levels 1 to 4 in PCCT; advanced modeled IR (ADMIRE) level 3 in DECT and SECT). Mixed DECT (linear blending of the images at two tube voltages) images were also reconstructed. The noise power spectrum and task transfer function of each scan protocol were quantified; the detectability index for each protocol was also determined using in-house implementations of model observers (non-prewhitening matched filters with internal noise, NPWI, and with an eye filter and internal noise, NPWEI) and human observers (in-house four-alternative forced choice, scoring with 95% confidence intervals). Results show that the image noise is minimized at a VMI energy corresponding to the applied spectrum's mean energy in PCCT and with VMI settings of 70 and 80 keV for 70/150Sn and 80/150Sn tube potential pairs, respectively, in DECT. With respect to the human observer detectability index calculations, the normalized root-mean-square error for the NPWI and NPWEI model observers was 5% and 12%, respectively. PCCT VMI improves low-contrast detectability. Additionally, detectability can be matched between PCCT protocols by increasing the QIR strength level when reducing the dose. Not only does PCCT VMI outperform DECT VMI, but also DECT VMI outperforms DECT mixed imaging in improving low-contrastdetectability. Low-contrast detectability is optimized when the appropriate VMI energy level is selected in PCCT and DECT to minimize image noise. PCCT improves low-contrast detectability and may allow for dose reduction in abdominal protocols compared to both DECT and SECT. The non-prewhitening model observer with internal noise better quantified low-contrast detectability without the inclusion of an eyefilter.

Recently, new dual energy (DE) computed tomography (CT) systems—dual source CT (DSCT) and photon counting CT (PCCT) have been introduced. Although these systems have the same clinical targets, they have major differences as they use dual and single kVp acquisitions and different x-ray detection and energy resolution concepts. The purpose of this study was theoretical and experimental comparisons of DSCT and PCCT. The DSCT Siemens Somatom Flash was modeled for simulation study. The PCCT had the same configuration as DSCT except it used a photon counting detector. The soft tissue phantoms with 20, 30, and 38 cm diameters included iodine, CaCO3, adipose, and water samples. The dose (air kerma) was 14 mGy for all studies. The low and high energy CT data were simulated at 80 kVp and 140 kVp for DSCT, and in 20–58 keV and 59–120 keV energy ranges for PCCT, respectively. The experiments used Somatom Flash DSCT system and PCCT system based on photon counting CdZnTe detector with 2 × 256 pixel configuration and 1 × 1 mm2 pixels size. In simulated general CT images, PCCT provided higher contrast-to-noise ratio (CNR) than DSCT with 0.4/0.8 mm Sn filters. The PCCT with K-edge filter provided higher CNR than the PCCT with a Cu filter, and DSCT with 0.4 mm Sn filter provided higher CNR than the DSCT with a 0.8 mm Sn filter. In simulated DE subtracted images, CNR of the DSCT was comparable to the PCCT with a Cu filter. However, DE PCCT with Ho a K-edge filter provided 30–40% higher CNR than the DE DSCT with 0.4/0.8 mm Sn filters. The experimental PCCT provided higher CNR in general imaging compared to the DSCT. In experimental DE subtracted images, the DSCT provided higher CNR than the PCCT with a Cu filter. However, experimental CNR with DE PCCT with K-edge filter was 15% higher than in DE DSCT, which is less than 30–40% increase predicted by the simulation study. It is concluded that ideal PCCT can provide substantial advantages over ideal DSCT in CT imaging including DE subtracted CT. However, the limitations of the PCCT detector does not allow it to reach its full potential and therefore further efforts are needed to improve PCCT detectors.

Magnetic resonance imaging (MRI) has the potential in assessing the inflammation of perivascular adipose tissue (PVAT) due to its excellent soft tissue contrast. However, evidence is lacking for the association between carotid PVAT measured by MRI and carotid vulnerable atherosclerotic plaques. This study aimed to investigate the association between signal intensity of PVAT and vulnerable plaques in carotid arteries using multi-contrast magnetic resonance (MR) vessel wall imaging. In this cross-sectional study, a total of 104 patients (mean age, 64.9±7.0 years; 86 men) with unilateral moderate-to-severe atherosclerotic stenosis referred to carotid endarterectomy (CEA) were recruited from April 2018 to December 2020 at Department of Neurosurgery of Peking University Third Hospital. All patients underwent multi-contrast MR vessel wall imaging including time-of-flight (ToF) MR angiography, black-blood T1-weighted (T1w) and T2-weighted (T2w) and simultaneous non-contrast angiography and intraplaque hemorrhage (IPH) imaging sequences. Patients with contraindications to endarterectomy or MRI examinations were excluded. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of PVAT were measured on ToF images and vulnerable plaque characteristics including IPH, large lipid-rich necrotic core (LRNC), and fibrous cap rupture (FCR) were identified. The SNR and CNR of PVAT were compared between slices with and without vulnerable plaque features using Mann-Whitney U test and their associations were analyzed using the generalized linear mixed model (GLMM). Carotid artery slices with IPH (30.93±14.56 vs. 27.34±10.02; P<0.001), FCR (30.35±13.82 vs. 27.53±10.37; P=0.006), and vulnerable plaque (29.15±12.52 vs. 27.32±10.05; P=0.016) had significantly higher value of SNR of PVAT compared to those without. After adjusting for clinical confounders, the SNR of PVAT was significantly associated with presence of IPH [odds ratio (OR) =0.627, 95% confidence interval (CI): 0.465-0.847, Puncorr=0.002, PFDR=0.016] and vulnerable plaque (OR =0.762, 95% CI: 0.629-0.924, Puncorr=0.006, PFDR=0.020). However, no significant association was found between the CNR of PVAT and presence of vulnerable plaque features (all P>0.05). The SNR of carotid artery PVAT measured by ToF MR angiography is independently associated with vulnerable atherosclerotic plaque features, suggesting that the signal intensity of PVAT might be an effective indicator for vulnerable plaque.

We compared plaque characteristics between symptomatic and asymptomatic sides in patients with bilateral carotid vulnerable plaques using magnetic resonance imaging (MRI). Participants (n = 67; mean age: 65.8 ± 7.7 years, 61 males) with bilateral carotid vulnerable plaques were included. Vulnerable plaques were characterized by intraplaque hemorrhage (IPH), large lipid-rich necrotic core (LRNC), or fibrous cap rupture (FCR) on MRI. Symptomatic vulnerable plaques showed greater plaque burden, LRNC volume (median: 221.4 vs 134.8 mm3, P = .003), IPH volume (median: 32.2 vs 22.5 mm3, P = .030), maximum percentage (Max%) LRNC (median: 51.3% vs 41.8%, P = .002), Max%IPH (median: 13.4% vs 9.5%, P = .022), cumulative slices of LRNC (median: 10 vs 8, P = .005), and more juxtaluminal IPH and/or thrombus (29.9% vs 6.0%, P = .001) and FCR (37.3% vs 16.4%, P = .007) than asymptomatic ones. After adjusting for plaque burden, differences in juxtaluminal IPH and/or thrombus (odds ratio [OR]: 5.49, 95% CI: 1.61-18.75, P = .007) and FCR (OR: 2.90, 95% CI: 1.16-7.24, P = .022) between bilateral sides remained statistically significant. For patients with bilateral carotid vulnerable plaques, symptomatic plaques had greater burden, more juxtaluminal IPH and/or thrombus, and FCR compared with asymptomatic ones. The differences in juxtaluminal IPH and/or thrombus and FCR between bilateral sides were independent of plaque burden.

BackgroundA substantial source of error in proton therapy is predicting the stopping power ratio (SPR) of tissues from computed tomography (CT). Due to its systematic nature, it is crucial to minimize this error as much as possible. Photon‐counting CT (PCCT) scanners, which utilize semiconductor detectors to resolve the energy of X‐rays, can extract more information per voxel compared to conventional CT scanners, offering potential improvements in material characterization and higher accuracy in proton range estimation.PurposeThis study explores the potential of PCCT for improving SPR predictions compared to conventional single‐energy CT (SECT) and dual‐energy CT (DECT).MethodsSECT, DECT and PCCT scans of the CIRS SPR/Density phantom with tissue‐equivalent inserts were acquired in body and head configurations using comparable scan and quantitative reconstruction settings. The SPR of each insert was predicted from SECT (SPRSECT) using a clinical Hounsfield look‐up table (HLUT) and directly derived from DECT (SPRDECT) and PCCT (SPRPCCT) scans using spectral information (DirectSPR application, provided by Siemens Healthineers). Results were compared against measurements (SPRMeasured), obtained via a multi‐layer ionization chamber, and differences relative to water (∆SPR) were calculated. Mean absolute errors (MAE) over the inserts were calculated for each imaging modality in both body and head configurations and per tissue subgroup. As a proof‐of‐concept, proton plans for a lung and neurological case were created to assess the impact on dose distribution using the SECT‐HLUT approach (with 3% range uncertainty) or DirectSPR from PCCT (with 2% range uncertainty).ResultsPCCT predicted SPR within 1.0% agreement with SPRMeasured, except for the insert “100% gland” (1.4%). The largest ∆SPR observed across all inserts and imaging modalities were found in lung and adipose inserts. For the soft tissue and bone inserts, estimated SPRs generally agreed well with SPRMeasured (∆SPR ≤1.0%), except for the inserts soft tissue grey and cortical bone (both ∆SPRSECT,head = 1.3%). Among the three imaging modalities, the overall mean absolute error (MAE) was lowest for PCCT by a small margin (body: 0.58% for SECT, 0.72% for DECT, 0.57% for PCCT, head: 0.58% for SECT, 0.48% for DECT, 0.46% for PCCT). However, for each tissue subgroup separately, MAEs for PCCT were not consistently lowest and MAEs were comparable across imaging modalities, ranging from 0.22% to 2.83%. In the clinical cases, dose distributions for SECT‐HLUT and PCCT plans showed dose differences particularly at the distal end of the beams, attributed to optimization with reduced range uncertainty in the PCCT plan or due to areas with thicker bone or air cavities.ConclusionsThe DirectSPR application for PCCT achieved promising accuracy in SPR prediction. Overall, the absolute deviations were small and comparable across all three imaging modalities. However, concerning the performance of SECT, it should be noted that the SECT‐based HLUT was calibrated using the same CIRS phantom as used during the evaluation, whereby these results are the best‐case scenario. Although the clinical cases showed minimal differences in dose distributions between SECT and PCCT plans, PCCT may offer improved reliability, as it provides patient‐specific direct SPR predictions without relying on HLUT conversion.

Vulnerable plaques have been a hot topic in the field of stroke and carotid atherosclerosis. Currently, risk stratification and intervention of carotid plaques are guided by the degree of luminal stenosis. Recently, it has been recognized that the vulnerability of plaques may contribute to the risk of stroke. Some classical interventions, such as carotid endarterectomy, significantly reduce the risk of stroke in symptomatic patients with severe carotid stenosis, while for asymptomatic patients, clinically silent plaques with rupture tendency may expose them to the risk of cerebrovascular events. Early identification of vulnerable plaques contributes to lowering the risk of cerebrovascular events. Previously, the identification of vulnerable plaques was commonly based on imaging technologies at the macroscopic level. Recently, some microscopic molecules pertaining to vulnerable plaques have emerged, and could be potential biomarkers or therapeutic targets. This review aimed to update the previous summarization of vulnerable plaques and identify vulnerable plaques at the microscopic and macroscopic levels.

Vulnerable atherosclerotic plaques serve as the primary pathological basis for fatal cardiovascular and cerebrovascular diseases. The precise identification and treatment of these vulnerable plaques hold paramount clinical importance in mitigating the incidence of myocardial infarction and stroke. Nevertheless, the identification of vulnerable plaques within the diffuse atherosclerotic plaques dispersed throughout the systemic circulation continues to pose a substantial challenge in clinical practice. Double emulsion solvent evaporation method, specifically the water-in-oil-in-water (W/O/W) technique, was employed to fabricate Fe3O4-based poly (lactic-co-glycolic acid) (PLGA) nanoparticles (Fe3O4@PLGA). Platelet membranes (PM) were extracted through hypotonic lysis, followed by ultrasound-assisted encapsulation onto the surface of Fe3O4@PLGA, resulting in the formation of PM-coated Fe3O4 nanoparticles (PM/Fe3O4@PLGA). Characterization of PM/Fe3O4@PLGA involved the use of dynamic light scattering, transmission electron microscopy, western blotting, and magnetic resonance imaging (MRI). A model of atherosclerotic vulnerable plaques was constructed by carotid artery coarctation and a high-fat diet fed to ApoE-/- (Apolipoprotein E knockout) mice. Immunofluorescence and MRI techniques were employed to verify the functionality of PM/Fe3O4@PLGA. In this study, we initially synthesized Fe3O4@PLGA as the core material. Subsequently, a platelet membrane was employed as a coating for the Fe3O4@PLGA, aiming to enable the detection of vulnerable atherosclerotic plaques through MRI. In vitro, PM/Fe3O4@PLGA not only exhibited excellent biosafety but also showed targeted collagen characteristics and MR imaging performance. In vivo, the adhesion of PM/Fe3O4@PLGA to atherosclerotic lesions was confirmed in a mouse model of vulnerable atherosclerotic plaques. Simultaneously, PM/Fe3O4@PLGA as a novel contrast agent for MRI has shown effective identification of vulnerable atherosclerotic plaques. In terms of safety profile in vivo, PM/Fe3O4@PLGA has not demonstrated significant organ toxicity or inflammatory response in the bloodstream. In this study, we successfully developed a platelet-membrane-coated nanoparticle system for the targeted delivery of Fe3O4@PLGA to vulnerable atherosclerotic plaques. This innovative system allows for the visualization of vulnerable plaques using MRI, thereby demonstrating its potential for enhancing the clinical diagnosis of vulnerable atherosclerotic plaques.

ObjectivesTo study whether photon-counting computed tomography (PCCT) can improve CT number accuracy and precision and reduce patient size dependence compared to dual-energy CT (DECT) virtual monoenergetic imaging (VMI) and single-energy CT (SECT).MethodsClinical PCCT, DECT, and SECT scanners were used to image a multi-energy quality assurance phantom and tissue-equivalent inserts with/without an outer nested annulus, representing 2 object sizes (18 and 33 cm). CT numbers were converted to linear attenuation coefficients (LAC) and regions of interest applied. Theoretical monoenergetic LAC were calculated from known elemental compositions as a ground truth. Percent differences in mean LAC between phantom sizes, between mean and theoretical LAC, and its coefficient of variation (COV) were calculated.ResultsMean LAC percent differences between small and larger phantoms were highest in DECT (within −3% to 9%) and SECT (within 1%-5%), particularly at higher calcium and iodine concentrations, while being relatively constant in PCCT over material concentrations and VMI energies (within ±2%). The COV in mean LAC was consistently lower (about 2-5 times) in PCCT relative to DECT and SECT for calcium in the large phantom. With consideration of the theoretical uncertainties of 2%, both PCCT and DECT showed comparable agreement to theoretical LAC.ConclusionsPCCT VMI produces CT numbers with less dependence on patient size and increased precision in large object sizes than DECT VMI and SECT.Advances in knowledgeClinical PCCT provides less variable CT numbers than DECT and SECT with less sensitivity to the imaged object size.

This editorial refers to ‘Imaging intraplaque inflammation in carotid atherosclerosis with 11C-PK11195 positron emission tomography/computed tomography’, by O. Gaemperli et al. , doi:10.1093/eurheartj/ehr367 Inflammation plays a major pathogenic role in the development of atheromatous plaques and the progression of atherosclerosis. Disruption of the fibrous cap of atheromatous lesions has been shown to lead to acute cardiovascular events. Atheromatous plaque disruption is the mechanism most commonly associated with the occurrence of acute coronary syndrome, i.e unstable angina and acute myocardial infarction.1 Plaque disruption is directly linked to inflammation, particularly to macrophage activation,1,2 which results in the release of proinflammatory cytokines and metalloproteases that contribute to the destruction of the fibrous cap of the atheroma thus weakening its structure and leading to the development of fissures that allow a direct contact between the prothrombotic atheromatous core and the circulating blood in the affected vessel. This process can result in the development of acute thrombosis and serious clinical events.3 The early identification—in a given individual—of plaques prone to disruption (‘vulnerable plaques’) is desirable, as this may allow the implementation of preventative strategies and, possibly, effective therapeutic intervention. Vulnerable plaques often show large necrotic core volumes, positive vascular remodelling, and attenuation of fibrous plaque caps ( Figure 1 ). Figure 1 The use of combined markers of risk, i.e. imaging and circulating biomarkers, may allow the early identification of vulnerable plaques and thus help clinicians to devise more rational preventative and therapeutic strategies. Multimodal imaging of atheromatous structures with PET and CTA, as in the study of Gaemperli et al. ,15 and other diagnostic modalities combining anatomical and functional measurements are likely to allow an effective, integrated assessment of atheromatous plaques. Current evidence that molecular imaging is suited for the identification of monocyte–macrophage infiltration in the setting of acute vascular events in …

To evaluate the spectral performance of dual-source (DS) compared to single-source (SS) mode on the photon counting CT (PCCT), and conventional dual-energy CT (DECT). Multi-Energy CT phantoms (20, 40cm) were configured with solid-iodine (2-15mgI/cc) and solid-water rods to simulate pediatric and adult-sized abdomens. PCCT scans were acquired with SS (pitch-1.5) and DS (pitch-3.0). DECT scans were performed using 80/Sn140 and 100/Sn140kV with a maximum-pitch 1.2. At the clinical dose setting, CTDI values were 0.63mGy (20-cm) and 4.30mGy (40-cm). Dose and reconstruction parameters were matched across all scan modes. Virtual monoenergetic images (VMI) between 40 and 80keV and iodine maps (IM) were generated. Noise, noise power spectra and section sensitive profiles of VMIs were then calculated. HU accuracy was evaluated using absolute percent error (APE) between measured and reference attenuation values, while iodine quantification accuracy was assessed by linear regression and root-mean-square-error (RMSE) comparing measured and reference concentrations. PCCT DS and SS modes showed comparable noise levels across keV. Both PCCT modes had lower noise than DECT across all conditions, although discrepancies diminished in larger phantoms and higher VMI keV. At the 20-cm phantom, median APEs for iodine CT numbers were lower for PCCT SS (0.53%) and DS (0.55%) than for DECT (0.98%, 1.06%). RMSE values of iodine quantification are 0.50mgI/cc for PCCT DS and 0.53mgI/cc for PCCT SS. Ultra-fast PCCT dual-source mode yields spectral image quality comparable to PCCT single-source and DECT, supporting its use when fast scanning is critical for pediatric and cardiac applications.

Objective: To analyze the relationship between carotid atherosclerotic plaque characteristics in magnetic resonance imaging (MRI) and perioperative hemodynamic instability in patients with severe carotid artery stenosis undergoing carotid artery stenting (CAS). Methods: A total of 89 patients with carotid artery stenosis who underwent CAS treatment at Beijing Tsinghua Changgung Hospital affiliated to Tsinghua University from January 1, 2017, to December 31, 2021, were prospectively included. Among them, 74 were male and 15 were female, with an age range of 43 to 87 years (mean age: 67.8±8.2 years). Preoperative examinations included carotid artery MRI vessel wall imaging to analyze the existence of large lipid-rich necrotic core (LRNC), intraplaque hemorrhage (IPH), and fibrous cap rupture in carotid artery plaques. Plaques without the above-mentioned risk factors were defined as stable plaque group (34 cases), while those with such risk factors were defined as vulnerable plaque group (55 cases). The number of risk factors present in each plaque was also calculated. Intraoperative changes in blood pressure and heart rate were recorded, and the use of dopamine postoperatively was noted. Using the risk factors that the plaque has as independent variables and the clinical outcomes as dependent variables, the RR values were calculated, and the differences in clinical outcomes of patients with different risk factors were compared. Results: The incidence rates of hypotension and bradycardia were higher in patients with vulnerable plaques than those with stable plaques (60.0% (33/55) vs 14.7%(5/34) and 38.2%(21/55) vs 14.7%(5/34), respectively; both P<0.05). Based on MRI imaging features, the large LRNC was present in 45 cases, with RR values for hypotension and bradycardia of 3.15 (1.69-5.87) and 2.20 (1.07-4.53), respectively; IPH was present in 37 cases, with RR values for hypotension and bradycardia of 2.70 (1.61-4.55) and 2.25 (1.15-4.39), respectively; and fibrous cap rupture was present in 29 cases, with RR values for hypotension and bradycardia of 1.50 (0.94-2.40) and 1.29 (0.67-2.49), respectively. The higher the number of risk factors in vulnerable plaques, the higher the incidence of intraoperative blood pressure and heart rate decrease: when the number of risk factors ranged from 0 to 3, the incidence of blood pressure decrease was 14.7% (5/34), 9/18, 11/18, and 13/19, respectively (P<0.001), and the incidence of heart rate decrease was 14.7% (5/34), 6/18, 7/18, and 8/19, respectively (P=0.022). There was no significant difference in the number of cases of dopamine use between the two groups (P>0.05). Conclusion: Patients with a higher number of risk factors for vulnerable carotid plaques, as indicated by carotid artery MRI vessel wall imaging, are at a higher risk of experiencing blood pressure and heart rate decrease during CAS surgery.

Photon counting computed tomography (PCCT) might offer an effective spatial resolution that is significantly improved compared with conventional state-of-the-art computed tomography (CT) and even provide a microstructural level of detail similar to high-resolution peripheral CT (HR-pQCT). The aim of this study was to evaluate the volumetric effective spatial resolution of clinically approved PCCT as an alternative to HR-pQCT for ex vivo or preclinical high-resolution imaging of bone microstructure. The experiment contained 5 human vertebrae embedded in epoxy resin, which were scanned 3 times each, and on 3 different clinical CT scanners: a PCCT (Naeotom Alpha), a dual-energy CT (Somatom Force [SF]), and a single-energy CT (Somatom Sensation 40 [S40]), all manufactured by Siemens Healthineers (Erlangen, Germany). Scans were performed with a tube voltage of 120 kVp and, to provide maximum scan performance and minimum noise deterioration, with exposures of 1500 mAs (SF), 2400 mAs (S40), and 4500 mAs (PCCT) and low slice increments of 0.1 (PCCT) and 0.3 mm (SF, S40). Images were reconstructed with sharp and very sharp bone kernels, Br68 and Br76 (PCCT), Br64 (SF), and B65s and B75h (S40). Ground truth information was obtained from an XtremeCT scanner (Scanco, Brüttisellen, Switzerland). Voxel-wise comparison was performed after registration, calibration, and resampling of the volumes to isotropic voxel size of 0.164 mm. Three-dimensional point spread- and modulation-transfer functions were calculated with Wiener's deconvolution in the anatomical trabecular structure, allowing optimum estimation of device- and kernel-specific smoothing properties as well as specimen-related diffraction effects on the measurement. At high contrast (modulation transfer function [MTF] of 10%), radial effective resolutions of PCCT were 10.5 lp/cm (minimum resolvable object size 476 μm) for kernel Br68 and 16.9 lp/cm (295 μm) for kernel Br76. At low contrast (MTF 5%), radial effective spatial resolutions were 10.8 lp/cm (464 μm) for kernel Br68 and 30.5 lp/cm (164 μm) for kernel Br76. Axial effective resolutions of PCCT for both kernels were between 27.0 (185 μm) and 29.9 lp/cm (167 μm). Spatial resolutions with kernel Br76 might possibly be still higher but were technically limited by the isotropic voxel size of 164 μm. The effective volumetric resolutions of PCCT with kernel Br76 ranged between 61.9 (MTF 10%) and 222.4 (MTF 5%) elements per cubic mm. Photon counting CT improved the effective volumetric resolution by factor 5.5 (MTF 10%) and 18 (MTF 5%) compared with SF and by a factor of 8.7 (MTF 10%) and 20 (MTF 5%) compared with S40. Photon counting CT allowed obtaining similar structural information as HR-pQCT. The effective spatial resolution of PCCT in trabecular bone imaging was comparable with that of HR-pQCT and more than 5 times higher compared with conventional CT. For ex vivo samples and when patient radiation dose can be neglected, PCCT allows imaging bone microstructure at a preclinical level of detail.

Carotid artery atherosclerosis is a major cause of stroke. It has been traditionally thought that luminal stenosis secondary to the presence of atherosclerotic plaques reduces blood flow along the carotid arteries, leading to cerebral ischaemia and infarction. However, recent advances have shown that atherosclerotic plaques which carry a high risk of developing complications, i.e. ‘vulnerable plaques’, display certain features which can be identified by various imaging techniques. Specifically, a variety of MRI sequences and modalities have been employed to recognise characteristics of fibrous cap, lipid-rich necrotic core, inflammation and biomechanical stress. They have been shown to be linked to the disease progression of atherosclerotic plaques, as well as the improvement following treatment. This chapter reviews the use of MRI in the investigation of carotid artery disease and the identification of vulnerable atherosclerotic plaques.