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Photon-counting computed tomography (PCCT) is a new advanced imaging technique that is going to transform the standard clinical use of computed tomography (CT) imaging. Photon-counting detectors resolve the number of photons and the incident X-ray energy spectrum into multiple energy bins. Compared with conventional CT technology, PCCT offers the advantages of improved spatial and contrast resolution, reduction of image noise and artifacts, reduced radiation exposure, and multi-energy/multi-parametric imaging based on the atomic properties of tissues, with the consequent possibility to use different contrast agents and improve quantitative imaging. This narrative review first briefly describes the technical principles and the benefits of photon-counting CT and then provides a synthetic outline of the current literature on its use for vascular imaging.

Objectives Although cardiovascular magnetic resonance (CMR) is widely used in the assessment of left ventricular non-compaction (LVNC), there are no universally accepted diagnostic criteria and limited data regarding their prognostic value. We assessed the long-term prognostic role of the planimetric global Grothoff’s criteria and of the CMR findings in predicting adverse cardiovascular events (CE). Methods We prospectively enrolled 78 patients (46.7 ± 18.7 years, 33.3% females) with documented positive Jenni’s echocardiographic criteria for LVNC. Cine images were used to quantify function parameters and to assess for the presence of all four quantitative Grothoff’s criteria (global Grothoff’s criteria). Late gadolinium enhancement (LGE) images were acquired to detect the presence of replacement myocardial fibrosis. Results Petersen’s CMR criterion for LVNC (NC/C ratio > 2.3 in at least one myocardial segment) was fulfilled in the whole population. Twenty-six patients fulfilled the global Grothoff’s criteria (four out of four). The mean duration of the follow-up was 44.2 ± 27.4 months and 28 CE were registered: 10 ventricular tachycardias, 12 episodes of heart failure (HF), four strokes, and two cardiac deaths. In the multivariate analysis, the independent predictive factors for CE were positive global Grothoff’s criteria (hazard ratio, HR = 3.33, 95% CI = 1.52–7.29; p = 0.003) and myocardial fibrosis (HR = 2.41, 95% CI = 1.08–5.36; p = 0.032). Conclusions Positive global Grothoff’s criteria and myocardial fibrosis were powerful predictors of CE in patients with a diagnosis of LVNC by CMR Petersen’s criterion. Thus, we strongly suggest a step approach confirming the diagnosis of LVNC by using the global planimetric Grothoff’s criteria, which showed a prognostic impact. Key Points • Positive global Grothoff’s criteria and replacement myocardial fibrosis were powerful predictors of cardiovascular events in patients with a diagnosis of LVNC by CMR Petersen’s criterion. • Positive global Grothoff’s criteria were associated with a higher frequency of ventricular arrhythmias in patients with a diagnosis of LVNC by CMR Petersen’s criterion.

Objectives Our aims were to obtain myocardial regional and global T2 values as a reference for normality for the first time using a GE scanner and to assess their association with physiological variables. Methods One hundred healthy volunteers aged 20–70 years (50% females) underwent cardiovascular magnetic resonance. Basal, mid-ventricular, and apical short-axis slices of the left ventricle were acquired by a multi-echo fast-spin-echo (MEFSE) sequence. Image analysis was performed with a commercially available software package. The T2 value was assessed in all 16 myocardial segments and the global value was the mean. Results The global T2 value averaged across all subjects was 52.2 ± 2.5 ms (range: 47.0–59.9 ms). Inter-study, intra-observer, and inter-observer reproducibility was good (coefficient of variation < 5%). 3.6% of the segments was excluded because of artifacts and/or partial-volume effects. Segmental T2 values differed significantly ( p < 0.0001), with the lowest value in the basal anterolateral segment (50.0 ± 3.5 ms) and the highest in the apical lateral segment (54.9 ± 5.1 ms). Mean T2 was significantly lower in the basal slice compared to both mid-ventricular and apical slices and in the mid-ventricular slice than in the apical slice. Aging was associated with increased segmental and global T2 values. Females showed higher T2 values than males. T2 values were not correlated to heart rate. A significant inverse correlation was detected between global T2 values and mean wall thickness. Conclusions The optimized MEFSE sequence allows for robust and reproducible quantification of segmental T2 values. Gender- and age-specific segmental reference values must be defined for distinguishing healthy and diseased myocardium. Key Points • In healthy subjects, T2 values differ among myocardial segments and are influenced by age and gender. • Normal T2 values in the myocardium, usable as a benchmark by other GE sites, were established.

Background We compared cardiovascular magnetic resonance segmental native T1 against T2* values for the detection of myocardial iron overload (MIO) in thalassaemia major and we evaluated the clinical correlates of native T1 measurements. Methods We considered 146 patients (87 females, 38.7 ± 11.1 years) consecutively enrolled in the Extension-Myocardial Iron Overload in Thalassaemia Network. T1 and T2* values were obtained in the 16 left ventricular (LV) segments. LV function parameters were quantified by cine images. Post-contrast late gadolinium enhancement (LGE) and T1 images were acquired. Results 64.1% of segments had normal T2* and T1 values while 10.1% had pathologic T2* and T1 values. In 526 (23.0%) segments, there was a pathologic T1 and a normal T2* value while 65 (2.8%) segments had a pathologic T2* value but a normal T1 and an extracellular volume (ECV) ≥ 25% was detected in 16 of 19 segments where ECV was quantified. Global native T1 was independent from gender or LV function but decreased with increasing age. Patients with replacement myocardial fibrosis had significantly lower native global T1. Patients with cardiac complications had significantly lower native global T1. Conclusions The combined use of both segmental native T1 and T2* values could improve the sensitivity for detecting MIO. Native T1 is associated with cardiac complications in thalassaemia major.

: We measured hepatic T2*, T1, and T2 values in = 81 transfusion-dependent thalassemia (TDT) patients to assess and compare their reproducibility, evaluate their correlations with demographics and clinical parameters, and explore their association with disease-related complications. All TDT patients (52 females, 38.13 ± 10.79 years), were enrolled in the Extension-Myocardial Iron Overload in Thalassaemia Network. The magnetic resonance imaging protocol (1.5 T) included: multi-echo gradient echo sequences for T2* relaxometry, modified look-locker inversion recovery (MOLLI) sequences for T1 mapping, and multi-echo fast-spin-echo (MEFSE) sequences for T2 mapping. All three relaxation times demonstrated good intra- and inter-observer reproducibility and were significantly correlated with each other. Of the 59 patients with reduced T2*, 45 (76.3%) also had reduced T1, and 42 (71.2%) had reduced T2 values. Among 22 patients with normal T2*, 3 (13.6%) exhibited reduced T1. No patients showed increased T1, and only one had elevated T2. Liver relaxation times were not associated with gender or splenectomy status. All relaxation times inversely correlated with serum ferritin levels, while T2 and T2* inversely correlated with mean alanine aminotransferase levels. Cirrhosis and glucose metabolism alterations were associated with lower relaxation times. All three relaxation times effectively discriminated between the absence and presence of cirrhosis [areas under the curve (AUCs) with 95% confidence intervals (CIs): 0.85 (0.75-0.92) for T2*, 0.78 (0.68-0.87) for T1, and 0.92 (0.84-0.97) for T2]. T2* showed comparable accuracy to T1 and T2, while a significant difference was observed between T1 and T2 values. All liver relaxation times demonstrated similar diagnostic performance in identifying glucose metabolism alterations [AUCs with 95% CIs: 0.67 (0.55-0.77) for T2*, 0.69 (0.57-0.79) for T1, and 0.67 (0.56-0.77) for T2]. In TDT, a comprehensive assessment of hepatic relaxation times may enhance clinical monitoring and management of iron overload and its related complications.

Left Ventricle (LV) detection from Cardiac Magnetic Resonance (CMR) imaging is a fundamental step, preliminary to myocardium segmentation and characterization. This paper focuses on the application of a Visual Transformer (ViT), a novel neural network architecture, to automatically detect LV from CMR relaxometry sequences. We implemented an object detector based on the ViT model to identify LV from CMR multi-echo T2* sequences. We evaluated performances differentiated by slice location according to the American Heart Association model using 5-fold cross-validation and on an independent dataset of CMR T2*, T2, and T1 acquisitions. To the best of our knowledge, this is the first attempt to localize LV from relaxometry sequences and the first application of ViT for LV detection. We collected an Intersection over Union (IoU) index of 0.68 and a Correct Identification Rate (CIR) of blood pool centroid of 0.99, comparable with other state-of-the-art methods. IoU and CIR values were significantly lower in apical slices. No significant differences in performances were assessed on independent T2* dataset (IoU = 0.68, p = 0.405; CIR = 0.94, p = 0.066). Performances were significantly worse on the T2 and T1 independent datasets (T2: IoU = 0.62, CIR = 0.95; T1: IoU = 0.67, CIR = 0.98), but still encouraging considering the different types of acquisition. This study confirms the feasibility of the application of ViT architectures in LV detection and defines a benchmark for relaxometry imaging.

ObjectivesR2* cardiac magnetic resonance (CMR) allows the non-invasive measurement of myocardial iron. We calibrated cardiac R2* values against myocardial tissue–measured iron concentration by using a segmental approach and we assessed the iron distribution.MethodsFive hearts of thalassemia patients were donated after death/transplantation to the CoreLab of the Myocardial Iron Overload in Thalassemia Network. A multislice multiecho R2* approach was adopted. After CMR, used as guidance, the heart was cut in three short-axis slices and each slice was cut into different equiangular segments according to AHA segmentation and differentiated into endocardial and epicardial layers. Tissue iron concentration was measured by atomic absorption spectrometer technique.ResultsFifty-five samples were used since only for two hearts all the 16 samples were analyzed. Mean iron concentration was 4.71 ± 4.67 mg/g dw. Segmental iron levels ranged from 0.24 to 13.78 mg/g dw. The coefficient of variability of iron for myocardial segments ranged from 8.08 to 24.54% (mean 13.49 ± 6.93%). Iron concentration was significantly higher in the epicardial than in the endocardial layer (5.99 ± 6.01 vs 4.84 ± 4.87 mg/g dw; p = 0.042). Four different circumferential regions (anterior, septal, inferior, and lateral) were defined. A circumferential heterogeneity was noted, with more iron in the anterior region, followed by the inferior region. The direct nonlinear fitting of R2* and [Fe] data led to the calibration curve: [Fe] = 0.0022 ∙ (R2*-ROI)1.462 (R-square = 0.956).ConclusionsOur data further validate R2* CMR using a segmental approach as a sensitive and early technique for quantifying iron distribution in the current clinical practice.Key Points• Calibration in humans for cardiovascular magnetic resonance R2* against myocardial iron concentration was provided.• A circumferential heterogeneity in cardiac iron distribution was detected: more iron was observed in the anterior region, followed by the inferior region. This finding corroborates the use of a segmental T2* CMR approach in the clinical practice to detect a heterogeneous iron distribution.• The comparison between the cardiac T2* values obtained with the region-based and the pixel-wise approaches showed a significant correlation and no significant difference but, in presence of significant iron load, the region-based approach resulted in significantly higher T2* values.

The photon-counting detector (PCD) is a new computed tomography detector technology (photon-counting computed tomography, PCCT) that provides substantial benefits for cardiac and coronary artery imaging. Compared with conventional CT, PCCT has multi-energy capability, increased spatial resolution and soft tissue contrast with near-null electronic noise, reduced radiation exposure, and optimization of the use of contrast agents. This new technology promises to overcome several limitations of traditional cardiac and coronary CT angiography (CCT/CCTA) including reduction in blooming artifacts in heavy calcified coronary plaques or beam-hardening artifacts in patients with coronary stents, and a more precise assessment of the degree of stenosis and plaque characteristic thanks to its better spatial resolution. Another potential application of PCCT is the use of a double-contrast agent to characterize myocardial tissue. In this current overview of the existing PCCT literature, we describe the strengths, limitations, recent applications, and promising developments of employing PCCT technology in CCT.

Background: This retrospective cross-sectional study evaluated the association of the global wall thickness index (GTI), derived from cardiovascular magnetic resonance (CMR), with demographic, clinical, and imaging findings, as well as heart failure history in transfusion-dependent thalassemia (TDT) patients. Methods: We analyzed 1154 TDT patients (52.9% female, 37.46 ± 10.67 years) from the Extension-Myocardial Iron Overload in Thalassemia project and 167 healthy controls (54.5% female, 36.33 ± 15.78 years). The CMR protocol included the T2* technique for the assessment of iron overload, cine imaging for the assessment of left ventricular (LV) function and size, and late gadolinium enhancement (LGE) imaging for the detection of replacement myocardial fibrosis (in the subset of 366 patients who underwent contrast administration). GTI (in mm/m2) was calculated from LV mass and end-diastolic volume. Results: GTI discriminated TDT patients from controls better than the LV end-diastolic volume index. Among TDT patients, GTI was higher in males, in those with diabetes, and in those with severe myocardial iron overload (cardiac T2* < 10 ms), but was unrelated to age, hemoglobin and ferritin levels, splenectomy, hepatic and pancreatic T2* values, LV ejection fraction, and fibrosis. GTI showed a diagnostic performance comparable to global heart T2* and superior to LV ejection fraction in identifying patients with prior heart failure. Conclusions: GTI is elevated in TDT patients compared with healthy controls. Male sex and severe myocardial iron overload are key determinants of GTI in TDT. Increased GTI is linked to a history of heart failure, supporting its role as a complementary tool to conventional CMR indices.