Twin samples allow to conduct a quasi-experimental co-twin case-control approach that can control for genetic and environmental confounding in brain-cognition associations, being more informative on causality compared with studies in unrelated individuals. We conducted a review of studies that have utilized discordant co-twin design to investigate the associations of brain imaging markers of Alzheimer\'s disease and cognition. Inclusion criteria encompassed twin pairs discordant for cognition or Alzheimer\'s disease imaging markers and reporting of within-twin pair comparison on the association between cognition and brain measures. Our PubMed search (2022 April 23, updated 2023 March 9) resulted in 18 studies matching these criteria. Alzheimer\'s disease imaging markers have been addressed only by few studies, most with small sample size. Structural magnetic resonance imaging studies have indicated greater hippocampal volume and thicker cortex in co-twins with better cognitive performance compared with their co-twins with poorer cognitive performance. No studies have looked at cortical surface area. Positron emission tomography imaging studies have suggested that lower cortical glucose metabolism rate and higher cortical neuroinflammation, amyloid, and tau accumulations are related to poorer episodic memory in within-twin pair comparisons. Thus far, only cross-sectional within-twin pair associations of cortical amyloid and hippocampal volume with cognition have been replicated.

Little is known about the sequelae of chronic sympathetic nervous system (SNS) activation in patients with pulmonary arterial hypertension (PAH) and right heart failure (RHF). We aimed to, (1) validate the use of [11C]-meta-hydroxyephedrine (HED) for assessing right ventricular (RV) SNS integrity, and (2) determine the effects of β-receptor blockade on ventricular function and myocardial SNS activity in a PAH rat model.
PAH was induced in male Sprague-Dawley rats (N = 36) using the Sugen+chronic hypoxia model. At week 5 post-injection, PAH rats were randomized to carvedilol (15 mg·kg-1·day-1 oral; N = 16) or vehicle (N = 16) for 4 weeks. Myocardial SNS function was assessed with HED positron emission tomography(PET).
With increasing PAH disease severity, immunohistochemistry confirmed selective sympathetic denervation within the RV and sparing of parasympathetic nerves. These findings were confirmed on PET with a significant negative relationship between HED volume of distribution(DV) and right ventricular systolic pressure (RVSP) in the RV (r = -0.90, p = 0.0003). Carvedilol did not reduce hemodynamic severity compared to vehicle. RV ejection fraction (EF) was lower in both PAH groups compared to control (p < 0.05), and was not further reduced by carvedilol. Carvedilol improved SNS function in the LV with significant increases in the HED DV, and decreased tracer washout in the LV (p < 0.05) but not RV.
PAH disease severity correlated with a reduction in HED DV in the RV. This was associated with selective sympathetic denervation. Late carvedilol treatment did not lead to recovery of RV function. These results support the role of HED imaging in assessing SNS innervation in a failing right ventricle.
Poco se sabe de las secuelas en la activación del sistema nervioso simpático (SNS) en pacientes con hipertensión arterial pulmonar (HAP) y falla cardíaca derecha (FCD). Nuestros objetivos fueron: (1) validar el uso de la 11C-Meta-hidroxiepinefrina (HED) para evaluar al ventrículo derecho y la integridad del SNS y (2) determinar los efectos del bloqueo de B-receptores en la función ventricular y la actividad miocárdica del SNS en un modelo murino de HAP. MéTODOS: Se indujo HAP en modelos murinos Sprague-Dawley machos (n = 36) usando el modelo Sugen-hipoxia crónica. A la semana 5 postinyección, los modelos murinos con HAP fueron randomizados a carvedilol (15mg/kg/día oral n = 16) o vehículo (n = 16) durante 4 semanas. La función miocárdica del SNS fue evaluada con tomografía por emisión de positrones (PET) con HED.
Con el incremento de la severidad de la HAP, por inmunohistoquímica se demostró denervación simpática selectiva y preservación de nervios parasimpáticos en el ventrículo derecho. Estos hallazgos fueron confirmados con la PET con una significativa relación inversa entre el volumen de distribución (VD) del HED y la presión sistólica (PSVD) en ventrículo derecho (r = 0.90, p = 0.0003). El Carveridol no redujo la severidad hemodinámica en comparación con el vehículo. La fracción de eyección (FE)del ventrículo derecho fue menor en ambos grupos con PAH comparada con el grupo control (p < 0.05) y no se redujo más con el uso del carveridol. El Carveridol mejoró la función del SNS en el ventrículo derecho con incremento significativo del HED VD, y una disminución en el lavado del radiotrazador por el ventrículo izquierdo (p < 0.05) pero no por el derecho.
La severidad enfermedad por HAP se correlacionó con una reducción del HED VD en VD. Esto fue asociado con denervación simpática selectiva. El tratamiento tardío con carveridol no condujó a la recuperación de la función del VD. Estos resultados apoyan el rol de la imagen con HED para evaluar la inervación del SNS en el ventrículo derecho en falla.
背景: 对于肺动脉高压 (PAH) 和右心衰竭 (RHF) 患者的慢性交感神经系统 (SNS) 激活的后遗症知之甚少。 本文研究目标: 1)验证[11C]-间-羟基麻黄碱 (HED) 用于评估右心室SNS完整性, 2) 确定在PAH大鼠模型中β受体阻滞剂对改善心室功能和心肌SNS活性的作用。 方法: 在雄性Sprague-Dawley大鼠 (n = 36) 中使用Sugen +慢性缺氧模型诱导PAH。 在注射后第5周, 将PAH大鼠随机分为卡维地洛组 (15 mg / kg /天, 口服; n = 16) 和溶剂组 (n = 16), 共治疗4周。 采用HED正电子发射断层扫描 (PET)评估心肌SNS功能。 结果: 随着PAH病情恶化, 免疫组化证实了右室选择性交感神经去神经化和副交感神经的保留。 这些发现在PET上得到证实, 右室的HED容积分布 (DV) 与右室收缩压 (RVSP) 之间存在显着的负相关 (r = -0.90,p = 0.0003) 。 与溶剂组相比, 卡维地洛组并不能降低血流动力学的严重程度。与对照组相比, 两个PAH组的右心室射血分数 (EF) 均较低(p <.05) , 且并没有因为卡维地洛的使用而进一步降低。左室HED DV显著增加, 提示卡维地洛改善了左心室的SNS功能。左心室的示踪剂洗脱减少 (p <0.05) , 但右心室的洗脱没有减少。 结论: PAH疾病严重程度与右室HED DV降低相关。 这与选择性交感神经去神经化有关。 晚期给予卡维地洛治疗未能使RV功能得到恢复。 这些结果支持了HED成像在评估右心室衰竭中的SNS神经分布中的作用。.
On sait peu de choses sur les séquelles de l\'activation chronique du système nerveux sympathique (SNS) chez les patients souffrant d\'hypertension artérielle pulmonaire (HTAP) et d\'insuffisance ventriculaire droite (IVD). Nous avons tenté de :1) valider l\'utilisation de la [11C] -meta-hydroxyephedrine (MHED) pour évaluer l’intégrité du SNS ventriculaire droit (VD) et 2) déterminer les effets du blocage des récepteurs β sur la fonction ventriculaire et l’activité du SNS myocardique en utilisant un modèle de rat HTAP. MéTHODES: L\'HTAP a été induite chez des rats mâles Sprague-Dawley (N = 36) à l\'aide du modèle Sugen + hypoxie chronique. À la 5ieme semaine après l\'injection, les rats HTAP ont été randomisés pour recevoir du Carvédilol (15 mg / kg / jour par voie orale; n = 16) ou le véhicule (n = 16) pour 4 semaines. La fonction SNS myocardique a été évaluée par tomographie par émission de positons (TEP) avec du MHED marqué au carbone 11. RéSULTATS: Avec l\'augmentation de la sévérité de l\'HTAP, l\'immunohistochimie a confirmé la dénervation sélective du système nerveux sympathique du VD et l’épargne des nerfs parasympathiques. Ces résultats ont été confirmés sur le PET avec une corrélation négative significative entre le montant de captation de MHED et la pression systolique du ventricule droit (PSVD) (r = -0,90, p = 0,0003). En comparaison avec le véhicule, le Carvédilol n\'a pas réduit la sévérité de l’HTAP. La fraction d\'éjection du VD s’est avérée inférieure faible dans les deux groupes d’HTAP par rapport au groupe témoin (p <0,05), et n\'a pas été réduite davantage par le Carvédilol. Le Carvédilol a amélioré la fonction SNS du ventricule gauche (VG) en parallèle à augmentation significative de la captation de l’MHED et une diminution de la disparition du traceur au niveau du VG (p <0,05) mais pas au niveau du VD CONCLUSIONS: La sévérité de l\'HTAP est corrélée à une réduction de la captation de MHED au niveau du VD reflétant sa dénervation sympathique sélective. Un traitement tardif au Carvédilol ne permet pas de récupérer la fonction du VD. Ces résultats supportent le rôle de l\'imagerie MHED-TEP dans l\'évaluation de l\'innervation SNS en cas d’insuffisance du VD.

[18F]Fluorodeoxyglucose (FDG)-PET/CT and US are both well established for diagnosing GCA. The present study investigates their accuracy and whether they provide overlapping or complementary information in a cohort of patients presenting with suspicion of GCA.
We selected consecutive patients from our cohort of suspected GCA cases that underwent both extended vascular US and PET/CT for diagnostic work-up between December 2006 and August 2012.
A total of 102 patients were included. Diagnosis of GCA was confirmed in 68 patients and excluded in 34 patients (controls). Vasculitic changes in US were most often found in the temporal artery with 32 positive findings on each side, followed by the popliteal artery (10 right, 9 left) and the subclavian/axillary artery (7 right, 8 left). By contrast, PET/CT showed vasculitis most frequently in the vertebral (23 right, 33 left) and common carotid arteries (32 right, 24 left), followed by the subclavian arteries (16 right, 18 left), and the thoracic (17) and abdominal aorta (23). In 37/68 GCA patients PET/CT and US both revealed vasculitic findings, 11/68 had positive findings in US only and 14/68 in PET/CT only. Specificity of US was higher (one false-positive vs five false-positive in PET/CT). On a single segment level, only 20 of 136 positive segments were positive in both imaging modalities.
PET/CT measuring vessel wall metabolism and US vessel wall morphology showed a comparable diagnostic accuracy for GCA. However PET/CT and US were often discrepant within single vascular regions. Thus PET/CT and US should be considered as complementary methods, with a second imaging modality increasing the diagnostic yield by 16-20%.

Abnormalities in the cardiac sympathetic nervous system have been documented in various heart diseases and have been directly implicated in their pathogenesis and disease progression. Noninvasive techniques using single-photon-emitting radiotracers for planar scintigraphy and single-photon emission computed tomography, and positron-emitting tracers for positron emissions tomography, have been used to characterize the cardiac sympathetic nervous system with norepinephrine analogs [123I]meta-iodobenzylguanidine for planar and single-photon emission computed tomography imaging and [11C]meta-hydroxyephedrine for positron emissions tomography. Their usefulness in prognostication and risk stratification for cardiac events has been demonstrated. This review bridges basic and clinical research and focuses on applying an understanding of tracer kinetics and neuronal biology, to aid in the interpretation of nuclear imaging of cardiac sympathetic innervation.

The spine is the third most common site for distant metastasis in cancer patients with approximately 70% of patients with metastatic cancer having spinal involvement. Positron emission tomography (PET), combined with computed tomography (CT) or magnetic resonance imaging (MRI), has been deeply integrated in modern clinical oncology as a pivotal component of the diagnostic work-up of patients with cancer. PET is able to diagnose several neoplastic processes before any detectable morphological changes can be identified by anatomic imaging modalities alone. In this review, we discuss the role of PET/CT and PET/MRI in the diagnostic management of non-osseous metastatic disease of the spinal canal. While sometimes subtle, recognizing such disease on FDG PET/CT and PET/MRI imaging done routinely in cancer patients can guide treatment strategies to potentially prevent irreversible neurological damage.