Aims: The aims of our study were to evaluate whether point‐of‐care β‐hydroxybutyrate (BHB) measurement can be used to identify patients with adequate cardiac glucose metabolism suppression for cardiac [¹⁸F]‐fluoro‐2‐deoxy‐d‐glucose‐positron emission tomography with computerized tomography (FDG‐PET/CT) and to develop a pretest probability calculator of myocardial suppression using other metabolic factors attainable before imaging.Methods and Results: We recruited 193 patients with any clinical indication for whole body [¹⁸F]‐FDG‐PET/CT. BHB level was measured with a point‐of‐care device. Maximal myocardial standardized uptake value using lean body mass (SULmax) was measured from eight circular regions of interest with 1 cm circumference and background from left ventricular blood pool. Correlations SULmax and point‐of‐care measured BHB were analysed. The ability of BHB test to predict adequate suppression was evaluated with receiver operating characteristic analysis. Liver and spleen attenuation in computed tomography were measured to assess the presence of fatty liver. BHB level correlated with myocardial uptake and, using a cut‐off value of 0.35 mmol/L to predict adequate myocardial suppression, we reached specificity of 90% and sensitivity of 56%. Other variables to predict adequate suppression were diabetes, obesity, ketogenic diet and fatty liver. Using information attainable before imaging, we created a pretest probability calculator of inadequate myocardial glucose metabolism suppression. The area under the curve for BHB test alone was 0.802 and was 0.857 for the pretest calculator (p = 0.319).Conclusions: BHB level measured with a point‐of‐care device is useful in predicting adequate myocardial glucose metabolism suppression. More detailed assessment of other factors potentially contributing to cardiac metabolism is needed.

Background: Inadequate myocardial glucose metabolism suppression (GMS) can hamper interpretation of cardiac [¹⁸F]fluorodeoxyglucose (FDG) positron emission tomography (PET/CT). Use of β-hydroxybutyrate (BHB) measurement before [¹⁸F]FDG injection has been proposed for predicting adequate GMS. However, limited information is available on BHB measurement in guiding preparations for [¹⁸F]FDG-PET/CT. The purpose of this study was to evaluate if point-of-care measured BHB is useful in guiding heparin premedication for cardiac [¹⁸F]FDG-PET/CT. Results: 155 patients (82 male) had followed a high-fat, low-carbohydrate diet and fasted for at least twelve hours. For the first 63 patients, BHB was measured, but it was not used to guide premedication. For the subsequent 92 patients, heparin 50 IU/kg was injected intravenously 15–20 min before [¹⁸F]FDG injection if the BHB level was low (< 0.35 mmol/l). Cardiac [¹⁸F]FDG uptake pattern was evaluated visually and [¹⁸F]FDG uptake in the myocardium and blood pool were measured. Median BHB level was 0.4 (range 0.1–5.8) mmol/l. Eighty-eight patients (57%) reached a BHB level higher than 0.35 mmol/l. 112 patients (72%) had adequate GMS. In the high BHB group, 74 patients (84%) had adequate GMS, whereas of those with low BHB, only 38 (57%) had adequate GMS (p < 0.001). In the low BHB group, the prevalence of inadequate GMS was comparable in patients with and without heparin (44% vs. 42%, p = 0.875). Conclusions: While high BHB predicts adequate GMS, unfractionated heparin does not improve GMS in patients with low BHB.

Background: Corresponding to impaired insulin response in skeletal muscle, insulin resistance may occur in the myocardium, suggesting a link between cardiometabolic disorders and cardiac glucose metabolism. We aimed to investigate whether cardiometabolic disorders predict myocardial [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) uptake suppression in cardiac positron emission tomography / computed tomography (PET/CT) following a ketogenic diet and fasting. Results: The study included 100 patients undergoing [¹⁸F]FDG-PET/CT following a ketogenic diet of 1–2 days and a 12 h fast. Blood glucose, insulin, β-hydroxybutyrate (BHB), cholesterol, triglycerides and free fatty acid (FFA) levels were measured before [¹⁸F]FDG injection and later off-diet following overnight fast. The homeostatic model assessment–insulin resistance (HOMA-IR) value was calculated. Non-contrast computed tomography was used to assess the presence of fatty liver and visceral and subcutaneous fat areas. Suppression of myocardial [¹⁸F]FDG uptake was considered adequate if myocardial uptake was equal to or lower than the blood pool background. Compared to inadequate suppression, adequate suppression was associated with higher levels of BHB (median 0.26 mmol/l for inadequate and 0.43 mmol/l for adequate suppression, p = 0.004), FFA (0.58 mmol/l and 0.76 mmol/l respectively, p < 0.001), triglycerides (0.87 mmol/l and 1.12 mmol/l respectively, p = 0.028), and lower liver-spleen attenuation ratios (1.17 and 1.04 respectively, p = 0.013). Low HDL cholesterol, high triglycerides and off-diet HOMA-IR, as well as visceral adiposity, fatty liver and hypertension, predicted adequate suppression in men. Elevated BHB and FFA were significant predictors of adequate suppression in women. Conclusions: Cardiometabolic disorders are associated with lower myocardial [¹⁸F]FDG uptake. Insulin resistance and several other cardiometabolic risk factors are associated with attenuated uptake, especially in men. In women, factors reflecting metabolic response to a ketogenic diet and fasting have a more pronounced effect on myocardial [¹⁸F]FDG uptake.

Background: Magnetic resonance imaging (MRI) enables the non-invasive assessment of myocardial tissue properties through the T1, T2, and T2* relaxation mapping. Establishing population-specific normal reference values enhances diagnostic accuracy. Purpose: To study the effect of sex and age on the T1, T2, and T2* relaxation time constants in a healthy Finnish population. Methods: We recruited 47 healthy volunteers aged 18–60 years from Eastern Finland from 2023 to 2024 and categorised them by sex and age (18–30 years, 31–41 years, and 42–60 years). The participants underwent a comprehensive screening process to eliminate the possibility of cardiac disease. MRI scans were conducted on 40 participants at 1.5 T. The T1, T2, and T2* relaxation time constants were calculated for basal, mid-ventricular, and apical short-axis slices. Results: The T1 and T2 relaxation time constants were higher in females than males (T1: 1040 ± 29 vs 1020 ± 17 ms, p < .01; T2: 51 ± 4 vs 48 ± 3 ms, p < .001). The 95% normal T1 range was 981–1098 ms for females and 985–1054 ms for males. The normal T2 range was 44–58 ms for females and 43–53 ms for males. No sex differences were found in the T2* relaxation times. The septal T2* across the whole population was 36 ± 7 ms (95% normal limit: 22–49 ms). Conclusion: This study established age-independent and sex-specific reference values for the native myocardial T1, T2, and T2* relaxation time constants at 1.5 T. Females had higher T1 and T2 values than males, and age did not affect these values.

Background: Cardiovascular diseases, particularly myocardial ischemia from coronary artery obstruction, remain a leading cause of global morbidity. This review explores cardiac molecular magnetic resonance imaging (mMRI) and other molecular imaging techniques for the evaluation of myocardial ischemia, scarring, and viability. Results and findings: mMRI imaging methods provide detailed information on myocardial ischemia, edema, and scar tissue using techniques like cine imaging, T1 and T2 mapping, and gadolinium-based contrast agents. These methods enable the precise assessment of the myocardial tissue properties, crucial in diagnosing and treating cardiovascular diseases. Advanced techniques, such as the T1ρ and RAFFn methods, might provide enhanced contrast and sensitivity for the detection of myocardial scarring without contrast agents. Molecular probes, including gadolinium-based and protein-targeted contrast agents, improve the detection of molecular changes, facilitating early diagnosis and personalized treatment. Integrating MRI with positron emission tomography (PET) combines the high spatial and temporal resolution with molecular and functional imaging. Conclusion: Recent advancements in mMRI and molecular imaging have changed the evaluation of myocardial ischemia, scarring, and viability. Despite significant progress, extensive research is needed to validate these techniques clinically and further develop imaging methods for better diagnostic and prognostic outcomes.

Background: In patients with suspected coronary artery disease (CAD), diffusely impaired hyperaemic myocardial blood flow (MBF) may indicate a multivessel epicardial CAD but also impaired coronary microcirculation. We assessed whether relative hyperaemic MBF—that is, the ratio of the lowest to the highest regional hyperaemic MBF—predicts obstructive CAD in patients with diffusely impaired hyperaemic MBF. Methods: We studied 874 patients who underwent coronary computed tomography angiography and [ ¹⁵ O]H ₂ O myocardial perfusion imaging with positron emission tomography at Kuopio University Hospital, Finland, in 2017–2023. The final analyses included 64 patients who had diffusely impaired hyperaemic MBF and were subsequently referred to invasive coronary angiography (ICA). Results: In ICA, 34/64 (53%) patients had obstructive CAD. Compared to patients with non‐obstructive CAD, those with obstructive CAD had lower relative hyperaemic MBF: 66% (95% CI 62–69%) versus 52% (95% CI 47–57%), respectively ( p < 0.001). When relative hyperaemic MBF was used to predict the presence of obstructive CAD in ICA, the receiver operating characteristic analysis showed an area under the curve of 0.778 (95% CI 0.666–0.891). In binary logistic regression analysis, relative hyperaemic MBF independently predicted obstructive CAD (OR = 0.92 [95% CI 0.86–0.97], p = 0.004). Conclusion: Obstructive CAD is more likely in patients with lower relative hyperaemic MBF. Consequently, relative hyperaemic MBF may have clinical utility in patients with suspected CAD and diffusely impaired hyperaemic MBF.