Partial volume correction incorporating Rb-82 positron range for quantitative myocardial perfusion PET based on systolic-diastolic activity ratios and phantom measurements.

BACKGROUND: Quantitative myocardial PET perfusion imaging requires partial volume corrections. METHODS: Patients underwent ECG-gated, rest-dipyridamole, myocardial perfusion PET using Rb-82 decay corrected in Bq/cc for diastolic, systolic, and combined whole cycle ungated images. Diastolic partial volume correction relative to systole was determined from the systolic/diastolic activity ratio, systolic partial volume correction from phantom dimensions comparable to systolic LV wall thicknesses and whole heart cycle partial volume correction for ungated images from fractional systolic-diastolic duration for systolic and diastolic partial volume corrections. RESULTS: For 264 PET perfusion images from 159 patients (105 rest-stress image pairs, 54 individual rest or stress images), average resting diastolic partial volume correction relative to systole was 1.14 ± 0.04, independent of heart rate and within ±1.8% of stress images (1.16 ± 0.04). Diastolic partial volume corrections combined with those for phantom dimensions comparable to systolic LV wall thickness gave an average whole heart cycle partial volume correction for ungated images of 1.23 for Rb-82 compared to 1.14 if positron range were negligible as for F-18. CONCLUSION: Quantitative myocardial PET perfusion imaging requires partial volume correction, herein demonstrated clinically from systolic/diastolic absolute activity ratios combined with phantom data accounting for Rb-82 positron range.

Perfusion in rat brain at 7 T with arterial spin labeling using FAIR-TrueFISP and QUIPSS.

Measurement of perfusion in longitudinal studies allows for the assessment of tissue integrity and the detection of subtle pathologies. In this work, the feasibility of measuring brain perfusion in rats with high spatial resolution using arterial spin labeling is reported. A flow-sensitive alternating recovery sequence, coupled with a balanced gradient fast imaging with steady-state precession readout section was used to minimize ghosting and geometric distortions, while achieving high signal-to-noise ratio. The quantitative imaging of perfusion using a single subtraction method was implemented to address the effects of variable transit delays between the labeling of spins and their arrival at the imaging slice. Studies in six rats at 7 T showed good perfusion contrast with minimal geometric distortion. The measured blood flow values of 152.5+/-6.3 ml/100 g per minute in gray matter and 72.3+/-14.0 ml/100 g per minute in white matter are in good agreement with previously reported values based on autoradiography, considered to be the gold standard.

Re-thinking resuscitation: leaving blood pressure cosmetics behind and moving forward to permissive hypotension and a tissue perfusion-based approach

Definitions of shock and resuscitation endpoints traditionally focus on blood pressures and cardiac output. This carries a high risk of overemphasizing systemic hemodynamics at the cost of tissue perfusion. In line with novel shock definitions and evidence of the lack of a correlation between macro- and microcirculation in shock, we recommend that macrocirculatory resuscitation endpoints, particularly arterial and central venous pressure as well as cardiac output, be reconsidered. In this viewpoint article, we propose a three-step approach of resuscitation endpoints in shock of all origins. This approach targets only a minimum individual and context-sensitive mean arterial blood pressure (for example, 45 to 50 mm Hg) to preserve heart and brain perfusion. Further resuscitation is exclusively guided by endpoints of tissue perfusion irrespectively of the presence of arterial hypotension ('permissive hypotension'). Finally, optimization of individual tissue (for example, renal) perfusion is targeted. Prospective clinical studies are necessary to confirm the postulated benefits of targeting these resuscitation endpoints.

Contrast-enhanced ultrasound for myocardial perfusion imaging.

Ultrasound contrast agents are gas-filled microbubbles that enhance visualization of cardiac structures, function and blood flow during contrast-enhanced ultrasound (CEUS). An interesting cardiovascular application of CEUS is myocardial contrast echocardiography, which allows real-time myocardial perfusion imaging. The intraoperative use of this technically challenging imaging method is limited at present, although several studies have examined its clinical utility during cardiac surgery in the past. In the present review we provide general information on the basic principles of CEUS and discuss the methodology and technical aspects of myocardial perfusion imaging.

The effects of endothelin-1 on coronary perfusion pressure during cardiopulmonary resuscitation in a canine model

OBJECTIVE To study the hemodynamic effects of exogenously administered endothelin-1 (ET-1), a peptide produced by endothelial cells with potent non-adrenergically mediated vasoconstrictor properties. METHODS A prospective drug intervention study was carried out in a resuscitation research laboratory. Fifteen mixed-breed dogs were anesthetized and instrumented for hemodynamic monitoring. Asphyxia arrest was produced by clamping the endotracheal tube. Hemodynamic data were collected continuously. Following loss of aortic fluctuations monitored by thoracic aortic catheter, the animals remained in pulseless electrical activity (PEA) for 10 minutes. After 10 minutes of no-flow PEA, closed-chest CPR was begun and the animals were randomized to one of three treatment groups (EPI, 0.02 mg/kg epinephrine IV every 3 minutes; ENDO, 100 micrograms ET-1 IV at 0 minutes; and EPI/ENDO, a combination of the EPI and ENDO treatments). RESULTS ENDO and EPI alone produced similar coronary perfusion pressures (CPPs). The EPI/ENDO combination produced significantly improved CPP compared with that of either EPI or ENDO alone. In the EPI group, the best mean CPP was 16 +/- 14 mm Hg and occurred 7 minutes after drug administration. In the ENDO group, the best mean CPP was 28 +/- 7 mm Hg and occurred 13 minutes after drug administration. In the EPI/ENDO combination group, the best mean CPP was 61 +/- 37 mm Hg and occurred 7 minutes after drug administration (p < 0.05 compared with the EPI and ENDO groups alone). CONCLUSION ET-1 is a potent vasoconstrictor. The combination of EPI and ENDO significantly improved CPP compared with that for either agent alone. ET-1 should be investigated further as a vasoconstrictor in cardiac arrest.

Interhemispheric cerebral blood flow balance during recovery of motor hand function after ischemic stroke - a longitudinal MRI study using arterial spin labeling perfusion

BACKGROUND Unilateral ischemic stroke disrupts the well balanced interactions within bilateral cortical networks. Restitution of interhemispheric balance is thought to contribute to post-stroke recovery. Longitudinal measurements of cerebral blood flow (CBF) changes might act as surrogate marker for this process. OBJECTIVE To quantify longitudinal CBF changes using arterial spin labeling MRI (ASL) and interhemispheric balance within the cortical sensorimotor network and to assess their relationship with motor hand function recovery. METHODS Longitudinal CBF data were acquired in 23 patients at 3 and 9 months after cortical sensorimotor stroke and in 20 healthy controls using pulsed ASL. Recovery of grip force and manual dexterity was assessed with tasks requiring power and precision grips. Voxel-based analysis was performed to identify areas of significant CBF change. Region-of-interest analyses were used to quantify the interhemispheric balance across nodes of the cortical sensorimotor network. RESULTS Dexterity was more affected, and recovered at a slower pace than grip force. In patients with successful recovery of dexterous hand function, CBF decreased over time in the contralesional supplementary motor area, paralimbic anterior cingulate cortex and superior precuneus, and interhemispheric balance returned to healthy control levels. In contrast, patients with poor recovery presented with sustained hypoperfusion in the sensorimotor cortices encompassing the ischemic tissue, and CBF remained lateralized to the contralesional hemisphere. CONCLUSIONS Sustained perfusion imbalance within the cortical sensorimotor network, as measured with task-unrelated ASL, is associated with poor recovery of dexterous hand function after stroke. CBF at rest might be used to monitor recovery and gain prognostic information.

Relative indexes of cutaneous blood perfusion measured by real-time laser Doppler imaging (LDI) in healthy volunteers.

We used real-time LDI to study regional variations in microcirculatory perfusion in healthy candidates to establish a new methodology for global perfusion body mapping that is based on intra-individual perfusion index ratios. Our study included 74 (37 female) healthy volunteers aged between 22 and 30 years (mean 24.49). Imaging was performed using a recent microcirculation-imaging camera (EasyLDI) for different body regions of each volunteer. The perfusion values were reported in Arbitrary Perfusion Units (APU). The relative perfusion indexes for each candidate's body region were then obtained by normalization with the perfusion value of the forehead. Basic parameters such as weight, height, and blood pressure were also measured and analyzed. The highest mean perfusion value was reported in the forehead area (259.21APU). Mean perfusion in the measured parts of the body correlated positively with mean forehead value, while there was no significant correlation between forehead blood perfusion values and room temperature, BMI, systolic blood pressure and diastolic blood pressure (p=0.420, 0.623, 0.488, 0.099, respectively). Analysis of the data showed that perfusion indexes were not significantly different between male and female volunteers except for the ventral upper arm area (p=.001). LDI is a non-invasive, fast technique that opens several avenues for clinical applications. The mean perfusion indexes are useful in clinical practice for monitoring patients before and after surgical interventions. Perfusion values can be predicted for different body parts for patients only by taking the forehead perfusion value and using the perfusion index ratios to obtain expected normative perfusion values.

Hypoxic treatment of human dual placental perfusion induces a preeclampsia-like inflammatory response.

Preeclampsia is a human pregnancy-specific disorder characterized by a placental pro-inflammatory response in combination with an imbalance of angiogenic factors and clinical symptoms, including hypertension and proteinuria. Insufficient uteroplacental oxygenation in preeclampsia due to impaired trophoblast invasion during placentation is believed to be responsible for many of the molecular events leading to the clinical manifestations of this disease. We investigated the use of hypoxic treatment of the dual placental perfusion system as a model for preeclampsia. A modified perfusion technique allowed us to achieve a mean soluble oxygen tension within the intervillous space (IVS) of 5-7% for normoxia and <3% for hypoxia (as a model for preeclampsia). We assayed for the levels of different inflammatory cytokines, oxidative stress markers, as well as other factors, such as endothelin (ET)-1 that are known to be implicated as part of the inflammatory response in preeclampsia. Our results show a significant increase under hypoxia in the levels of different inflammatory cytokines, including IL-6 (P=0.002), IL-8 (P<0.0001), TNF-α (P=0.032) and IFN-γ (P=0.009) at 360 min in maternal venous samples (n=6). There was also a significant increase in ET-1 levels under hypoxia both on the maternal side at 30 min (P=0.003) and fetal side at 360 min (P=0.036) (n=6). Other markers of oxidative stress, including malondialdehyde and 8-iso-protaglandin F2α (P=0.009) also show increased levels. Overall, these findings indicate that exposure of ex vivo dually perfused placental tissue to hypoxia provides a useful model for mimicking the inflammatory response characteristic of preeclampsia. This would therefore provide a powerful tool for studying and further delineating the molecular mechanisms involved in the underlying pathophysiology of preeclampsia.

Novel Approaches to Myocardial Perfusion: 3D First-Pass CMR Perfusion Imaging and Oxygenation-Sensitive

This article reviews technical aspects and the current status of novel cardiovascular magnetic resonance (CMR) approaches to assessing myocardial perfusion, specifically oxygenation-sensitive magnetic resonance imaging, comparing their diagnostic targets and clinical role with those of other imaging approaches. The paper includes discussions of relevant pathophysiological aspects of myocardial ischemia and the clinical context of revascularization in patients with suspected or known coronary artery disease. Research using oxygenation-sensitive CMR may play an important role for a better understanding of the interplay of coronary artery stenosis, blood flow reduction, and their impact on actual myocardial ischemia.

Systematic analysis of the intravoxel incoherent motion threshold separating perfusion and diffusion effects: Proposal of a standardized algorithm

PURPOSE To systematically evaluate the dependence of intravoxel-incoherent-motion (IVIM) parameters on the b-value threshold separating the perfusion and diffusion compartment, and to implement and test an algorithm for the standardized computation of this threshold. METHODS Diffusion weighted images of the upper abdomen were acquired at 3 Tesla in eleven healthy male volunteers with 10 different b-values and in two healthy male volunteers with 16 different b-values. Region-of-interest IVIM analysis was applied to the abdominal organs and skeletal muscle with a systematic increase of the b-value threshold for computing pseudodiffusion D*, perfusion fraction Fp , diffusion coefficient D, and the sum of squared residuals to the bi-exponential IVIM-fit. RESULTS IVIM parameters strongly depended on the choice of the b-value threshold. The proposed algorithm successfully provided optimal b-value thresholds with the smallest residuals for all evaluated organs [s/mm2]: e.g., right liver lobe 20, spleen 20, right renal cortex 150, skeletal muscle 150. Mean D* [10(-3) mm(2) /s], Fp [%], and D [10(-3) mm(2) /s] values (±standard deviation) were: right liver lobe, 88.7 ± 42.5, 22.6 ± 7.4, 0.73 ± 0.12; right renal cortex: 11.5 ± 1.8, 18.3 ± 2.9, 1.68 ± 0.05; spleen: 41.9 ± 57.9, 8.2 ± 3.4, 0.69 ± 0.07; skeletal muscle: 21.7 ± 19.0; 7.4 ± 3.0; 1.36 ± 0.04. CONCLUSION IVIM parameters strongly depend upon the choice of the b-value threshold used for computation. The proposed algorithm may be used as a robust approach for IVIM analysis without organ-specific adaptation. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.