Comparison of dual to single contrast bolus magnetic resonance myocardial perfusion imaging for detection of significant coronary artery disease

Purpose:

To investigate the incremental diagnostic value of dual‐bolus over single‐contrast‐bolus first pass magnetic resonance myocardial perfusion imaging (MR‐MPI) for detection of significant coronary artery disease (CAD).

Materials and Methods:

Patients (n = 49) with suspected CAD underwent first pass adenosine stress and rest MR‐MPI and invasive coronary angiography (CA). Gadolinium diethylenetriamine pentaacetic acid (Gd‐DTPA) was injected with a prebolus (1 mL) and a large bolus (0.1 mmol/kg). For the single‐bolus technique, the arterial input function (AIF) was obtained from the large‐contrast bolus. For the dual‐bolus technique, the AIF was reconstructed from the prebolus. Absolute myocardial perfusion was calculated by Fermi‐model constrained deconvolution. Receiver operating characteristic (ROC) analysis was used to investigate diagnostic accuracy of MR myocardial perfusion imaging for detection of significant CAD on CA at vessel‐based analysis.

Results:

The area under the curve (AUC) of the minimal stress perfusion value for the detection of significant CAD using the single‐bolus and dual‐bolus technique was 0.85 ± 0.04 (95% confidence interval [CI], 0.77–0.93) and 0.77 ± 0.05 (95% CI, 0.67–0.86), respectively.

Conclusion:

In this study the dual‐bolus technique had no incremental diagnostic value over single‐bolus technique for detection of significant CAD with the used contrast concentrations. J. Magn. Reson. Imaging 2010;32:88–93. © 2010 Wiley‐Liss, Inc.     

Capillary transfer constant of Gd-DTPA in the myocardium at rest and during vasodilation assessed by MRI

The purpose of this study was to determine whether the capillary transfer constant (K_i) of gadolinium-DTPA was sensitive to perfusion changes and whether ischemic regions in the myocardium could be identified using the modified Kety formula. K_i was measured at rest and during dipyridamole-induced vasodilation in 10 healthy volunteers and in 10 patients with ischemic heart disease. K_i increased by a factor of 2.5 ± 1.2 (mean ± SD) from 55 ± 16 ml 100 g^?1min^?1 at rest to 136 ± 46 ml 100 9^?1min^?1 (P < 0.01) during vasodilation in the healthy subjects. In the patients, there were no changes in K_i during vasodilation in ischemic regions (50 ± 18 versus 49 ± 30 ml 100 g^?1min^?1 (P > 04)). K_i increased in nonischemic regions by a factor of 2.0 ± 0.8 from 44 ± 17 to 81 ± 32 ml 100 g^?1min^?1 during vasodilation (P < 0.02). It is concluded that the capillary transfer constant is sensitive to perfusion changes and that regional ischemia can be detected with MRI. This noninvasive and quantitative method may prove useful in the evaluation of patients with ischemic heart disease.     

Assessment of myocardial perfusion by dynamic O-15-labeled water PET imaging: Validation of a new fast factor analysis

Background  Factor analysis (FA) is an established method for separating myocardium from blood pool by use of oxygen 15-labeled water and positron emission tomography for analyzing myocardial blood flow (MBF). Conventional FA methods generating images from sinograms (sinoFA) are time-consuming, whereas FA can be performed on the reconstructed images (reconFA) in a fraction of time. We validated the MBF values obtained by reconFA versus sinoFA. Methods and Results  In 23 volunteers (mean age, 26.6±3.4 years) MBF was calculated from sinoFA and reconFA and blindly reanalyzed 1 month later by the same observer. Intraobserver agreement and reconFA-versus-sinoFA agreement were assessed according to Bland and Altman (BA). Reproducibility proved excellent for global sinoFA (r=0.968; P<.001; BA limits, −0.617 to 0.676 mL·min⁻¹·g⁻¹) and slightly superior for reconFA (r=0.979; P<.001; BA limits, −0.538 to 0.558 mL·min⁻¹·g⁻¹), with wider limits of agreement for segmental MBF from sinoFA (r=0.777; P<.001; BA limits, −1.676 to 1.656 mL·min⁻¹·g⁻¹) and reconFA (r=0.844; P<.001; BA limits, −1.999 to 1.992 mL·min⁻¹·g⁻¹). In addition, sinoFA and reconFA showed excellent correlation (r=0.975, P<.001) and agreement (BA limits, −0.528 to 0.648 mL·min⁻¹·g⁻¹) for global and segmental values (r=0.955; P<.001; BA limits, −1.371 to 1.491 mL·min⁻¹·g⁻¹). Conclusions  Use of reconFA allows rapid and reliable quantitative MBF assessment with O-15-labeled water. This study was supported by a grant from the Swiss National Science Foundation (professorship grant PP00A-114706).     

Mouse myocardial first‐pass perfusion MR imaging

A first‐pass myocardial perfusion sequence for mouse cardiac MRI is presented. A segmented ECG‐triggered acquisition combined with parallel imaging acceleration was used to capture the first pass of a Gd‐DTPA bolus through the mouse heart with a temporal resolution of 300–400 msec. The method was applied in healthy mice (N = 5) and in mice with permanent occlusion of the left coronary artery (N = 6). Baseline semiquantitative perfusion values of healthy myocardium showed excellent reproducibility. Infarct regions revealed a significant decrease in the semiquantitative myocardial perfusion values (0.05 ± 0.02) compared to remote myocardium (0.20 ± 0.04). Myocardial areas of decreased perfusion correlated well to infarct areas identified on the delayed‐enhancement scans. This protocol is a valuable addition to the mouse cardiac MRI toolbox for preclinical studies of ischemic heart disease. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Myocardial blood flow and perfusion reserve in infarcted patients with stress-induced normalization of previously negative T waves: A positron emission tomography study

Background  The clinical correlations between stress-induced normalization of previously negative T waves (NTW) and regional myocardial blood flow (MBF) regulation and tissue viability remain debatable. Methods and Results  To confirm these correlations, 14 patients with previous anterior myocardial infarction (13 Q waves) and NTW on baseline electrocardiographic precordial leads and 10 healthy subjects were studied by means of positron emission tomography (PET). The MBF values were obtained in the anterior infarcted myocardial regions in either resting condition or during dipyridamole infusion, using N-13 ammonia as a flow tracer. Seven subjects had normalization of NTW (Group 1) and 7 had persistent NTW (Group 2) during dipyridamole infusion. The resting MBF values were similar for both Group 1 and Group 2 (0.43±0.13 versus 0.51±0.15 mL·min⁻¹.g⁻¹, respectively; P=not significant) and were significantly lower than in the anterior myocardial regions of healthy subjects (1.03±0.23 mL·min⁻¹.g⁻¹, P<.001). After administration of dipyridamole, the MBF was significantly higher in Group 1 than in Group 2 (0.88±0.37 versus 0.55±0.17 mL·min⁻¹.g⁻¹, respectively; P<.05) and markedly lower than in healthy subjects (3.78±0.64 mL·min⁻¹.g⁻¹, respectively; P<.05) and markedly lower than in healthy subjects (3.78±0.64 mL·min⁻¹.g⁻¹, P<.001). Coronary reserves (dipyridamole/resting MBF) were 2.03±0.40 and 1.14±0.44 in Group 1 and Group 2, respectively (P<.002). Conclusion  Despite similar values of resting perfusion, infarcted dysfunctional areas with or without NTW during stress may present different regional MBF responses; normalization of NTW demonstrates higher coronary flow reserve than persistent NTW, suggesting a better preserved coronary microcirculatory function in the former, indicative of the presence of myocardial viability. Presented in part at the 3rd International Congress on Nuclear Cardiology, Florence, April 1997.     

Quantification of myocardial blood flow using model based analysis of first‐pass perfusion MRI: Extraction fraction of Gd‐DTPA varies with myocardial blood flow in human myocardium

For the absolute quantification of myocardial blood flow (MBF), Patlak plot‐derived K1 need to be converted to MBF by using the relation between the extraction fraction of gadolinium contrast agent and MBF. This study was conducted to determine the relation between extraction fraction of Gd‐DTPA and MBF in human heart at rest and during stress. Thirty‐four patients (19 men, mean age of 66.5 ± 11.0 years) with normal coronary arteries and no myocardial infarction were retrospectively evaluated. First‐pass myocardial perfusion MRI during adenosine triphosphate stress and at rest was performed using a dual bolus approach to correct for saturation of the blood signal. Myocardial K1 was quantified by Patlak plot method. Mean MBF was determined from coronary sinus flow measured by phase contrast cine MRI and left ventricle mass measured by cine MRI. The extraction fraction of Gd‐DTPA was calculated as the K1 divided by the mean MBF. The extraction fraction of Gd‐DTPA was 0.46 ± 0.22 at rest and 0.32 ± 0.13 during stress (P < 0.001). The relationship between extraction fraction (E) and MBF in human myocardium can be approximated as E = 1 ? exp(?(0.14 × MBF + 0.56)/MBF). The current results indicate that MBF can be accurately quantified by Patlak plot method of first‐pass myocardial perfusion MRI by performing a correction of extraction fraction. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.     

Comparison of intravascular and extracellular contrast media for absolute quantification of myocardial rest-perfusion using high-resolution MRI

Purpose:

To use the contrast agent gadofosveset for absolute quantification of myocardial perfusion and compare it with gadobenate dimeglumine (Gd‐BOPTA) using a high‐resolution generalized autocalibrating partially parallel acquisition (GRAPPA) sequence.

Materials and Methods:

Ten healthy volunteers were examined twice at two different dates with a first‐pass perfusion examination at rest using prebolus technique. We used a 1.5 T scanner and a 32 channel heart‐array coil with a steady‐state free precession (SSFP) true fast imaging with steady state precession (trueFISP) GRAPPA sequence (acceleration‐factor 3). Manual delineation of the myocardial contours was performed and absolute quantification was performed after baseline and contamination correction. At the first appointment, 1cc/4cc of the extracellular contrast agent Gd‐BOPTA were administered, on the second date, 1cc/4cc of the blood pool contrast agent (CA) gadofosveset. At each date the examination was repeated after a 15‐minute time interval.

Results:

Using gadofosveset perfusion the value (in cc/g/min) at rest was 0.66 ± 0.25 (mean ± standard deviation) for the first, and 0.55 ± 0.24 for the second CA application; for Gd‐BOPTA it was 0.62 ± 0.25 and 0.45 ± 0.23. No significant difference was found between the acquired perfusion values. The apparent mean residence time in the myocardium was 23 seconds for gadofosveset and 19.5 seconds for Gd‐BOPTA. Neither signal‐to‐noise ratio (SNR) nor subjectively rated image contrast showed a significant difference.

Conclusion:

The application of gadofosveset for an absolute quantification of myocardial perfusion is possible. Yet the acquired perfusion values show no significant differences to those determined with Gd‐BOPTA, maintained the same SNR and comparable perfusion values, and did not picture the expected concentration time‐course for an intravasal CA in the first pass. J. Magn. Reson. Imaging 2011;33:1047–1051. © 2011 Wiley‐Liss, Inc.     

Prebolus quantitative MR heart perfusion imaging.

The purpose of this study was to present the prebolus technique for quantitative multislice myocardial perfusion imaging. In quantitative MR perfusion studies the maximum contrast agent dose is limited by the requirement to determine the arterial input function (AIF). The prebolus technique consists of two consecutive contrast agent administrations. The AIF is determined from a first low-dose bolus, while a second, high-dose bolus allows the measurement of the myocardium with improved signal increase. The results of the prebolus technique using a multislice saturation recovery trueFISP sequence in healthy volunteers are presented. In comparison to a standard dose of 3 ml Gd-DTPA, perfusion values are maintained while the signal increase in the concentration time courses was considerably improved, accompanied by reduced standard deviations of the obtained perfusion values (0.72 +/- 0.13 ml/g/min for 1 ml/8 ml and 0.67 +/- 0.10 ml/g/min for 1 ml/12 ml Gd-DTPA, respectively).     

Quantitative contrast-enhanced first-pass cardiac perfusion MRI at 3 tesla with accurate arterial input function and myocardial wall enhancement

Purpose:

To develop, and validate in vivo, a robust quantitative first‐pass perfusion cardiovascular MR (CMR) method with accurate arterial input function (AIF) and myocardial wall enhancement.

Materials and Methods:

A saturation‐recovery (SR) pulse sequence was modified to sequentially acquire multiple slices after a single nonselective saturation pulse at 3 Tesla. In each heartbeat, an AIF image is acquired in the aortic root with a short time delay (TD) (50 ms), followed by the acquisition of myocardial images with longer TD values (～150–400 ms). Longitudinal relaxation rates (R₁ = 1/T₁) were calculated using an ideal saturation recovery equation based on the Bloch equation, and corresponding gadolinium contrast concentrations were calculated assuming fast water exchange condition. The proposed method was validated against a reference multi‐point SR method by comparing their respective R₁ measurements in the blood and left ventricular myocardium, before and at multiple time‐points following contrast injections, in 7 volunteers.

Results:

R₁ measurements with the proposed method and reference multi‐point method were strongly correlated (r > 0.88, P < 10^?5) and in good agreement (mean difference ±1.96 standard deviation 0.131 ± 0.317 / 0.018 ± 0.140 s^?1 for blood/myocardium, respectively).

Conclusion:

The proposed quantitative first‐pass perfusion CMR method measured accurate R₁ values for quantification of AIF and myocardial wall contrast agent concentrations in 3 cardiac short‐axis slices, in a total acquisition time of 523 ms per heartbeat. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.

     

A comparison of tracer kinetic models for T1‐weighted dynamic contrast‐enhanced MRI: Application in carcinoma of the cervix

The Tofts tracer kinetic models are often used to analyze dynamic contrast‐enhanced MRI data. They are derived from a general two‐compartment exchange model (2CXM) but assume negligible plasma mean transit time. The 2CXM estimates tissue plasma perfusion and capillary permeability‐surface area; the Tofts models estimate the transfer constant K^trans, which reflects a combination of these two parameters. The aims of this study were to compare the 2CXM and Tofts models and report microvascular parameters in patients with cervical cancer. Thirty patients were scanned pretreatment using a dynamic contrast‐enhanced MRI protocol with a 3 sec temporal resolution and a total scan duration of 4 min. Whole‐tumor parameters were estimated with both models. The 2CXM provided superior fits to the data for all patients (all 30 P values < 0.005), and significantly different parameter estimates were obtained (P < 0.01). K^trans (mean = 0.35 ± 0.26 min^?1) did not equal absolute values of tissue plasma perfusion (mean = 0.65 ± 0.56 mL/mL/min) or permeability‐surface area (mean = 0.14 ± 0.09 mL/mL/min) but correlated strongly with tissue plasma perfusion (r = 0.944; P = 0.01). Average plasma mean transit time, calculated with the 2CXM, was 22 ± 16 sec, suggesting the assumption of negligible plasma mean transit time is not appropriate in this dataset and the 2CXM is better suited for its analysis than the Tofts models. The results demonstrate the importance of selecting an appropriate tracer kinetic model in dynamic contrast‐enhanced MRI. Magn Reson Med 63:691–700, 2010. © 2010 Wiley‐Liss, Inc.     

Myocardial perfusion in type 2 diabetes with left ventricular hypertrophy: normalisation by acute angiotensin-converting enzyme inhibition

The purpose of this study was to assess whether acute angiotensin-converting enzyme (ACE) inhibition would improve myocardial perfusion and perfusion reserve in a subpopulation of normotensive patients with diabetes and left ventricular hypertrophy (LVH), both independent risk factors of coronary disease. Using positron emission tomography (PET), we investigated the response of regional myocardial perfusion to acute ACE inhibition with i.v. infusion of perindoprilat (vs saline infusion as control, minimum interval 3 days) in 12 diabetic patients with LVH. Myocardial perfusion was quantified with PET using nitrogen-13 ammonia infused at rest and during dipyridamole hyperaemia. Twelve healthy control subjects were included in the study, five of whom were also studied with perindoprilat. Mean blood pressure in normo-albuminuric, asymptomatic patients was 123±7/65±9 mmHg. Compared with controls, maximal perfusion was reduced in patients (1.8±0.6 vs 2.5±1.0 ml min^–1 g^–1; P<0.05), and perfusion reserve was also lower, at borderline significance (2.7±1.0 vs 3.6±1.3; P=0.059). During perindoprilat infusion, myocardial perfusion reserve in patients increased to 3.9±0.9 (P<0.001) due to normalisation of maximal perfusion (2.3±0.5 ml min^–1 g^–1, P<0.01). In the five control subjects both resting and hyperaemic perfusion remained unchanged during perindoprilat infusion. It is concluded that acute ACE inhibition with perindoprilat improves maximal achieved myocardial perfusion in non-hypertensive patients with diabetes and LVH.     

Model‐based blind estimation of kinetic parameters in dynamic contrast enhanced (DCE)‐MRI

A method to simultaneously estimate the arterial input function (AIF) and pharmacokinetic model parameters from dynamic contrast‐enhanced (DCE)‐MRI data was developed. This algorithm uses a parameterized functional form to model the AIF and k‐means clustering to classify tissue time‐concentration measurements into a set of characteristic curves. An iterative blind estimation algorithm alternately estimated parameters for the input function and the pharmacokinetic model. Computer simulations were used to investigate the algorithm's sensitivity to noise and initial estimates. In 12 patients with sarcomas, pharmacokinetic parameter estimates were compared with “truth” obtained from model regression using a measured AIF. When arterial voxels were included in the blind estimation algorithm, the resulting AIF was similar to the measured input function. The “true” K^trans values in tumor regions were not significantly different than the estimated values, 0.99 ± 0.41 and 0.86 ± 0.40 min^?1, respectively, P = 0.27. “True” k_ep values also matched closely, 0.70 ± 0.24 and 0.65 ± 0.25 min^?1, P = 0.08. When only tissue curves free of significant vascular contribution are used (v_p < 0.05), the resulting AIF showed substantial delay and dispersion consistent with a more local AIF such as has been observed in dynamic susceptibility contrast imaging in the brain. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Image‐based calculation of perfusion and oxyhemoglobin saturation in skeletal muscle during submaximal isometric contractions

The relative oxygen saturation of hemoglobin and the rate of perfusion are important physiological quantities, particularly in organs such as skeletal muscle, in which oxygen delivery and use are tightly coupled. The purpose of this study was to demonstrate the image‐based calculation of the relative oxygen saturation of hemoglobin and quantification of perfusion in skeletal muscle during isometric contractions. This was accomplished by establishing an empirical relationship between the rate of radiofrequency‐reversible dephasing and near‐infrared spectroscopy–observed oxyhemoglobin saturation (relative oxygen saturation of hemoglobin) under conditions of arterial occlusion and constant blood volume. A calibration curve was generated and used to calculate the relative oxygen saturation of hemoglobin from radiofrequency‐reversible dephasing changes measured during contraction. Twelve young healthy subjects underwent 300 s of arterial occlusion and performed isometric contractions of the dorsiflexors at 30% of maximal contraction for 120 s. Muscle perfusion was quantified during contraction by arterial spin labeling and measures of muscle T₁. Comparisons between the relative oxygen saturation of hemoglobin values predicted from radiofrequency‐reversible dephasing and that measured by near‐infrared spectroscopy revealed no differences between methods (P = 0.760). Muscle perfusion reached a value of 34.7 mL 100 g^?1 min^?1 during contraction. These measurements hold future promise in measuring muscle oxygen consumption in healthy and diseased skeletal muscle. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Measurement of both left ventricular function and regional myocardial perfusion with 133Xe in dogs

A technique to measure left ventricular (LV) function and myocardial perfusion was validated in 12 dogs. ¹³³Xe in saline was injected into the left atrium (LA) or LV and two data sets were obtained using gamma camera imaging: 1) A first pass gated scan for LV function; followed by 2) Sequential images for regional myocardial perfusion. LV ejection fraction and wall motion measurements from the ¹³³Xe blood pool images were compared to ejection fraction (r=0.88, P<0.01) and wall motion (r=0.83, P<0.01) data from ^99mTc labeled blood pool scans. The perfusion measurements obtained with the ¹³³Xe method were compared to microsphere data (r=0.79, P<0.01). Measurements after LV ¹³³Xe injection were similar to data following LA injection. Thus, quantitative assessment of global LV function, regional wall motion and myocardial perfusion is possible with LA or LV ¹³³Xe injection and gamma camera imaging.     

Quantitative contrast‐enhanced perfusion measurements of the human lung using the prebolus approach

Purpose

To investigate dynamic contrast‐enhanced MRI (DCE‐MRI) for quantification of pulmonary blood flow (PBF) and blood volume (PBV) using the prebolus approach and to compare the results to the global lung perfusion (GLP).

Materials and Methods

Eleven volunteers were examined by applying different contrast agent doses (0.5, 1.0, 2.0, and 3.0 mL gadolinium diethylene triamine pentaacetic acid [Gd‐DTPA]), using a saturation‐recovery (SR) true fast imaging with steady precession (TrueFISP) sequence. PBF and PBV were determined for single bolus and prebolus. Region of interest (ROI) evaluation was performed and parameter maps were calculated. Additionally, cardiac output (CO) and lung volume were determined and GLP was calculated as a contrast agent–independent reference value.

Results

The prebolus results showed good agreement with low‐dose single‐bolus and GLP: PBF (mean ± SD in units of mL/minute/100 mL) = single bolus 190 ± 73 (0.5‐mL dose) and 193 ± 63 (1.0‐mL dose); prebolus 192 ± 70 (1.0–2.0‐mL dose) and 165 ± 52 (1.0–3.0‐mL dose); GLP (mL/minute/100 mL) = 187 ± 34. Higher single‐bolus resulted in overestimated values due to arterial input function (AIF) saturation.

Conclusion

The prebolus approach enables independent determination of appropriate doses for AIF and tissue signal. Using this technique, the signal‐to‐noise ratio (SNR) from lung parenchyma can be increased, resulting in improved PBF and PBV quantification, which is especially useful for the generation of parameter maps. J. Magn. Reson. Imaging 2009;30:104–111. © 2009 Wiley‐Liss, Inc.     

Measurement of left ventricular ejection fraction from gated technetium-99m sestamibi myocardial images

Left ventricular ejection fraction (LVEF) and single-photon emission tomographic (SPET) imaging of the myocardium can be performed after a single technetium-99m sestamibi (MIBI) injection. Sixty patients underwent SPET imaging with MIBI. Immediately after SPET acquisition ECG-gated^99mTc-MIBI perfusion images were acquired using 24 planar images per R-R interval. A new method for measurement of LVEF from the ECG-gated 99mTc-MIBI perfusion images was developed. To validate the method, LVEF derived from MIBI perfusion images was compared with that from conventional radionuclide ventriculography in all 60 patients. Forty patients had evidence of myocardial infarction and 20 had normal perfusion on MIBI imaging. There was no statistically significant difference between LVEF computed from^99mTc-MIBI perfusion images and that from radionuclide ventriculography (r=0.7062,P<0.001). There was little difference associated with the technique (intraobserver variabilityr=0.9772,P<0.001). Interobserver variability was also good (r-0.8233,P<0.001). LVEF from^99mTc-MIBI perfusion images can be obtained at the same time as assessment of myocardial perfusion and in the same orientation and metabolism of the myocardium, thereby permitting more accurate and realistic prognosis and diagnosis in patients with coronary artery disease.     

MRI for the evaluation of regional myocardial perfusion in an experimental animal model

Myocardial perfusion was assessed in nine pigs using ultrafast gradient-echo MRI (.5 T, 15-mT/m gradients) at different levels of myocardial blood flow (range, .005–1.84 ml/min/g), generated either by adenosine infusion or by a mechanical occluder, and measured independently using radiolabeled microspheres. Sixty-four consecutive, ECG-triggered, diastolic, short axis images of the left ventricle were obtained during intravenous bolus injections (y = 30) of .05 mmol/kg of gadopentetate dimeglumine. Relative changes in peak intensity, time to peak intensity, washin slope, correlation coefficient, and cross-correlation coefficient were computed from the time-intensity curves obtained from four regions of interest, namely septal, anterior, lateral, and inferior walls. The values from the inferior wall acted as reference for evaluating relative changes in the other three regions. The cross-correlation coefficient (P < .001, r = 60) and the peak intensity (P < .001, r = .72) showed the best correlation with myocardial blood flow. The washin slope showed a weak positive trend (P < .05), but the low value of r (r = .28) indicated that the use of this parameter to predict flow was invalid; the correlation coefficient and time to peak intensity were not correlated ( P = ns). In conclusion, this study shows that it is possible to evaluate relative myocardial perfusion after the first pass of a an intravenously injected bolus of gadopentetate dimeglumine, using dynamic MRI on a conventional medium field MRI system. The cross-correlation coefficient and the peak intensity resulted in more efficient parameters to evaluate relative inhom-ogeneity of regional myocardial perfusion.     

Evaluation of iterative reconstruction (OSEM) versus filtered back-projection for the assessment of myocardial glucose uptake and myocardial perfusion using dynamic PET

Purpose Iterative reconstruction methods based on ordered-subset expectation maximisation (OSEM) has replaced filtered backprojection (FBP) in many clinical settings owing to the superior image quality. Whether OSEM is as accurate as FBP in quantitative positron emission tomography (PET) is uncertain. We compared the accuracy of OSEM and FBP for regional myocardial ¹⁸F-FDG uptake and ¹³NH₃ perfusion measurements in cardiac PET. Methods Ten healthy volunteers were studied. Five underwent dynamic ¹⁸F-FDG PET during hyperinsulinaemic–euglycaemic clamp, and five underwent ¹³NH₃ perfusion measurement during rest and adenosine-induced hyperaemia. Images were reconstructed using FBP and OSEM ± an 8-mm Gaussian post-reconstruction filter. Results Filtered and unfiltered images showed agreement between the reconstruction methods within ±2SD in Bland-Altman plots of K _i values. The use of a Gaussian filter resulted in a systematic underestimation of K _i in the filtered images of 11%. The mean deviation between the reconstruction methods for both unfiltered and filtered images was 1.3%. Agreement within ±2SD between the methods was demonstrated for perfusion rate constants up to 2.5 min⁻¹, corresponding to a perfusion of 3.4 ml g⁻¹ min⁻¹. The mean deviation between the two methods for unfiltered data was 2.7%, and for filtered data, 5.3%. Conclusion The ¹⁸F-FDG uptake rate constants showed excellent agreement between the two reconstruction methods. In the perfusion range up to 3.4 ml g⁻¹ min⁻¹, agreement between ¹³NH₃ perfusion obtained with OSEM and FBP was acceptable. The use of OSEM for measurement of perfusion values higher than 3.4 ml g⁻¹ min⁻¹ requires further evaluation.     

Sex differences in myocardial oxygen and glucose metabolism

Background  Both physiologic and pathophysiologic conditions affect the myocardium’s substrate use and, consequently, its structure, function, and adaptability. The effect of sex on myocardial oxygen, glucose, and fatty acid metabolism in humans is unknown. Methods and Results  We studied 25 young subjects (13 women and 12 men) using positron emission tomography, quantifying myocardial blood flow, myocardial oxygen consumption (MVO₂), and glucose and fatty acid extraction and metabolism. MVO₂ was higher in women than in men (5.74±1.08 μmol·g⁻¹·min⁻¹ vs 4.26±0.69 μmol·g⁻¹·min⁻¹,P<.005). Myocardial glucose extraction fraction and utilization were lower in women than in men (0.025±0.019 vs 0.062±0.028 [P<.001] and 133±96 nmol·g⁻¹·min⁻¹ vs 287±164 nmol·g⁻¹·min⁻¹ [P<.01], respectively). There were no sex differences in myocardial blood flow, fatty acid metabolism, or plasma glucose, fatty acid, or insulin levels. Female sex was an independent predictor of increased MVO₂ (P=.01) and decreased myocardial glucose extraction fraction and utilization (P<.005 andP<.05, respectively). Insulin sensitivity was an independent predictor of increased myocardial glucose extraction fraction and utilization (P<.01 andP=.01, respectively). Conclusions  Further studies are necessary to elucidate the mechanisms responsible for sex-associated differences in myocardial metabolism. However, the presence of such differences may provide a partial explanation for the observed sex-related differences in the prevalence and manifestation of a variety of cardiac disorders. This work was supported by grants HD145902 (Building Interdisciplinary Research in Women’s Health), RR00036 (General Clinical Research Center), DK56341 (Clinical Nutrition Research Unit), K23-HL077179, RO1-AG15466, PO1-HL13581, and HL73120 from the National Institutes of Health (Bethesda, Md) and grant 051893 (AHA02255732) from the Robert Wood Johnson Foundation (Princeton, NJ).     

Test‐retest variability of VO2max using total‐capture indirect calorimetry reveals linear relationship of VO2 and Power

This study aimed to analyze the intra‐individual variation in VO_2max of human subjects using total‐capture and free‐flow indirect calorimetry. Twenty‐seven men (27 ± 5 year; VO_2max 49‐79 mL?kg^?1?min^?1) performed two maximal exertion tests (CPETs) on a cycle ergometer, separated by a 7 ± 2 day interval. VO₂ and VCO₂ were assessed using an indirect calorimeter (Omnical) with total capture of exhalation in a free‐flow airstream. Thirteen subjects performed a third maximal exertion test using a breath‐by‐breath calorimeter (Oxycon Pro). On‐site validation was deemed a requirement. For the Omnical, the mean within‐subject CV for VO_2max was 1.2 ± 0.9% (0.0%‐4.4%) and for ergometer workload P _max 1.3 ± 1.3% (0%‐4.6%). VO_2max values with the Oxycon Pro were significantly lower in comparison with Omnical (P < 0.001; t test) with mean 3570 vs 4061 and difference SD 361 mL?min^?1. Validation results for the Omnical with methanol combustion were ?0.05 ± 0.70% (mean ± SD; n = 31) at the 225 mL?min^?1 VO₂ level and ?0.23 ± 0.80% (n = 31) at the 150 mL?min^?1 VCO₂ level. Results using gas infusion were 0.04 ± 0.75% (n = 34) and ?0.99 ± 1.05% (n = 24) over the respective 500‐6000 mL?min^?1 VO₂ and VCO₂ ranges. Validation results for the Oxycon Pro in breath‐by‐breath mode were ‐ 2.2 ± 1.6% (n = 12) for VO₂ and 5.7 ± 3.3% (n = 12) for VCO₂ over the 1000‐4000 mL?min^?1 range. On a Visual analog scale, participants reported improved breathing using the free‐flow indirect calorimetry (score 7.6 ± 1.2 vs 5.1 ± 2.7, P = 0.008). We conclude that total capturing free‐flow indirect calorimetry is suitable for measuring VO₂ even with the highest range. VO_2max was linear with the incline in P _max over the full range.