Effects of short‐term training and detraining on VO2 kinetics: Faster VO2 kinetics response after one training session

This study examined the time course of short‐term training and detraining‐induced changes in oxygen uptake () kinetics. Twelve men (24 ± 3 years) were assigned to either a 50% or a 70% of training intensity (n = 6 per group). was measured breath‐by‐breath. Changes in deoxygenated‐hemoglobin concentration (Δ[HHb]) were measured by near‐infrared spectroscopy. Moderate‐intensity exercise on‐transient and Δ[HHb] were modeled with a mono‐exponential and normalized (0–100% of response) and the ratio was calculated. Similar changes in time constant of () were observed in both groups. The combined group mean for decreased ～14% (32.3 to 27.9 s, P < 0.05) after one training session with a further ～11% decrease (27.9 to 24.8 s, P < 0.05) following two training sessions. The remained unchanged throughout the remaining of training and detraining. A significant “overshoot” in the ratio was decreased (albeit not significant) after one training session, and abolished (P < 0.05) after the second one, with no overshoot observed thereafter. Speeding of kinetics was remarkably quick with no further changes being observed with continuous training or during detraining. Improve matching of local O₂ delivery to O₂ utilization is a mechanism proposed to influence this response.     

Relationship between changes in pulmonary kinetics and autonomic regulation of blood flow

Various regulatory mechanisms of pulmonary oxygen uptake () kinetics have been postulated. The purpose of this study was to investigate the relationship between vagal withdrawal, measured using RMSSDRR, the root mean square of successive differences in cardiac interval (RR) kinetics, a mediator of oxygen delivery, and kinetics. Forty‐nine healthy adults (23 ± 3 years; 72 ± 13 kg; 1.80 ± 0.08 m) performed multiple repeat transitions to moderate‐ and heavy‐intensity exercise. Electrocardiography, impedance cardiography, and pulmonary gas exchange parameters were measured throughout; time domain measures of heart rate variability were subsequently derived. The parameters describing the dynamic response of , cardiac output () and RMSSDRR were determined using a mono‐exponential model. During heavy‐intensity exercise, the phase II τ of was significantly correlated with the τ of RR (r = 0.36, P < 0.05), Q (r = 0.67, P < 0.05), and RMSSDRR (r = 0.38, P < 0.05). The τ describing the rise in Q explained 47% of the variation in τ, with 30% of the rate of this rise in Q explained by the τ of RR and RMSSDRR. No relationship was evident between kinetics and those of Q, RR, or RMSSDRR during moderate exercise. Vagal withdrawal kinetics support the concept of a centrally mediated oxygen delivery limitation partly regulating kinetics during heavy‐, but not moderate‐, intensity exercise.     

Aerobic capacity in speed‐power athletes aged 20–90 years vs endurance runners and untrained participants

We studied relationships between age and aerobic capacity in three groups of subjects adhering to different exercise modalities. A total of 203 men aged 20–90 years were examined: 52 speed‐power track and field athletes (SP), 89 endurance runners (ER) and 62 untrained individuals (UT). Maximal exercise characteristics were obtained during a graded treadmill test until exhaustion: oxygen uptake (), heart rate (HR_max), oxygen pulse (O₂ Pulse_max) and maximal distance (Dist_max). Information about training history and weekly training amount was collected. A linear model of regression was adopted. in SP was lower than in ER, but significantly higher than in UT. The cross‐sectional rates of decline in body mass‐adjusted and Dist_max were significantly smaller in SP than in ER and UT. About 80 years of age, the levels of and Dist_max reached similar values in SP and ER. The decline in HR_max, but not in O₂ Pulse_max was suggested as a cardiac adaptation accounting for between‐group differences in loss. Weekly training volume was a significant positive predictor of age‐related changes in aerobic capacity. In conclusion, not only endurance, but also speed‐power exercise appears adequate to ensure an elevated aerobic capacity at old age.     

Peak oxygen uptake and regional oxygenation in response to a 10‐day confinement to normobaric hypoxia

We investigated the effect of hypoxic acclimatization per se, without any concomitant influence of strenuous physical activity on muscle and cerebral oxygenation. Eight healthy male subjects participated in a crossover‐designed study. In random order, they conducted a 10‐day normoxic (CON) and a 10‐day hypoxic (EXP) confinement. Pre and post both CON and EXP confinements, subjects conducted two incremental‐load cycling exercises to exhaustion; one under normoxic, and the other under hypoxic (F_IO₂ = 0.154) conditions. Oxygen uptake (), ventilation (), and relative changes in regional hemoglobin oxygenation (Δ([HbO₂]) in the cerebral cortex and in the serratus anterior (SA) and vastus lateralis (VL) muscles were measured. No changes were observed in the CON confinement. Peak work rate and were similar pre and post in the EXP confinement, whereas increased in the EXP post normoxic and hypoxic trials (P < 0.05). The exercise‐induced drop in VL Δ[HbO₂] was less in the post‐ than pre‐EXP trial by 4.0 ± 0.4 and 4.2 ± 0.6 μM during normoxic and hypoxic exercise, respectively. No major changes were observed in cerebral or SA oxygenation. These results demonstrate that a 10‐day hypoxic exposure without any concomitant physical activity had no effect on normoxic or hypoxic , despite the enhanced VL oxygenation.     

A 4‐week instructed minimalist running transition and gait‐retraining changes plantar pressure and force

The purpose of this study is to compare changes in plantar pressure and force using conventional running shoes (CRS) and minimalist footwear (MFW) pre and post a 4‐week MFW familiarization period. Ten female runners (age: 21 ± 2 years; stature: 165.8 ± 4.5 cm; mass: 55.9 ± 3.2 kg) completed two 11 km/h treadmill runs, 24 hours apart, in both CRS and MFW (pretest). Plantar data were measured using sensory insoles for foot strike patterns, stride frequency, mean maximum force (), mean maximum pressure () and eight mean maximum regional pressures. Subjects then completed a 4‐week familiarization period consisting of running in MFW and simple gait‐retraining, before repeating the tests (posttest). During the pretests, 30% of subjects adopted a forefoot strike in MFW, following familiarization this increased to 80%; no change occurred in CRS. A significant decrease in in both MFW and CRS (P = 0.024) was observed from pre‐post, and a significant decrease in heel pressures in MFW. was higher in MFW throughout testing (P < 0.001).A 4‐week familiarization to MFW resulted in a significant reduction in in both the CRS and MFW conditions, as well as a reduction in heel pressures. Higher was observed throughout testing in the MFW condition.     

Faster pulmonary oxygen uptake kinetics in children vs adults due to enhancements in oxygen delivery and extraction

This study aimed to examine if the faster pulmonary oxygen uptake (VO_2p) phase 2 in children could be explained by increased O ₂ availability or extraction at the muscle level. For that purpose, O ₂ availability and extraction were assessed using deoxyhemoglobin (HHb) estimated by near‐infrared spectroscopy during moderate‐intensity constant load cycling exercise in children and young adults. Eleven prepubertal boys and 12 men volunteered to participate in the study. They performed one maximal graded exercise to determine the power associated with the gas exchange threshold (GET) and four constant load exercises at 90% of GET. VO_2p and HHb were continuously monitored. VO_2p, HHb, and estimated capillary blood flow () kinetics were modelled after a time delay and characterized by the time to achieve 63% of the amplitude (τ) and by mean response time (MRT: time delay + τ), respectively. Mean values of τ for VO_2p (P < 0.001), of MRT for HHb (P < 0.01) and of MRT for (P < 0.001) were significantly shorter in children. Faster VO_2p kinetics have been shown in children; these appear due to both faster O ₂ extraction and delivery kinetics as indicated by faster HHb and kinetics, respectively.     

A steep ramp test is valid for estimating maximal power and oxygen uptake during a standard ramp test in type 2 diabetes

A short maximal steep ramp test (SRT, 25 W/10 s) has been proposed to guide exercise interventions in type 2 diabetes, but requires validation. This study aims to (a) determine the relationship between W_max and reached during SRT and the standard ramp test (RT); (b) obtain test‐retest reliability; and (c) document electrocardiogram (ECG) abnormalities during SRT. Type 2 diabetes patients (35 men, 26 women) performed a cycle ergometer‐based RT (women 1.2; men 1.8 W/6 s) and SRT on separate days. A random subgroup (n = 42) repeated the SRT. ECG, heart rate, and were monitored. W_max during RT: 193 ± 63 (men) and 106 ± 33 W (women). W_max during SRT: 193 ± 63 (men) and 188 ± 55 W (women). The relationship between RT and SRT was described by men RT (mL/min) = 152 + 7.67 × W_max SRT1 (r: 0.859); women RT (mL/min) = 603 + 4.75 × W_max SRT1 (r: 0.771); intraclass correlation coefficients between first (SRT1) and second SRT W_max (SRT2) were men 0.951 [95% confidence interval (CI) 0.899–0.977] and women 0.908 (95% CI 0.727–0.971). No adverse events were noted during any of the exercise tests. This validation study indicates that the SRT is a low‐risk, accurate, and reliable test to estimate maximal aerobic capacity during the RT to design exercise interventions in type 2 diabetes patients.     

Reduced oxygen cost of running is related to alignment of the resultant GRF and leg axis vector: A pilot study

This pilot study investigated whether a 10‐week running program (10wkRP), which reduced the oxygen cost of running, affected resultant ground reaction force (GRF), leg axis alignment, joint moment characteristics, and gear ratios. Ten novice, female runners completed a 10wkRP. Running kinematics and kinetics, in addition to oxygen consumption () during steady‐state running, were recorded pre‐ and post‐10wkRP. decreased (8%) from pre‐10wkRP to post‐10wkRP. There was a better alignment of the resultant GRF and leg axis at peak propulsion post‐10wkRP compared with pre‐10wkRP (10.8 ± 4.9 vs 1.6 ± 1.2°), as the resultant GRF vector was applied 7 ± 0.6° (P = 0.008) more horizontally. There were shorter external ankle moment arms (24%) and smaller knee extensor moments (23%) at peak braking post‐10wkRP. The change in was associated with the change in alignment of the resultant GRF and leg axis (r_s = 0.88, P = 0.003). As runners became more economical, they exhibited a more aligned resultant GRF vector and leg axis at peak propulsion. This appears to be a self‐optimization strategy that may improve performance. Additionally, changes to external ankle moment arms indicated beneficial low gear ratios were achieved at the time of peak braking force.     

Effects of reduced‐volume of sprint interval training and the time course of physiological and performance adaptations

This study sought to determine the time course of training adaptations to two different sprint interval training programmes with the same sprint: rest ratio (1:8) but different sprint duration. Nine participants (M: 7; F: 2) were assigned to 15‐second training group (15TG) consisting of 4‐6 × 15‐second sprints interspersed with 2‐minute recovery, whereas eight participants (M: 5; F: 3) were assigned to 30‐second training group (30TG) consisting of 4‐6 × 30 second sprints interspersed with 4‐minute recovery. Both groups performed their respective training twice per week over 9 weeks and changes in peak oxygen uptake () and time to exhaustion (TTE) were assessed every 3 weeks. Additional eight healthy active adults (M: 6; F: 2) completed the performance assessments 9 weeks apart without performing training (control group, CON). Following 9 weeks of training, both groups improved (15TG: 12.1%; 30TG: 12.8%, P<.05) and TTE (15TG: 16.2%; 30TG: 12.8%, P<.01) to a similar extent. However, while both groups showed the greatest gains in at 3 weeks (15TG: 16.6%; 30TG: 17.0%, P<.001), those in TTE were greatest at 9 weeks. CON did not change any of performance variables following 9 weeks. This study demonstrated that while the changes in cardiorespiratory function plateau within several weeks with sprint interval training, endurance capacity (TTE) is more sensitive to such training over a longer time frame in moderately‐trained individuals. Furthermore, a 50% reduction in sprint duration does not diminish overall training adaptations over 9 weeks.     

Cardiorespiratory fitness and heart rate recovery in obese premenopausal women

Post‐exercise heart rate recovery (HRR) has been proposed as a measure of cardiac autonomic dysfunction in apparently healthy adults. We aimed to determine the effects of a lifestyle intervention on HRR among clinically obese premenopausal women. A randomized controlled trial was conducted to investigate the effects of a 3‐month non‐dieting lifestyle intervention program on cardiorespiratory fitness (CRF) and HRR among healthy clinically obese premenopausal women. Thirty‐one were randomly assigned to 3‐month intensive lifestyle intervention and 31 served as controls. Sixty‐one participants performed a maximal treadmill walking test with metabolic gas exchange. Baseline anthropometric measures were closely related to HRR at 1 min, which may indicate reduced parasympathetic reactivation. Post‐exercise HRR at 60 s (HRR60) increased from 21.3 ± 6.2 to 27.8 ± 10.2 bpm in the intervention group compared with a smaller reduction (26.8 ± 12.3 to 24.5 ± 9.9 bpm) in controls (test for interaction P = 0.0001). HRR120 showed a significant effect of time (P = 0.0002) with no significant interaction with lifestyle intervention. A significant increase in was evident in the lifestyle group (21.6 to 23.6 mL/kg/min) compared with a modest reduction in the controls (22.6 to 21.6 mL/kg/min; test for interaction, P = 0.001). Clinically obese healthy premenopausal women achieved significant improvements in HRR60 and following a 3‐month intensive lifestyle intervention.     

Influence of 4 weeks of bovine colostrum supplementation on neutrophil and mucosal immune responses to prolonged cycling

Bovine colostrum (COL) has been advocated as a nutritional countermeasure to exercise‐induced immune dysfunction. The aims of this study were to identify the effects of 4 weeks of COL supplementation on neutrophil responses and mucosal immunity following prolonged exercise. In a randomized double‐blind, parallel group design, participants [age 28 ± 8 years; body mass 79 ± 7 kg; height 182 ± 6 cm; maximal oxygen uptake () 55 ± 9 mL/kg/min] were assigned to 20 g per day of COL (n = 10) or an isoenergetic/isomacronutrient placebo (PLA; n = 10) for 4 weeks. Venous blood and unstimulated saliva samples were obtained before and after 2.5 h of cycling at 15% Δ (～55–60% ). A significantly greater formyl‐methionyl‐leucyl phenylalanine‐stimulated oxidative burst was observed in the COL group compared with PLA group (P < 0.05) and a trend toward a time × group interaction (P = 0.06). However, there was no effect of COL on leukocyte trafficking, phorbol‐12‐myristate‐13‐acetate‐stimulated oxidative burst, bacterial‐stimulated neutrophil degranulation, salivary secretory IgA, lactoferrin or lysozyme (P > 0.05). These findings provide further evidence of the beneficial effects of COL on receptor‐mediated stimulation of neutrophil oxidative burst in a model of exercise‐induced immune dysfunction.     

Stimulating whole saliva affects the response of antimicrobial proteins to exercise

This study investigated the salivary secretion rates of antimicrobial proteins in response to prolonged, exhaustive exercise in both stimulated (STIM) and unstimulated (UNSTIM) saliva flow sample methods. Twenty‐four trained men cycled for 2.5 h at 60% and then to exhaustion at 75% . Timed collections of whole saliva were made before exercise, mid‐exercise, at the end of the moderate exercise bout and post‐exhaustive exercise. After each UNSTIM collection, a STIM sample was collected following chewing flavored gum for 1 min. Saliva was analysed for lysozyme, α‐amylase and salivary immunoglobulin A (s‐IgA), and secretion rates were calculated. Saliva flow was 156% higher in STIM compared with UNSTIM (P < 0.001) and decreased with exercise in STIM only (P < 0.001). Exercise increased lysozyme and α‐amylase levels and secretion rates were 144% higher and 152% higher in STIM compared with UNSTIM for lysozyme and α‐amylase, respectively (all P < 0.001). S‐IgA concentration (P < 0.05) and secretion rate (P < 0.001) increased with exercise but were both lower in STIM compared with UNSTIM (P < 0.001). In conclusion, a STIM saliva flow collection during exercise by chewing flavored gum increased the quantity of saliva and the secretion of lysozyme and α‐amylase, but had a limited impact on the secretion of s‐IgA.     

The effect of ageing and fitness on thermoregulatory response to high-intensity exercise

There are conflicting reports as to whether ageing causes a decreased thermoregulatory response, or if observed differences in previous studies are related to maximal aerobic capacity or training status. This study hypothesized that thermoregulatory response to severe exercise‐heat stress is maintained with ageing when both young and older subjects are well trained. Seven older highly trained (OHT = 51–63 years) cyclists were matched with two groups of young cyclists (19–35 years); one group matched for training status [young highly trained (YHT) participants, n = 7] and another for [young moderately trained (YMT), n = 7]. Each participant exercised at 70% in hot (35°C, 40% relative humidity) and thermoneutral (20°C, 40% relative humidity) conditions for 60 min. Final rectal temperature in the thermoneutral and heat (YHT = 39.13 ± 0.33°C, YMT = 39.11 ± 0.38°C, OHT = 39.11 ± 0.51°C) tests were similar between all three groups. %HR_max (heat test: YHT = 92.5 ± 6.0%, YMT = 91.6 ± 4.4%, OHT = 88.6 ± 5.1%), skin temperature, and cutaneous vascular conductance during cycling in both environments were similar between groups. Lower sweat loss and evaporative heat loss in the heat test in the OHT and YMT groups when compared with the YHT group reflected lower metabolic heat production. The findings of the present study suggest that thermoregulatory response is maintained with age among highly trained subjects.     

Heritability estimates of endurance‐related phenotypes: A systematic review and meta‐analysis

The aim of this study was to clarify heritability estimates for endurance‐related phenotypes and the underlying factors affecting these estimates. A systematic literature search was conducted for studies reporting heritability estimates of endurance‐related phenotypes using the PubMed database (up to 30 September 2016). Studies that estimated the heritability of maximal oxygen uptake (), submaximal endurance phenotypes, and endurance performance were selected. The weighted mean heritability for endurance‐related phenotypes was calculated using a random‐effects model. A total of 15 studies were selected via a systematic review. Meta‐analysis revealed that the weighted means of the heritability of absolute values and those adjusted for body weight and for fat‐free mass were 0.68 (95% CI : 0.59‐0.77), 0.56 (95% CI : 0.47‐0.65), and 0.44 (95% CI : 0.13‐0.75), respectively. There was a significant difference in the weighted means of the heritability of across these different adjustment methods (P  < .05). Moreover, there was evidence of statistical heterogeneity in the heritability estimates among studies. Meta‐regression analysis revealed that sex could partially explain the heterogeneity in the heritability estimates adjusted by body weight. For submaximal endurance phenotypes and endurance performance, the weighted mean heritabilities were 0.49 (95% CI : 0.33‐0.65) and 0.53 (95% CI : 0.27‐0.78), respectively. There was statistically significant heterogeneity in the heritability estimates reported among the studies, and we could not identify the specific factors explaining the heterogeneity. Although existing studies indicate that genetic factors account for 44%‐68% of the variability in endurance‐related phenotypes, further studies are necessary to clarify these values.     

Adiabatic RF pulse design for Bloch‐Siegert B mapping

The Bloch–Siegert (B–S) mapping method has been shown to be fast and accurate, yet it suffers from high Specific Absorption Rate (SAR) and moderately long echo time. An adiabatic RF pulse design is introduced here for optimizing the off‐resonant B–S RF pulse to achieve more B–S measurement sensitivity for a given pulse width. The extra sensitivity can be used for higher angle‐to‐noise ratio maps or traded off for faster scans. Using numerical simulations and phantom experiments, it is shown that a numerically optimized 2‐ms adiabatic B‐S pulse is 2.5 times more efficient than a conventional 6‐ms Fermi‐shaped B–S pulse. The adiabatic B–S pulse performance is validated in a phantom, and in vivo brain mapping at 3T and 7T are shown. Magn Reson Med 70:829–835, 2013. © 2012 Wiley Periodicals, Inc.     

Sex differences in fitness and cardiac function during exercise in adolescents with chronic fatigue

Females demonstrate less robust Frank‐Starling mechanism with respect to cardiac preload than males at rest. We asked whether this phenomenon would also affect cardiac performance during exercise. We hypothesized that stroke volume (SV ) response to exercise would be more limited in deconditioned females such that cardiac output would be mainly rate dependent, compared with males. We conducted a chart audit of clinical exercise tests performed by adolescents with chronic fatigue. Oxygen uptake () was measured breath‐by‐breath at rest and during cycle ergometry, while cardiac output was measured by acetylene rebreathing at rest plus 2‐3 subthreshold workloads. SV response was analyzed in two ways: after normalization for body surface area (SV index, SVI ) and as percentage change from resting values. Among 304 adolescents (78% females) with chronic fatigue, 189 (80%) of 236 females and 52 (76%) of 68 males were deconditioned (peakO₂ <90% predicted). Heart rate trajectory during exercise was steeper for unfit than fit females, 70 vs 61 beat·min⁻¹ per L·min⁻¹ , (P =.003); but not for males, 47 vs 42 beat·min⁻¹ per L·min⁻¹ (P =.23). The highest measured SVI did not differ between unfit vs fit females (42.8 vs 41.5 mL·m⁻², P =.39) while fit males showed larger SV during exercise than their unfit peers (highest SVI 55.9 vs 48.0 mL·m⁻², P =.014). Both qualitative and quantitative sex differences exist in SV responses to exercise among chronically fatigued adolescents, suggesting volume loading may be more efficacious in girls.     

A single‐scan T mapping method based on two gradient‐echo images with compensation for macroscopic field inhomogeneity

T‐weighted imaging (TWI) and quantitative T mapping with conventional gradient‐echo acquisition are often hindered by severe signal loss induced by macroscopic field inhomogeneity. Various z‐shimming approaches have been developed for TWI/T mapping in which the effects of macroscopic field inhomogeneity are suppressed while the sensitivity of T‐related signal intensity to alterations in the microscopic susceptibility is maintained. However, this is often done at the cost of significantly increased imaging time. In this work, a fast T mapping method with compensation for macroscopic field inhomogeneity was developed. A proton density‐weighted image and a composite T‐weighted image, both of which were essentially free from macroscopic field inhomogeneity‐induced signal loss, were used for the T calculation. The composite T‐weighted image was reconstructed from a number of gradient‐echo images acquired with successively incremented z‐shimming compensation. Because acquisition of the two images and z‐shimming compensation were realized in a single scan, the total acquisition time for obtaining a T map with the proposed method is the same as the time taken for a conventional multiecho gradient‐echo imaging sequence without compensation. The performance and efficiency of the proposed method were demonstrated and evaluated at 4.7 T. Magn Reson Med 60:1388–1395, 2008. © 2008 Wiley‐Liss, Inc.     

Ultrashort T relaxometry for quantitation of highly concentrated superparamagnetic iron oxide (SPIO) nanoparticle labeled cells

A new method was developed to measure ultrashort T relaxation in tissues containing a focal area of superparamagnetic iron oxide (SPIO) nanoparticle‐labeled cells in which the T decay is too short to be accurately measured using regular gradient echo T mapping. The proposed method utilizes the relatively long T₂ relaxation of SPIO‐labeled cells and acquires a series of spin echo images with the readout echo shifted to sample the T decay curve. MRI experiments in phantoms and rats with SPIO‐labeled tumors demonstrated that it can detect ultrashort T down to 1 ms or less. The measured T values were about 10% higher than those from the ultrashort TE (UTE) technique. The shorter the TE, the less the measurements deviated from the UTE T mapping. Combined with the regular T mapping, this technique is expected to provide quantitation of highly concentrated iron‐labeled cells from direct cell transplantation. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

B(1) mapping with selective pulses

Knowledge of B distribution is crucial for many applications, such as quantitative MRI. A novel method has been developed to improve the accuracy of the conventionally applied double‐angle method for B mapping. It solves the remaining issues raised by the use of selective pulses for slice selection to accelerate the acquisition process. A general approach for reconstructing B maps is presented first. It takes B‐induced slice profile distortions over off‐resonance frequencies into account. It is then shown how the ratio between the prescribed flip angles can be adjusted to reach a compromise between the level of noise propagated onto B maps and the width of the range in which the field can be mapped. Lastly, several solutions are proposed for reducing the B‐dependent pollution of regions distal to the image slice which participates significantly in the inaccuracy of B mapping. These methods were experimentally tested by comparison with gold standard B maps obtained on a phantom using a non‐selective and thus much slower technique. As they are independent and lead to significant improvements, these solutions can be combined to achieve high precision and fast B mapping using spin‐echo DAM. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.     

Validation of MRI biomarkers of hepatic steatosis in the presence of iron overload in the ob/ob mouse

Purpose:

To validate the utility and performance of a T correction method for hepatic fat quantification in an animal model of both steatosis and iron overload.

Materials and Methods:

Mice with low (n = 6), medium (n = 6), and high (n = 8) levels of steatosis were sedated and imaged using a chemical shift‐based fat‐water separation method to obtain magnetic resonance imaging (MRI) fat‐fraction measurements. Imaging was performed before and after each of two superparamagnetic iron oxide (SPIO) injections to create hepatic iron overload. Fat‐fraction maps were reconstructed with and without T correction. Fat‐fraction with and without T correction and T measurements were compared after each injection. Liver tissue was harvested and imaging results were compared to triglyceride extraction and histology grading.

Results:

Excellent correlation was seen between MRI fat‐fraction and tissue‐based fat quantification. Injections of SPIOs led to increases in R (=1/T). Measured fat‐fraction was unaffected by the presence of iron when T correction was used, whereas measured fat‐fraction dramatically increased without T correction.

Conclusion:

Hepatic fat‐fraction measured using a T‐corrected chemical shift‐based fat‐water separation method was validated in an animal model of steatosis and iron overload. T correction enables robust fat‐fraction estimation in both the presence and absence of iron, and is necessary for accurate hepatic fat quantification. J. Magn. Reson. Imaging 2012;35:844–851. © 2011 Wiley Periodicals, Inc.