Design and development of a novel flexible ultra-short echo time (FUSE) sequence.

PURPOSE: To present the validation of a new Flexible Ultra-Short Echo time (FUSE) pulse sequence using a short-T2 phantom. METHODS: FUSE was developed to include a range of RF excitation pulses, trajectories, dimensionalities, and long-T2 suppression techniques, enabling real-time interchangeability of acquisition parameters. Additionally, we developed an improved 3D deblurring algorithm to correct for off-resonance artifacts. Several experiments were conducted to validate the efficacy of FUSE, by comparing different approaches for off-resonance artifact correction, variations in RF pulse and trajectory combinations, and long-T2 suppression techniques. All scans were performed on a 3 T system using an in-house short-T2 phantom. The evaluation of results included qualitative comparisons and quantitative assessments of the SNR and contrast-to-noise ratio. RESULTS: Using the capabilities of FUSE, we demonstrated that we could combine a shorter readout duration with our improved deblurring algorithm to effectively reduce off-resonance artifacts. Among the different RF and trajectory combinations, the spiral trajectory with the regular half-inc pulse achieves the highest SNRs. The dual-echo subtraction technique delivers better short-T2 contrast and superior suppression of water and agar signals, whereas the off-resonance saturation method successfully suppresses water and lipid signals simultaneously. CONCLUSION: In this work, we have validated the use of our new FUSE sequence using a short T2 phantom, demonstrating that multiple UTE acquisitions can be achieved within a single sequence. This new sequence may be useful for acquiring improved UTE images and the development of UTE imaging protocols.

caliPER: A software for blood-free parametric Patlak mapping using PET/MRI input function.

Routine clinical use of absolute PET quantification techniques is limited by the need for serial arterial blood sampling for input function and more importantly by the lack of automated pharmacokinetic analysis tools that can be readily implemented in clinic with minimal effort. PET/MRI provides the ability for absolute quantification of PET probes without the need for serial arterial blood sampling using image-derived input functions (IDIFs). Here we introduce caliPER, a modular and scalable software for simplified pharmacokinetic modeling of PET probes with irreversible uptake or binding based on PET/MR IDIFs and Patlak Plot analysis. caliPER generates regional values or parametric maps of net influx rate (Ki) using reconstructed dynamic PET images and anatomical MRI aligned to PET for IDIF vessel delineation. We evaluated the performance of caliPER for blood-free region-based and pixel-wise Patlak analyses of [18F] FDG by comparing caliPER IDIF to serial arterial blood input functions and its application in imaging brain glucose hypometabolism in Frontotemporal dementia. IDIFs corrected for partial volume errors including spill-out and spill-in effects were similar to arterial blood input functions with a general bias of around 6-8%, even for arteries <5 mm. The Ki and cerebral metabolic rate of glucose estimated using caliPER IDIF were similar to estimates using arterial blood sampling (<2%) and within limits of whole brain values reported in literature. Overall, caliPER is a promising tool for irreversible PET tracer quantification and can simplify the ability to perform parametric analysis in clinical settings without the need for blood sampling.

Assessment of hepatic arterial hemodynamics with 4D flow MRI: in vitro analysis of motion and spatial resolution related error and in vivo feasibility study in 20 volunteers.

OBJECTIVES: To assess the ability of four-dimensional (4D) flow MRI to measure hepatic arterial hemodynamics by determining the effects of spatial resolution and respiratory motion suppression in vitro and its applicability in vivo with comparison to two-dimensional (2D) phase-contrast MRI. METHODS: A dynamic hepatic artery phantom and 20 consecutive volunteers were scanned. The accuracies of Cartesian 4D flow sequences with k-space reordering and navigator gating at four spatial resolutions (0.5- to 1-mm isotropic) and navigator acceptance windows (± 8 to ± 2 mm) and one 2D phase-contrast sequence (0.5-mm in -plane) were assessed in vitro at 3 T. Two sequences centered on gastroduodenal and hepatic artery branches were assessed in vivo for intra - and interobserver agreement and compared to 2D phase-contrast. RESULTS: In vitro, higher spatial resolution led to a greater decrease in error than narrower navigator window (30.5 to -4.67% vs -6.64 to -4.67% for flow). In vivo, hepatic and gastroduodenal arteries were more often visualized with the higher resolution sequence (90 vs 71%). Despite similar interobserver agreement (κ = 0.660 and 0.704), the higher resolution sequence had lower variability for area (CV = 20.04 vs 30.67%), flow (CV = 34.92 vs 51.99%), and average velocity (CV = 26.47 vs 44.76%). 4D flow had lower differences between inflow and outflow at the hepatic artery bifurcation (11.03 ± 5.05% and 15.69 ± 6.14%) than 2D phase-contrast (28.77 ± 21.01%). CONCLUSION: High-resolution 4D flow can assess hepatic artery anatomy and hemodynamics with improved accuracy, greater vessel visibility, better interobserver reliability, and internal consistency. KEY POINTS: • Motion-suppressed Cartesian four-dimensional (4D) flow MRI with higher spatial resolution provides more accurate measurements even when accepted respiratory motion exceeds voxel size. • 4D flow MRI with higher spatial resolution provides substantial interobserver agreement for visualization of hepatic artery branches. • Lower peak and average velocities and a trend toward better internal consistency were observed with 4D flow MRI as compared to 2D phase-contrast.

Accelerated muscle and adipose tissue loss may predict survival in pancreatic cancer patients: the relationship with diabetes and anaemia.

Weight loss leading to cachexia is associated with poor treatment response and reduced survival in pancreatic cancer patients. We aim to identify indicators that allow for early detection that will advance our understanding of cachexia and will support targeted anti-cachexia therapies. A total of fifty pancreatic cancer patients were analysed for skeletal muscle and visceral adipose tissue (VAT) changes using computed tomography (CT) scans. These changes were related to physical characteristics, secondary disease states and treatment parameters. Overall, patients lost 1.72 (SD 3.29) kg of muscle and 1.04 (SD 1.08) kg of VAT during the disease trajectory (413 (SD 213) d). After sorting patients into tertiles by rate of VAT and muscle loss, patients losing VAT at > -0.40 kg/100 d had poorer survival outcomes compared with patients with < -0.10 kg/100 d of VAT loss (P= 0.020). Patients presenting with diabetes at diagnosis demonstrated significantly more and accelerated VAT loss compared with non-diabetic patients. In contrast, patients who were anaemic at the first CT scan lost significantly more muscle tissue and at accelerated rates compared with non-anaemic patients. Accelerated rates of VAT loss are associated with reduced survival. Identifying associated features of cachexia, such as diabetes and anaemia, is essential for the early detection of cachexia and may facilitate the attenuation of complications associated with cachexia.

Design of a Patient-Specific Respiratory-Motion-Simulating Platform for In Vitro 4D Flow MRI.

Four-dimensional (4D) flow magnetic resonance imaging (MRI) is a leading-edge imaging technique and has numerous medicinal applications. In vitro 4D flow MRI can offer some advantages over in vivo ones, especially in accurately controlling flow rate (gold standard), removing patient and user-specific variations, and minimizing animal testing. Here, a complete testing method and a respiratory-motion-simulating platform are proposed for in vitro validation of 4D flow MRI. A silicon phantom based on the hepatic arteries of a living pig is made. Under the free-breathing, a human volunteer's liver motion (inferior-superior direction) is tracked using a pencil-beam MRI navigator and is extracted and converted into velocity-distance pairs to program the respiratory-motion-simulating platform. With the magnitude displacement of about 1.3 cm, the difference between the motions obtained from the volunteer and our platform is ≤ 1 mm which is within the positioning error of the MRI navigator. The influence of the platform on the MRI signal-to-noise ratio can be eliminated even if the actuator is placed in the MRI room. The 4D flow measurement errors are respectively 0.4% (stationary phantom), 9.4% (gating window = 3 mm), 27.3% (gating window = 4 mm) and 33.1% (gating window = 7 mm). The vessel resolutions decreased with the increase of the gating window. The low-cost simulation system, assembled from commercially available components, is easy to be duplicated.

Radiation doses originating from diagnostic procedures during the treatment and follow-up of children and adolescents with malignant lymphoma.

Children with malignant lymphoma undergo many diagnostic procedures that involve exposure to ionising radiation. In addition, many, but by no means all, undergo further exposure to ionising radiation during radiotherapy. While therapeutic radiation exposures are prescribed, the extent of radiation exposure arising from diagnostic procedures utilised in such children is largely unknown. We completed an audit of the radiation doses arising from diagnostic imaging procedures performed in a cohort of children with malignant lymphoma. The cumulative effective radiation dose associated with radiographic and radioisotopic procedures was derived for 81 children and adolescents with malignant lymphoma during their diagnosis, treatment and follow-up. Thirty-eight of the 42 patients (90%) with Hodgkin lymphoma were alive at study termination, with follow-up periods ranging from 1.9 to 11.7 years (median 5.3). Thirty-three of the 39 patients (85%) with non-Hodgkin lymphoma were alive at study termination with follow-up periods ranging from 2.4 to 12.3 years (median 7.5). The median effective dose was 518 mSv for patients with Hodgkin lymphoma and 309 mSv for those with non-Hodgkin lymphoma. The maximum effective dose was 1.7 Sv. The principal contributors to the effective dose were computed tomography (CT) and nuclear medicine imaging procedures using (67)Ga. Protocols for the management of children and adolescents with malignant lymphoma should be reviewed in order to reduce the radiation detriment without loss of essential diagnostic information.

Navigation of Microrobots by MRI: Impact of Gravitational, Friction and Thrust Forces on Steering Success.

INTRODUCTION: Magnetic resonance navigation (MRN) uses MRI gradients to steer magnetic drug-eluting beads (MDEBs) across vascular bifurcations. We aim to experimentally verify our theoretical forces balance model (gravitational, thrust, friction, buoyant and gradient steering forces) to improve the MRN targeted success rate. METHOD: A single-bifurcation phantom (3 mm inner diameter) made of poly-vinyl alcohol was connected to a cardiac pump at 0.8 mL/s, 60 beats/minutes with a glycerol solution to reproduce the viscosity of blood. MDEB aggregates (25 ± 6 particles, 200 [Formula: see text]) were released into the main branch through a 5F catheter. The phantom was tilted horizontally from - 10° to +25° to evaluate the MRN performance. RESULTS: The gravitational force was equivalent to 71.85 mT/m in a 3T MRI. The gradient duration and amplitude had a power relationship (amplitude=78.717 [Formula: see text]). It was possible, in 15° elevated vascular branches, to steer 87% of injected aggregates if two MRI gradients are simultaneously activated ([Formula: see text] = +26.5 mT/m, [Formula: see text]= +18 mT/m for 57% duty cycle), the flow velocity was minimized to 8 cm/s and a residual pulsatile flow to minimize the force of friction. CONCLUSION: Our experimental model can determine the maximum elevation angle MRN can perform in a single-bifurcation phantom simulating in vivo conditions.

An evaluation of the diagnostic equivalence of 18F-FDG-PET between hybrid PET/MRI and PET/CT in drug-resistant epilepsy: A pilot study.

OBJECTIVE: Hybrid PET/MRI may improve detection of seizure-onset zone (SOZ) in drug-resistant epilepsy (DRE), however, concerns over PET bias from MRI-based attenuation correction (MRAC) have limited clinical adoption of PET/MRI. This study evaluated the diagnostic equivalency and potential clinical value of PET/MRI against PET/CT in DRE. MATERIALS AND METHODS: MRI, FDG-PET and CT images (n = 18) were acquired using a hybrid PET/MRI and a CT scanner. To assess diagnostic equivalency, PET was reconstructed using MRAC (RESOLUTE) and CT-based attenuation correction (CTAC) to generate PET/MRI and PET/CT images, respectively. PET/MRI and PET/CT images were compared qualitatively through visual assessment and quantitatively through regional standardized uptake value (SUV) and z-score assessment. Diagnostic accuracy and sensitivity of PET/MRI and PET/CT for SOZ detection were calculated through comparison to reference standards (clinical hypothesis and histopathology, respectively). RESULTS: Inter-reader agreement in visual assessment of PET/MRI and PET/CT images was 78 % and 81 %, respectively. PET/MRI and PET/CT were strongly correlated in mean SUV (r = 0.99, p < 0.001) and z-scores (r = 0.92, p < 0.001) across all brain regions. MRAC SUV bias was <5% in most brain regions except the inferior temporal gyrus, temporal pole, and cerebellum. Diagnostic accuracy and sensitivity were similar between PET/MRI and PET/CT (87 % vs. 85 % and 83 % vs. 83 %, respectively). CONCLUSION: We demonstrate here that PET/MRI with optimal MRAC can yield similar diagnostic performance as PET/CT. Nevertheless, further exploration of the potential added value of PET/MRI is necessary before clinical adoption of PET/MRI for epilepsy imaging.

A randomized trial of coenzyme Q10 in mitochondrial disorders.

Case reports and open-label studies suggest that coenzyme Q(10) (CoQ(10)) treatment may have beneficial effects in mitochondrial disease patients; however, controlled trials are warranted to clinically prove its effectiveness. Thirty patients with mitochondrial cytopathy received 1200 mg/day CoQ(10) for 60 days in a randomized, double-blind, cross-over trial. Blood lactate, urinary markers of oxidative stress, body composition, activities of daily living, quality of life, forearm handgrip strength and oxygen desaturation, cycle exercise cardiorespiratory variables, and brain metabolites were measured. CoQ(10) treatment attenuated the rise in lactate after cycle ergometry, increased (∽1.93 ml) VO(2)/kg lean mass after 5 minutes of cycling (P < 0.005), and decreased gray matter choline-containing compounds (P < 0.05). Sixty days of moderate- to high-dose CoQ(10) treatment had minor effects on cycle exercise aerobic capacity and post-exercise lactate but did not affect other clinically relevant variables such as strength or resting lactate.

Magnetic Resonance Navigation for Targeted Embolization in a Two-Level Bifurcation Phantom.

This work combines a particle injection system with our proposed magnetic resonance navigation (MRN) sequence with the intention of validating MRN in a two-bifurcation phantom for endovascular treatment of hepatocellular carcinoma (HCC). A theoretical physical model used to calculate the most appropriate size of the magnetic drug-eluting bead (MDEB, 200 µm) aggregates was proposed. The aggregates were injected into the phantom by a dedicated particle injector while a trigger signal was automatically sent to the MRI to start MRN which consists of interleaved tracking and steering sequences. When the main branch of the phantom was parallel to B0, the aggregate distribution ratio in the (left-left, left-right, right-left and right-right divisions was obtained with results of 8, 68, 24 and 0% respectively at baseline (no MRN) and increased to 84%, 100, 84 and 92% (p < 0.001, p = 0.004, p < 0.001, p < 0.001) after implementing our MRN protocol. When the main branch was perpendicular to B0, the right-left branch, having the smallest baseline distribution rate of 0%, reached 80% (p < 0.001) after applying MRN. Moreover, the success rate of MRN was always more than 92% at the 1st bifurcation in the experiments above.

Selective embolization with magnetized microbeads using magnetic resonance navigation in a controlled-flow liver model.

PURPOSE: The purpose of this study was to demonstrate the feasibility of using a custom gradient sequence on an unmodified 3T magnetic resonance imaging (MRI) scanner to perform magnetic resonance navigation (MRN) by investigating the blood flow control method in vivo, reproducing the obtained rheology in a phantom mimicking porcine hepatic arterial anatomy, injecting magnetized microbead aggregates through an implantable catheter, and steering the aggregates across arterial bifurcations for selective tumor embolization. MATERIALS AND METHODS: In the first phase, arterial hepatic velocity was measured using cine phase-contrast imaging in seven pigs under free-flow conditions and controlled-flow conditions, whereby a balloon catheter is used to occlude arterial flow and saline is injected at different rates. Three of the seven pigs previously underwent selective lobe embolization to simulate a chemoembolization procedure. In the second phase, the measured in vivo controlled-flow velocities were approximately reproduced in a Y-shaped vascular bifurcation phantom by injecting saline at an average rate of 0.6 mL/s with a pulsatile component. Aggregates of 200-µm magnetized particles were steered toward the right or left hepatic branch using a 20-mT/m MRN gradient. The phantom was oriented at 0°, 45°, and 90° with respect to the B0 magnetic field. The steering differences between left-right gradient and baseline were calculated using Fisher's exact test. A theoretical model of the trajectory of the aggregate within the main phantom branch taking into account gravity, magnetic force, and hydrodynamic drag was also designed, solved, and validated against the experimental results to characterize the physical limitations of the method. RESULTS: At an injection rate of 0.5 mL/s, the average flow velocity decreased from 20 ± 15 to 8.4 ± 5.0 cm/s after occlusion in nonembolized pigs and from 13.6 ± 2.0 to 5.4 ± 3.0 cm/s in previously embolized pigs. The pulsatility index measured to be 1.7 ± 1.8 and 1.1 ± 0.1 for nonembolized and embolized pigs, respectively, decreased to 0.6 ± 0.4 and 0.7 ± 0.3 after occlusion. For MRN performed at each orientation, the left-right distribution of aggregates was 55%, 25%, and 75% on baseline and 100%, 100%, and 100% (P < 0.001, P = 0.003, P = 0.003) after the application of MRN, respectively. According to the theoretical model, the aggregate reaches a stable transverse position located toward the direction of the gradient at a distance equal to 5.8% of the radius away from the centerline within 0.11 s, at which point the aggregate will have transited through a longitudinal distance of 1.0 mm from its release position. CONCLUSION: In this study, we showed that the use of a balloon catheter reduces arterial hepatic flow magnitude and variation with the aim to reduce steering failures caused by fast blood flow rates and low magnetic steering forces. A mathematical model confirmed that the reduced flow rate is low enough to maximize steering ratio. After reproducing the flow rate in a vascular bifurcation phantom, we demonstrated the feasibility of MRN after injection of microparticle aggregates through a dedicated injector. This work is an important step leading to MRN-based selective embolization techniques in humans.

Radiation dose in interventional cardiology procedures: urgent need for monitoring dose and establishing diagnostic reference levels.

The use of fluoroscopy in interventional cardiology procedures may expose patients to levels of radiation that manifest in unintended outcomes. Such outcomes may include skin injury and cancer. Currently, there is limited understanding of the magnitude of dose administered in an individual procedure. Canada does not have a formal policy for monitoring and recording the radiation dose administered to patients. This article reviews existing American, European and international policies for both monitoring administered radiation dose and patient follow-up. As a subsequent focus, this article presents the process for setting benchmarks for optimizing administered dose in the Hamilton Health Sciences Heart Investigation Unit.

Dogleg trust-region application in electrical impedance tomography.

This paper presents a trust-region implementation for image reconstruction of conductivity changes in electrical impedance tomography. A dogleg trust-region algorithm is applied in different cases to detect abnormalities. The dogleg algorithm approximates a Levenberg-Marquardt step within the trust region of the model function with a quadratic model. The comparison of Levenberg-Marquardt and dogleg algorithms is presented using the reconstructed images. This comparison of two techniques suggests the implementation of the dogleg method could result in the reduction of the execution time to less than 50% of that of the Levenberg-Marquardt algorithm without any quantifiable loss of quality of reconstructed images.

A novel approach for EIT regularization via spatial and spectral principal component analysis.

Electrical impedance tomography, EIT, is an imaging modality in which the internal conductivity distribution of an object is reconstructed based on voltage measurements on the boundary. This reconstruction problem is a nonlinear and ill-posed inverse problem, which requires regularization to ensure a stable solution. Most popular regularization approaches enforce smoothness in the inverse solution. In this paper, we propose a novel approach to build a subspace for regularization using a spectral and spatial multi-frequency analysis approach. The approach is based on the construction of a subspace for the expected conductivity distributions using principal component analysis. It is shown via simulations that the reconstructed images obtained with the proposed method are better than with the standard regularization approach. Using this approach, the percentage of misclassified finite elements was reduced up to twelve fold from the initial percentages after five iterations. The advantage of this technique is that prior information is extracted from the characteristic response of an object at different frequencies and spatially across the finite elements.

Changes in tissue water content measured with multiple-frequency bioimpedance and metabolism measured with 31P-MRS during progressive forearm exercise.

Multiple-frequency bioimpedance analysis (MFBIA) has been used to determine the cellular water composition in the human body. It is noninvasive and has demonstrated good correlations with other invasive measures of tissue water. However, the ability of this method to study transient changes in tissue water in specific muscle groups has not been explored. In this study, MFBIA was used to assess changes in forearm intracellular water (ICW), extracellular water (ECW), and total water (TW) in seven healthy volunteers during and after a progressive wrist flexion exercise protocol. In an identical trial, (31)P magnetic resonance spectroscopy ((31)P-MRS) was used to assess changes in intracellular pH and phosphocreatine (PCr). At the completion of exercise, forearm ICW increased 12.6% (SD 0.07, P = 0.003), TW increased 10.1% (SD 0.06, P = 0.005), and no significant changes were recorded for ECW. A significant correlation was found between the changes in intracellular pH and changes in ICW during exercise (r = -0.84, P = 0.018). With the use of regression analysis, average changes in P(i), PCr, and pH were found to predict changes in ICW (R(2) = 0.98, P = 0.005). In conclusion, MFBIA was sensitive enough to measure transient changes in the exercising forearm muscle. The changes seen were consistent with the hypothesis that intracellular acidification and PCr hydrolysis are important mediators of cellular osmolality and therefore may be responsible for the increased volume of water in the intracellular space that is often recorded after short-term high-intensity exercise.

Impact of audio/visual systems on pediatric sedation in magnetic resonance imaging.

PURPOSE: To evaluate the use of an audio/visual (A/V) system in pediatric patients as an alternative to sedation in magnetic resonance imaging (MRI) in terms of wait times, image quality, and patient experience. MATERIALS AND METHODS: Pediatric MRI examinations from April 8 to August 11, 2008 were compared to those 1 year prior to the installation of the A/V system. Data collected included age, requisition receive date, scan date, and whether sedation was used. A posttest questionnaire was used to evaluate patient experience. Image quality was assessed by two radiologists. RESULTS: Over the 4 months in 2008 there was an increase of 7.2% (115; P < 0.05) of pediatric patients scanned and a decrease of 15.4%, (67; P = 0.32) requiring sedation. The average sedation wait time decreased by 33% (5.8 months) (P < 0.05). Overall, the most positively affected group was the 4-10 years. The questionnaire resulted in 84% of participants expressing a positive reaction to the A/V system. Radiological evaluation revealed no changes in image quality between A/V users and sedates. CONCLUSION: The A/V system was a successful method to reduce patient motion and obtain a quality diagnostic MRI without the use of sedation in pediatric patients. It provided a safer option, a positive experience, and decreased wait times.

A DSP based multi-frequency 3D electrical impedance tomography system.

This paper describes the design of a multi-frequency Electrical impedance tomography (EIT) system, which provides a flexible mechanism for addressing up to 48 electrodes for imaging conductivity and permittivity distributions. A waveform generator based on a digital signal processor is used to produce sinusoidal waveforms with the ability to select frequencies in the range of 0.1-125 kHz. A software based phase-sensitive demodulation technique is used to extract amplitudes and phases from the raw measurements. Signal averaging and automatic gain control are also implemented in voltage and phase measurements. System performance was validated using a Cardiff-Cole Phantom and a saline filled cylindrical tank. The signal-to-noise ratio (SNR) using saline tank was greater than 60 dB and the maximum reciprocity error less than 4% for most frequencies. The common-mode rejection ratio (CMRR) was nearly 60 dB at 50 kHz. Image reconstruction performance was assessed using data acquired through a range of frequencies. This EIT system offers image reconstruction of both conductivity and permittivity distributions in three dimensions. The imaging results are presented in time difference and frequency difference imaging.

Dual X-ray absorptiometry model for characterizing water in the human forearm using multiple frequency bioimpedance analysis.

The purpose of this study was to develop a method for measuring intracellular (ICW) and extracellular water (ECW) in the human forearm using multiple frequency bioimpedance analysis (MFBIA). The approach was (i) to measure whole-body and forearm fat-free mass using dual X-ray absorptiometry (DXA); (ii) to use these measurements to estimate the fat-free mass (FFM) resistivity in both the forearm and in the whole body; and (iii) to use the ratio of these FFM resistivities to estimate the resistivity in the ICW and ECW compartments of the forearm. To first demonstrate the accuracy of the DXA software in differentiating lean body mass from fat and bone within a volume of tissue, ex-vivo bovine muscle tissue samples (n = 3) were used to approximate the physical properties of the human forearm. It was found that although the human whole-body software overestimates FFM, it was slightly underestimated by the small animal software. Using this technique, DXA measures of FFM were obtained from human volunteers (n = 11; age = 20 +/- 5 years; height = 170 +/- 12 cm; mass = 64 +/- 16 kg). These measures were used in conjunction with MFBIA measures of impedance of the whole body and of the forearm to determine the resistivities of the ICW and ECW compartments of the forearm, namely 375.8 +/- 25.2 ohms cm and 55.6 +/- 3.7 ohms cm, respectively. These were used in MFBIA equations to calculate the ICW, ECW, and total arm water (TAW) volumes of the human forearm. The calculated TAW and the ECW (+/- SD) volume fraction (667.29 +/- 200.15 mL and 0.169 +/- 0.039 mL, respectively) were in agreement with literature values. MFBIA results were compared with those obtained using nuclear magnetic resonance relaxometry (NMRR). MFBIA was performed on 15 subjects before and after an intense maximal handgrip exercise to estimate changes in water volume in muscle. Following exercise, the total and intracellular water of the forearm increased on average by 8% +/- 3% and 10% +/- 4% (mean +/- SD), respectively. In 5 healthy volunteers, MFBIA and NMRR were performed before and after a similar exercise of the forearm muscle. The changes with exercise of intracellular and total arm water volumes as measured by MFBIA were estimated. The percent increases in total water were found to be 9.4% +/- 4.2% and 9.4% +/- 2.6% and in intracellular water were found to be 10.6% +/- 4.6% and 12.0% +/- 2.8% (mean +/- SD) for NMRR and MFBIA, respectively. The results show that the exercise-induced changes in ICW and TAW determined with the MFBIA model are consistent with those observed with NMRR and radiotracer literature.

Determining the extent to which delayed-enhancement images reflect the partition-coefficient of Gd-DTPA in canine studies of reperfused and unreperfused myocardial infarction.

MRI after a constant infusion (CI) of Gd-DTPA has been used to identify the extent of myocardial infarction (MI). However, Gd-DTPA-enhanced "viability" imaging is more commonly performed with a bolus (for "delayed-enhancement" (DE) imaging). This study sought to determine how image delay time and time postinfarction influence the assessment of necrosis by DE. Both infusion and DE imaging was performed in dogs with reperfused (N = 6) or unreperfused (N = 4) MI. Estimates of the partition-coefficient of Gd-DTPA (lambda) with DE were compared with those calculated after 60 min of infusion, and the comparisons were repeated until 4 (reperfused) or 8 (unreperfused) weeks postinfarction. In reperfused animals, the concordance (Rc) between DE and infusion estimates of lambda was > 0.90 for most image delays > 8 min postinjection, for day 0 through week 3, with Rc at day 0 greater than at week 4 (P = 0.022). In unreperfused animals, there was an interaction between image delay time and time postinfarction (P < 0.001): Rc > 0.90 corresponded to longer image delays at week 1 than at weeks 4-8. Therefore, when image delays are selected appropriately, DE images can strongly reflect lambda and identify irreversibly injured myocardium.