Anaesthesia for Pancreatic Surgery.

This article provides a broad perspective on the salient perioperative issues encountered when caring for patients undergoing pancreatic surgery in the setting of pancreatic cancer. It describes the epidemiology of pancreatic cancer, the indications for and evolution of pancreatic resection surgery, the challenges faced perioperatively including patient selection, optimization, anesthetic considerations, postoperative analgesia, fluid management, and nutrition and discusses some of the common complications and their management. It finishes by outlining the future directions for research and development required to continue improving outcomes for these patients.

Modifying the Stress Response - Perioperative Considerations and Controversies.

The idea that perioperative outcomes may be improved through the implementation of measures that modify the surgical stress response has been around for several decades. Many techniques have been trialled with varying success. In addition, how the response to modification is measured, what constitutes a positive result and how this translates into clinical practice is the subject of debate. Modification of the stress response is the principal tenet behind the enhanced recovery after surgery (ERAS) movement which has seen the development of guidelines for perioperative care across a variety of surgical specialties bringing with them significant improvements in outcomes.

Anaesthesia for Hepatic Resection Surgery.

This article will focus on the perioperative management of hepatic resection for colorectal cancer (CRC) liver metastases (CLRMs) (the liver is the dominant metastatic site for CRC) within the context of the Enhanced Recovery After Surgery (ERAS) paradigm. It discusses the epidemiology and outcomes along with the history of hepatic resection surgery and pertinent anatomy. The discussion of the preoperative phase includes patient selection, assessment of liver functional status, and new developments in prehabilitation. The intraoperative phase details developments in surgical and anesthetic techniques to minimize liver hemorrhage and reduce the risk of postoperative hepatic failure. Newer analgesic options are included. Management of potential complications is outlined in the postoperative section followed by a description of current evidence for ERAS and future directions.

T(1rho) relaxation can assess longitudinal proteoglycan loss from articular cartilage in vitro.

Objective To assess the correlation between changes in spin-lattice relaxation in the rotating frame (T(1rho)) and proteoglycan (PG) loss from bovine articular cartilage and to demonstrate the feasibility of performing T(1rho) MR imaging on a 1.5T clinical scanner. Design MR relaxation times (T(1rho), T(2) and T(1)) were measured from excised cartilage plugs (N=3) before and after two sequential digestions with trypsin on a 2T whole-body magnet. Proteoglycan and collagen loss induced by the trypsin digestion was measured using standard biochemical techniques. The correlation between changes in relaxation times and PG loss were tested with regression analysis. T(1rho) MRI was also performed on a clinical 1.5T MRI system to determine whether the spatial distribution of PG loss could be detected. The MRI results were compared with histology sections of native and PG-depleted tissue. Results Increase in T(1rho) relaxation times correlated with PG loss (R(2)=0.81). T(1rho) measurements alone were indicative of PG loss (R(2)=0.8), the addition of T1 and T2 data into the statistical model did not improve the correlation substantially (R(2)=0.83). T(1rho)-weighted imaging demonstrated a hyperintense lamina at the articular surface of the digested tissue, which was subjected to trypsin digestion that correlated with a superficial zone of PG loss observed on histological sections. Conclusion The results of this study demonstrate that T(1rho) relaxation changes are correlated with PG loss in vitro. Furthermore, T(1rho) measurements alone can be used to indicate PG loss data. T(1rho) MRI may thus be developed into a useful adjunct to existing techniques for the evaluation of cartilage disease.

1H spectroscopy without solvent suppression: characterization of signal modulations at short echo times.

While most proton ((1)H) spectra acquired in vivo utilize selective suppression of the solvent signal for more sensitive detection of signals from the dilute metabolites, recent reports have demonstrated the feasibility and advantages of collecting in vivo data without solvent attenuation. When these acquisitions are performed at short echo times, the presence of frequency modulations of the water resonance may become an obstacle to the identification and quantitation of metabolite resonances. The present report addresses the characteristics, origin, and elimination of these sidebands. Sideband amplitudes were measured as a function of delay time between gradient pulse and data collection, as a function of gradient pulse amplitude, and as a function of spatial location of the sample for each of the three orthogonal gradient sets. Acoustic acquisitions were performed to demonstrate the correlation between mechanical vibration resonances and the frequencies of MR sidebands. A mathematical framework is developed and compared with the experimental results. This derivation is based on the theory that these frequency modulations are induced by magnetic field fluctuations generated by the transient oscillations of gradient coils.

Quantitative T1rho magnetic resonance imaging of RIF-1 tumors in vivo: detection of early response to cyclophosphamide therapy.

This study compares two potential magnetic resonance imaging (MRI) indices for noninvasive early detection of tumor response to chemotherapy: the spin-lattice relaxation in the rotating frame (T1rho) and the transverse relaxation time (T2). Measurements of these relaxation parameters were performed on a s.c. murine radiation-induced fibrosarcoma (RIF-1) model before and after cyclophosphamide treatment. The number of pixels exhibiting T1rho values longer than controls in viable regions of the tumor increased significantly as early as 18 h after drug administration and remained elevated up to 36 h after treatment (P < 0.005). Although a trend of increasing T2s relative to controls was noted in viable regions of the tumor 36 h after treatment, the changes were not statistically significant. Histological examination indicated a decrease in mitotic index that paralleled the changes in T1rho. We conclude that T1rho measurements may be useful for noninvasive monitoring of early response of tumors to chemotherapy.

Water magnetic relaxation dispersion in biological systems: the contribution of proton exchange and implications for the noninvasive detection of cartilage degradation.

Magnetic relaxation has been used extensively to study and characterize biological tissues. In particular, spin-lattice relaxation in the rotating frame (T(1rho)) of water in protein solutions has been demonstrated to be sensitive to macromolecular weight and composition. However, the nature of the contribution from low frequency processes to water relaxation remains unclear. We have examined this problem by studying the water T(1rho) dispersion in peptide solutions ((14)N- and (15)N-labeled), glycosaminoglycan solutions, and samples of bovine articular cartilage before and after proteoglycan degradation. We find in model systems and tissue that hydrogen exchange from NH and OH groups to water dominates the low frequency water T(1rho) dispersion, in the context of the model used to interpret the relaxation data. Further, low frequency dispersion changes are correlated with loss of proteoglycan from the extra-cellular matrix of articular cartilage. This finding has significance for the noninvasive detection of matrix degradation.

Significant precision improvement for temperature mapping.

MR temperature measurements are important for applications such as the evaluation of thermal therapies and radiofrequency (RF) coil heating effects. In this work the spherical mean value (SMV) method has been applied to significantly improve the precision of MR temperature mapping in a homogeneous gel phantom. Temperature-increase maps of the phantom were obtained with three-dimensional (3D) MR phase difference mapping after heating with the RF coil. The temperature-increase distribution in most regions in the phantom is a harmonic function with the mean value property. Based on this property, the precision of temperature-increase maps was improved up to sixfold with the SMV method. Comparison of this method with conventional smoothing, further precision improvement, and the in vivo application of the SMV method are discussed.

Proteoglycan-induced changes in T1rho-relaxation of articular cartilage at 4T.

Proteoglycan (PG) depletion-induced changes in T1rho (spin-lattice relaxation in rotating frame) relaxation and dispersion in articular cartilage were studied at 4T. Using a spin-lock cluster pre-encoded fast spin echo sequence, T1rho maps of healthy bovine specimens and specimens that were subjected to PG depletion were computed at varying spin-lock frequencies. Sequential PG depletion was induced by trypsinization of cartilage for varying amounts of time. Results demonstrated that over 50% depletion of PG from bovine articular cartilage resulted in average T1rho increases from 110-170 ms. Regression analysis of the data showed a strong correlation (R2 = 0.987) between changes in PG and T1rho. T1rho values were highest at the superficial zone and decreased gradually in the middle zone and again showed an increasing trend in the region near the subchondral bone. The potentials of this method in detecting early degenerative changes of cartilage are discussed. Also, T(1rho)-dispersion changes as a function of PG depletion are described.

Human knee: in vivo T1(rho)-weighted MR imaging at 1.5 T--preliminary experience.

A fast spin-echo sequence weighted with a time constant that defines the magnetic relaxation of spins under the influence of a radio-frequency field (T1(rho)) was used in six subjects to measure magnetic resonance (MR) relaxation times in the knee joint with a 1.5-T MR imager. A quantitative comparison of T2- and T1(rho)-weighted MR images was also performed. Substantial T1(rho) dispersion was demonstrated in human articular cartilage, but muscle did not demonstrate much dispersion. T1(rho)-weighted images depicted a chondral lesion with 25% better signal-difference-to-noise ratios than comparable T2-weighted images. This technique may depict cartilage and muscular abnormalities.

Water distribution patterns inside bovine articular cartilage as visualized by 1H magnetic resonance imaging.

OBJECTIVE: To develop a magnetic resonance imaging (MRI) technique to non-invasively map water volume fraction (WVF) in articular cartilage. Special emphasis was placed on spatial resolution and temporal considerations, aimed at creating a procedure feasible for eventual human studies. DESIGN: Absolute proton density MR images of intact, ex vivo bovine patellae were calculated from fully T(1) relaxed, short echo time images. This was accomplished through compensation for T(2) decay with calculated T(2) maps. Calibration of the signal intensity in the image was accomplished with the use of H2O:D2O phantoms, where the WVF was varied from 0.95 to 0.75. Application of the calibration curve to the entire image yielded images that represent WVF on a pixel by pixel basis. Calculations of water content by weight were performed by considering the density of the solid content. RESULTS: Using four echo time points, experiments comparing MR images from single-echo and multi-echo spin echo sequences yielded similar results. T(2) decreased with depth through the cartilage, with a maximum at the articular surface of approx 100 ms, and a approximately 50 ms minimum at the bone/cartilage interface. The WVF through the depth of the cartilage showed a similar trend, decreasing from 0.9 at the surface, to 0.7 at the bone/cartilage interface. Translation to a weight percent yielded approximately 86% weight at the surface, trending down to approximately 63% at the bone/cartilage interface, with an average of 74.5% for five patellae. These MRI derived values were compared to the measured weight of water in excised cartilage plugs from the same patellae and showed remarkably close agreement. CONCLUSION: We have demonstrated that MRI can non-invasively map WVF in cartilage in a pixel by pixel manner. This was accomplished in a time span that was clinically feasible, allowing the routine use of this method in a clinical setting. Moreover, this procedure employed standard MRI equipment and pulse sequences, avoiding the need for hardware modifications and using simple post processing methods. However, baseline studies need to be performed prior to incorporation into a standard radiological evaluation. Implications in the diagnosis of osteoarthritis (OA) are discussed.

High-precision mapping of the magnetic field utilizing the harmonic function mean value property.

The spatial distributions of the static magnetic field components and MR phase maps in space with homogeneous magnetic susceptibility are shown to be harmonic functions satisfying Laplace's equation. A mean value property is derived and experimentally confirmed on phase maps: the mean value on a spherical surface in space is equal to the value at the center of the sphere. Based on this property, a method is implemented for significantly improving the precision of MR phase or field mapping. Three-dimensional mappings of the static magnetic field with a precision of 10(-11) approximately 10(-12) T are obtained in phantoms by a 1.5-T clinical MR scanner, with about three-orders-of-magnitude precision improvement over the conventional phase mapping technique. In vivo application of the method is also demonstrated on human leg phase maps.

T1rho imaging of murine brain tumors at 4 T.

RATIONALE AND OBJECTIVES: The goal of this study was to evaluate the utility of T1rho weighting in magnetic resonance imaging of murine brain tumors. MATERIALS AND METHODS: S91 Cloudman melanoma was implanted in mouse brains (n = 4). A T2-weighted spin-echo (SE) and a T1rho-weighted fast SE-based sequence were performed on a 4-T clinical imager. T2 and T1rho maps were computed. The tumor-to-normal-tissue contrast was compared between T2-weighted, T1rho-weighted, proton-density-weighted, and pre- and postcontrast T1-weighted SE images. RESULTS: The tumor-tissue contrast of the T1rho-weighted images was similar to that of the T2-weighted images but less than that of the postcontrast T1-weighted images. The T1rho-weighted images provided better definition of tumor boundaries than T2-weighted images. At spin-locking powers of 0.5 and 1.5 kHz, the T1rho of the tumor was 64.0 msec +/- 0.46 and 68.65 msec +/- 0.59, respectively. There was no significant inter- or intra-animal variation in T1rho for tumor or normal brain cortex. CONCLUSION: T1rho-weighted imaging performed at low spin-lock strengths qualitatively depicted tumor borders better than proton-density or T2-weighted imaging and could be useful in treatment planning when combined with other imaging sequences.

Detection and localization of pulmonary air leaks using laser-polarized (3)He MRI.

Pulmonary air leaks were created in the lungs of Yorkshire pigs. Dynamic, 3D MRI of laser-polarized (3)He gas was then performed using a gradient-echo pulse sequence. Coronal magnitude images of the helium distribution were acquired during gas inhalation with a voxel resolution of approximately 1.2 x 2.5 x 8 mm, and a time resolution of 5 sec. In each animal, the ventilation images reveal focal high-signal intensity within the pleural cavity at the site of the air leaks. In addition, a wedge-shaped region of increased parenchymal signal intensity was observed adjacent to the site of the air leak in one animal. (3)He MRI may prove helpful in the management of patients with pulmonary air leaks.

In vivo, in utero microscopic magnetic resonance imaging: application in a rat model of diaphragmatic hernia.

This article presents a microscopic MR technique for imaging small mammalian fetuses in utero and in vivo which can be used as a tool for studying normal and abnormal development in small animal fetal models, for targeting in utero intervention in such models, and for following development serially. This new method is applied to a rat model of congenital diaphragmatic hernia (CDH). Pregnant Sprague-Dawley rats were fed nitrofen at 9.5 days postcoitus to induce CDH in the fetuses. The dams were imaged to identify fetuses with CDH for targeted in utero intervention, which consisted of fetal tracheal ligation. Following tracheal ligation, the fetuses were followed serially with our MR technique. For MR imaging, the dam was anesthetized with intramuscular ketamine and intraperitoneal pentobarbital. In utero imaging was performed on a 4 Tesla MRI system using a multislice, fast spin echo sequence with a long TR and short effective TE. These results were validated by examining individual fetuses postmortem using high-resolution MR and anatomic dissection. The in utero, in vivo MR technique is highly accurate for diagnosing CDH and following the effects of surgical intervention, and shows promise as a tool for the study of embryogenesis in small animal models. Magn Reson Med 44:331-335, 2000.

Intermolecular dipole-dipole relaxation of (129)Xe dissolved in water.

Intermolecular (129)Xe-(1)H nuclear Overhauser effects and (129)Xe longitudinal relaxation time measurements were used to demonstrate that the dipole-dipole coupling is the dominant relaxation mechanism for (129)Xe in water, at room temperature. (129)Xe-(1)H cross-relaxation rates were derived to be sigma(XeH) approximately 3.2 +/- 0.3 x 10(-3) s(-1), independent of xenon pressure (in the range of 1-10 bar) and of the presence of oxygen. Corresponding xenon-proton internuclear distances were calculated to be 2.69 +/- 0.12 A. Using the magnitude of the dipole-dipole coupling and the spin density ratio between dissolved xenon and bulk water, it is estimated that (129)Xe-(1)H spin polarization-induced nuclear Overhauser effects would yield little net proton signal enhancement in water.

Intermolecular zero-quantum coherence imaging of the human brain.

The first intermolecular zero-quantum coherence (iZQC) MR images of the human brain at 4T are presented. To generate iZQC images, a modified echo-planar imaging pulse sequence was used which included an additional 45 degrees RF pulse and a correlation gradient. The observability and nonconventional contrast of human brain iZQC images at 4T is demonstrated. Axial images are presented for various pulse sequence parameters, and a zero-quantum relaxation map is obtained.

17O-decoupled (1)H spectroscopy and imaging with a surface coil: STEAM decoupling.

(17)O-decoupled (1)H spin-echo imaging has been reported as a means of indirect (17)O detection, with potential application to measurement of blood flow and metabolism. In its current form, (17)O decoupling requires large RF amplitudes and a 180 degrees refocusing pulse, complicating its application in volume and surface coils, respectively. To overcome this problem, we have developed an (17)O-decoupled proton stimulated echo sequence ("STEAM decoupling") to allow (17)O detection with a surface coil. A high B(1) amplitude is easily generated, allowing complete decoupling of (17)O and (1)H. Slice-selective, (17)O-decoupled (1)H imaging is readily performed and the sequence is easily adapted for localized spectroscopy. Intrinsic correction for variations in B(1) and further compensation for B(1) inhomogeneity are discussed.

Temperature-dependent chemical shift and relaxation times of (23)Na in Na(4)HTm[DOTP].

We describe the characterization of a (23)Na temperature-dependent chemical shift and relaxation rates in the complex, Na(4)HTm[DOTP]. This is the first characterization of a (23)Na temperature-dependent chemical shift in a nonmetallic sample. The (23)Na temperature-dependent chemical shift coefficient is approximately -0. 5 PPM/ degrees C for both an aqueous solution and a 6% agarose gel of this compound. This is 50 times the magnitude of the temperature-dependent chemical shift coefficient of water protons. The relaxation times, T(1), T(2f), and T(2s) increased by 0.1, 0.01, and 0.05 ms/ degrees C, respectively. Applications of these unique properties for designing an MRI technique for monitoring heat deposition in tissue and tissue phantoms are discussed.

Demonstration of a compact compressor for application of metastability-exchange optical pumping of 3He to human lung imaging.

Hyperpolarized gas magnetic resonance imaging has recently emerged as a method to image lungs, sinuses, and the brain. The best lung images to date have been produced using hyperpolarized 3He, which is produced by either spin-exchange or metastability-exchange optical pumping. For hyperpolarized gas MRI, the metastable method has demonstrated higher polarization levels and higher polarizing rates, but it requires compression of the hyperpolarized gas. Prior to this work, compression of hyperpolarized gas had only been accomplished using a large, complex and expensive apparatus. Here, human lung ventilation images are presented that were obtained using a compact compressor that is relatively simple and inexpensive. For this test, 1.1 bar-L of 15% hyperpolarized 3He gas was produced at the National Institute of Standards and Technology using a modified commercial diaphragm pump. The hyperpolarized gas was transported to the University of Pennsylvania in a holding field provided by a portable solenoid.