Intraspecific variation and plasticity in mitochondrial oxygen binding affinity as a response to environmental temperature.

Mitochondrial function has been suggested to underlie constraints on whole-organism aerobic performance and associated hypoxia and thermal tolerance limits, but most studies have focused on measures of maximum mitochondrial capacity. Here we investigated whether variation in mitochondrial oxygen kinetics could contribute to local adaptation and plasticity in response to temperature using two subspecies of the Atlantic killifish (Fundulus heteroclitus) acclimated to a range of temperatures (5, 15, and 33 °C). The southern subspecies of F. heteroclitus, which has superior thermal and hypoxia tolerances compared to the northern subspecies, exhibited lower mitochondrial O2 P50 (higher O2 affinity). Acclimation to thermal extremes (5 or 33 °C) altered mitochondrial O2 P50 in both subspecies consistent with the effects of thermal acclimation on whole-organism thermal tolerance limits. We also examined differences between subspecies and thermal acclimation effects on whole-blood Hb O2-P50 to assess whether variation in oxygen delivery is involved in these responses. In contrast to the clear differences between subspecies in mitochondrial O2-P50 there were no differences in whole-blood Hb-O2 P50 between subspecies. Taken together these findings support a general role for mitochondrial oxygen kinetics in differentiating whole-organism aerobic performance and thus in influencing species responses to environmental change.

Validation of the i-STAT system for the analysis of blood gases and acid-base status in juvenile sandbar shark (Carcharhinus plumbeus).

Accurate measurements of blood gases and acid-base status require an array of sophisticated laboratory equipment that is typically not available during field research; such is the case for many studies on the stress physiology, ecology and conservation of elasmobranch fish species. Consequently, researchers have adopted portable clinical analysers that were developed for the analysis of human blood characteristics, but often without thoroughly validating these systems for their use on fish. The aim of our study was to test the suitability of the i-STAT system, the most commonly used portable clinical analyser in studies on fish, for analysing blood gases and acid-base status in elasmobranchs, over a broad range of conditions and using the sandbar shark (Carcharhinus plumbeus) as a model organism. Our results indicate that the i-STAT system can generate useful measurements of whole blood pH, and the use of appropriate correction factors may increase the accuracy of results. The i-STAT system was, however, unable to generate reliable results for measurements of partial pressure of oxygen (PO2) and the derived parameter of haemoglobin O2 saturation. This is probably due to the effect of a closed-system temperature change on PO2 within the i-STAT cartridge and the fact that the temperature correction algorithms used by i-STAT assume a human temperature dependency of haemoglobin-O2 binding; in many ectotherms, this assumption will lead to equivocal i-STAT PO2 results. The in vivo partial pressure of CO2 (PCO2) in resting sandbar sharks is probably below the detection limit for PCO2 in the i-STAT system, and the measurement of higher PCO2 tensions was associated with a large measurement error. In agreement with previous work, our results indicate that the i-STAT system can generate useful data on whole blood pH in fishes, but not blood gases.

PET/CT-guided percutaneous liver mass biopsies and ablations: targeting accuracy of a single 20 s breath-hold PET acquisition.

AIM: To determine whether a single 20 s breath-hold positron-emission tomography (PET) acquisition obtained during combined PET/computed tomography (CT)-guided percutaneous liver biopsy or ablation procedures has the potential to target 2-[(18)F]-fluoro-2-deoxy-d-glucose (FDG)-avid liver masses as accurately as up to 180 s breath-hold PET acquisitions. MATERIALS AND METHODS: This retrospective study included 10 adult patients with 13 liver masses who underwent FDG PET/CT-guided percutaneous biopsies (n = 5) or ablations (n = 5). PET was acquired as nine sequential 20 s, monitored, same-level breath-hold frames and CT was acquired in one monitored breath-hold. Twenty, 40, 60, and 180 s PET datasets were reconstructed. Two blinded readers marked tumour centres on randomized PET and CT datasets. Three-dimensional spatial localization differences between PET datasets and either 180 s PET or CT were analysed using multiple regression analyses. Statistical tests were two-sided and p < 0.05 was considered significant. RESULTS: Targeting differences between 20 s PET and 180 s PET ranged from 0.7-20.3 mm (mean 5.3 ± 4.4 mm; median 4.3) and were not statistically different from 40 or 60 s PET (p = 0.74 and 0.91, respectively). Targeting differences between 20 s PET and CT ranged from 1.4-36 mm (mean 9.6 ± 7.1 mm; median 8.2 mm) and were not statistically different from 40, 60, or 180 s PET (p = 0.84, 0.77, and 0.35, respectively). CONCLUSION: Single 20 s breath-hold PET acquisitions from PET/CT-guided percutaneous liver procedures have the potential to target FDG-avid liver masses with equivalent accuracy to 180 s summed, breath-hold PET acquisitions and may facilitate strategies that improve image registration and shorten procedure times.

MR imaging-guided percutaneous cryotherapy of liver tumors: initial experience.

PURPOSE: To describe the cryoablation of liver tumors by using a percutaneous approach and intraprocedural magnetic resonance (MR) imaging monitoring and to assess the feasibility and safety of the procedure. MATERIALS AND METHODS: Fifteen hepatic tumors (mean diameter, 2.9 cm) in 12 patients were treated (18 total cryoablations). Fourteen were metastases and one was a hemangioma; all were proved at biopsy. By using a 0.5-T open MR imaging system, cryoneedles were placed and lesions ablated by using real-time monitoring. Clinical signs and symptoms were assessed and laboratory tests performed. Intraprocedural depictions of iceballs were compared with contrast material-enhanced MR imaging-based estimates of cryonecrosis that were obtained 24 hours after cryoablation. RESULTS: MR imaging-guided percutaneous cryotherapy resulted in no serious complications and no clinically important changes in serum liver enzymes or creatinine or myoglobin levels. Intraprocedural MR imaging demonstrated iceballs as sharply marginated regions of signal loss that expanded and engulfed tumors. The maximal iceball size was 4.9 x 2.2 x 2.2 cm with the use of one cryoneedle and 6.0 x 5.6 x 4.9 cm with three cryoneedles. Intraprocedural iceball depictions correlated well with postprocedural cryonecrosis estimates. CONCLUSION: MR imaging-guided percutaneous cryotherapy of liver tumors is feasible and safe. MR imaging can be used to estimate cryotherapy effects and guide therapy intraprocedurally.

MR-based temperature monitoring for hot saline injection therapy.

We applied magnetic resonance (MR) phase mapping methods to monitor the thermal frequency shift of water in order to study temperature changes from percutaneous hot saline injection therapy (PSIT) using in vitro swine livers and in vivo rabbit livers. The thermal coefficients calculated from the shifts of the water frequency with thermocouple based temperature measurements were -0.0085 +/- 0.0019 ppm/ degrees C for the in vitro studies and -0.0089 ppm/ degrees C for the in vivo studies. The error range was estimated to be +/- 3 degrees C and +/- 4.5 degrees C, respectively. Color-coded temperature maps were compared with macroscopic lesion sizes of the specimen. Regions defined using a 20 degrees C elevation in the initial images following hot saline injection (around 55 degrees C in absolute temperature) closely correlated with visible coagulation in size. We conclude that MR temperature monitoring of PSIT is quite feasible and may be helpful in expanding the clinical use of this thermal therapeutic tool for liver tumors.

MRI monitoring of laser ablation using optical flow.

The optical flow method is used for visualizing and quantifying the dynamics of tissue changes observed by MRI during thermal ablations. An approach was implemented for parallel two-dimensional optical flow calculations including the replacement of spurious velocities. Velocity magnitude results were found to be accurate in low-noise cases in tests using series of synthetic images. Optical flow results are presented from thermal ablation experiments utilizing a homogeneous polyacrylamide gel phantom and heterogeneous rabbit liver tissue in vivo, exhibiting heating and cooling with the accompanying quantitative characterization of the dilation and contraction of the thermally affected region. Results demonstrate that optical flow is capable of noninvasive real-time monitoring and control of interstitial laser therapy (ILT).

Endoscopic sinus surgery with magnetic resonance imaging guidance: initial patient experience.

We report the first endoscopic surgeries performed with patients under general anesthesia using intraoperative guidance with MRI. The procedures were experimental and intended to test (1) the unusual working environment of a unique new "open-configuration" MRI unit for head and neck surgery, and (2) real-time image guidance. Twelve patients underwent endoscopic sinus surgery while under general anesthesia in a new open MRI unit that provides the surgeon with access to the patient while imaging is performed. Eleven patients had chronic sinusitis (eight of them had bilateral disease), and one had a right nasoethmoid and antral tumor. All 12 surgeries were performed without complications. Both the endoscopic view and the MRI scans were available at the surgical field. The image plane was surgeon controlled, and the MRI updated images in as little as 14 seconds. MRI provided adequate visualization of both the disease and the related anatomy and allowed the surgeon to navigate during the procedure. The intraoperative data reflect the tissue changes during surgery and provide optimum feedback for surgical guidance. Although the operating environment poses some limitations, it has become apparent that intraoperative MRI has a role in the treatment of head and neck disorders and warrants further study.

Monitoring and visualization techniques for MR-guided laser ablations in an open MR system.

Our purpose was to develop temperature-sensitive MR sequences and image-processing techniques to assess their potential of monitoring interstitial laser therapy (ILT) in brain tumors (n = 3) and liver tumors (n = 7). ILT lasted 2 to 26 minutes, whereas images from T1-weighted fast-spin-echo (FSE) or spoiled gradient-recalled (SPGR) sequences were acquired within 5 to 13 seconds. Pixel subtraction and visualization of T1-weighted images or optical flow computation was done within less than 110 msec. Alternating phase-mapping of real and imaginary components of SPGR sequences was performed within 220 msec. Pixel subtraction of T1-weighted images identified thermal changes in liver and brain tumors but could not evaluate the temperature values as chemical shift-based imaging, which was, however, more affected by susceptibility effects and motion. Optical flow computation displayed the predicted course of thermal changes and revealed that the rate of heat deposition can be anisotropic, which may be related to heterogeneous tumor structure and/or vascularization.

Computer-augmented endoscopic sinus surgery.

Review of current literature on computer-augmented endoscopic sinus surgery reflects a sustained interest in developing a role for available frameless stereotactic technologies to provide image guidance for the surgeon. The interest is motivated by the prospect of increased intraoperative patient safety in that image guidance assists the surgeon in navigating through diseased or surgically revised complex anatomy. The authors feel that in time the technique will enable a new level of efficiency in endoscopic sinus surgery.

Compatible instrumentation for intraoperative MRI: expanding resources.

Steadfast progress has been made from biopsy to surgery with interventional MRI (iMRI). Such image-guided interventions require specialized instrumentation due to the unusual elements of the MR environment. Suppliers/manufacturers of MR-compatible instrumentation were few in 1994, but now there are more than 50. We present fundamental issues of MR compatibility and a list of known suppliers/manufacturers.

MRI of laser-induced interstitial thermal injury in an in vivo animal liver model with histologic correlation.

Laser-induced interstitial thermal therapy (LITT) is a preferred method of minimally invasive therapy. MRI is a noninvasive method by which to monitor the thermal effects of LITT. To properly control such effects, changes in MRI parameters during and after LITT should be correlated with changes in the tissue. T1-weighted fast spin echo (FSE) MRI (1 image/10 seconds) at 1.5 T monitored LITT in vivo in rabbit liver (n = 6) using an interstitial bare delivery fiber (600-microm diameter; 3.0 W; 1,064 nm; 150 seconds). During laser irradiation, MRI signal intensity decreased around the fiber tip; after irradiation, this hypointensity proved reversible and permanent lesions were evident. The lesions had hyperintense margins that were brighter than surrounding normal tissue (P < .001); the tissue in these bright regions was mapped to tissue necrosis characterized by the presence of thermally damaged ghost red blood cells amid generally normal hepatocytes. T1-FSE identified the spatial extent of the LITT lesions.

Computer-assisted intra-operative magnetic resonance imaging monitoring of interstitial laser therapy in the brain: a case report.

Hardware and software for a customized system to use magnetic resonance imaging (MRI) to noninvasively monitor laser-induced interstitial thermal therapy of brain tumors are reported. An open-configuration interventional MRI unit was used to guide optical fiber placement and monitor the deposition of laser energy into the targeted lesion. T1-weighted fast spin echo and gradient echo images were used to monitor the laser tissue interaction. The images were transferred from the MRI scanner to a customized research workstation and were processed intraoperatively. Newly developed software enabled rapid (27-221 ms) availability of calculated images. A case report is given showing images which reveal the laser-tissue interaction. The system design is feasible for on-line monitoring of interstitial laser therapy. © 1998 Society of Photo-Optical Instrumentation Engineers.

Image guidance with laser applications.

Image-guided laser surgery is defined, and an outline of its development is provided. Recent advances in radiologic imaging provide added visualization of laser-induced tissue effects. Current research around the world illustrates the power and potential of this technique in both laser and nonlaser applications. Future studies will reveal the actual contribution to laser surgery in otolaryngology.

Dynamic T1-weighted magnetic resonance imaging of interstitial laser photocoagulation in the liver: observations on in vivo temperature sensitivity.

BACKGROUND AND OBJECTIVE: Magnetic resonance imaging's (MRI) potential to monitor interstitial laser photocoagulation (ILP) has been previously demonstrated and is further tested here with improved spatial and temporal resolution. STUDY DESIGN/MATERIALS AND METHODS: In vivo experiments employed fiber-delivered 1,064 nm light (3.0 W, 150 sec) in six rabbit livers monitored under T1-weighted FSE MRI as 1 image/10 sec and a 3 mm thick 8 cm FOV. Image signal intensities (SI) were compared with temperatures (T) at 7, 10, and 15 mm from the fiber. RESULTS: Data showed 33 degrees C < T < 60 degrees C. SI did not vary inverselinearly with T; changes in the tissue altered the MRI signal interfering with the SI changes due to temperature. CONCLUSION: MRI cannot map SI-derived temperatures over the entire treatment site. The role of MRI's temperature sensitivity must be coordinated with organ- and dose-specific tissue changes.

Comparative cell targeting in vitro using the CO2 laser.

In keeping with current interest in bactericidal effects of lasers to treat localized infection, we examined the effect of CO2 laser light on three bacterial species. Cell monolayers were placed atop filters minimizing the presence of extracellular water. Samples were exposed to irradiance values between 0 and 520 W/cm2 for 0.1 s. Cell survival was determined by colony counts. There was logarithmic killing of the bacteria with increasing irradiance; 90% kill was effected at 180 W/cm2 for Escherichia coli, 350 W/cm2 for Streptococcus mutans, and 250 W/cm2 for Bacillus stearothermophilus. However, standard deviations suggest no significant difference between cell types. Our results show the bactericidal effect of the CO2 laser with no remarkable difference between Gram types. However, substantial cell kill was achieved at relatively low irradiance. Whereas selectivity of damage may not be afforded by the CO2 laser, it may minimize collateral damage.

Altered actin and myosin expression in muscle during exposure to microgravity.

The mechanism for cardiovascular deconditioning and skeletal muscle atrophy during microgravity is not known. The purpose of the present study was to determine whether a decrease in contractile protein gene expression in the muscle of rats occurred after 14 days of microgravity. No differences existed in the profile of myosin protein isoforms or beta-myosin heavy chain mRNA in hearts between the flight and synchronous control groups. On the other hand, differences in the expression of beta-myosin heavy chain mRNA relative to the 18S and 28S rRNA in the heart between flight and synchronous control groups were noted with a covariance mapping analysis. Both the vastus intermedius and lateral gastrocnemius muscles exhibited significant (P less than 0.05) decreases in skeletal alpha-actin mRNA per unit of extractable RNA in the flight group compared with the synchronous control group. However, no significant difference for skeletal alpha-actin mRNA occurred in the triceps brachii muscle between these groups. Cytochrome c mRNA per unit of extractable RNA decreased (P less than 0.05) only in the vastus intermedius but not in the lateral gastrocnemius or triceps brachii muscles. In summary, changes in the pretranslational regulation of contractile protein gene expression occur in both heart and skeletal muscle after 14 days of microgravity.

Pulse duration effects on cutaneous pigment.

Melanin, an endogenous chromophore in pigment containing cells in skin, is being specifically altered by lasers using the principle of selective photothermolysis (SPT). This implies that a combination of specific laser parameters of wavelength, pulse duration, spotsize, and energy density are required to confine the delivered laser energy to the targeted cells alone. Because the bulk of cutaneous pigment is localized to epidermal basal cells, pigmentary incontinence has been found to occur in skin exposed to laser irradiation. This study demonstrates that pulse duration or exposure time of the laser affect the severity of pigmentary incontinence induced. Pigment granules are more abundant, aggregated, and located deeper in the dermis following exposure to 500 nsec pulse duration than 100 nsec at a wavelength of 504 nm. This relationship appears to be independent of the laser energy density used.

Cytochrome c mRNA levels decrease in senescent rat heart.

The concentration of mitochondria decreases in the heart as rodents age from maturity to senescence. The reason for this change is not known. One purpose of the present study was to determine if cytochrome c mRNA, representative of proteins of the inner mitochondrial membrane, decreased in the hearts of Fischer 344 rats as they aged from 12 to 24 months. Twenty-two percent less cytochrome c mRNA existed per given quantity of extracted RNA from the heart in 24-month-old rats as compared with the 12-month-old group. No change in the quantities of cardiac alpha-actin mRNA, Ca2+/calmodulin protein kinase II mRNA or 18S rRNA was noted between 12- and 24-month-old hearts. Thus, the decrease in cytochrome c mRNA suggests that decreases in mRNAs for proteins of the inner mitochondrial membrane could play some role in the diminished concentration of mitochondria that exists in the senescent heart.

Daily running for 2 wk and mRNAs for cytochrome c and alpha-actin in rat skeletal muscle.

The purpose of the study was to determine whether daily running durations that were 7-14% of the durations employed in the chronic stimulation protocols (consisting of 24 h of daily indirect electrical stimulation of skeletal muscles) still resulted in increases in a mitochondrial protein mRNA. Adult female rats were run 100 min/day on motor-driven treadmills for 2 wk. Documentation that rats underwent the stated training program was obtained by a 30-41% increase in citrate synthase activity in hindlimb muscles after 2 wk of the training. Cytochrome c mRNA was increased 17-56% in hindlimb muscles after the 2-wk training program. Thus shorter durations of exercise (100 min/day rather than 24 h/day) can increase cytochrome c mRNA. alpha-Actin mRNA increased 61-62% in fast-twitch muscles in the hindlimbs of the same rats that underwent the 2 wk of run training but did not increase in the predominantly slow-twitch soleus muscle. The increase in alpha-actin mRNA was unexpected, since it is well known that this type of physical exercise does not increase the size of fast-twitch skeletal muscle.