Comparison of dynamic contrast-enhanced MRI parameters of breast lesions at 1.5 and 3.0 T: a pilot study

OBJECTIVE

To compare dynamic contrast-enhanced (DCE) MRI parameters from scans of breast lesions at 1.5 and 3.0 T.

METHODS

11 patients underwent paired MRI examinations in both Philips 1.5 and 3.0 T systems (Best, Netherlands) using a standard clinical fat-suppressed, T1 weighted DCE-MRI protocol, with 70-76 s temporal resolution. Signal intensity vs time curves were fit with an empirical mathematical model to obtain semi-quantitative measures of uptake and washout rates as well as time-to-peak enhancement (TTP). Maximum percent enhancement and signal enhancement ratio (SER) were also measured for each lesion. Percent differences between parameters measured at the two field strengths were compared.

RESULTS

TTP and SER parameters measured at 1.5 and 3.0 T were similar; with mean absolute differences of 19% and 22%, respectively. Maximum percent signal enhancement was significantly higher at 3 T than at 1.5 T (p = 0.006). Qualitative assessment showed that image quality was significantly higher at 3 T (p = 0.005).

CONCLUSION

Our results suggest that TTP and SER are more robust to field strength change than other measured kinetic parameters, and therefore measurements of these parameters can be more easily standardized than measurements of other parameters derived from DCE-MRI. Semi-quantitative measures of overall kinetic curve shape showed higher reproducibility than do discrete classification of kinetic curve early and delayed phases in a majority of the cases studied.

ADVANCES IN KNOWLEDGE

Qualitative measures of curve shape are not consistent across field strength even when acquisition parameters are standardized. Quantitative measures of overall kinetic curve shape, by contrast, have higher reproducibility.

Monitoring anti-angiogenic therapy in colorectal cancer murine model using dynamic contrast-enhanced MRI: comparing pixel-by-pixel with region of interest analysis

Sorafenib is a multi-kinase inhibitor that blocks cell proliferation and angiogenesis. It is currently approved for advanced hepatocellular and renal cell carcinomas in humans, where its major mechanism of action is thought to be through inhibition of vascular endothelial growth factor and platelet-derived growth factor receptors. The purpose of this study was to determine whether pixel-by-pixel analysis of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is better able to capture the heterogeneous response of Sorafenib in a murine model of colorectal tumor xenografts (as compared with region of interest analysis). MRI was performed on a 9.4 T pre-clinical scanner on the initial treatment day. Then either vehicle or drug were gavaged daily (3 days) up to the final image. Four days later, the mice were again imaged. The two-compartment model and reference tissue method of DCE-MRI were used to analyze the data. The results demonstrated that the contrast agent distribution rate constant (K(trans)) were significantly reduced (p < 0.005) at day-4 of Sorafenib treatment. In addition, the K(trans) of nearby muscle was also reduced after Sorafenib treatment. The pixel-by-pixel analysis (compared to region of interest analysis) was better able to capture the heterogeneity of the tumor and the decrease in K(trans) four days after treatment. For both methods, the volume of the extravascular extracellular space did not change significantly after treatment. These results confirm that parameters such as K(trans), could provide a non-invasive biomarker to assess the response to anti-angiogenic therapies such as Sorafenib, but that the heterogeneity of response across a tumor requires a more detailed analysis than has typically been undertaken.

Characterizing early contrast uptake of ductal carcinoma in situ with high temporal resolution dynamic contrast-enhanced MRI of the breast: a pilot study

Improvements in the reliable diagnosis of preinvasive ductal carcinoma in situ (DCIS) by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) are needed. In this study, we present a new characterization of early contrast kinetics of DCIS using high temporal resolution (HiT) DCE-MRI and compare it with other breast lesions and normal parenchyma. Forty patients with mammographic calcifications suspicious for DCIS were selected for HiT imaging using T(1)-weighted DCE-MRI with ∼7 s temporal resolution for 90 s post-contrast injection. Pixel-based and whole-lesion kinetic curves were fit to an empirical mathematical model (EMM) and several secondary kinetic parameters derived. Using the EMM parameterized and fitted concentration time curve for subsequent analysis allowed for calculation of kinetic parameters that were less susceptible to fluctuations due to noise. The parameters' initial area under the curve (iAUC) and contrast concentration at 1 min (C(1 min)) provided the highest diagnostic accuracy in the task of distinguishing pathologically proven DCIS from normal tissue. There was a trend for DCIS lesions with solid architectural pattern to exhibit a negative slope at 1 min (i.e. increased washout rate) compared to those with a cribriform pattern (p < 0.04). This pilot study demonstrates the feasibility of quantitative analysis of early contrast kinetics at high temporal resolution and points to the potential for such an analysis to improve the characterization of DCIS.

In vivo magnetic resonance imaging of the progression of murine ductal carcinoma in situ: finding timescales and predictors of future invasion

Abstract #6011

Background: Understanding the natural history of breast cancer is important for effective patient management and treatment. For example, some evidence suggests that preinvasive ductal carcinoma in situ (DCIS) may be over-treated, since not all will progress to invasive cancer. Unfortunately, due to obligate surgical excision of newly diagnosed breast cancers, the natural history of disease is difficult to study in women. However, mouse models of breast cancer can serve as an alternative; the purpose of this study was to use magnetic resonance imaging (MRI) to investigate the progression of DCIS into invasive cancer in a transgenic model.&#x2028; Methods:12 SV40 Tag mice were imaged every 2-3 weeks (wks) starting at 10 wks of age. SV40 mice develop mammary cancer similar to DCIS and IDC, and usually live to 22 wks when they succumb to breast cancer. T1-weighted gradient echo images of inguinal mammary glands were obtained. DCIS lesions and invasive tumors were identified and volumes were measured over time. For each lesion we measured: the time at initial development (TDCIS and Ttumor), the growth rate of DCIS and invasive tumors (calculated from 'V=V0exp(αt)'), and for DCIS lesions that progressed to invasive tumors the progression time Tprog was measured.&#x2028; Results:DCIS (n=21) and invasive (n=16) tumors developed, at an average initial age of TDCIS =12.7±2.6 wks and Ttumor =16.3±3.1 wks, and at an initial volume of 0.3±0.2 mm3 and 1.7 mm3, respectively. The average growth rate for DCIS lesions was αDCIS= 0.08±0.23 wk-1, significantly smaller than that of invasive tumors (αtumor= 0.55±0.35 wk-1, p =0.001). 9/21 DCIS lesions progressed to invasive cancers in an average time of Tprog=4.56 ± 1.9 wks(Figure 1a). 11/21 DCIS did not progress within the study window and 5/21 were stable for over 8 wks (Figure 1b).&#x2028; &#x2028; The volume of DCIS was not a predictor of progression, but there was a trend for DCIS growth rate to be related to eventual development of invasiveness.&#x2028; Discussion:To our knowledge, the results reported here are the first direct measurements of the timescales and characteristics of progression from in situ to invasive carcinoma. Surprisingly, even in transgenic mice that are strongly pre-disposed to develop cancer, some DCIS lesions did not progress to invasive cancer. Interestingly, DCIS volume did not predict future progression to invasive tumors, but growth rate may have been a predictor. The methods and data here provide a foundation for using MRI in pre-clinical studies of early cancer progression, prevention and targeted treatment. Extensions of this pilot study may yield image-based biomarkers of progressing vs. indolent DCIS.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6011.

Detection of in situ mammary cancer in a transgenic mouse model: in vitro and in vivo MRI studies demonstrate histopathologic correlation

Improving the prevention and detection of preinvasive ductal carcinoma in situ (DCIS) is expected to lower both morbidity and mortality from breast cancer. Transgenic mouse models can be used as a 'test bed' to develop new imaging methods and to evaluate the efficacy of candidate preventive therapies. We hypothesized that despite its microscopic size, early murine mammary cancer, including DCIS, might be accurately detected by MRI. C3(1) SV40 TAg female mice (n=23) between 10 and 18 weeks of age were selected for study. Eleven mice were subjected to in vitro imaging using a T(2)-weighted spin echo sequence and 12 mice were selected for in vivo imaging using a T(1)-weighted gradient echo, a T(2)-weighted spin echo and high spectral and spatial resolution imaging sequences. The imaged glands were carefully dissected, formalin fixed and paraffin embedded, and then H&E stained sections were obtained. The ratio of image-detected versus histologically detected cancers was obtained by reviewing the MR images and H&E sections independently and using histology as the gold standard. MR images were able to detect 12/12 intramammary lymph nodes, 1/1 relatively large (approximately 5 mm) tumor, 17/18 small (approximately 1 mm) tumors and 13/16 ducts distended with DCIS greater than 300 microm. Significantly, there were no false positives--i.e., image detection always corresponded to a histologically detectable cancer in this model. These results indicate that MR imaging can reliably detect both preinvasive in situ and early invasive mammary cancers in mice with high sensitivity. This technology is an important step toward the more effective use of non-invasive imaging in pre-clinical studies of breast cancer prevention, detection and treatment.

Quantitative analysis of water proton spectral lineshape: a novel source of contrast in MRI

Previous work in this laboratory has demonstrated improved anatomic and functional images produced from high spectral and spatial resolution (HiSS) MRI of the water proton signal. The present work tests the hypothesis that different Fourier components of the water resonance represent anatomically and/or physiologically distinct populations of water molecules within each small image voxel. HiSS datasets were acquired from tomatoes and rodent tumors at 4.7 T using echo-planar spectroscopic imaging (spatial and spectral resolutions were 117-150 microm and 1.5-3.1 Hz, respectively). Images of each Fourier component of the water resonance (referred to as Fourier component images, or FCIs) were produced. FCIs at frequencies offset from the peak of the water resonance ('off-peak' FCIs) were compared to images of the Fourier component with largest amplitude, i.e. the water peak-height image. Results demonstrate that off-peak FCIs differ significantly from the water peak-height image and that water resonances are often asymmetric. These results show that water signal at various frequency offsets from the peak of the water resonance come from water molecules in different anatomic/physiologic environments. Off-peak FCIs are a new source of structural and functional information and may have clinical utility.

Differentiation of nonmetastatic and metastatic rodent prostate tumors with high spectral and spatial resolution MRI

MR images can be acquired with high spectral and spatial resolution to precisely measure lineshapes of the water and fat resonances in each image voxel. Previous work suggests that the high-resolution spectral information can be used to improve image contrast, SNR, sensitivity to contrast agents and to physiologic and biochemical processes that affect local magnetic susceptibility gradients. The potential advantages of high-resolution spectroscopic imaging (SI) suggest that it might be useful for early detection and characterization of tumors. The present experiments evaluate the use of high-resolution SI to discriminate between metastatic and nonmetastatic rodent Dunning prostate tumors. SI datasets were obtained at 4.7 Tesla with an in-plane resolution of 350-500 micron in a single 1.0-mm slice, and 6-8 Hz spectral resolution, before and after i.v. injection of an iron oxide contrast agent. Images of water signal peak height in nonmetastatic tumors were smoother in the tumor interior than images of metastatic tumors (P <.004 by t-test) before contrast media injection. This difference was stronger in contrast-enhanced images (P <.0004). In addition, the boundary between the tumor and muscle was more clearly demarcated in nonmetastatic than metastatic tumors. Combinations of image texture, tumor edge morphology, and changes in T2* following contrast media injection improved discrimination between metastatic and nonmetastatic tumors. The data presented here do not demonstrate that effective discrimination between metastatic and nonmetastatic tumors depends on the use of high-resolution SI. However, the results suggest that SI and/or other MR methods that provide similar contrast might be used clinically for early and accurate detection of metastatic disease.

MRI measurements correctly predict the relative effects of tumor oxygenating agents on hypoxic fraction in rodent BA1112 tumors

PURPOSE

We evaluate whether magnetic resonance imaging (MRI) with blood oxygenation level-dependent (BOLD) contrast correctly predicts the relative effects of tumor-oxygenating agents on hypoxic fraction in BA1112 rhabdomyosarcomas in WAG/Rij rats.

METHODS AND MATERIALS

The response of ten tumors to carbogen (95% O(2)/5% CO(2)), a perfluorocarbon emulsion (PFC), and the combination of PFC + carbogen was studied with high spectral and spatial resolution MR imaging of the water resonance at 4.7 Tesla. Decreases in MR signal linewidth indicate increases in tumor blood oxygen levels.

RESULTS

Average MR signal linewidth was decreased 2.0% by carbogen, 2.5% by PFC + air, and 4.9% by PFC + carbogen. PFC + carbogen caused a larger linewidth decrease than either treatment alone (p < 0.04 by ANOVA). Maps of pixels responding to treatment indicate that combining PFC with carbogen significantly enlarges the area of the tumor in which oxygen levels are increased (p < 0.01 by ANOVA).

CONCLUSION

MRI predicts that PFC + carbogen will increase radiosensitivity more than either treatment alone; this agrees with the known effects of these treatments on hypoxic fraction. Utilizing MRI to choose the treatment that maximizes the size and extent of increases in tumor oxygenation could reduce hypoxic fraction.

Uptake of a superparamagnetic contrast agent imaged by MR with high spectral and spatial resolution

Conventional MRI implicitly treats the proton signal as a single, narrow Lorentzian. However, water signals in vivo are often in homogeneously broadened and have multiple resolvable components. These components represent discrete populations of water molecules within each pixel which are affected differently by physiology and contrast agents. Accurate measurement of each component of the water resonance can improve anatomic and functional MR images and provide insight into the structure and dynamics of subpixelar microenvironments. This report describes high spectral and spatial resolution (HiSS) MR imaging of rodent prostate tumors before and after injection of a superparamagnetic contrast agent. HiSS datasets were used to synthesize images in which intensity is proportional to peak height, peak frequency, and linewidth. These images showed anatomic features which were not clearly delineated in conventional T(2) and gradient echo images. HiSS images obtained after injection of the contrast agent showed T *(2) and T(1) changes which were not seen in conventional images. These changes are associated with microvessel density and permeability. The results suggest HiSS with superparamagnetic contrast agents has the potential to improve characterization of tumors.

Applications of magnetic resonance in model systems: cancer therapeutics

The lack of information regarding the metabolism and pathophysiology of individual tumors limits, in part, both the development of new anti-cancer therapies and the optimal implementation of currently available treatments. Magnetic resonance [MR, including magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and electron paramagnetic resonance (EPR)] provides a powerful tool to assess many aspects of tumor metabolism and pathophysiology. Moreover, since this information can be obtained nondestructively, pre-clinical results from cellular or animal models are often easily translated into the clinic. This review presents selected examples of how MR has been used to identify metabolic changes associated with apoptosis, detect therapeutic response prior to a change in tumor volume, optimize the combination of metabolic inhibitors with chemotherapy and/or radiation, characterize and exploit the influence of tumor pH on the effectiveness of chemotherapy, characterize tumor reoxygenation and the effects of modifiers of tumor oxygenation in individual tumors, image transgene expression and assess the efficacy of gene therapy. These examples provide an overview of several of the areas in which cellular and animal model studies using MR have contributed to our understanding of the effects of treatment on tumor metabolism and pathophysiology and the importance of tumor metabolism and pathophysiology as determinants of therapeutic response.

A new method for imaging perfusion and contrast extraction fraction: input functions derived from reference tissues

This study describes a new method for analysis of dynamic MR contrast data that greatly increases the time available for data acquisition. The capillary input function, CB(t), is estimated from the rate of contrast agent uptake in a reference tissue such as muscle, based on literature values for perfusion rate, extraction fraction, and extracellular volume. The rate constant for contrast uptake (the product of perfusion rate, F, and extraction fraction, E; F x E) is then determined in each image pixel using CB(t), extracellular volume (relative to the reference tissue) measured from MR and the tissue concentration of contrast media as a function of time calculated from the MR data. The "reference tissue method" was tested using rats with mammary (n = 10) or prostate (n = 15) tumors implanted in the hindlimb. Dynamic MR images at 4.7 T were acquired before and after Gd-DTPA intravenous bolus injections to determine F x E(Gd-DTPA). Acquisition parameters were optimized for detection of the first pass of the contrast agent bolus, so that "first-pass analysis" could be used as the "gold standard" for determination of F x E. The accuracy of values of F x E determined using the reference tissue method was determined based on comparison with first-pass analysis. In some cases, deuterated water (D2O) was injected i.v. immediately after Gd-DTPA measurements, and the reference tissue method was used to calculate F, based on the rate of uptake of D2O. Comparison of rate constants for Gd-DTPA uptake and D2O uptake allowed calculation of E(Gd-DTPA). Values for F x E(Gd-DTPA), F, and E(Gd-DTPA) were determined for selected regions and on a pixel-by-pixel basis. Values for F x E and E(Gd-DTPA) measured using the reference tissue method correlated well (P = .90 with a standard error of +/- .016, n = 15) with values determined based on first-pass contrast media uptake. The reference tissue method has important advantages: (a) A large volume of reference tissue can be used to determine the contrast agent input function with high precision. (b) Data obtained for 20 minutes after injection are used to calculate F or F x E. The greatly increased acquisition time can be used to increase the spatial resolution, field of view or SNR of measurements. The reference tissue method is most useful when the volume of tissue that must be imaged and/or the spatial resolution required precludes use of traditional first-pass methods.

Fast spectroscopic imaging of water and fat resonances to improve the quality of MR images

RATIONALE AND OBJECTIVES

The authors evaluated whether fast spectroscopic imaging of water and fat resonances can produce high-quality anatomic magnetic resonance (MR) images of rodent tumors and human breast.

MATERIALS AND METHODS

Fast MR spectroscopic images of eight rats with mammary tumors were acquired by using a 4.7-T MR unit equipped with self-shielded gradient coils. MR spectroscopic images of four human breasts were acquired with a 1.5-T MR unit.

RESULTS

Artifacts due to eddy currents were minimal. Images synthesized from MR spectroscopic data, in which intensity was proportional to water signal peak height, were similar to T2-weighted MR images. Boundaries of rodent mammary tumors are similar but not identical on peak height-weighted and T2-weighted images. MR spectroscopic images of human breast showed improved detail compared to gradient-echo MR images.

CONCLUSION

Preliminary results suggest that incorporation of fast MR spectroscopic imaging methods into many standard clinical MR imaging procedures may substantially improve image quality.

Correlation of magnetic resonance and oxygen microelectrode measurements of carbogen-induced changes in tumor oxygenation

PURPOSE

The aim of this work was to test the hypothesis that decreases in the linewidth of magnetic resonance (MR) water signals in tumors caused by oxygenating treatments are due to increases in capillary and venous oxygen saturation of hemoglobin, which are tightly coupled to increases in extravascular oxygen tension (pO2). To establish this link, changes measured by MR were compared to changes in tissue pO2 measured directly by oxygen microelectrodes during carbogen (95% O2/5% CO2) inhalation.

METHODS AND MATERIALS

Mammary adenocarcinomas (R3230AC) in nine rats were imaged at 4.7 Tesla. T1-weighted (TR = 200 ms, flip angle = 45 degrees) spectroscopic images of the water resonance in a single slice through each tumor were acquired with spectral resolution of 3.9 Hz and bandwidth of +/-1000 Hz. In the same slices in these tumors, microelectrode measurements were made using a non-Clark style oxygen electrode with a 350-micron tip. MR and microelectrode measurements were made during alternating periods of air and carbogen inhalation.

RESULTS

Water resonance linewidth decreased significantly during carbogen-induced hyperoxia. Paired Student's t-test analysis of microelectrode data indicated that pO2 was significantly (p < 0.05) increased as a result of carbogen inhalation. MR and microelectrode data averaged over each tumor demonstrated that decreased MR water signal linewidth is strongly correlated (r = 0.92, p < 0.05) with increased tumor pO2 levels.

CONCLUSION

Although tumor oxygenating agents increase response to radiation in rodent tumors, clinical studies have shown only marginal effects on the radiosensitivity of human tumors. This may be, in part, because the effects of tumor oxygenating treatments are highly heterogeneous both within each tumor and among a population of tumors. The noninvasive, high-resolution MR methods that are validated by the present work could guide the design of new and more effective tumor oxygenating agents and optimize treatments for individual patients.

In vivo imaging of extraction fraction of low molecular weight MR contrast agents and perfusion rate in rodent tumors

Tissue uptake of a fully extractable MR detectable tracer, deuterated water (D2O), was compared with that of a less extractable contrast agent, Gadolinium-DTPA-dimeglumine (Gd-DTPA), in rodent tumor and muscle tissue. This dual tracer method allowed calculation of relative (to muscle) tissue perfusion and extraction fraction of Gd-DTPA in each image pixel in vivo. Solutions of Gd-DTPA and D2O were injected intravenously into Fisher female rats (n = 9) with R3230 mammary adenocarcinomas implanted in the hind limb. Perfusion rate was approximately two times greater (P < 0.005 by paired t test) in tumor than in muscle. Gd-DTPA extraction fraction at the interface between tumor and muscle was 2.0 times the extraction fraction in normal muscle (P < 0.005 by paired t test). Extraction fraction at the tumor center was 1.6 times the extraction fraction in muscle (P < 0.01 by paired t test). High extraction fraction of Gd-DTPA correlated with high capillary permeability determined from Evans Blue staining. Low molecular weight Gd-DTPA derivatives are widely used in clinical practice, and their extraction fractions are crucial determinants of image contrast during the first few passes of the contrast agent bolus. Therefore spatially resolved measurements of contrast agent extraction fractions obtained in vivo have significant clinical utility. The data demonstrate that extraction of low molecular weight tracers is sensitive to increased permeability in tumor vasculature and that this increased permeability can be imaged.

Spectroscopic imaging of the water resonance with short repetition time to study tumor response to hyperoxia

A variety of treatments that modulate tumor oxygen tension are used clinically to improve the outcome of radiotherapy. High resolution, noninvasive measurements of the effects of these treatments would greatly facilitate the development of improved therapies and could guide treatment of cancer patients. Previous work demonstrated that magnetic resonance (MR) gradient echo imaging of the water proton resonance detects changes in T2* and T1 in tumors during hyperoxia that may reflect increased tumor oxygenation. This report describes the use of high resolution MR spectroscopic imaging with short repetition time (TR = 0.2 s) to improve the accuracy with which changes in T2* and T1 are measured. Mammary adenocarcinomas grown in the hind limbs of rats were studied. Carbogen inhalation was used to induce hyperoxia. A single 2-mm slice through the center of tumors and underlying muscle was imaged at 4.7 Tesla with in-plane resolution of approximately 1.2 mm and frequency resolution of 5.8 Hz. The peak integral increased by an average of 6% in tumors during carbogen inhalation suggesting a decrease in T1 (n = 8, P < 0.001). Peak height increased by an average of 15% in tumors during carbogen inhalation (n = 8, P < 0.001). The large difference between increases in peak height and peak integral demonstrates that the width of the water resonance decreased. Assuming a Lorentzian lineshape, an average increase of 12% in T2* was observed in tumors. In muscle, peak integral and peak height increased slightly (about 1.2% and 3%, respectively; P < 0.02) during carbogen inhalation but no significant change in T2* was observed. Spectroscopic imaging detects changes in the water proton resonance in tumors during hyperoxia accurately and reproducibly with high signal-to-noise ratio and allows clear separation of T1 and T2* effects. Increases in T2* may be due to decreased deoxyhemoglobin in tumor blood vessels (i.e., the BOLD effect) and may provide a clinically useful index of increases in tumor oxygenation.

Differentiating between T1 and T2* changes caused by gadopentetate dimeglumine in the kidney by using a double-echo dynamic MR imaging sequence

Dynamic MR images of the passage of gadopentetate dimeglumine through the kidneys of normal rats are obtained using a dual gradient-echo sequence. The amplitudes of gradient echoes are defined by local T1 and T2* values in the tissue. The ratio of these amplitudes, primarily defined by local T2*, can be used to differentiate between T1 and T2* effects. This is particularly important with regard to renal studies because, due to a highly inhomogeneous distribution of gadopentetate dimeglumine in the kidney, T2* shortening can impede MR data analysis. To study changes in the observed signal caused by gadopentetate dimeglumine, curves of MR renal intensity versus time were obtained in the cortex and medulla after administration of the contrast agent. Using T2* compensation, distinct temporal peaks were observed in the cortex and outer medulla, indicating a high concentration of gadopentetate dimeglumine in the vascular phase. The authors conclude that this technique can be a useful tool for studying renal function noninvasively.

Measurement of differences in pO2 in response to perfluorocarbon/carbogen in FSa and NFSa murine fibrosarcomas with low-frequency electron paramagnetic resonance oximetry

We have used very low-frequency electron paramagnetic resonance (EPR) oximetry to measure the change in oxygen concentration (delta pO2) due to change in breathing atmosphere in FSa and NFSa fibrosarcomas implanted in the legs of C3H mice infused with perfluoro-octylbromine (PFOB). Measurements in each tumor were made before and after the administration of the high-density (47% v/v) perfluorocarbon PFOB, perflubron (Alliance Pharmaceutical Corporation, San Diego, CA). Measurements in each tumor were also made, after the administration of the PFOB, both before (PFOB/air) and after the administration of carbogen (95% O2 + 5% CO2, PFOB/carbogen). Large changes (delta p02) relative to PFOB/air oxygenation were seen with the administration of PFOB/carbogen. No significant difference in oxygen concentration was seen between air-breathing mice with and without PFOB. The mean delta pO2 for FSa tumors was 13 +/- 6 torr, while the mean for NFSa fibrosarcomas was 28 +/- 7 torr. There were such large intertumor differences that the trend toward a smaller change in the more hypoxic FSa tumors was not significant (P = 0.13). This paper describes a novel method of measuring differences in oxygenation in tumor tissues. The results of such measurements indicate large differences in pO2 response to different breathing atmospheres in PFOB-infused tumors of similar histology. The intertumor delta pO2 differences may correlate with differences in radiation response.

Granular Convection Observed by Magnetic Resonance Imaging

Vibrations in a granular material can spontaneously produce convection rolls reminiscent of those seen in fluids. Magnetic resonance imaging provides a sensitive and noninvasive probe for the detection of these convection currents, which have otherwise been difficult to observe. A magnetic resonance imaging study of convection in a column of poppy seeds yielded data about the detailed shape of the convection rolls and the depth dependence of the convection velocity. The velocity was found to decrease exponentially with depth; a simple model for this behavior is presented here.

Changes in T2*-weighted images during hyperoxia differentiate tumors from normal tissue

Experiments were performed to determine whether changes in T2*-weighted MR images during and after hyperoxia differentiate tumors from normal tissue. Mammary adenocarcinomas implanted in the right hind limbs of rats were studied. Gradient echo images were obtained at 2 Tesla with an evolution time of 20 ms and a recycle time of 1 s. Breathing gas was either air or 100% O2. Significant increases in image intensity were observed in tumor centers and rims during hyperoxia while much smaller changes were detected in the surrounding muscle. The relaxation rate (1/T2*) in tumors decreased during hyperoxia by an average of 2.5 +/- 1.0 s-1, while in muscle the average change was an increase of 0.6 +/- 2.1 s-1. The largest decreases in relaxation rate were detected in non-necrotic tumor regions with relatively low density of blood vessels. Immediately following hyperoxia significant decreases in intensity were detected in tumors while much smaller decreases were detected in the surrounding muscle.

Effects of hyperoxia on T2* and resonance frequency weighted magnetic resonance images of rodent tumours

Experiments were performed to determine whether T2* and resonance frequency weighted MR images are sensitive to effects of hyperoxia on model tumors. Hyperoxia can increase tumor oxygen tension and thus affect T2* and/or the average resonance frequency within each image voxel due to the paramagnetism of oxygen itself or through modulation of the oxidation state of hemoglobin. Alternatively, changes in T2* during hyperoxia may reflect changes in tumor water content due to changes in systemic blood pressure. Mammary adenocarcinomas implanted in the flanks of rats were studied. Imaging sequences were preceded by two 90 degrees pulses separated by an evolution period of 50 or 75 ms and followed by a crusher gradient to eliminate transverse magnetization. This pulse sequence produced images which were sensitized to both T2* and the average resonance frequency of each voxel. Images were produced at 2 T using a gradient echo imaging method with a TR of 3 s. Images obtained during inhalation of air and 100% O2 were compared. Significant increases in image intensity were observed in most tumors during hyperoxia, particularly at the tumor center. The increase was accentuated when the evolution period was increased and greatly reduced when a 180 degrees refocusing pulse was placed at the center of the evolution period. These results suggest that hyperoxia reduces local magnetic susceptibility gradients leading to an increase in T2* or causes a shift in resonance frequency. The magnitude of this change may be a function of the rate at which oxygen is delivered to and metabolized by tumors and may also reflect tumor oxygen tension under normoxic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetic resonance imaging of rodent tumors using radiofrequency gradient echoes

This paper evaluates the use of radiofrequency (RF) magnetic field gradient echoes to provide contrast in magnetic resonance (MR) images of model tumors. Decay of RF gradient echoes as a function of evolution time was measured and sensitivity of the decay to changes in blood pressure was evaluated. Previous investigators have demonstrated that static field (B0) gradient echoes provide MR image contrast which is sensitive to the rate of self-diffusion of tissue water and may also be sensitive to the rate of tissue perfusion. Gradient echoes produced by RF magnetic field gradients provide a useful alternative to the conventional B0 methods. Unlike B0 gradient echoes RF gradient echoes are relatively insensitive to local magnetic susceptibility gradients and to magnetic field gradients produced by eddy currents. Differences between the two methods may be particularly significant for studies of tumors where large concentrations of deoxyhemoglobin and other paramagnetic substances may cause significant susceptibility gradients. Mammary adenocarcinomas subcutaneously implanted in the flanks of female Fisher rats were studied. Magnetic resonance experiments were performed at 2 T. A surface coil was used to provide an RF gradient and to excite and detect signals from the tumors. The decay of echo amplitude as a function of evolution time was measured and the decay at short and long evolution times was analyzed independently to calculate two apparent diffusion coefficients (ADCs). The preparation was extremely stable and the standard error for 10 consecutive measurements of gradient echo amplitude made over 30-60 min with an RF gradient strength of 50 kHz/cm, gradient duration of 1 ms (i.e., 50 cycles/cm), and echo evolution time (td) of 1 s was generally +/- 0.8%. The ADC calculated from the decay at short evolution times was approximately 3 x 10(-5) cm2/s. The ADC calculated from the decay at longer evolution times was approximately 0.5 x 10(-5) cm2/s. Both ADCs decreased immediately following sacrifice and administration of Hydralazine. The experiments demonstrate that measurements of RF gradient echo amplitudes in tumors can be made in vivo with a high degree of reproducibility and suggest that RF gradient echo amplitudes are sensitive to acute physiological changes in tumors. This method may be useful for characterization of tumors and prediction and monitoring of effects of therapeutic agents.

Hepatic cancers and their response to chemoembolization therapy. Quantitative image-guided 31P magnetic resonance spectroscopy

RATIONALE AND OBJECTIVES

Hepatic embolization combined with intra-arterial administration of cytostatic drugs (chemoembolization) is frequently used to treat primary and metastatic cancers to the liver. Quantitative phosphorus-31 magnetic resonance spectroscopy (31P MRS) was used to assess the metabolic state of hepatic cancers and their metabolic response to chemoembolization.

METHODS

Fifteen localized 31P MRS studies were performed on five patients with liver tumors. Thirteen healthy volunteers served as controls. Metabolite ratios and molar metabolite concentrations were calculated.

RESULTS

Untreated hepatic tumors, relative to normal controls, showed elevated phosphomonoester/adenosine triphosphate (PME/ATP) ratios, reduced concentrations of ATP and inorganic phosphate (Pi), and normal phosphodiester (PDE) concentrations. As an acute response to chemoembolization, ATP, PME, and/or PDE concentrations diminished, whereas Pi concentrations increased or stayed relatively constant. Long-term follow-up after chemoembolization showed decreased PME/ATP and increased ATP concentrations in the absence of changes on standard magnetic resonance and computed tomographic images.

CONCLUSIONS

These preliminary spectroscopic data suggest that quantitative 31P MRS can be successfully used to monitor directly metabolic response to hepatic chemoembolization.

Selective depletion of tumor ATP by 2-deoxyglucose and insulin, detected by 31P magnetic resonance spectroscopy

The purpose of this study was to investigate whether substrate deprivation acutely and selectively decreases ATP concentration in an experimental sarcoma. Two methods of substrate deprivation were examined: glycolysis was inhibited using 2-deoxyglucose (2DG), and plasma substrate levels were reduced using insulin. The effects of treatment on tumor ATP, inorganic phosphate, and pH were studied by 31P nuclear magnetic resonance spectroscopy. 2DG (2 g/kg) was administered i.p. to rats bearing s.c. methylcholanthrene-induced sarcomas. Inhibition of glycolysis by 2DG caused a 52 +/- 13% (SE) decrease in the tumor ATP to inorganic phosphate ratio, associated with a decrease in pH of 0.38 +/- 0.10 unit. The same dose of 2DG caused no significant change in the ratio of phosphocreatine to ATP in brain. Insulin (125 units/kg, i.p.) caused a 68% decline in plasma glucose and a 71% decline in betahydroxybutyrate compared to saline-treated animals. Concomitantly, 31P nuclear magnetic resonance spectroscopy detected a 48 +/- 13% decrease in sarcoma ATP, with a reciprocal elevation of inorganic phosphate in insulin-treated animals. In contrast, the brain phosphocratine/ATP ratio was unaffected by insulin. These results suggest that large tumors are acutely sensitive to inhibition of glycolysis and reductions in plasma levels of substrates for oxidative phosphorylation and glycolysis, while the brain is unaffected. In addition, this work provides support for the use of 31P nuclear magnetic resonance spectroscopy to monitor tumor response to therapy.

31P MRS of myocardial inorganic phosphate using radiofrequency gradient echoes

Determination of the chemical shift and integral of the myocardial intracellular inorganic phosphate (Pi) resonance by 31P magnetic resonance spectroscopy (MRS) is often precluded due to a large overlapping signal from 2,3-diphosphoglycerate (2,3-DPG) from chamber and myocardial blood. This report demonstrates the use of radiofrequency (RF) magnetic field gradient echoes (RFGE) to eliminate signals from 2,3-DPG in flowing blood, while retaining signals from intracellular myocardial Pi, ATP, and phosphocreatine (PCr). The ECG-triggered 31P spectra were acquired from the myocardium of open chest pigs using a Philips Gyroscan 2-T magnetic resonance spectrometer. A 2.5-cm-diameter surface coil attached to the myocardium was used to provide the RF gradient as well as for excitation and detection of signals. Optimal performance of the RFGE pulse sequence was obtained when the RF gradient pulses were centered at peak diastole or peak systole. Under these conditions, 2,3-DPG signals were completely suppressed, and sensitivity was usually sufficient to allow detection of a well-resolved Pi signal. Myocardial pH determined from RFGE experiments was 7.16 +/- 0.10, and the ratio of the integrals of the Pi and ATP resonances (Pi/ATP) was 0.24. The mean signal-to-noise ratio (S/N) for PCr in control spectra acquired in 4 min was 19/1, while the mean S/N for PCr in RFGE-edited spectra acquired in 15 min was 11/1, demonstrating that the present implementation of the RFGE method results in significant loss in sensitivity. These experiments demonstrate that RFGE-editing allows accurate determination of the chemical shift and integral of the Pi resonance in blood-perfused myocardium in situ.

P-31 spectroscopy study of response of superficial human tumors to therapy

Studies were performed to characterize phosphorus-31 magnetic resonance (MR) spectra obtained from 10 superficial human tumors outside the brain and to determine whether P-31 MR spectroscopy could allow detection of a response to therapy before a change in tumor size was measured. The ratio of phosphomonoester to adenosine triphosphate peak intensities (PME/ATP) was unusually large in all tumors studied. The average PME/ATP in lymphomas (1.8 +/- 0.5) was greater than in nonlymphoma cancers (1.1 +/- 0.15). The average PME/ATP for all tumors studied (1.4 +/- 0.5) was much greater than that of underlying skeletal muscle (0.23 +/- .09). Eight of the tumors were studied before and after therapy. Responders were distinguished from nonresponders on the basis of changes in tumor size. PME/ATP decreased during therapy in three lymphomas that responded to therapy. In an adenocarcinoma and Ewing sarcoma that did not respond to therapy, PME/ATP increased. PME/ATP remained constant in two squamous cell carcinomas that responded to therapy and decreased in one squamous cell carcinoma that decreased in size by 40% but was classified as a nonresponder. Changes in PME/ATP did not always parallel changes in tumor size during therapy. In two patients, a decrease in PME/ATP preceded a decrease in tumor size. In four patients, PME/ATP increased transiently during periods when tumor size remained constant.

Image-guided 31P magnetic resonance spectroscopy of normal and transplanted human kidneys

Image-guided 31-phosphorus magnetic resonance spectroscopy (MRS) was used to obtain spatially localized 31P spectra of good quality from healthy normal human kidneys and from well-functioning renal allografts. A surface coil of 14 cm diameter was used for acquiring phosphorus signals solely from a volume-of-interest located within the kidney. To determine the effects of kidney transplantation on renal metabolism, patients with well functioning allografts were studied. Little or no phosphocreatine in all spectra verifies the absence of muscle contamination, and is consistent with proper volume localization. The intensity ratio of phosphomonoesters (PME) to adenosine triphosphate (ATP) resonances in transplanted kidneys (PME/ATP = 1.1 +/- 0.4) was slightly elevated (P = 0.2) compared to that of healthy normal kidneys (PME/ATP = 0.8 +/- 0.3). The inorganic phosphate (Pi) to ATP ratio was similar in the two groups (Pi/ATP = 1.1 +/- 0.1 in transplanted kidneys vs. 1.2 +/- 0.6 in normal kidneys). Acid/base status, as evidenced from the chemical shift of Pi, was the same in both normal controls and transplanted kidneys. Despite the practical problems produced by organ depth, respiratory movement, and tissue heterogeneity, these results demonstrate that image-guided 31P MR spectra can reliably be obtained from human kidneys.

Comparison of 31P MRS and 1H MRI at 1.5 and 2.0 T

The goals of this study were to compare 31P magnetic resonance spectroscopy (MRS) and 1H magnetic resonance imaging (MRI) of human subjects and phantoms at 1.5 and 2.0 T. The 31P signal-to-noise (S/N) ratios in phantom standards and in localized volumes in human brain and liver were compared at 1.5 and 2.0 T. In addition, T1 values for 31P resonances in human brain, 31P linewidths of metabolites in human brain and liver, 1H S/N in a phantom standard, and MR image quality in human head and body were compared at the two field strengths. The results of our study showed that at the higher strength field, (1) in vivo 31P MRS studies benefited from up to 32% improvement in S/N; (2) in vivo 31P MRS studies also benefited from increased spectral dispersion; (3) the quality of MR head images remained comparable; and (4) body images showed some decrease in image quality due to increased chemical shift, and flow and motion artifacts.

Response of tumors to therapy studied by 31P magnetic resonance spectroscopy

Magnetic resonance (MR) methods have been used to study the metabolic and vascular response of model tumors to tumor necrosis factor (TNF). Magnetic resonance measurements demonstrated acute reductions in tumor blood flow, measured from tumor uptake of D2O, and in tumor adenosine triphosphate (ATP), measured by 31P magnetic resonance spectroscopy (MRS) following administration of TNF. The decrease in ATP generally followed reduction in tumor blood flow, and therefore was probably due to ischemia caused by damage to tumor vasculature. Superficial human tumors have been studied by MRS to characterize their 31P spectra, and to measure metabolic changes during therapy. The ratio of the intensities of the phosphomonoester (PME) and ATP resonances (PME/ATP) was much higher in tumors than in the normal tissue displaced by the tumors. During therapy, decreases in PME/ATP were detected that paralleled, but did not anticipate, decreases in tumor size. In some cases, a transient increase in PME/ATP was detected during therapy, which did not correlate with changes in tumor size, and which may reflect stimulation of cell growth in some tumor zones.

Abnormalities of the liver evaluated by 31P MRS

Clinical phosphorus-31 magnetic resonance spectroscopy (31P MRS) of the liver requires the use of whole-body magnets and of spectroscopy techniques that acquire signal from defined volumes-of-interest within the liver. Such localization techniques and recent clinical studies are briefly reviewed. These studies indicate that (1) high phosphomonoester levels are present in liver diseases involving structural damage, and (2) that MRS of liver tumors may provide a sensitive and rapid indication of response to cancer therapy. Abnormalities of the liver such as alcoholic liver disease, viral hepatitis, and metastasis were analyzed to determine hepatic acid/base status (pH) and to derive absolute molar concentrations of hepatic phosphorus metabolites rather than metabolite ratios. These parameters allow diagnosis and differentiation of several liver pathologies, suggesting an increasing future role of MRS in medical investigation, clinical diagnosis, and patient treatment.

Use of radio-frequency field gradients to image blood flow and perfusion in vivo

A magnetic resonance imaging method based on the use of radio-frequency (RF) magnetic field gradients to detect molecular motion has been combined with GRASS (gradient-recalled acquisition in a steady state) imaging to detect arterial blood flow in vivo. The method has been used to selectively attenuate signals from flowing blood in the human finger. Attenuation of signals from arterial blood was greatly reduced when blood flow was decreased with the application of a tourniquet. This result demonstrated the sensitivity of the technique to the rate of blood flow. RF gradient coils can be used to generate very high RF gradients with submicrosecond rise times and minimal eddy currents. Therefore, this method may prove useful for imaging very slow, nonuniform flow through capillary beds and in the extravascular space.

Regulation of hepatic inorganic phosphate and ATP in response to fructose loading: an in vivo 31P-NMR study

Fructose loading results in hepatic accumulation of fructose 1-phosphate (Fru1 P). The goals of the present experiments were: first, to distinguish between ATP, intracellular inorganic phosphate (Pi), and extracellular Pi as sources of phosphate for the phosphorylation of fructose, and second, to examine the influence of ATP and Fru1 P on movement of phosphate into and out of these three pools. To achieve these goals, 31P-NMR was used to monitor the response of hepatic ATP, Pi and Fru1 P to two consecutive injections of fructose. The first was administered with ATP at the control level, and the second, 1 h after the first, with ATP at 65% of the control level. Changes in intra- and extracellular Pi were distinguished by correlating measurements of total NMR-detectable phosphorus and NMR-detectable Pi with measurements of plasma Pi. The initial fructose injection resulted in rapid accumulation of Fru1 P, small decreases in plasma and NMR-detectable Pi and a dramatic decrease in ATP. Total NMR-detectable phosphorus did not change, suggesting that phosphate did not enter or leave the liver. Therefore, accumulation of Fru1 P was initially balanced by an equivalent decrease in ATP, without large changes in Pi. Following the second injection, when ATP was at 65% of control. Fru1 P accumulated at approximately the same rate and to the same level as achieved following the first injection. There was little further change in ATP and a marked decrease in NMR-detectable Pi, while plasma Pi was higher than after the first injection. Therefore the greater decrease in NMR-detectable Pi following the second injection represented a significant decrease in intracellular Pi. Return of Fru1 P to control coincided with a dramatic increase in plasma Pi, and a decrease in total NMR-detectable phosphate. This suggests that phosphate released from Fru1 P entered the extracellular space. These data suggest the mechanisms by which intracellular Pi is regulated. When sufficient ATP is available, ATP hydrolysis supplies phosphate for the synthesis of Fru1 P, and prevents a significant decrease in intracellular Pi. When ATP is reduced, accumulation of Fru1 P depletes intracellular Pi. Therefore, decreased availability of ATP correlates with increased utilization of intracellular Pi. When Fru1 P returns to control, the increase in intracellular Pi is limited by release of Pi into the plasma.

Early metabolic response to tumor necrosis factor in mouse sarcoma: a phosphorus-31 nuclear magnetic resonance study

To investigate the effects of recombinant human tumor necrosis factor alpha (rHuTNF-alpha) on high-energy phosphate metabolism of cancer cells, 31P nuclear magnetic resonance (NMR) studies were performed on a murine methylcholanthrene-induced sarcoma. Injection of 15 micrograms of rHuTNF-alpha caused progressive depletion of ATP and phosphocreatine within 90 min, together with an increase in inorganic phosphate. Metabolic changes were correlated with the early histological appearance of thrombosis and hemorrhage. A spatially localized NMR technique demonstrated that these changes were specific for the tumor. Acute ischemia of the tumor produced similar metabolic changes; thus the metabolic effects of rHuTNF-alpha could be due to either a primary action on tumor biochemistry or a secondary action produced by ischemia. These findings indicate that rHuTNF-alpha has a very rapid onset of action, which can be detected by 31P NMR. Furthermore, the results suggest that 31P NMR spectroscopy will be extremely useful for detecting early biochemical changes produced by rHuTNF-alpha or other treatments in animal and human cancers.

Computer simulation of MRS localization techniques: an analysis of ISIS

Computer simulations were used to evaluate the ISIS localization technique as implemented with both head and surface coils. The effects of chemical shift, B1 inhomogeneity, repetition time, T2 relaxation, a postacquisition saturation pulse, and a B1 insensitive observation pulse were examined. Integrals of ISIS signals over the sample volume showed that significant signal loss from the volume of interest (VOI) and contamination from outside the VOI can occur for both head and surface coil ISIS experiments. The results showed that the saturation pulse, order of the various ISIS acquisitions, and repetition time affect contamination but not signal loss. In addition, short T2 and high RF power can combine synergistically to degrade the selective inversion pulses, causing further contamination and signal loss.

A 31P NMR study of the GI tract: effect of fructose loading and measurement of transverse relaxation times

The effect of fructose loading on high-energy phosphates in the jejunum, ileum, and large intestine of rats was studied using 31P NMR. Following fructose loading, an increase in the intensity of the PME resonance was observed in the jejunum, indicating an accumulation of fructose-1-phosphate. There were no significant changes in ATP or Pi. This demonstrates that the activity of fructokinase in the jejunum can be monitored by 31P NMR. Fructose loading had no detectable effect on metabolite levels in the ileum and large intestine. Resolution of intestinal spectra was poor due to unusually large linewidths and the presence of broad underlying signals. To study the mechanism of line broadening, the T2's of the phosphorus resonances were measured using a solenoidal coil. The T2's of the ATP, Pi, PME, and PCr resonances were much longer than the T2's, suggesting that the linewidths of these resonances are primarily due to susceptibility gradients and/or compartmentation of metabolites. Other signals, particularly in the PDE region, were homogeneously broadened and had very short T2's. Spin echoes obtained with evolution times of 1 to 4 ms suppressed these broad components, with little loss of intensity in the inhomogeneously broadened resonances; as a result, resolution was improved.

Nuclear magnetic resonance imaging-guided phosphorus-31 spectroscopy of the human heart

Phosphorus-31 nuclear magnetic resonance spectroscopy can determine the status of high energy phosphates in vivo. However, its application to human cardiac studies requires precise spatial localization without significant contamination from other tissues. Using image-selected in-vivo spectroscopy (ISIS), a technique that allows three-dimensional localization of the volume of interest, 12 subjects were studied to determine the feasibility and reproducibility of phosphorus-31 spectroscopy of the human heart. Nuclear magnetic resonance imaging was performed using a commercial 1.5 tesla system to define the volume of interest. Phosphorus-31 spectra were obtained from the septum and anteroapical region of the left ventricle in 10 studies. Relative peak heights and areas were determined for high energy phosphates. The mean phosphocreatine to adenosine triphosphate ratio was 1.33 +/- 0.19 by height analysis and 1.23 +/- 0.27 by area analysis. Duplicate measurements in four subjects showed a reproducibility of less than or equal to 10% in three of the subjects. All spectra showed significant signal contribution from the 2,3 diphosphoglycerate in chamber red cells without evidence of skeletal muscle contamination. These results demonstrate the feasibility of image-guided phosphorus-31 spectroscopy for human cardiac studies and indicate the potential of this technique to study metabolic disturbances in human myocardial disease.

Application of image-guided surface coil P-31 MR spectroscopy to human liver, heart, and kidney

Localized phosphorus-31 magnetic resonance (MR) spectroscopy in humans has previously been accomplished with surface coils by means of depth-resolved surface coil spectroscopy or rotating frame experiments, in which the extent of tissue sampled critically depends on surface coil placement. The authors' goal was to modify the surface coil image-selected in vivo spectroscopy (ISIS) experiment to accomplish three-dimensional volume selection through application of selective pulses in the presence of B0 gradients. Advantages of ISIS include the ability to use proton images to define the volume of interest (VOI) and reduced dependence on exact positioning of the surface coil. However, rapid replication of the surface coil ISIS experiment can cause spectral contamination from signals originating outside the VOI. A modified version of the ISIS experiment was developed to alleviate contamination under conditions of rapid replication. Applications of localized P-31 MR spectroscopy for observation of high-energy phosphorus metabolites are presented in human liver, heart, and transplanted and normal kidney.

Inhibition of tumor high-energy phosphate metabolism by insulin combined with rhodamine 123

The purpose of this study was to determine whether the energy metabolism of an experimental rodent sarcoma was selectively depressed by the combination of inhibition of glycolysis and respiration. In vivo phosphorus-31 nuclear magnetic resonance spectroscopy was used to monitor the response of tumor or brain high-energy phosphate compounds to insulin hypoglycemia, rhodamine 123, or both agents in fasting rats with subcutaneous methylcholanthrene-induced sarcomas. Insulin or rhodamine 123 alone produced a similar 50% to 60% reduction in tumor adenosine triphosphate (ATP) concentration compared with controls injected with saline solution (p less than 0.05, one-way analysis of variance [ANOVA]). The combination of insulin plus rhodamine 123 resulted in a 90% reduction of tumor ATP concentration, which was significantly different from the effect of either agent alone (p less than 0.05, one-way ANOVA). Brain phosphocreatine and ATP concentrations were unchanged by these agents. Administration of dimethyl sulfoxide (DMSO)/glycerol, the vehicle for rhodamine, produced a 35% reduction of tumor ATP, which was similar to the effect of insulin alone but significantly different from rhodamine. The combination of DMSO/glycerol plus insulin hypoglycemia resulted in a 70% reduction in tumor ATP, which was significantly elevated compared with the combination of rhodamine plus insulin. Glucose deprivation induced by insulin, and combined with the inhibition of oxidative phosphorylation, produces an additive depression of tumor energetics. The drug vehicle DMSO/glycerol significantly depresses tumor energy metabolism, presumably because of its DMSO component, which may explain the previously reported antineoplastic efficacy of this solvent. Combinations of inhibitors directed at different points of tumor metabolism produced an enhanced depression of tumor energetics, whereas host tissue was protected.

Detection of motion using B1 gradients

An NMR method which makes use of a radiofrequency (RF) field gradient to detect diffusion, perfusion, or flow is demonstrated. The technique is analogous to the detection of motion using pulsed B0 gradients. The simplest form of the experiment is as follows: A spatially imhomogeneous RF field generated by a surface coil produces dispersal of magnetization in the Y Z plane. After a delay, the RF field is applied within reversed phase to restore polarization along +Z, which is then sampled using an observe pulse or pulse sequence. If molecular motion occurs during the delay period the amplitude of Z magnetization will be reduced. The lengths of the RF pulses and the delay period are varied so that the effects of relaxation, flow, and diffusion or perfusion can be distinguished. The present study demonstrates the use of this method to detect slow fluid flow. Advantages of this method include the availability of large RF gradients, and the avoidance of eddy currents. It is suggested that the method may have application to the study of perfusion and flow in vivo.

A single acquisition localization technique

A method is demonstrated for detection of magnetization from a selected region within the sensitive volume of a surface coil in a single acquisition. Composite pulses are described which eliminate signals from regions where magnetization is rotated 270 and 450 degrees. There is a loss of 1.3% or less of signal from regions where magnetization is rotated 90 degrees.

The interaction of adriamycin with small unilamellar vesicle liposomes. A fluorescence study

The interaction of the antineoplastic agent adriamycin with sonicated liposomes composed of phosphatidylcholine alone and with small amounts (1-6%) of cardiolipin has been studied by fluorescence techniques. Equilibrium binding data show that the presence of cardiolipin increases the amount of drug bound to liposomes when the bilayer is below its phase transition temperature and when the ionic strength is relatively low (0.01 M). At higher ionic strength (0.15 M) and above the Tm (i.e. conditions which are closer to the physiological state) the binding of the drug to the two liposome types is nearly the same. Thus the differences in the interactions of adriamycin with cardiolipin-containing membranes, as opposed to those composed of phosphatidylcholine alone, are not due simply to increased binding but rather to an altered membrane structure when this lipid is present. Quenching of adriamycin fluorescence by iodide shows that bound drug is partially, but not completely, buried in the liposomal membrane. Both in the presence and absence of cardiolipin the bulk of the adriamycin is more accessible to the quencher below the Tm than above it; that is, a solid membrane tends to exclude the drug from deep penetration. Above the Tm, the presence of cardiolipin alters the nature of liposome-adriamycin interaction. Here the fluorescence quenching data suggest that the presence of small amounts of cardiolipin (3%) in a phosphatidylcholine matrix creates two types of binding environments for drug, one relatively exposed and the other more deeply buried in the membrane. The temperature dependence of the adriamycin fluorescence and the liposome light scattering reveal that cardiolipin alters the thermal properties of the bilayer as well as its interaction with adriamycin. At low ionic strength lateral phase separations may occur with both pure phosphatidylcholine and when 3% cardiolipin is present; under these conditions the bound adriamycin exists in two kinds of environment. It is notable that only adriamycin fluorescence reveals this phenomenon; thebulk property of liposome light scattering reports only on the overall membrane phase change. These data suggest that under certain conditions the drug binding sites in the membranes are decoupled from the bulk of the lipid bilayer.