Multinuclear MR investigation of the metabolic response of the murine RIF-1 tumor to 5-fluorouracil chemotherapy

The metabolic response of the RIF-1 tumor to 5-fluorouracil (a single dose of 260 mg 5FU/kg, ip) was monitored in 10 mice using 19F and 31P MR spectroscopy. 19F MRS revealed a continuous drop in tumor 5FU level and an increase in the fluoronucleotide (Fnuc) signal to a plateau value of 50% of the initial 5FU level, during the first 2 h after chemotherapy. Although the 31P MR spectra of the tumors showed no significant initial changes, the total level of MR visible tumor phosphate decreased and tumor pH increased during the subsequent days. The changes in phosphate metabolism and tumor pH did not correlate with the detected fluorine levels or tumor response. However, the pretreatment Pi level, the plateau Fnuc level, and the 5FU induced decrease in tumor volume showed significant correlation. This indicates that both 19F and 31P MR spectroscopy have potential for predicting response to 5FU chemotherapy.     

化学位移成像及MR波谱分析在体外水脂模型中对脂肪定量的研究

目的 评价化学位移成像(chemical shift imaging,CSI)和MRS两种方法在脂肪研究中的作用,为进一步活体实验提供定量标准.方法 在7.0 T MR成像仪上运用CSI和MRS方法对体外水脂模型进行水脂定量分析.体外水脂模型的脂肪含量从0～100%平均分成11个组,各组间浓度相差10%,分别应用水、脂肪选择性CSI和1H-MRS对体外水脂模型进行图像和波谱数据采集,对2种方法所得结果分别与实际水脂含量进行单样本t检验及相关分析并比较两种方法问的相关性.MRS计算100%油模型饱和脂肪酸(fraction of saturated fatty acids,FS)、不饱和脂肪酸(fraction of unsaturated fatty acids,FU)的相对含量及多聚不饱和程度(polyunsaturation degree,PUD).结果 CSI法测定实际脂肪含量为50%～100%的测量值分别为(48.0±1.0)%、(57.0±0.5)%、(67.3±0.6)%、(77.3 ±0.6)%、(83.3±0.6)%和(91.0±1.0)%;MRS测定实际脂肪含量为10%～60%的测量值分别为(8.3±0.6)%、(16.3±0.7)%、(27.7±0.6)%、(36.0±1.0)%、(43.5±0.6)%和(56.5±1.0)%,均轻度低估了脂肪含量,差异均有统计学意义(P值均<0.05).CSI与MRS计算的脂肪含量与实际脂肪含量间均呈线性相关(CSI:r=0.998,MRS:r=0.996;P值均<0.01);两种方法间也呈线性相关(r=0.992,P<0.01),两种方法定量脂肪含量差异无统计学意义(t=-0.125,P:0.903).MRS计算橄榄油的FS和FU相对含量分别为0.15和0.85,PUD为0.0325,与实际含量一致.结论 在7.0 T MR成像仪上,体外水脂模型证实CSI和MRS定量脂肪的准确性及在脂肪研究上的可行性.     

Proton two-dimensional chemical shift imaging for evaluation of prostate cancer: external surface coil vs. endorectal surface coil

PURPOSE: To compare the diagnostic ability of proton magnetic resonance spectroscopy (MRS) using an external surface coil with that using an endorectal surface coil in patients with prostate cancer. MATERIALS AND METHODS: MR imaging (MRI) and two-dimensional chemical shift imaging (2D CSI) were performed in 5 healthy volunteers and in 35 patients with prostate cancer. The receiver coil was the anterior lower part of a phased-array coil or an endorectal surface coil. RESULTS: Receiver-operating characteristic analysis for diagnosing prostate cancer showed no significant difference (P = 0.784) between the area under the curve of phased-array coil CSI and that of endorectal surface coil CSI. CONCLUSION: The phased-array coil CSI could provide comparable detection accuracy to endorectal surface coil CSI. In patients with rectal diseases or patients who could not tolerate the discomfort with insertion of an endorectal surface coil, we recommend the phased-array coil CSI.     

Monitoring of release of cargo from nanocarriers by MRI/MR spectroscopy (MRS): Significance of T2/T effect of iron particles

To monitor the release of cargo molecules from nanocarriers, a novel MRI/MRS technique was developed and tested. This novel approach uses a simultaneous encapsulation of superparamagnetic iron oxide (SPIO) nanoparticles and either a gadolinium (Gd)‐based paramagnetic contrast agent, Gd‐diethylenetriamine pentaacetic acid bismethylamide(GdDTPA‐BMA), for MRI, or an anticancer agent, 5‐fluorouracil (5‐FU), for MRS. These agents have significantly different diffusion properties due to their different molecular sizes. Strong negative signal enhancement due to the T₂ effects of SPIO dominates the positive T₁ contrast generated by GdDTPA‐BMA when SPIO and GdDTPA‐BMA are in close proximity (intact form). Positive T₁ contrast becomes evident upon release of GdDTPA‐BMA from the carrier once the distance between GdDTPA‐BMA and SPIO molecules is beyond the T₂ enhancement range. Similarly, intact nanocarriers loaded with 5‐FU and SPIO have a broad ¹⁹F resonance line because line‐width is inversely proportional to T^*₂, while free 5‐FU appears as a narrow resonance line once it is released from the liposomes. This technique allowed monitoring of the release of cargo molecules from liposomes encapsulating both SPIO and either GdDTPA‐BMA or 5‐FU by MRI/MRS in vitro using 2% agarose gel phantoms. Experimental results demonstrate successful demarcation of the released cargo molecules vs. encapsulated molecules. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Quantitative 19F imaging of nmol‐level F‐nucleotides/‐sides from 5‐FU with T2 mapping in mice at 9.4T

A unique acquisition method is proposed for quantitative, high‐sensitivity ¹⁹F MR spectroscopic imaging for the study of drug distribution aiming at nmol‐level metabolite information in mice. The use of fast spin echo (FSE) at 9.4T allowed us to obtain whole‐body images with minimal effect of magnetic susceptibility and to acquire several metabolite signals simultaneously by the method of interleaved multifrequency selection. Modified 2‐shot FSE was designed for simultaneous, high‐sensitivity ¹⁹F imaging and T₂ mapping. A time course study including all the main metabolites at 10‐minute resolution was attained with an oral dose of 1–2 mmol 5‐fluorouracil (5‐FU) (130–260 mg)/kg in mice. With acquisition parameters optimized for in vivo T₂ of 40 ms, images of F‐nucleotides/‐sides, effective anabolites of the anticancer drug 5‐FU, were obtained at the level of 200 nmol in the tumor for all the mice studied with a linear correlation (R = 0.96) between image intensity and the quantity determined in the excised tissue. The method exhibits potential capability of molecular imaging with a variety of ¹⁹F‐labeled compounds and drug evaluation. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Development of an in vivo 19F magnetic resonance method for measuring oxygen deficiency in tumors.

A 19F magnetic resonance spectroscopy (MRS) approach to measuring hypoxia in experimental tumors in rats at a field strength of 2.35 T has been investigated in a combined study of in situ and excised tumors. The detection of tumor hypoxia is based on the hypoxia marker approach which depends on the selective, covalent binding of a fluorinated 2-nitroimidazole to hypoxic cells. The 19F MRS measurement of in vivo hypoxia marker binding was made at a fixed postinjection time when unbound, circulating marker molecule concentrations had dropped below detectable levels. A correlation between 19F MRS and scintillation counting measures of tumor-bound, tritium-labeled hypoxia marker was observed. There was no correlation between integrated 19F MRS hypoxia marker signals and the in vivo 31P MRS parameters of hypoxia which have been developed to measure normal tissue ischemia. Radiolabeling studies and previous immunohistochemical studies with the fluorinated hypoxia marker support the conclusion that the 19F MRS approach has promise as a physically noninvasive guide to the use of hypoxia-dependent therapies at clinically usable MRS field strengths.     

Simultaneous 3D NMR spectroscopy of proton-decoupled fluorine and phosphorus in human liver during 5-fluorouracil chemotherapy

Simultaneous acquisition of ¹H-decoupled ³¹P and ¹⁹F 3D CSI is demonstrated in the liver of a patient undergoing 5-fluorouracil chemotherapy. Both ³¹P and ¹⁹F shared the same voxel size (64 or 27 ml), bi-level ¹H-decoupling and 0.35 s TR. The measurements were done in a 1.5 Tesla clinical imager with three radio-frequency (RF) channels and a triple-tuned surface-coil. The overall MRI and MRS examination time was under 90 min. Simultaneous acquisition of ³¹P and ¹⁹F permits localized study of the influence of hepatic metabolism on the uptake and catabolism of fluoropyrimidine drugs without extra measurement time or higher SAR.     

磁共振波谱技术在乳腺癌诊断中的应用

目的:利用氢质子磁共振波谱(1H MRS)技术检测活体乳腺癌病灶与对侧正常乳腺组织内的物质代谢和物质生化含量的差异及其反映在分子水平上的病理改变。方法:对30例经乳腺钼靶摄影疑为一侧乳腺癌的患者行1H MRS检查,比较其病侧与对侧相应部位正常腺体组织的胆碱(Choline,Cho)、乳酸(Lactine,Lac)含量有无显著性差异。结果:正常乳腺组织1H MRS在1.32ppm处显示一独立清晰的乳酸峰,胆碱峰显示低平,Cho峰顶与Lac峰顶的连线呈上升趋势。30例病侧组在3.2ppm处Cho峰显著增高,Lac峰明显降低,Cho峰顶与Lac峰顶的连线呈下降趋势;两组间行秩和检验,差异有显著性(P<0.05)。结论:氢质子磁共振波谱(1H MRS)对于乳腺癌的定性诊断可提供有价值的辅助信息。     

The role of MRS in the differentiation of benign and malignant soft tissue and bone tumors

Objective

The aim of our study was to investigate the value of choline in the discrimination of benign and malignant soft tissue and bone tumors.

Materials and methods

The study group consisted of thirty subjects with bone or soft tissue tumors larger than 1.5 cm in diameter. The experiments were performed in a 1.5 T MR scanner. Coils were selected according to specific locations. A single-voxel MRS was performed for three different TE (time to echo) (31, 136, 272 ms). The volume of interest was positioned on the brightest enhancement. The presence of a cholin peak on at least 2 of these spectrums was considered as the marker of malignancy. The sensitivity, specificity and accuracy of the MRS in the detection and diagnosis of malignant lesions were calculated. The reproducibility of MRS and histopathological results were tested with kappa statistics.

Results

Histopathologically, 18 (60%) of the lesions were classed as malignant whereas 12 (40%) were classed as benign. With MRS, 15 (50%) of these lesions were classed as malignant and 15 (50%) as benign. Two patients who were found spectroscopically to have malignant tumors were shown histopathologically to have benign types. Five patients with an MRS showing a benign type were classed with malignant types in histopathological examinations. MRS had a sensitivity rate of 72.2%, specificity of 83.3%, and an accuracy rate of 76.6% in detecting malignant bone and soft tissue tumors. The interrater reliability of both techniques had a kappa value of 0.533.

Conclusions

MRS may help in the differentiation of benign and malignant soft tissue and bone tumors.     

Examination of the optimum condition that determines contamination for three-dimensions chemical shift imaging

Magnetic resonance spectroscopy (MRS) is a useful tool for obtaining metabolic information non-invasively. However, low reducibility of MRS data, measuring biases caused by the operator, effects of relaxation time, and environmental contamination may sometimes become problematic. In this study, we examined contamination in echo time (TE) and the availability of outer volume suppression (OVS) by using the excitation and localization methods. In addition, we investigated the optimized condition for three-dimensions (3D)-chemical shift imaging (CSI) in gliomas. Contamination was dependent on resolution in the excitation and localization methods and on CSI resolution, but it was not dependent on TE. The additional installation of OVS and saturation pulse (SAT) corresponding to the target sites were extremely useful. There was concern about the influence of chemical shift, crosstalk, contamination, and no radio frequency (RF) uniformity in the marginal volume of interest (VOI). Metabolite distribution was deteriorated along the Z-axis but not in the X-Y plane. It, however, was improved by using a small voxel size in the Z-axis.     

Application of (19)F chemical shift imaging in studies of mice with orally administered 5-fluorouracil.

In vivo quantitative metabolic mapping is an ideal tool for pharmacokinetic studies. Oral 5-fluorouracil (5-FU) and its metabolites in mice were imaged simultaneously by the (19)F fast spin echo (FSE) sequence using interleaved frequency selection at 9.4T. However, 5-FU images in the small intestine have never been obtained regardless of concentration. The reason for the discrepancy between image intensity and concentration was T(2). At a pH above 6, a dramatic decrease in T(2) of a (19)F 5-FU signal in an aqueous solution was found; T(2) was shorter in the small intestine (14 ms) than in the stomach (52 ms). The (19)F CSI sequence in FID sampling mode was employed for detecting short T(2) signals. With a 13-min resolution time, the detection of the 5-FU signals in the region of the small intestine (0.6 mmol/kg) was successful with a 5 x 5 mm(2) in-plane resolution. Furthermore, two signals separated by 2 ppm were clearly distinguishable, but failed to be separately detectable with the (19)F FSE sequence. For quantitative simultaneous monitoring of 5-FU and its metabolites of varying T(2), the (19)F CSI sequence in FID sampling mode was found to be superior to the (19)F FSE sequence.     

Reproducibility of cerebral phenylalanine levels in patients with phenylketonuria determined by 1H‐MR spectroscopy

The reproducibility of metabolite content determined by MR spectroscopy (MRS) is usually at best a few percent for the prominent singlets. When studying low‐concentration metabolites, like phenylalanine (Phe), where tissue content can be <100 μmol/kg, better reproducibility is paramount—particularly in view of using MRS results for potential individual treatment advice. An optimized, targeted spectroscopy method was established at 1.5T and reproducibility was established in 21 patients with phenylketonuria (PKU) where three spectra were recorded in each of three independent sessions, two of which were in immediate succession to minimize physiologic variation. Intersession variation was found to be only 7 μmol/kg Phe for back‐to‐back repetition of sessions, in close agreement with the variation of 16 μmol/kg observed for single spectra within a session. Analysis of variance proved the individuality of the blood/brain Phe ratio—though this ratio seems to be influenced by physiologic factors that are not stable in time. The excellent reproducibility was achieved through optimization of various factors, including signal‐to‐noise ratio, repositioning, and prescan calibrations, but also by enforcing as much prior information as possible (e.g., lineshape and phase from reference scans, constant prior‐knowledge‐locked baseline). While the application of maximum general prior knowledge is a general method to reduce fluctuations, one should remember that it may introduce systematic errors. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

1H chemical shift imaging reveals loss of brain tumor choline signal after administration of Gd-contrast

¹H MR spectra obtained by chemical shift imaging (CSI) of contrast-enhancing brain tumors before and after the administration of Gd-contrast agent were quantitated and compared with the results in normal brain tissue included in the volume of interest. Twenty-seven combined magnetic resonance imaging and spectroscopy (MRI, MRS) examinations of brain tumor lesions included T₁-weighted MRI and CSI (TR/TE 1500/135 ms double-spin echo) repeated 5–10 min after the administration of Gd-contrast agent (0.1–0.2 mM). In ¹H MR spectra of contrast-enhancing tumor Gd-contrast induced a mean loss of 15% of the peak area of choline-containing compounds (Cho, P < 0.001) that was correlated with precontrast Cho linewidth (r = ?0.72, P < 0.00001). This phenomenon limits the diagnostic use of brain tumor MRS examinations performed immediately after contrast-enhanced MRI.     

A new method for the evaluation of the liver injury by 19F MRS of 5-fluorouracil.

An investigation was made of 5-fluorouracil metabolism in rat liver by 19F MRS. Fluoronucleotide synthesis increased markedly with liver injury and accelerated with uracil treatment, indicating that 19F MRS may serve as a new method for evaluating liver viability.     

Assessment of the variations in fat content in normal liver using a fast MR imaging method in comparison with results obtained by spectroscopic imaging

A recently published Dixon-based MRI method for quantifying liver fat content using dual-echo breath-hold gradient echo imaging was validated by phantom experiments and compared with results of biopsy in two patients (Radiology 2005;237:1048-1055). We applied this method in ten healthy volunteers and compared the outcomes with the results of MR spectroscopy (MRS), the gold standard in quantifying liver fat content. Novel was the use of spectroscopic imaging yielding the variations in fat content across the liver rather than a single value obtained by single voxel MRS. Compared with the results of MRS, liver fat content according to MRI was too high in nine subjects (range 3.3–10.7% vs. 0.9–7.7%) and correct in one (21.1 vs. 21.3%). Furthermore, in one of the ten subjects the MRI fat content according to the Dixon-based MRI method was incorrect due to a (100-x) versus x percent lipid content mix-up. The second problem was fixed by a minor adjustment of the MRI algorithm. Despite systematic overestimation of liver fat contents by MRI, Spearman’s correlation between the adjusted MRI liver fat contents with MRS was high (r = 0.927, P < 0.001). Even after correction of the algorithm, the problem remaining with the Dixon-based MRI method for the assessment of liver fat content,is that, at the lower end range, liver fat content is systematically overestimated by 4%.     

Alanine peak in central neurocytomas on proton MR spectroscopy

Introduction We present three consecutive patients with central neurocytoma in whom proton MRS demonstrated the presence of alanine. Materials and methods Three patients in the age range 24 to 30 years underwent MRI and proton MRS using a 1.5-T system. MRS was performed with the multivoxel PRESS sequence. All three patients underwent surgery and the diagnosis of central neurocytoma was established by histopathological examination and immunostaining. Results With an echo time of 135 ms glycine, high choline, small NAA and alanine were observed in all three patients. Conclusion Alanine may be observed in central neurocytomas as it is in meningiomas. Other spectral peaks such as those for glycine and NAA should help to identify this tumor correctly.     

Hepatic steatosis assessment with H-spectroscopy and chemical shift imaging at 3.0 T before hepatic surgery: Reliable enough for making clinical decisions?

Purpose

To compare the accuracy of liver fat quantification using chemical shift imaging (CSI) and H1 MR-spectroscopy (MRS) at 3.0 T in patients undergoing liver resection.

Methods

Totally 35 patients were included in this prospective IRB approved study. The histopathologically assessed liver fat was compared to the hepatic fat fractions calculated with CSI (with and without spleen correction) and MRS. Spearman's rank correlation and Fisher z-test were used for correlation analysis. Sensitivity and specificity regarding the detection of marked steatosis were calculated for the different modalities and compared using the McNemar test.

Results

MRS (r = .85) and CSI with spleen correction (r = .85) showed a significantly better correlation (p = .03) with histology compared to CSI without spleen correction (r = .67). Sensitivity and specificity for the detection of marked steatosis was 100% (12/12) and 87% (20/23) for MRS and 92% (11/12) and 83% (19/23) for CSI with spleen correction (p > .12).

Conclusion

For the assessment of hepatic steatosis both CSI with spleen correction and MRS at 3.0 T, show a good correlation with histology. CSI without spleen correction should not be used. Sensitivity and specificity for the detection of marked steatosis are high with both modalities. However, results that are scattered around the cut-off values are not reliable enough for clinical decisions.     

In vivo metabolite profile of adult zebrafish brain obtained by high‐resolution localized magnetic resonance spectroscopy

Purpose

To optimize high‐resolution MR spectroscopy (MRS) for obtaining neurochemical composition of adult zebrafish brain in vivo.

Materials and Methods

A flow‐through setup for supporting MRS of living zebrafish has been designed. In vivo MR microscopy (MRM) images were obtained using a rapid acquisition with relaxation enhancement (RARE) sequence to select a volume of interest. In vivo MR spectra from zebrafish brain were obtained using an optimized point‐resolved spectroscopy (PRESS) sequence preceded by a variable pulse power and optimized relaxation delays (VAPOR) sequence for global water suppression interleaved with outer volume suppression (OVS). In vitro MR spectra in the brain extract were obtained by using correlated spectroscopy (COSY) sequences.

Results

Optimized high‐resolution localized MRS at 9.4T in conjunction with a strong gradient system, efficient shimming, and the water suppression scheme resulted in a reasonable separation of resonances from various metabolites in vivo from a voxel as small as 3.3 μL placed in the zebrafish brain. In addition, more than 14 metabolites were identified in adult zebrafish brain extracts.

Conclusion

We have successfully optimized a high‐resolution localized in vivo MRS technique to get access to the zebrafish brain, and obtained for the first time the neurochemical composition of the zebrafish brain. J. Magn. Reson. Imaging 2009;29:275–281. © 2009 Wiley‐Liss, Inc.     

Localized in vivo 1H spectroscopy and chemical shift imaging of the bone marrow in leukemic patients

Six healthy volunteers, ten patients with acute leukemia, one patient with hypersplenia and two with bone marrow carcinoris were studied. Nine patients with leukemia were restudied during chemotheraphy. A double spin echo localization method, implemented on a 1.5 T whole body unit was used for ¹H magnetic resonance spectroscopy (MRS). A cubic (13 mm)³ voxel was chosen in a midlumbar vertebra. For chemical shift imaging (CSI) the SENEX sequence was used. We recorded fat and water images in a representative midsagittal plane. Patients with acute leukemia and hypercellular bone marrow a severe reduction or loss bone marrow fat signal and an increased water signal. Water T1 increaed during therapy in three patients. The bone marrow fat reappeared in the spectra and chemical shift images within 2 or 3 weeks in responders and remained unchanged or reappeared later in non-responders. A normal fat signal could be detected in leukemic patients without hypercellular bone marrow. Specificity was missing for ¹H MRS and CSI; marrow carcinosis and benign stimulation (hypersplenia) could not be seperated from leukemia. In clinical routine, CSI may have advantages over ¹H MRS, because a large anatomic field can be examined. Inhomogenous fat signal distrbutions can be detected and were seen in sveral cases during therapy. ¹H MRS and CSI allow non-invasive therapy monitoring of leukemic patients adn might be of prognostic value. Correspondence to: H. Bongers     

Blocking catabolism with eniluracil enhances PET studies of 5-[18F]fluorouracil pharmacokinetics.

Noninvasive methods for measuring the pharmacokinetics of chemotherapeutic drugs such as 5-fluorouracil (FU) are needed for individualized optimization of treatment regimens. PET imaging of [18F]FU (PET/[18F]FU) is potentially useful in this context, but PET/[18F]FU is severely hampered by low tumor uptake of radiolabel and rapid catabolism of FU in vivo. Pretreatment with eniluracil (5-ethynyluracil) prevents catabolism of FU. Hypothesizing that suppression of catabolism would enhance PET/[18F]FU, we examined the effects of eniluracil on the short-term pharmacokinetics of the radiotracer. METHODS: Anesthetized rats bearing a subcutaneous rat colorectal tumor were given eniluracil or placebo and injected intravenously 1 h later with [18F]FU or [3H]FU. In the 18F studies, dynamic PET image sequences were obtained 0-2 h after injection. Tumors were excised and frozen at 2 h and then analyzed for labeled metabolites by high-performance liquid chromatography. Biodistribution of radiolabel was determined by direct tissue assay. RESULTS: Eniluracil improved tumor visualization in PET images. With eniluracil, tumor standardized uptake values ([activity/g]/[injected activity/g body weight]) increased from 0.72 +/- 0.06 (mean +/- SEM; n = 6) to 1.57 +/- 0.20 (n = 12; P < 0.01), and tumor uptake increased by factors of 2 or more relative to plasma (P < 0.05) and bone, liver, and kidney (P < 0.01). Without eniluracil (n = 5), 57% +/- 4% of recovered radiolabel in tumor at 2 h was on catabolites, with the rest divided among FU (2% +/- 1%), anabolites of FU (38% +/- 7%), and unidentified peaks (4% +/- 2%). With eniluracil (n = 8), catabolites, FU, and anabolites comprised 2% +/- 1%, 41% +/- 5%, and 57% +/- 4%, respectively, of the recovered radiolabel in tumors. CONCLUSION: Eniluracil increased tumor accumulation of 18F relative to host tissues and fundamentally changed the biochemical significance of that accumulation. With catabolism suppressed, tumor radioactivity reflected the therapeutically relevant aspect of FU pharmacokinetics--namely, uptake and anabolic activation of the drug. With this approach, it may be feasible to measure the transport and anabolism of [18F]FU in tumors by kinetic modeling and PET. Such information may be useful in predicting and increasing tumor response to FU.