Detection of tumor response to radiation therapy by in vivo proton MR spectroscopy

Magnetic resonance spectroscopic imaging in gliomas: clinical diagnosis and radiotherapy planning

The reprogramming of cellular metabolism is a hallmark of cancer diagnosis and prognosis. Proton magnetic resonance spectroscopic imaging (MRSI) is a non-invasive diagnostic technique for investigating brain metabolism to establish cancer diagnosis and IDH gene mutation diagnosis as well as facilitate pre-operative planning and treatment response monitoring. By allowing tissue metabolism to be quantified, MRSI provides added value to conventional MRI. MRSI can generate metabolite maps from a single volume or multiple volume elements within the whole brain. Metabolites such as NAA, Cho and Cr, as well as their ratios Cho:NAA ratio and Cho:Cr ratio, have been used to provide tumor diagnosis and aid in radiation therapy planning as well as treatment assessment. In addition to these common metabolites, 2-hydroxygluterate (2HG) has also been quantified using MRSI following the recent discovery of IDH mutations in gliomas. This has opened up targeted drug development to inhibit the mutant IDH pathway. This review provides guidance on MRSI in brain gliomas, including its acquisition, analysis methods, and evolving clinical applications.

MRI and MRS of intact perfused cancer cell metabolism, invasion, and stromal cell interactions

Because of the spatial and temporal heterogeneities of cancers, technologies to investigate cancer cells and the consequences of their interactions with abnormal physiological environments, such as hypoxia and acidic extracellular pH, with stromal cells, and with the extracellular matrix, under controlled conditions, are valuable to gain insights into the functioning of cancers. These insights can lead to an understanding of why cancers invade and metastasize, and identify effective treatment strategies. Here we have provided an overview of the applications of MRI/MRS/MRSI to investigate intact perfused cancer cells, their metabolism and invasion, and their interactions with stromal cells and the extracellular matrix.

Intraoperative serum lactate is not a predictor of survival after glioblastoma surgery

BACKGROUND

Cancer cells can produce lactate in high concentrations. Two previous studies examined the clinical relevance of serum lactate as a biomarker in patients with brain tumors. Patients with high-grade tumors have higher serum concentrations of lactate than those with low-grade tumors. We hypothesized that serum lactic could be used of biomarker to predictor of survival in patients with glioblastoma (GB).

METHODS

This was a retrospective study. Demographic, lactate concentrations and imaging data from 275 adult patients with primary GB was included in the analysis. The progression free survival (PFS) and overall survival (OS) rates were compared in patients who had above and below the median concentrations of lactate. We also investigated the correlation between lactate concentrations and tumor volume. Multivariate analyses were conducted to test the association lactate, tumor volume and demographic variables with PFS and OS.

RESULTS

The median serum concentration of lactate was 2.3mmol/L. A weak correlation was found between lactate concentrations and tumor volume. Kaplan-Meier curves demonstrated similar survival in patients with higher or lower than 2.3mmol/L of lactate. The multivariate analysis indicated that the intraoperative levels of lactate were not independently associated with changes in survival. On another hand, a preoperative T1 volume was an independent predictor PFS (HR 95%CI: 1.41, 1.02-1.82, p=0.006) and OS (HR 95%CI: 1.47, 1.11-1.96, p=0.006).

CONCLUSION

This retrospective study suggests that the serum concentrations of lactate cannot be used as a biomarker to predict survival after GB surgery. To date, there are no clinically available serum biomarkers to determine prognosis in patients with high-grade gliomas. These tumors may produce high levels of lactic acid. We hypothesized that serum lactic could be used of biomarker to predictor of survival in patients with glioblastoma (GB). In this study, we collected perioperative and survival data from 275 adult patients with primary high-grade gliomas to determine whether intraoperative serum acid lactic concentrations can serve as a marker of prognosis. The median serum concentration of lactate was 2.3mmol/L. Our analysis indicated the intraoperative levels of lactate were not independently associated with changes in survival. This retrospective study suggests that the serum concentrations of lactate cannot be used as a biomarker to predict survival after GB surgery.

Evaluation of lactate detection using selective multiple quantum coherence in phantoms and brain tumours

Lactate is a product of glucose metabolism. In tumour tissues, which exhibit enhanced glycolytic metabolism, lactate signals may be elevated, making lactate a potential useful tumour biomarker. Methods of lactate quantitation are complicated because of overlap between the lactate methyl doublet CH3 resonance and a lipid resonance at 1.3 ppm. This study presents the use of a selective homonuclear multiple quantum coherence transfer sequence (SelMQC-CSI), at 1.5 T, to better quantify lactate in the presence of lipids. Work performed on phantoms showed good lactate detection (49%) and lipid suppression (98%) efficiencies. To evaluate the method in the brain, the sequence was tested on a group of 23 patients with treated brain tumours, either glioma (N=20) or secondary metastases in the brain (N=3). Here it was proved to be of use in determining lactate concentrations in vivo. Lactate was clearly seen in SelMQC spectra of glioma, even in the presence of lipids, with high grade glioma (7.3 ± 1.9 mM, mean ± standard deviation) having higher concentrations than low grade glioma (1.9 ± 1.5 mM, p=0.048). Lactate was not seen in secondary metastases in the brain. SelMQC-CSI is shown to be a useful technique for measuring lactate in tumours whose signals are otherwise contaminated by lipid.

Serum lactate as a potential biomarker of malignancy in primary adult brain tumours

Lactate, a by-product of glycolysis, is an indicator of poor tissue perfusion and is a useful biomarker with prognostic value in risk-stratifying patients in several diseases. Furthermore, elevated lactate production is observed in tumour glycolysis, also known as the Warburg effect, and is essential in promoting tumour cell invasion, metastasis, and immune system evasion, promoting resistance to cell death. However, there are no studies of elevated serum lactate in brain tumour patients as a potential biomarker, to our knowledge. The aim of this study is to determine possible correlations between the malignancy of tumours and pre- and intraoperative serum lactate elevation in patients undergoing craniotomy for tumour resection. We provide initial evidence that a rise in serum lactate can be used as a non-invasive biomarker that correlates with brain tumour grade. The results from this study and future prospective studies may allow for determination of tumour progression and response to therapy using serum lactate as a biomarker.

Rapid diagnosis and staging of colorectal cancer via high-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR) spectroscopy of intact tissue biopsies

OBJECTIVE

To develop novel metabolite-based models for diagnosis and staging in colorectal cancer (CRC) using high-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR) spectroscopy.

BACKGROUND

Previous studies have demonstrated that cancer cells harbor unique metabolic characteristics relative to healthy counterparts. This study sought to characterize metabolic properties in CRC using HR-MAS NMR spectroscopy.

METHODS

Between November 2010 and January 2012, 44 consecutive patients with confirmed CRC were recruited to a prospective observational study. Fresh tissue samples were obtained from center of tumor and 5 cm from tumor margin from surgical resection specimens. Samples were run in duplicate where tissue volume permitted to compensate for anticipated sample heterogeneity. Samples were subjected to HR-MAS NMR spectroscopic profiling and acquired spectral data were imported into SIMCA and MATLAB statistical software packages for unsupervised and supervised multivariate analysis.

RESULTS

A total of 171 spectra were acquired (center of tumor, n = 88; 5 cm from tumor margin, n = 83). Cancer tissue contained significantly increased levels of lactate (P < 0.005), taurine (P < 0.005), and isoglutamine (P < 0.005) and decreased levels of lipids/triglycerides (P < 0.005) relative to healthy mucosa (R2Y = 0.94; Q2Y = 0.72; area under the curve, 0.98). Colon cancer samples (n = 49) contained higher levels of acetate (P < 0.005) and arginine (P < 0.005) and lower levels of lactate (P < 0.005) relative to rectal cancer samples (n = 39). In addition unique metabolic profiles were observed for tumors of differing T-stage.

CONCLUSIONS

HR-MAS NMR profiling demonstrates cancer-specific metabolic signatures in CRC and reveals metabolic differences between colonic and rectal cancers. In addition, this approach reveals that tumor metabolism undergoes modification during local tumor advancement, offering potential in future staging and therapeutic approaches.

Assessment of the intrinsic radiosensitivity of glioma cells and monitoring of metabolite ratio changes after irradiation by 14.7-T high-resolution ¹H MRS

Gliomas are the most common type of primary brain tumor. Radiation therapy (RT) is the primary adjuvant treatment to eliminate residual tumor tissue after surgery. However, the current RT guided by conventional imaging is unsatisfactory. A fundamental question is whether it is possible to further enhance the effectiveness and efficiency of RT based on individual radiosensitivity. In this research, to probe the correlation between radiosensitivity and the metabolite characteristics of glioma cells in vitro, a perchloric acid (PCA) extracting method was used to obtain water-soluble metabolites [such as N-acetylaspartate (NAA), choline (Cho), creatine (Cr) and succinate (Suc)]. Spectral patterns from these processed water-soluble metabolite samples were acquired by in vitro 14.7-T high-resolution ¹H MRS. Survival fraction analysis was performed to test the intrinsic radiosensitivity of glioma cell lines. Good ¹H MRS of PCA extracts from glioma cells was obtained. The radiosensitivity of glioma cells correlated positively with the Cho/Cr and Cho/NAA ratios, but negatively with the Suc/Cr ratio. Irradiation of the C6 cell line at different X-ray dosages led to changes in metabolite ratios and apoptotic rates. A plateau phase of metabolite ratio change and a decrease in apoptotic rate were found in the C6 cell line. We conclude that in vitro high-resolution ¹H MRS possesses the sensitivity required to detect subtle biochemical changes at the cellular level. ¹H MRS may aid in the assessment of the individual radiosensitivity of brain tumors, which is pivotal in the identification of the biological target volume.

Repeatability of edited lactate and other metabolites in astrocytoma at 3T

PURPOSE

To assess the repeatability of measurement of lactate and other metabolites in tumors using magnetic resonance spectroscopy (MRS).

MATERIALS AND METHODS

MRS with spectral editing for lactate was performed on 10 patients with astrocytoma (two Grade III, eight Grade IV) using an 8-channel receive coil at 3T. Lactate, lipid, choline, creatine, and N-acetyl aspartate (NAA) signals were measured in regions of tumor and contralateral white matter. Metabolites were quantified relative to unsuppressed water using LCModel fitting software.

RESULTS

The within-patient coefficients of variation were ≈16% (tumor lactate), 6%-8% (tumor choline and contralateral choline, creatine, and NAA), and 22% (tumor lipid). As expected due to their low concentration in normal tissue, lactate and lipid were not reliably detected in white matter but were found at high levels in most tumors. NAA and creatine were lower in tumors than in normal white matter, and choline varied between above- and below-normal values. No consistent short-term variation in metabolite levels was observed, despite differences in the time elapsed since administration of contrast agent.

CONCLUSION

MRS appears repeatable enough to provide longitudinal measures of metabolite content in tumors and contralateral tissue in the brain in vivo.

Magnetic resonance spectroscopy of cancer metabolism and response to therapy

Magnetic resonance spectroscopy allows noninvasive in vivo measurements of biochemical information from living systems, ranging from cultured cells through experimental animals to humans. Studies of biopsies or extracts offer deeper insights by detecting more metabolites and resolving metabolites that cannot be distinguished in vivo. The pharmacokinetics of certain drugs, especially fluorinated drugs, can be directly measured in vivo. This review briefly describes these methods and their applications to cancer metabolism, including glycolysis, hypoxia, bioenergetics, tumor pH, and tumor responses to radiotherapy and chemotherapy.

Reduced phosphocholine and hyperpolarized lactate provide magnetic resonance biomarkers of PI3K/Akt/mTOR inhibition in glioblastoma

The phosphatidylinositol-3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathway is activated in more than88% of glioblastomas (GBM). New drugs targeting this pathway are currently in clinical trials. However, noninvasive assessment of treatment response remains challenging. By using magnetic resonance spectroscopy (MRS), PI3K/Akt/mTOR pathway inhibition was monitored in 3 GBM cell lines (GS-2, GBM8, and GBM6; each with a distinct pathway activating mutation) through the measurement of 2 mechanistically linked MR biomarkers: phosphocholine (PC) and hyperpolarized lactate.(31)P MRS studies showed that treatment with the PI3K inhibitor LY294002 induced significant decreases in PC to 34 %± 9% of control in GS-2 cells, 48% ± 5% in GBM8, and 45% ± 4% in GBM6. The mTOR inhibitor everolimus also induced a significant decrease in PC to 62% ± 14%, 57% ± 1%, and 58% ± 1% in GS-2, GBM8, and GBM6 cells, respectively. Using hyperpolarized (13)C MRS, we demonstrated that hyperpolarized lactate levels were significantly decreased following PI3K/Akt/mTOR pathway inhibition in all 3 cell lines to 51% ± 10%, 62% ± 3%, and 58% ± 2% of control with LY294002 and 72% ± 3%, 61% ± 2%, and 66% ± 3% of control with everolimus in GS-2, GBM8, and GBM6 cells, respectively. These effects were mediated by decreases in the activity and expression of choline kinase α and lactate dehydrogenase, which respectively control PC and lactate production downstream of HIF-1. Treatment with the DNA damaging agent temozolomide did not have an effect on either biomarker in any cell line. This study highlights the potential of PC and hyperpolarized lactate as noninvasive MR biomarkers of response to targeted inhibitors in GBM.

Lactate MRSI and DCE MRI as surrogate markers of prostate tumor aggressiveness

Longitudinal studies of lactate MRSI and dynamic contrast-enhanced MRI were performed at 4.7 T in two prostate tumor models grown in rats, Dunning R3327-AT (AT) and Dunning R3327-H (H), to determine the potential of lactate and the perfusion/permeability parameter Ak(ep) as markers of tumor aggressiveness. Subcutaneous AT (n = 12) and H (n = 6) tumors were studied at different volumes between 100 and 2900 mm(3) (Groups 1-5). Lactate concentration was determined using selective multiple quantum coherence MRSI with the phantom substitution method. Tumor enhancement after the administration of gadolinium diethylenetriaminepenta-acetic acid was analyzed using the Brix-Hoffmann model and the Ak(ep) parameter was used as a measure of tumor perfusion/permeability. Lactate was not detected in the smallest AT tumors (Group 1; 100-270 mm(3) ). In larger AT tumors, the lactate concentration increased from 2.8 ± 1.0 mm (Group 2; 290-700 mm(3)) to 8.4 ± 2.9 mm (Group 3; 1000-1340 mm(3)) and 8.2 ± 2.2 mm (Group 4; 1380-1750 mm(3) ), and then decreased to 5.0 ± 1.7 mm (Group 5; 1900-2500 mm(3)), and was consistently higher in the tumor core than in the rim. Lactate was not detected in any of the H tumors. The mean tumor Ak(ep) values decreased with increasing volume in both tumor types, but were significantly higher in H tumors. In AT tumors, the Ak(ep) values were significantly higher in the rim than in the core. Histological hypoxic and necrotic fractions in AT tumors increased with volume from 0% in Group 1 to about 20% and 30%, respectively, in Group 5. Minimal amounts of hypoxia and necrosis were found in H tumors of all sizes. Thus, the presence of lactate and heterogeneous perfusion/permeability are signatures of aggressive, metabolically deprived tumors.

Noninvasive monitoring of radiation-induced early therapeutic response using high-resolution MR imaging and proton MR spectroscopy in VX2 carcinoma

The purpose of this study was to evaluate the usefulness of high-resolution MRI (HR-MRI) and proton MR spectroscopy ((1)H-MRS) for monitoring the early therapeutic response to radiotherapy. Twenty rabbits with VX2 carcinoma were divided into control (n = 8) and irradiation (n = 12) groups. The irradiation group underwent HR-MRI and (1)H-MRS using a microscopy coil at 1, 3, 7 or 14 days after irradiation. Rabbits in the control group were subjected to HR-MRI and (1)H-MRS at the same time intervals. All rabbits were killed after imaging and subjected to histopathologic examinations. The diameter of necrosis by HR-MRI was then compared to that on the gross specimens. The ratios of choline/creatine (Cho/Cr) and lactate/creatine (Lac/Cr) on the tumor and necrotic area detected by in vivo (1)H-MRS were compared between the control and irradiation groups, respectively. In addition, the ratios of Cho/Cr and Lac/Cr were compared between the tumor and necrotic area in each irradiation group. A significant correlation was found between the diameter of necrosis in each sequence of HR-MRI and that in the gross specimens (r = 0.84-0.91, p = 0.03- < 0.003). The ratios of Lac/Cr in the tumors of the irradiation groups were significantly higher than those in the control groups after 1 day and 3 days of irradiation (p = 0.04, and p = 0.02). Histological analysis showed necrosis and swelling of the endothelia of capillaries and arterioles at 1 day and 3 days after irradiation. It was suggested that HR-MRI and (1)H-MRS are useful methods for monitoring the early therapeutic response to radiotherapy.

Early detection of radiation therapy response in non-Hodgkin's lymphoma xenografts by in vivo 1H magnetic resonance spectroscopy and imaging

The purpose of the study was to investigate the capability of (1)H MRS and MRI methods for detecting early response to radiation therapy in non-Hodgkin's lymphoma (NHL). Studies were performed on the WSU-DLCL2 xenograft model in nude mice of human diffuse large B-cell lymphoma, the most common form of NHL. Radiation treatment was applied as a single 15 Gy dose to the tumor. Tumor lactate, lipids, total choline, T(2) and apparent diffusion coefficients (ADC) were measured before treatment and at 24 h and 72 h after radiation. A Hadamard-encoded slice-selective multiple quantum coherence spectroscopy sequence was used for detecting lactate (Lac) while a stimulated echo acquisition mode sequence was used for detection of total choline (tCho) and lipids. T(2)- and diffusion-weighted imaging sequences were used for measuring T(2) and ADC. Within 24 h after radiation, significant changes were observed in the normalized integrated resonance intensities of Lac and the methylenes of lipids. Lac/H(2)O decreased by 38 +/- 15% (p = 0.03), and lipid (1.3 ppm, CH(2))/H(2)O increased by 57 +/- 14% (p = 0.01). At 72 h after radiation, tCho/H(2)O decreased by 45 +/- 14% (p = 0.01), and lipid (2.8 ppm, polyunsaturated fatty acid)/H(2)O increased by 970 +/- 36% (p = 0.001). ADC increased by 14 +/- 2% (p = 0.003), and T(2) did not change significantly. Tumor growth delay and regression were observed thereafter. This study enabled comparison of the relative sensitivities of various (1)H MRS and MRI indices to radiation and suggests that (1)H MRS/MRI measurements detect early responses to radiation that precede tumor volume changes.

Detection of lactate with a hadamard slice selected, selective multiple quantum coherence, chemical shift imaging sequence (HDMD-SelMQC-CSI) on a clinical MRI scanner: Application to tumors and muscle ischemia

Lactate is an important metabolite in normal and malignant tissues detectable by NMR spectroscopy; however, it has been difficult to clinically detect the lactate methyl resonance because it is obscured by lipid resonances. The selective homonuclear multiple quantum coherence transfer technique offers a method for distinguishing lipid and lactate resonances. We implemented a three-dimensional selective homonuclear multiple quantum coherence transfer version with Hadamard slice selection and two-dimensional phase encoding (Hadamard encoded-selective homonuclear multiple quantum coherence transfer-chemical shift imaging) on a conventional clinical MR scanner. Hadamard slice selection is explained and demonstrated in vivo. This is followed by 1-cm(3) resolution lactate imaging with detection to 5-mM concentration in 20 min on a 3-T clinical scanner. An analysis of QSel gradient duration and amplitude effects on lactate and lipid signal is presented. To demonstrate clinical feasibility, a 5-min lactate scan of a patient with a non-Hodgkin's lymphoma in the superficial thigh is reported. The elevated lactate signal coincides with the T(2)-weighted image of this tumor. As a test of selective homonuclear multiple quantum coherence transfer sensitivity, a thigh tourniquet was applied to a normal volunteer and an increase in lactate was detected immediately after tourniquet flow constriction. In conclusion, the Hadamard encoded-selective homonuclear multiple quantum coherence transfer-chemical shift imaging sequence is demonstrated on a phantom and in two lipid-rich, clinically relevant, in vivo conditions.

Noninvasive detection of target modulation following phosphatidylinositol 3-kinase inhibition using hyperpolarized 13C magnetic resonance spectroscopy

Numerous mechanism-based anticancer drugs that target the phosphatidylinositol 3-kinase (PI3K) pathway are in clinical trials. However, it remains challenging to assess responses by traditional imaging methods. Here, we show for the first time the efficacy of hyperpolarized (13)C magnetic resonance spectroscopy (MRS) in detecting the effect of PI3K inhibition by monitoring hyperpolarized [1-(13)C]lactate levels produced from hyperpolarized [1-(13)C]pyruvate through lactate dehydrogenase (LDH) activity. In GS-2 glioblastoma cells, PI3K inhibition by LY294002 or everolimus caused hyperpolarized lactate to drop to 42 +/- 12% and to 76 +/- 5%, respectively. In MDA-MB-231 breast cancer cells, hyperpolarized lactate dropped to 71 +/- 15% after treatment with LY294002. These reductions were correlated with reductions in LDH activity to 48 +/- 4%, 63 +/- 4%, and 69 +/- 12%, respectively, and were associated with a drop in levels of LDHA mRNA and LDHA and hypoxia-inducible factor-1alpha proteins. Supporting these findings, tumor growth inhibition achieved by everolimus in murine GS-2 xenografts was associated with a drop in the hyperpolarized lactate-to-pyruvate ratio detected by in vivo MRS imaging, whereas an increase in this ratio occurred with tumor growth in control animals. Taken together, our findings illustrate the application of hyperpolarized (13)C MRS of pyruvate to monitor alterations in LDHA activity and expression caused by PI3K pathway inhibition, showing the potential of this method for noninvasive imaging of drug target modulation.

In vivo (1)H MRS of WSU-DLCL2 human non-Hodgkin's lymphoma xenografts: response to rituximab and rituximab plus CHOP

In order to identify early (1)H MRS metabolic markers of response to rituximab immunotherapy and to rituximab plus CHOP (cyclophosphamide, hydroxydoxorubicin, vincristine, and prednisone) combination therapy, we performed an in vivo MRS investigation of a non-Hodgkin's lymphoma (NHL) xenograft model. Human WSU-DLCL2 NHL cells were subcutaneously implanted into flanks of female severe combined immunodeficient mice. When tumor volumes reached approximately 600 mm(3), rituximab was administered for three weekly cycles at a dose of 25 mg/kg per cycle with or without CHOP. Before and after treatment, tumor lactate (Lac) and total choline (tCho) were detected using the selective multiple quantum coherence sequence and the stimulated echo acquisition mode sequence, respectively. Rituximab produced a small tumor growth delay ( approximately 5 days), whereas treatment with rituximab plus CHOP (RCHOP) led to approximately 20% tumor regression after three cycles of therapy. After one cycle of rituximab, the tCho/H(2)O ratio had decreased significantly (5%, P = 0.003), whereas the Lac/H(2)O ratio had not changed (P = 0.58). Both Lac/H(2)O and tCho/H(2)O had decreased after one cycle of RCHOP treatment (26%, P = 0.001; 10%, P = 0.016, respectively). After two cycles of RCHOP, Ki67 assay of histological tumor specimens indicated approximately 40% decrease in proliferation (P < 0.001) in the RCHOP-treated tumors; no change was detected after treatment with rituximab alone. This study suggests that decreases in tCho/H(2)O are more sensitive indices of response to rituximab, whereas decreases in Lac/H(2)O are more sensitive to response to CHOP combination therapy.

Lactate imaging with Hadamard-encoded slice-selective multiple quantum coherence chemical-shift imaging

The ability to generate in vivo maps of lactate may have significant diagnostic utility in staging and treatment planning of a wide variety of cancers. The double selective multiple quantum filter technique (SelMQC) has been shown to be effective for nonlocalized detection of lactate with little or no interference from other signals. Here the SelMQC technique has been combined with longitudinal Hadamard slice selection and chemical shift imaging (CSI) to yield slice-selective images of lactate. The technique is shown to be effective in phantoms and in WSU-DLCL2 xenografts implanted in flanks of SCID mice. Tumors exhibited an annulus of elevated lactate concentration surrounding a necrotic tumor core.

Monitoring response to chemotherapy of non-Hodgkin's lymphoma xenografts by T(2)-weighted and diffusion-weighted MRI

An effective method for in vivo detection of early therapeutic response of patients with non-Hodgkin's lymphoma would enable personalized clinical management of cancer therapy and facilitate the design of optimal treatment regimens. This study evaluates the feasibility of T(2)-weighted MRI (T2WI) and diffusion-weighted MRI (DWI) for in vivo detection of response of human diffuse large B-cell lymphoma xenografts in severe combined immunodeficient mice to chemotherapy. Each cycle of combination chemotherapy with cyclophosphamide, hydroxydoxorubicin, Oncovin, prednisone, and bryostatin 1 (CHOPB) was administered to tumor-carrying mice weekly for up to four cycles. T2WI and DWI were performed before the initiation of CHOPB and after each cycle of CHOPB. In order to corroborate the MRI results, histological analyses were carried out on control tumors and treated tumors after completion of all MRI studies. DWI revealed a significant (P < 0.03) increase in the mean apparent diffusion coefficient in CHOPB-treated tumors as early as 1 week after initiation of CHOPB. However, a significant (P < 0.03) decrease in mean T(2) was observed only after two cycles of CHOPB. Both MRI methods produced high-resolution (0.1 x 0.1 x 1.0 mm(3)) maps of regional therapeutic response in the treated tumors based on local apparent diffusion coefficient and T(2). Only a specific region of the tumors (in 3 of the 5 tumors) corresponding to about one third of the tumor volume exhibited a response-associate increase in ADC and decrease in T(2). An adjacent region exhibited an increase in T(2) and no change in ADC. The rest of the tumor was indistinguishable from sham-treated controls by MRI criteria. The therapeutic response of the treated tumors detected by MRI was accompanied by changes in tumor cell density, proliferation and apoptosis revealed by histological studies performed upon completion of the longitudinal study. The mechanism producing the regional response of the tumor remains to be elucidated.

Functional MRI and Diffusion Tensor Imaging

Above discussed aspects, considerations and technical possibilities, as well as methodological requirements, guidelines and clinical applications of proton spectroscopy strengthens our belief in the power of this method used in neurooncological diagnosis.

Tumor cell metabolism imaging

Molecular imaging of tumor metabolism has gained considerable interest, since preclinical studies have indicated a close relationship between the activation of various oncogenes and alterations of cellular metabolism. Furthermore, several clinical trials have shown that metabolic imaging can significantly impact patient management by improving tumor staging, restaging, radiation treatment planning, and monitoring of tumor response to therapy. In this review, we summarize recent data on the molecular mechanisms underlying the increased metabolic activity of cancer cells and discuss imaging techniques for studies of tumor glucose, lipid, and amino acid metabolism.

In vivo MRS markers of response to CHOP chemotherapy in the WSU-DLCL2 human diffuse large B-cell lymphoma xenograft

To identify 1H-MRS molecular biomarkers of early clinical therapeutic response in non-Hodgkin's lymphoma, an in vivo longitudinal study was performed on human non-Hodgkin's diffuse large B-cell lymphoma xenografts (WSU-DLCL2) grown in the flanks of female SCID mice. 31P-MRS measurements, which have been demonstrated to be prognostic clinical indices of response (Arias-Mendoza et al. Acad. Radiol. 2004; 11: 368-376) but which provide lower spatial resolution, were included for comparison. The animals received CHOP (cyclophosphamide, hydroxydoxorubicin, oncovin and prednisone) chemotherapy for three 1-week cycles, resulting in stable disease based on tumor volume. Localization of total choline and phosphorus metabolites in vivo was achieved with stimulated echo acquisition mode and image selected in vivo spectroscopy sequences, respectively. Significant decreases in lactate were detected by the selective multiple quantum coherence spectral editing technique after the first cycle of CHOP, whereas total choline and the phosphomonoester/nucleoside triphosphate ratio did not change until the third cycle. Ex vivo extract MRS of tumors corroborated the in vivo results. Histological staining with antibodies to Ki67 revealed a decrease in proliferation rate in CHOP-treated tumors that coincided with the decrease in lactate. This study demonstrates the utility of lactate as an early proliferation-sensitive indicator of therapeutic response in a mouse model of non-Hodgkin's lymphoma and serves as a basis for future clinical implementation of these methods.

Metabolomics using 1H-NMR of apoptosis and Necrosis in HL60 leukemia cells: differences between the two types of cell death and independence from the stimulus of apoptosis used

High-resolution proton nuclear magnetic resonance ((1)H-NMR) spectroscopy was used to examine and compare the metabolic variations that occur in cells of the HL60 promyelocytic leukemia cell line after induction of apoptosis by ionizing radiation and the antineoplastic drug doxorubicin as well as after induction of necrosis by heating. Apoptosis and necrosis were confirmed by fluorescence microscopy using the chromatin stain Hoechst 33258, agarose gel electrophoresis of DNA, and determination of caspase 3 enzymatic activity. The 1H-NMR experiments revealed that the spectra of both samples containing apoptotic cells were characterized by the same trend of several important metabolites. Specifically, an increase in CH2 and CH3 mobile lipids, principally of CH2, decreases in glutamine and glutamate, choline-containing metabolites, taurine and reduced glutathione were observed. By contrast, the sample containing necrotic cells presented a completely different profile of 1H-NMR metabolites since it was characterized by a significant increase in all the metabolites examined, with the exception of CH2 mobile lipids, which remain unchanged, and reduced glutathione, which decreased. The results suggest that variations in 1H-NMR metabolites are specific to apoptosis independent of the physical or chemical nature of the stimulus used to induce this mode of cell death, while cells dying from necrosis are characterized by a completely different behavior of the same metabolites.

In vivo monitoring response to chemotherapy of human diffuse large B-cell lymphoma xenografts in SCID mice by 1H and 31P MRS

RATIONALE AND OBJECTIVES

A reliable noninvasive method for in vivo detection of early therapeutic response of non-Hodgkin's lymphoma (NHL) patients would be of great clinical value. This study evaluates the feasibility of (1)H and (31)P magnetic resonance spectroscopy (MRS) for in vivo detection of response to combination chemotherapy of human diffuse large B-cell lymphoma (DLCL2) xenografts in severe combined immunodeficient (SCID) mice.

MATERIALS AND METHODS

Combination chemotherapy with cyclophosphamide, hydroxy doxorubicin, Oncovin, prednisone, and bryostatin 1 (CHOPB) was administered to tumor-bearing SCID mice weekly for up to four cycles. Spectroscopic studies were performed before the initiation of treatment and after each cycle of the CHOPB. Proton MRS for detection of lactate and total choline was performed using a selective multiple-quantum-coherence-transfer (Sel-MQC) and a spin-echo-enhanced Sel-MQC (SEE-Sel-MQC) pulse sequence, respectively. Phosphorus-31 MRS using a nonlocalized, single-pulse sequence without proton decoupling was also performed on these animals.

RESULTS

Significant decreases in lactate and total choline were detected in the DLCL2 tumors after one cycle of CHOPB chemotherapy. The ratio of phosphomonoesters to beta-nucleoside triphosphate (PME/betaNTP, measured by (31)P MRS) significantly decreased in the CHOPB-treated tumors after two cycles of CHOPB. The control tumors did not exhibit any significant changes in either of these metabolites.

CONCLUSIONS

This study demonstrates that (1)H and (31)P MRS can detect in vivo therapeutic response of NHL tumors and that lactate and choline offer a number of advantages over PMEs as markers of early therapeutic response.

Advances in methods for assessing tumor hypoxia in vivo: implications for treatment planning

Tumor hypoxia and its downstream effects have remained of considerable interest for decades due to its negative impact on response to various cancer therapies and promotion of metastasis. Diagnosing hypoxia non-invasively can provide a significant advancement in cancer treatment and is the dire necessity for implementing specific targeted therapies now emerging to treat different aspects of cancer. A variety of techniques are being proposed to do so. However, none of them has yet been established in the clinical arena. This review summarizes the methods currently available to assess tumor hypoxia in vivo and their respective advantages and shortcomings. It also points out the impedances that need to be overcome to establish any particular method in the clinic, along with a broad overview of requirements for further advancement in this sphere of cancer research.

Temporal Dynamics of1H-NMR-Visible Metabolites during Radiation-Induced Apoptosis in MG-63 Human Osteosarcoma Spheroids

The metabolic changes that occur as a function of time in MG-63 osteosarcoma three-dimensional tumor spheroids undergoing radiation-induced apoptosis were studied using high-resolution proton nuclear magnetic resonance ((1)H-NMR) spectroscopy. Specifically, the (1)H-NMR spectra of MG-63 spheroids collected at 24, 48 and 72 h after exposure to 5 Gy of ionizing radiation were compared to the spectra of their respective controls. Small spheroids (about 50-80 microm in diameter) with no hypoxic center were used. Apoptosis was verified by both staining of spheroid DNA with the Hoechst 33258 dye and determination of caspase 3 enzyme activity at the three times examined. The results demonstrate that, as the percentage of apoptosis rises with time after exposure to ionizing radiation, the metabolic changes that take place in MG-63 spheroids follow very precise temporal dynamics. In particular, significant time-related increases in both CH(2) and CH(3) mobile lipids, considered by many authors as markers of apoptosis, were observed. In addition, temporal variations were also observed in choline-containing metabolites, reduced glutathione (GSH), glutamine/glutamate, taurine, alanine, creatine/phosphocreatine and lactate. These data show that in addition to CH(2) and CH(3) lipids, other metabolites can also be extremely useful in a deeper understanding of the temporal dynamics of radiation-induced apoptosis. This comprehension is particularly important in spheroids, a cell model of great complexity that resembles in vivo tumors much more closely than monolayer cultures. Ultimately, it is hoped that such studies can help to evaluate the outcome of radiotherapy protocols more accurately.

Long-term normal-appearing brain tissue monitoring after irradiation using proton magnetic resonance spectroscopy in vivo: statistical analysis of a large group of patients

PURPOSE

The aim of this study was to detect the non-neoplastic white-matter changes vs. time after irradiation using 1H nuclear magnetic resonance (NMR) spectroscopy in vivo.

METHODS AND MATERIALS

A total of 394 1H MR spectra were acquired from 100 patients (age 19-74 years; mean and median age, 43 years) before and during 2 years after radiation therapy (the mean absorbed doses calculated for the averaged spectroscopy voxels are similar and close to 20 Gy).

RESULTS

Oscillations were observed in choline-containing compounds (Cho)/creatine and phosphocreatine (Cr), Cho/N-acetylaspartate (NAA), and center of gravity (CG) of the lipid band in the range of 0.7-1.5 ppm changes over time reveal oscillations. The parameters have the same 8-month cycle period; however the CG changes precede the other by 2 months.

CONCLUSIONS

The results indicate the oscillative nature of the brain response to irradiation, which may be caused by the blood-brain barrier disruption and repair processes. These oscillations may influence the NMR results, depending on the cycle phase in which the NMR measurements are performed in. The earliest manifestation of radiation injury detected by magnetic resonance spectroscopy is the CG shift.

Treatment of neuroblastoma using the fused imaging guided radiotherapy (FIGURA) system

PURPOSE

The purpose of this study was to describe our department's experience with the fused imaging-guided radiotherapy (FIGURA) system for planning radiation treatment of high-risk neuroblastoma.

PATIENTS AND METHODS

Between 1999 and 2002, 11 patients received radiation therapy as consolidation after chemotherapy in 9 and for palliation in 2. Diagnostic metaiodobenzylguanidine (MIBG) imaging was used, which is specific for neuroblastoma, to identify the residual tumor, followed by computed tomography scanning in the radiation treatment position. The FIGURA software fused the images obtained by the 2 modalities and transferred the result to a 3-dimensional radiation treatment planning system. Radiation was delivered at a total dose of 25.2 Gy according to the FIGURA.

RESULTS

Five patients achieved complete remission and 2 partial remission; 3 were stabilized. One child with a highly rapid progressive course died of the disease.

CONCLUSION

FIGURA is a new, feasible technique for defining target volumes. By using standard hospital equipment, it is possible to treat residual disease identified by sensitive metaiodobenzylguanidine imaging and localized with the anatomic computed tomography scan. Treating a more accurate target volume spares normal tissue and organs and minimizes side effects.

Increases in 1H-NMR mobile lipids are not always associated with overt apoptosis: evidence from MG-63 human osteosarcoma three-dimensional spheroids exposed to a low dose (2 Gy) of ionizing radiation

The metabolic changes that occur in MG-63 osteosarcoma three-dimensional tumor spheroids exposed to 2 Gy of ionizing radiation, a dose that is comparable to radiation therapy, were studied using high-resolution proton nuclear magnetic resonance ((1)H-NMR) spectroscopy. Specifically, the (1)H-NMR spectra of control and exposed MG-63 spheroids were compared. Small spheroids (about 50-80 microm in diameter) with no hypoxic center were used. The spectra of whole MG-63 spheroids as well as the perchloric acid extracts of these systems were evaluated. Cell damage was also examined by lactate dehydrogenase release and changes in cell growth. No cell damage was observed, but numerous metabolic changes took place in spheroids after exposure to ionizing radiation. In particular, significant increases in both CH(2) and CH(3) mobile lipids, considered by many authors as markers of apoptosis and also present in MG-63 spheroids undergoing overt apoptosis, were observed in spheroids irradiated with 2 Gy. However, the chromatin dye Hoechst 33258 and DNA fragmentation assays showed no overt apoptosis up to 7 days after irradiation with this low dose. Thus it is evident that increases in mobile lipids do not always indicate actual cell death. A detailed analysis of the other metabolic changes observed appears to suggest that the cell death program was initiated but not completed. In fact, the completely different behavior of two important cellular defense mechanisms, reduced glutathione and taurine, in spheroids irradiated with 2 Gy and in those undergoing overt apoptosis seems to indicate that these systems are protecting spheroids from actual cell death. In addition, these data also suggest that (1)H-NMR can be used to examine the effects of low doses of ionizing radiation in spheroids, a cell model of great complexity that closely resembles tumors in vivo. The importance of this possibility in relation to reaching the ultimate goal of a better evaluation of the outcome of radiotherapy protocols should not be ignored.

In vivo magnetic resonance spectroscopy in cancer

Magnetic resonance spectroscopy (MRS) has been used for more than two decades to interrogate metabolite distributions in living cells and tissues. Techniques have been developed that allow multiple spectra to be obtained simultaneously with individual volume elements as small as 1 uL of tissue (i.e., 1 x 1 x 1 mm(3)). The most common modern applications of in vivo MRS use endogenous signals from (1)H, (31)P, or (23)Na. Important contributions have also been made using exogenous compounds containing (19)F, (13)C, or (17)O. MRS has been used to investigate cardiac and skeletal muscle energetics, neurobiology, and cancer. This review focuses on the latter applications, with specific reference to the measurement of tissue choline, which has proven to be a tumor biomarker that is significantly affected by anticancer therapies.

Investigation of metabolic changes in irradiated rat brain tissue by means of 1H NMR in vitro relaxation study

The effect of irradiation on concentrations and relaxation behaviour of brain metabolites was studied by means of high-resolution 1H NMR in vitro. The studies were performed on rat brains irradiated with the doses of 20 Gy applied in fractions of 2 Gy. Standard procedures were used to obtain HClO4 extracts of rat brains. The 1H NMR studies of the extracts solutions in D2O were performed using a Varian Inova-300 NMR spectrometer. The integral intensities of the metabolite signals were found to change during the irradiation cycle and after it. These changes are accompanied by the variations in the T1 relaxation times. N-acetylaspartate, glycerophosphocholine, phosphocholine, choline, creatine and phosphocreatine, myoinositol and taurine were analysed as potential markers of irradiation injury.

Detecting early response to cyclophosphamide treatment of RIF-1 tumors using selective multiple quantum spectroscopy (SelMQC) and dynamic contrast enhanced imaging

The purpose of this study was to develop a reliable, noninvasive method for early detection of tumor response to therapy that would facilitate optimization of treatment regimens to the needs of the individual patient. In the present study, the effects of cyclophosphamide (Cp, a widely used alkylating agent) were monitored in a murine radiation induced fibrosarcoma (RIF-1) using in vivo (1)H NMR spectroscopy and imaging to evaluate the potential of these techniques towards early detection of treatment response. Steady-state lactate levels and Gd-DTPA uptake kinetics were measured using selective multiple quantum coherence (Sel-MQC) transfer spectroscopy and dynamic contrast enhanced imaging, respectively in RIF-1 tumors before, 24 and 72 h after 300 mg/kg of Cp administration. High-resolution (1)H NMR spectra of perchloric acid extracts of the tumor were correlated with lactate and glucose concentrations determined enzymatically. In vivo NMR experiments showed a decrease in steady-state lactate to water ratios (5.4 +/- 1.6 to 0.6 +/- 0.5, p < 0.05) and an increase in Gd-DTPA uptake kinetics following treatment response. The data indicate that decreases in lactate result from decreased glycolytic metabolism and an increase in tumor perfusion/permeability. Perchloric acid extracts confirmed the lower lactate levels seen in vivo in treated tumors and also indicated a higher glycerophosphocholine/phosphocholine (GPC/PC) integrated intensity ratio (1.39 +/- 0.09 vs 0.97 +/- 0.04, p < 0.01), indicative of increased membrane degradation following Cp treatment. Steady-state lactate levels provide metabolic information that correlates with changes in tumor physiology measured by Gd-DTPA uptake kinetics with high spatial and temporal resolution. Both of these parameters may be useful for monitoring early tumor response to therapy.

Early in vivo detection of metabolic response: a pilot study of 1H MR spectroscopy in extracranial lymphoma and germ cell tumours

Monitoring therapeutic efficacy is essential in oncological practice. We have investigated the feasibility of using proton (1)H MR spectroscopy (MRS), localized to malignant lymphoma and germ cell lesions outside the cranial cavity, to monitor tumour metabolism in vivo during chemotherapy treatment. (1)H single voxel MRS, (stimulated echo acquisition mode, repetition time/echo time=2000/20 ms) was performed prior to treatment in patients with lymphoma or germ cell tumours, and during the first cycle of chemotherapy. Patient response was assessed by independent clinical follow-up at a median of 57 days (range 44-93 days) post-treatment. All 12 non-cystic lesions scanned showed a signal assigned to choline-containing metabolites (tCho); 9 were scanned both pre- and post-treatment. Changes in the tCho:water ratio following treatment were found to predict subsequent patient response. In seven of these nine patients, the tCho:water ratio decreased in the first post-treatment scan, and all subsequently achieved a partial response to treatment. In the remaining two patients, both of whom progressed on treatment, the tCho:water ratio did not change significantly. Normalized to pre-treatment values, the non-responder group values (1.07 and 0.97) were clearly distinct from the responder group, whose values ranged from 0.43 to below detection level. To our knowledge, this is the first report of (1)H MR spectra from these tumour types and sites. These preliminary results indicate that metabolite signals can be detected using (1)H MRS in these tumour types and locations, as has already been established in the brain, breast and prostate. Moreover, the differential changes observed in the tCho region of the spectrum suggest that (1)H MRS could provide an early and sensitive indicator of metabolic response to chemotherapy.

Prediction of treatment response of head and neck cancers with P-31 MR spectroscopy from pretreatment relative phosphomonoester levels

RATIONALE AND OBJECTIVES

Combinations of chemotherapy and fractionated radiation therapy are the currently preferred nonsurgical treatment methods for squamous cell carcinoma of the head and neck, but to the authors' knowledge there is no reliable marker for predicting therapeutic response. Early identification of nonresponders would allow prompt replacement of ineffective, toxic therapy by alternative, potentially more effective procedures. Frequent regional node involvement facilitates surface coil investigation with phosphorus-31 magnetic resonance spectroscopy.

MATERIALS AND METHODS

P-31 magnetic resonance spectra were acquired from 12 patients before radiation therapy or chemotherapy. In vivo three-dimensional localized P-31 nuclear magnetic resonance chemical shift imaging was performed with a 1.5-T clinical imager and a dual-tuned H-1/P-31 surface coil. Proton decoupling and nuclear Overhauser enhancement were used to improve sensitivity and resolve overlapping signals in the phosphomonoester region of the spectrum.

RESULTS

The average pretreatment ratio of phosphomonoester to beta-nucleoside triphosphate was significantly smaller in complete responders (n = 4) than in incomplete responders (partial responders plus nonresponders, n = 8) (0.0 +/- 0.0 vs 1.22 +/- 0.17 [P = .004]).

CONCLUSION

Results of this preliminary study suggest that H-1-decoupled P-31 magnetic resonance spectroscopy may prove to be a useful predictor of therapeutic response in head and neck cancers.

Metabolism of alternative substrates and the bioenergetic status of EMT6 tumor cell spheroids

In order to evaluate the ability of EMT6/Ro multicellular spheroids to utilize various pathways of energy production, (13)C and (31)P MRS have been employed to monitor the metabolism of glucose, glutamine, acetate and propionate. EMT6/Ro spheroids perfused with culture medium containing 5.5 mM glucose maintain stable levels of nucleotide triphosphates (NTP) and phosphocreatine (PCr) for up to 48 h, even in the absence of glutamine. The metabolism of 1-(13)C-glucose was almost entirely to 3-(13)C-lactate (88 +/- 12%, n = 7), even though the perfusion medium was equilibrated with 95% O(2). Labeling was also observed in other glycolytic metabolites, primarily alanine and alpha-glycerolphosphate. A low level of (13)C labeling in glutamate, indicative of mitochondrial oxidative metabolism (TCA cycle), was consistently detected when spheroids were perfused with 1-(13)C-glucose, almost exclusively in the C4 position of glutamate. Labeling of glutamate C2 and C3 was always less than 20% of the labeling in C4 and was usually undetectable. No evidence of adjacent carbon labeling in individual glutamate molecules (indicative of multiple cycles of label incorporation) was found, even in high-resolution (13)C NMR spectra of extracts from cells or spheroids. Despite the predominantly glycolytic metabolism of glucose, the mitochondrial substrate glutamine (2 mM, in the presence of < or =0.5 mM glucose from fetal bovine serum), supported stable levels of NTP and PCr in the tumor cells for up to 12 h. In the presence of 2.5 mM acetate, the bioenergetic status of cells in EMT6 spheroids declined slowly but measurably, and no incorporation of label from 2-(13)C-acetate into other metabolites was detected either in intact perfused spheroids or in high-resolution spectra of extracts. In contrast, when the anaplerotic TCA cycle substrate 3-(13)C-propionate replaced acetate, the high-energy phosphate levels in EMT6/Ro spheroids were somewhat reduced, but stabilized at a new lower level. Incubation of spheroids with 3-(13)C-propionate (with natural abundance glucose and glutamine) resulted in label detectable in the C2 and C3 of glutamate, but the primary labeled compound was methylmalonate, an intermediate in propionate metabolism. Addition of vitamin B(12), a cofactor for methylmalonyl CoA reductase, to the growth medium 24 h prior to perfusion with propionate resulted in the elimination of the methylmalonate resonance. A variety of 2- and 3-labeled metabolites were detected, including succinate, malate and glutamate. Labeling of C2 and C3 of lactate implicated cytoplasmic malic enzyme activity.

Towards multidimensional radiotherapy (MD-CRT): biological imaging and biological conformality

PURPOSE

The goals of this study were to survey and summarize the advances in imaging that have potential applications in radiation oncology, and to explore the concept of integrating physical and biological conformality in multidimensional conformal radiotherapy (MD-CRT).

METHODS AND MATERIALS

The advances in three-dimensional conformal radiotherapy (3D-CRT) have greatly improved the physical conformality of treatment planning and delivery. The development of intensity-modulated radiotherapy (IMRT) has provided the "dose painting" or "dose sculpting" ability to further customize the delivered dose distribution. The improved capabilities of nuclear magnetic resonance imaging and spectroscopy, and of positron emission tomography, are beginning to provide physiological and functional information about the tumor and its surroundings. In addition, molecular imaging promises to reveal tumor biology at the genotype and phenotype level. These developments converge to provide significant opportunities for enhancing the success of radiotherapy.

RESULTS

The ability of IMRT to deliver nonuniform dose patterns by design brings to fore the question of how to "dose paint" and "dose sculpt", leading to the suggestion that "biological" images may be of assistance. In contrast to the conventional radiological images that primarily provide anatomical information, biological images reveal metabolic, functional, physiological, genotypic, and phenotypic data. Important for radiotherapy, the new and noninvasive imaging methods may yield three-dimensional radiobiological information. Studies are urgently needed to identify genotypes and phenotypes that affect radiosensitivity, and to devise methods to image them noninvasively. Incremental to the concept of gross, clinical, and planning target volumes (GTV, CTV, and PTV), we propose the concept of "biological target volume" (BTV) and hypothesize that BTV can be derived from biological images and that their use may incrementally improve target delineation and dose delivery. We emphasize, however, that much basic research and clinical studies are needed before this potential can be realized.

CONCLUSIONS

Whereas IMRT may have initiated the beginning of the end relative to physical conformality in radiotherapy, biological imaging may launch the beginning of a new era of biological conformality. In combination, these approaches constitute MD-CRT that may further improve the efficacy of cancer radiotherapy in the new millennium.

Applications of magnetic resonance in model systems: tumor biology and physiology

A solid tumor presents a unique challenge as a system in which the dynamics of the relationship between vascularization, the physiological environment and metabolism are continually changing with growth and following treatment. Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) studies have demonstrated quantifiable linkages between the physiological environment, angiogenesis, vascularization and metabolism of tumors. The dynamics between these parameters continually change with tumor aggressiveness, tumor growth and during therapy and each of these can be monitored longitudinally, quantitatively and non-invasively with MRI and MRS. An important aspect of MRI and MRS studies is that techniques and findings are easily translated between systems. Hence, pre-clinical studies using cultured cells or experimental animals have a high connectivity to potential clinical utility. In the following review, leaders in the field of MR studies of basic tumor physiology using pre-clinical models have contributed individual sections according to their expertise and outlook. The following review is a cogent and timely overview of the current capabilities and state-of-the-art of MRI and MRS as applied to experimental cancers. A companion review deals with the application of MR methods to anticancer therapy.

Application of magnetic resonance techniques for imaging tumour physiology

Magnetic resonance (MR) techniques have the unique ability to measure in vivo the biochemical content of living tissue in the body in a dynamic, non-invasive and non-destructive manner. MR also permits serial investigations of steady-state tumour physiology and biochemistry, as well as the response of a tumour to treatment. Magnetic resonance imaging (MRI), Magnetic resonance spectroscopy (MRS) and a mixture of the two techniques (spectroscopic imaging) allow some physiological parameters, for example pH, to be 'imaged'. Using these methods, information on tissue bioenergetics and phospolipid membrane turnover, pH, hypoxia, oxygenation, and various aspects of vascularity including blood flow, angiogenesis, permeability and vascular volume can be obtained. In addition, MRS methods can be used for monitoring anticancer drugs (e.g. 5FU, ifosfamide) and their metabolites at their sites of action. The role of these state-of-the-art MR methods in imaging tumour physiology and their potential role in the clinic are discussed.

Role of short TE 1H-MR spectroscopy in monitoring of post-operation irradiated patients

Post-surgical radiation therapy is a routine procedure in the treatment of primary malignant brain tumors. Along with modest therapeutic effects conventional fractionated radiotherapy, in spite of any modifications, produces damage to non-malignant brain tissues lying within the treatment volume, the extent of which depends on radiation dose. Serial 1H-MRS allows non-invasive investigation of tissue metabolic profiles. In the present study the ratios of resonance signals assigned to the major 1H-MRS-visible metabolites (N-acetylaspartate, choline, creatine, inositol, lactate and lipid methylene group) were evaluated before, during and after post-surgical fractionated radiotherapy in brain regions close to and more distant from the tumor bed, receiving different radiation exposures (60 and < 40 Gy, respectively). The study group consisted of ten patients (aged 28-51). A MRI/MRS system (Elscint 2T Prestige) operating at the field strength of 2 T and the proton resonance frequency of 81.3 MHz has been used and the 1H-MR spectra were acquired using single voxel double-spin-echo PRESS sequence with a short TE. The spectra were post-processed with automatic fitting in the frequency domain. It was found that although the metabolite profiles depend on the dose obtained, but other stress factors (like surgery) seem to contribute to the overall picture of the metabolic status of the brain as well. In studies of early irradiation injuries, an increase of choline related ratios may serve rather as cell proliferation indictors than as cell injury ones, whereas the mI/Cr ratio appears as one of the first indicators of local irradiation injury. In order to establish the prognostic marker for early radiation damage, however, it seems necessary to analyze all visible metabolites as well. None of the metabolites separately may serve as such an indicator due to the complexity of tissue metabolism. Interestingly, MRI reveals no changes during the therapy process, whereas the metabolite ratios are being affected in the course of time, thus supporting the presumption that the 1H-MRS is a valuable method of radiation therapy monitoring.

Evaluation of the effects of high dose irradiation on canine thigh muscle by follow-up magnetic resonance imaging and phosphorus-31 magnetic resonance spectroscopy

RATIONALE AND OBJECTIVES

The authors investigate alterations of proton T1 and T2 relaxation times and phosphorus metabolites of canine thigh muscle tissue after high dose x-ray irradiation by follow-up magnetic resonance imaging (MRI) and phosphorus-31 (31P) magnetic resonance spectroscopy (MRS).

METHODS

A group of 20 dogs was used for MRI and in vivo 31P MRS. Single doses of 5,000 and 10,000 cGy were delivered to the right thigh muscle of groups of 10 dogs each. All MRI and 31P MRS examinations were performed before irradiation and 1, 7, 14, 28, 42, and 56 days after irradiation. For measurement of T1, repetition time (TR) was measured at 300, 500, 1000, 1500, 2000 msec and echo time (TE) was fixed at 12 msec. Also, for measurement of T2, TE was measured at 20, 40, 60, and 80 msec and TR was fixed at 2000 msec. Image selected in vivo spectroscopy (ISIS) pulse sequence was used to obtain 31P MR spectra. Peak areas for each phosphorus metabolite were measured using a Marquart algorithm.

RESULTS

Magnetic resonance imaging signal began to change at 28 days after a single dose of 10,000 cGy, whereas there was no significant MRI signal change until 56 days after a single dose of 5,000 cGy. Also, extensive MRI signal changes were observed at 42 days after a single dose of 10,000 cGy. Significant correlation was established between T2 and a lapse of time although there was no correlation between T1 and a lapse of time. T2 value increased substantially corresponding to the time period after x-ray irradiation. Although MR spectral change was not observed until 42 days after a single dose of 5,000 cGy, it began at 14 days after a single dose of 10,000 cGy. And, significant MR spectral changes were observed at 28 and 42 days. Inorganic phosphate and phosphodiesters signal intensities increased while phosphocreatine signal intensity decreased. The pH value was 7.22 +/- 0.05 at control, and 6.98 +/- 0.04 at 42 days after a single dose of 10,000 cGy.

CONCLUSIONS

The postirradiation follow-up MRI and 31P MRS studies demonstrated that morphologic and metabolic changes were dependent upon the x-ray dose and a lapse of time.

Nuclear magnetic resonance spectroscopy of cancer

Nuclear magnetic resonance spectroscopy (MRS) offers a non-invasive approach for studying tumour biochemistry and physiology. This review highlights NMR nuclei (31P, 1H, 19F, 13C, 2H) that have been observed in both pre-clinical and clinical spectroscopic studies of cancer.