Clinical applicability of human in vivo localized phosphorus-31 magnetic resonance spectroscopy of bone and soft tissue tumors

Musculoskeletal tumors: Use of proton MR spectroscopic imaging for characterization

PURPOSE

To determine the value of multivoxel proton magnetic resonance spectroscopic imaging (MRSI) in distinguishing malignant skeletal tumors from benign tumors and normal bone marrow using the metabolite choline (Cho) as a marker for malignancy.

MATERIALS AND METHODS

Pathologic specimens obtained from 13 patients who had undergone wide resection for skeletal tumors underwent evaluation by MRSI at 1.5 T. Coronal T1-weighted gradient-echo sequence obtained for localization purposes (TR/TE = 250/1.8 msec, field of view [FOV] = 18 x 18), and single-slice MRSI (TR/TE = 2000/272 msec, FOV = 18 x 18, 10-mm slice-thickness) were performed. Water, lipid, and Cho images were reconstructed from MRSI data. Cho signal was measured in each specimen and expressed relative to background noise level (signal-to-noise ratio [SNR]) where noise was measured between 7.0 and 9.0 ppm. Cho SNRs were compared between areas containing malignant tumor and nonmalignant tissue (benign lesion or normal bone marrow) as determined by histopathology.

RESULTS

Specimens included 13 skeletal sarcomas (seven osteosarcomas, three chondrosarcomas, one malignant fibrous histiocytoma, one fibrosarcoma, and one leiomyosarcoma). All specimens included a sample of normal bone marrow and two specimens also contained benign lesions. All sarcomas demonstrated a signal at 3.2 ppm assigned to Cho-containing metabolites in areas of malignancy. Peak Cho SNR was significantly different for areas containing histologically-proven malignancy compared to nonmalignant tissue (9.8 +/- 5.1 vs. 2.7 +/- 1.4, respectively, P < 0.002).

CONCLUSION

These preliminary results indicate that MRSI at 1.5 T is a promising noninvasive method of differentiating malignant skeletal tumors from nonmalignant tissue. Using MRSI, Cho can be detected in skeletal tumors and may serve as a marker for malignancy.

Phosphorus MR spectroscopy in the treatment of human extremity sarcomas

The application of 31P MR spectroscopy in the characterization and treatment of malignant human extremity tumors is reviewed and placed in the perspective of results obtained in murine sarcomas. Despite the now widespread acquisition of gradient localized spectral maps, the low spatial resolution that can be achieved at 1.5 or 2 T with 31P MRS, greatly limits its use in the study of tumor heterogeneity. The potential of 31P MRS is in the evaluation and monitoring of large inoperable extremity tumors. There are early spectral changes in human extremity sarcomas monitored after therapy, and recent studies have shown that the 31P MR spectra measured before treatment, and the changes in phosphate metabolites measured shortly thereafter, correlate with the clinical response after 2 or 3 months. Larger clinical studies are needed to confirm whether correlations of, for instance, pretreatment tumor pH with necrosis at resection and Pi decrease with tumor regression, can be used as a predictive test for clinical response.

Detection of local recurrence of soft-tissue sarcoma with positron emission tomography using [18F]fluorodeoxyglucose

BACKGROUND

It is often difficult to detect a local recurrence of soft-tissue sarcomas due to disturbance of the normal anatomy by previous surgery and radiotherapy. The aim of this study was to assess the value of positron emission tomography (PET) with [18F]fluoro-2-deoxy-D-glucose (FDG) for detecting local recurrences.

METHODS

In the period 1992-1995, 17 patients with proven or suspected local recurrence of soft-tissue sarcoma were examined using FDG-PET. Fifteen of these patients were ultimately proven to have a recurrence.

RESULTS

Recurrence was visualized in 14 patients (93%). Small tumors (maximum diameter 0.5 cm) were as easily visible as large lesions (maximum diameter 20 cm). In one patient the PET scan was positive, but the recurrence could not be proven histologically. Recurrence was proven 1 year later. A recurrent low-grade liposarcoma was not visualized. The two patients with benign lesions had a negative PET scan. The mean glucose metabolic rate was calculated to be 13.2 mumol/100 g/min (range 1.9-28.4). A correlation was found between the histological malignancy grade and the metabolic rate (p < 0.05; Kruskal-Wallis).

CONCLUSION

PET with FDG is a useful addition to the diagnostic armamentarium for detecting local recurrence of soft-tissue sarcomas and provides an indication of the malignancy grade of the recurrent lesion.

Assessing prognosis for high-grade soft-tissue sarcomas: search for a marker

BACKGROUND

Although improved staging technology, limb-sparing surgery, and adjunctive radiation and chemotherapy have improved the outlook for patients with malignant soft-tissue tumors of the trunk and extremities, it is evident that we cannot predict which patients will develop distant metastases. Although local control is now frequently achieved, most series of high-grade soft-tissue sarcomas carry a mortality rate of > 50%.

METHODS

In a retrospective study of 93 patients with high-grade sarcomas treated between 1986 and 1992 for whom complete studies including size and volume measurements and DNA ploidy determinations as assessed by flow cytometry were available, a search for a marker for increased risk of metastasis or death was performed.

RESULTS

Grade of the lesion, sex, diagnosis, anatomical site, ploidic data (including mean DNA index and presence of an aneuploid peak), and treatment factors (including type of surgery, local recurrence, or radiation protocol) did not correlate with outcome. Age (younger patients did better), size (greatest diameter) and volume, and positive margins at surgery correlated with total survival.

CONCLUSIONS

The results of the study, although negative, point out that using anatomical site, diagnosis, or ploidic analysis offers little toward anticipating outcome, whereas the size of the tumor is important.