Diffusion-weighted MRI and in-phase/opposed-phase sequences in the assessment of bone tumors

Do contrast-enhanced and advanced MRI sequences improve diagnostic accuracy for indeterminate lipomatous tumors?

PURPOSE

Benign, intermediate-grade and malignant tumors sometimes have overlapping imaging and clinical characteristics. The purpose of this study was to evaluate the added value of contrast-enhanced sequences (dynamic contrast enhancement (DCE)), diffusion-weighted imaging (DWI), and chemical shift imaging (CSI) to noncontrast MRI sequences for the characterization of indeterminate lipomatous tumors.

MATERIALS AND METHODS

Thirty-two consecutive patients with histologically proven peripheral lipomatous tumors were retrospectively evaluated. Two musculoskeletal radiologists recorded the MRI features in three sessions: (1) with noncontrast T1-weighted and fluid-sensitive sequences; (2) with addition of static pre- and post-contrast 3D volumetric T1-weighted sequences; and (3) with addition of DCE, DWI, and CSI. After each session, readers recorded a diagnosis (benign, intermediate/atypical lipomatous tumor (ALT), or malignant/dedifferentiated liposarcoma (DDL)). Categorical imaging features (presence of septations, nodules, contrast enhancement) and quantitative metrics (apparent diffusion coefficient values, CSI signal loss) were recorded.

RESULTS

For 32 tumors, the diagnostic accuracy of both readers did not improve with the addition of contrast-enhanced sequences, DWI, or CSI (53% (17/32) session 1; 50% (16/30) session 2; 53% (17/32) session 3). Noncontrast features, including thick septations (p = 0.025) and nodules ≥ 1 cm (p < 0.001), were useful for differentiating benign tumors from ALTs and DDLs, as were DWI (p = 0.01) and CSI (p = 0.009) metrics.

CONCLUSION

The addition of contrast-enhanced sequences (static, DCE), DWI, and CSI to a conventional, noncontrast MRI protocol did not improve diagnostic accuracy for differentiating benign, intermediate-grade, and malignant lipomatous tumors. However, we identified potentially useful imaging features by DCE, DWI, and CSI that may help distinguish these entities.

Role of diffusion-weighted MRI in differentiating between benign and malignant bone lesions: a prospective study

AIM

To evaluate the ability of diffusion-weighted magnetic resonance imaging (DW-MRI) to differentiate between benign and malignant bony tumours.

MATERIALS AND METHODS

This prospective study was conducted from October, 2018 to December, 2019. The study included 62 patients (37 male and 25 female) with clinically suspected bony lesions referred to the Radiology Department. Patients underwent clinical examination, radiography, computed tomography (CT), and ultrasonography examinations. MRI studies were conducted using a 1.5-T MRI machine, and post-processing analysis was done using a Philips Extended MRI workspace workstation.

RESULTS

The mean apparent diffusion coefficient (ADC) value of benign lesions ranged between 0.85 × 10^-3 and 2.44 × 10^-3 mm²/s. The lowest ADC values were measured in a giant cell tumour and in an inclusion epidermoid cyst (0.85 × 10^-3 and 0.93 × 10^-3 mm²/s, respectively). The highest measurement was in bony cysts (2.44 × 10^-3 mm²/s) followed by osteoid osteoma (2.2 × 10^-3 mm²/s) and osteochondroma (1.85 × 10^-3 mm²/s). Amongst malignant lesions, ADC values ranged from 0.42 × 10^-3 to 2.4 × 10^-3 mm²/s. The lowest value was measured in malignant round cell tumour Ewing's/primitive neuroectodermal tumour (PNET), and the highest was measured in conventional chondrosarcoma. Metastatic lesions were observed in 11 patients with a mean ADC value of 0.71 × 10^-3 mm²/s, followed by osteosarcoma in six patients with a mean ADC value of 0.74 × 10^-3 mm²/s.

CONCLUSION

There was a significant difference between the mean, minimum, and maximum ADC values of benign and malignant tumours. The present findings indicate that the best cut-off ADC range to predict malignancy is 0.78-0.86 × 10^-3 mm²/s, with a sensitivity of 89.47%, specificity of 97.22%, and accuracy of 94.55%.

Role of in-phase and out-of-phase chemical shift MRI in differentiation of non-neoplastic versus neoplastic benign and malignant marrow lesions

OBJECTIVE

To determine its ability of in-phase (IP) and out-of-phase (OOP) chemical shift imaging (CSI) to distinguish non-neoplastic marrow lesions, benign bone tumours and malignant bone tumours.

METHODS

CSI was introduced into our musculoskeletal tumour protocol in May 2018 to aid in characterisation of suspected bone tumours. The % signal intensity (SI) drop between IP and OOP sequences was calculated and compared to the final lesion diagnosis, which was classified as non-neoplastic (NN), benign neoplastic (BN) or malignant neoplastic (MN).

RESULTS

The study included 174 patients (84 males; 90 females: mean age 44.2 years, range 2-87 years). Based on either imaging features (n = 105) or histology (n = 69), 44 lesions (25.3%) were classified as NN, 66 (37.9%) as BN and 64 (36.8%) as MN. Mean % SI drop on OOP for NN lesions was 36.6%, for BN 3.19% and for MN 3.24% (p < 0.001). The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and diagnostic accuracy of CSI for differentiating NN from neoplastic lesions were 65.9%, 94.6%, 80.6%, 89.1%% and 87.4% respectively, and for differentiating BN from MN were 9.1%, 98.4%, 85.7%, 51.2 and 53.1% respectively.

CONCLUSION

CSI is accurate for differentiating non-neoplastic and neoplastic marrow lesions, but is of no value in differentiating malignant bone tumours from non-fat containing benign bone tumours.

ADVANCES IN KNOWLEDGE

CSI is of value for differentiating non-neoplastic marrow lesions from neoplastic lesions, but not for differentiating benign bone tumours from malignant bone tumours as has been previously reported.

Chemical shift imaging with in-phase and opposed-phase sequences at 3 T: what is the optimal threshold, measurement method, and diagnostic accuracy for characterizing marrow signal abnormalities?

OBJECTIVE

To determine the threshold signal drop on 3-T chemical shift imaging (CSI), with in-phase (IP) and opposed-phase (OP) sequences, for accurately identifying bone marrow replacement with 100% sensitivity, and determine a clinically useful measurement method for deriving such a threshold.

MATERIALS AND METHODS

From a convenience series of 157 MRIs, 36 cases with histologically proven marrow-replacing lesions and 22 sites of red marrow (histologically proven (2) or with minimum 6-month stability) with 3-Tesla CSI were included. Two musculoskeletal radiologists performed two measurement methods (first: multiple algorithmic ROIs at the top, middle, and bottom of lesions (M-ROI); second: an ROI was drawn where there appeared to be the least opposed-phase signal reduction qualitatively/visually (Q-ROI)). Lesional and red marrow signal change (%,[(IP-OP)signal/IP signal]*100) was determined. Statistical analyses included Student's t test, Cohen's kappa, and receiver operator characteristic curve generation.

RESULTS

By M-ROI, lesion signal change was - 0.508% (confidence interval (CI) = - 5.537:4.521) and 1.348% (CI = - 3.541:6.311) for readers 1 and 2. By Q-ROI, lesion signal change was - 11.03% (CI = - 17.01:- 5.046) and - 5.657% (CI = - 12.36:1.048) for readers 1 and 2. For all M-ROI and Q-ROI measurement strategies, signal change between lesional tissue and red marrow was significantly different (p < 0.0001). QROI produced the best composite sensitivities and specificities with a maximized Youden index of 0.955-1. A threshold signal drop of 25% with Q-ROI produced at least 100%/86% sensitivity/specificity for both readers for identifying marrow replacement.

CONCLUSIONS

For 3-T CSI, a single visually targeted measurement using a 25% threshold is accurate for identifying marrow-replacing lesions.

Accuracy of Opposed-phase Magnetic Resonance Imaging for the Evaluation of Treated and Untreated Spinal Metastases

RATIONALE AND OBJECTIVES

To assess whether the accuracy of opposed-phase magnetic resonance (MR) imaging to differentiate spinal metastases from benign lesions is influenced by treatment.

MATERIALS AND METHODS

We retrospectively evaluated 25 benign lesions, 25 untreated spinal metastases, and 89 treated spinal metastases in 101 patients who underwent opposed-phase MR spine imaging at our institution. The largest possible region of interest was placed over the lesion in question on out-of-phase and in-phase MR sequences, and the signal intensity ratio (SIR) of the lesions was calculated. The SIRs were compared between benign, untreated, and treated lesions. Receiver operator characteristic (ROC) curves were used to identify the optimal threshold to differentiate benign lesions from untreated spinal metastases, and the accuracy of this threshold was assessed for treated spinal metastases, chemotherapy-treated spinal metastases, and radiated spinal metastases.

RESULTS

Benign lesions had lower mean SIR than untreated (P = 2.4 × 10^-8, 95% confidence interval [0.29, 0.51]) and treated spinal metastases (P = .51; 95% confidence interval [-0.13, 0.06]). A cutoff SIR of 0.856 had an accuracy of 88.00% for untreated lesions, 77.48% for previously treated lesions, and 70.45% for previously radiated lesions. The ROC curve to differentiate benign lesions from radiated spinal metastases was significantly different from the ROC curve to differentiate benign lesions from untreated spinal metastases (P = .0180). The ROC curve to differentiate benign lesions from lesions treated with chemotherapy only was significantly different from the ROC curve to differentiate between benign lesions and radiated spinal metastases (P = .041).

CONCLUSIONS

Opposed-phase imaging is less accurate for treated spinal metastases, in particular after radiation.

Solid bone tumors of the spine: Diagnostic performance of apparent diffusion coefficient measured using diffusion-weighted MRI using histology as a reference standard

PURPOSE

To assess the diagnostic performance of mean apparent diffusion coefficient (mADC) in differentiating benign from malignant bone spine tumors, using histology as a reference standard. Conventional magnetic resonance imaging (MRI) sequences have good reliability in evaluating spinal bone tumors, although some features of benign and malignant cancers may overlap, making the differential diagnosis challenging.

MATERIALS AND METHODS

In all, 116 patients (62 males, 54 females; mean age 59.5 ± 14.1) with biopsy-proven spinal bone tumors were studied. Field strength/sequences: 1.5T MR system; T₁ -weighted turbo spin-echo (repetition time / echo time [TR/TE], 500/13 msec; number of excitations [NEX], 2; slice thickness, 4 mm), T₂ -weighted turbo spin-echo (TR/TE, 4100/102 msec; NEX, 2; slice thickness, 4 mm), short tau inversion recovery (TR/TE, 4800/89 msec; NEX, 2; slice thickness, 4 mm, IT, 140 msec), axial spin-echo echo-planar diffusion-weighted imaging (DWI) (TR/TE 5200/72 msec; slice thickness 5 mm; field of view, 300; interslice gap, 1.5 mm; NEX, 6; echo-planar imaging factor, 96; no parallel imaging) with b-values of 0 and 1000 s/mm², and 3D fat-suppressed T₁ -weighted gradient-recalled-echo (TR/TE, 500/13 msec; slice thickness, 4 mm) after administration of 0.2 ml/kg body weight gadolinum-diethylenetriamine pentaacetic acid. Two readers manually drew regions of interest on the solid portion of the lesion (hyperintense on T₂ -weighted images, hypointense on T₁ -weighted images, and enhanced after gadolinium administration on fat-suppressed T₁ -weighted images) to calculate mADC. Histology was used as the reference standard. Tumors were classified into malignant primary tumors (MPT), bone metastases (BM), or benign primary tumors (BPT). Statistical tests: Nonnormality of distribution was tested with the Shapiro-Wilk test. The Kruskal-Wallis and Mann-Whitney U-test with Bonferroni correction were used. Sensitivity and specificity of the mADC values for BM, MPT, and BPT were calculated. Approximate receiver operating characteristic curves were created. Interobserver reproducibility was evaluated using the intraclass correlation coefficient (ICC).

RESULTS

The mADC values of MPT (n = 35), BM (n = 65), and BPT (n = 16) were 1.00 ± 0.32 (0.59-2.10) × 10^-3 mm² /s, 1.02 ± 0.25 (0.73-1.96) × 10^-3 mm² /s, 1.31 ± 0.36 (0.83-2.14) × 10^-3 mm² /s, respectively. The mADC was significantly different between BPT and all malignant lesions (BM+MPT) (P < 0.001), BM and BPT (P = 0.008), and MPT and BPT (P = 0.008). No difference was found between BM and MPT (P = 0.999). An mADC threshold of 0.952 × 10^-3 mm² /s yielded 81.3% sensitivity, 55.0% specificity. Accuracy was 76% (95% confidence interval [CI] = 63.9%-88.1%). Interobserver reproducibility was almost perfect (ICC = 0.916; 95% CI = 0.879-0.942).

CONCLUSION

DWI with mADC quantification is a reproducible tool to differentiate benign from malignant solid tumors with 76% accuracy. The mADC values of BPT were statistically higher than that of malignant tumors. However, the large overlap between cases may make mADC not helpful in a specific patient.

LEVEL OF EVIDENCE

3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:1034-1042.

Diffusion magnetic resonance imaging: A molecular imaging tool caught between hope, hype and the real world of “personalized oncology”

“Personalized oncology” is a multi-disciplinary science, which requires inputs from various streams for optimal patient management. Humongous progress in the treatment modalities available and the increasing need to provide functional information in addition to the morphological data; has led to leaping progress in the field of imaging. Magnetic resonance imaging has undergone tremendous progress with various newer MR techniques providing vital functional information and is becoming the cornerstone of “radiomics/radiogenomics”. Diffusion-weighted imaging is one such technique which capitalizes on the tendency of water protons to diffuse randomly in a given system. This technique has revolutionized oncological imaging, by giving vital qualitative and quantitative information regarding tumor biology which helps in detection, characterization and post treatment surveillance of the lesions and challenging the notion that “one size fits all”. It has been applied at various sites with different clinical experience. We hereby present a brief review of this novel functional imaging tool, with its application in “personalized oncology”.

Differentiation of focal indeterminate marrow abnormalities with multiparametric MRI

PURPOSE

To explore magnetic resonance imaging (MRI) parameters from intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI), multiecho Dixon imaging (ME-Dixon), and dynamic contrast-enhanced imaging (DCE) for differentiating focal indeterminate marrow abnormalities MATERIALS AND METHODS: Forty-two patients with 14 benign and 28 malignant focal marrow abnormalities were included. The following were independently analyzed by two readers: signal intensity (SI), contour, and margin on conventional MR images; SI on b-800 images (SI_b-800 ), apparent diffusion coefficient (ADC), IVIM parameters (D_slow, D_fast , and f), fat fraction (Ff), and DCE parameters (time-to-signal intensity curve pattern, iAUC, K^trans , k_ep , and v_e ). The MR characteristics and parameters from benign and malignant lesions were compared with a chi-squared test and the Mann-Whitney U-test, respectively. The area under receiver operating characteristic (ROC) curves (AUC) of each sequence were also compared. Interobserver agreements were assessed with Cohen's κ, and intraclass correlation coefficient (ICC).

RESULTS

ADC, D_slow , and Ff demonstrated a significant difference between benign and malignant marrow abnormalities for both readers (P < 0.001). SI_b-800 and perfusion-related parameters from IVIM-DWI and DCE were not significantly different between the two groups (P = 0.145, 0.439, and 0.337 for reader 1, P = 0.378, 0.368, and 0.343 for reader 2, respectively). The AUCs of ADC, D_slow , and Ff were significantly higher for differentiating indeterminate marrow abnormalities in both readers (P < 0.001). Interobserver agreements were substantial in SI_b-800 , and ICCs were almost perfect for ADC, D_slow , f, and Ff, and substantial for iAUC, k_ep , K^trans , v_e , and D_fast .

CONCLUSION

ADC, D_slow , and Ff may provide information for differentiating focal indeterminate abnormalities.

LEVEL OF EVIDENCE

3 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:49-60.

Advanced Neuroimaging in the Evaluation of Spinal Cord Tumors and Tumor Mimics: Diffusion Tensor and Perfusion-Weighted Imaging

Spinal cord tumors are an important component of pathologic diseases involving the spinal cord. Conventional magnetic resonance (MR) imaging only provides anatomical information. MR diffusion tensor imaging (DTI) and MR perfusion-weighted imaging (PWI) may detect microstructure diffusion and hemodynamic changes in these tumors. We review recent application studies of MR DTI and PWI in spinal cord tumors. Overall, MR DTI and MR PWI are promising imaging tools that are especially useful in improving differential diagnosis between spinal cord tumors and tumor mimics, preoperative evaluation of resectability, and providing assistance in surgical navigation.