Can High b Value Diffusion Be a Surrogate Marker for PET-A MR/PET Study in Neurooncology Set Up

Abstract

Purpose: Hybrid whole-body magnetic resonance/positron emission tomography (MR/PET) systems are new diagnostic tools enabling the simultaneous acquisition of morphologic and multiparametric functional data, which allow for a diversified characterization of oncological diseases. This study aimed to compare the diagnostic ability of MRI with the diffusion-weighted image (DWI), and simultaneous integrated positron emission tomography MR/PET to detect malignant lesions and elucidate the utility and limitations of these imaging modalities in preoperative and postoperative follow up in cancer patients. Material and Methods: A total of 45 patients undergoing simultaneous MR/PET for CNS ICSOL in our institution between January 2016 and July 2020 were considered in this study. Post-processing was done in Siemens syngo software to generate a b2000 image. This image was then inverted to grayscale and compared with the NAC image of PET. Results: The lesion-based sensitivity, specificity, positive predictive value, and negative predictive value for DWI were 92.3, 83.3, 97.3, and 62.5%, respectively (at 95% CI and p was 0.000). The lesion-based sensitivity, specificity, positive predictive value, and negative predictive value for PET were 97.4, 71.4, 94.9, and 83.3%, respectively (at 95% CI and p was 0.000). The lesion-based sensitivity and specificity of DWI were comparable with those of PET. Conclusions: Although DWI and FDG-PET reflect different tissue properties, there is an association between the measures of both methods in CNS tumors probably because of the coupling of cellularity with tumor metabolism as seen on FDG and other PET tracers. Our study shows that DWI acts as a surrogate biomarker for FDG PET and other tracers in tumors. The method of DWI image generation is simple, radiation-free, and cost-effective in a clinical setup. The simultaneous DWI-PET study provides evidence and confirms the role of DWI in surveillance imaging of tumors.

Keywords: CNS tumors; FDG-PET; PET-MR; glioma; high value diffusion weighted imaging.

Figure 1

A 43 year old male postoperative case of Glioblastoma IDH mutant in the left frontal lobe, 5 year follow up MRI FDG PET axial images T2-FLAIR (A) post-contrast T1 (B) Inverted DWI (C) DWI b2000 (D) ADC (E) NAC PET (F) showed a T2 heterogeneous hypointense lesion with Swiss cheese and nodular enhancement and elevated perfusion. The lesion shows DWI restriction with hypermetabolism on PET. There is a match on the inverted DWI image and the NAC PET image. Suggestive of recurrence.

Figure 2

A 24 year old female postoperative, post-RT case of Glioma left frontal lobe, 3 year follow up MRI FDG PET axial images T2-FLAIR (A) post-contrast T1 (B) Inverted DWI (C) DWI b2000 (D) ADC (E) NAC PET (F) show a postoperative cavity in the left frontal lobe with Swiss cheese-like enhancing lesion posterior to postoperative either no elevated perfusion. Neither DWI restriction nor elevated metabolism on PET is seen, which is suggestive of radiation necrosis.

Figure 3

A 52 year old female with imbalance, MRI FDG PET axial brain images T1 post-contrast (A) image showed an enhancing lesion in the right cerebellum. Whole-body MRI with fast sequences at axial hepatic sections (B) VIBE fat sat post-contrast (C) DWI b800 (D) ADC and NAC PET (E) showing an area of metastases to the vertebral body as an area of restricted diffusion and post-contrast enhancement. HPE was suggestive of Pilocytic astrocytoma with metastasis.

Figure 4

A 55 year old male with a progressive right-side weakness for one and a half month, MRI FDG PET axial images T2 (A) ASL (B) Inverted DWI (C) DWI b2000 (D) ADC (E) NAC PET (F) showed a well-defined lobulated T2 heterogeneous iso- hyperintense with increased perfusion on ASL. The lesion shows DWI restriction with hypermetabolism on PET. There is a match on the inverted DWI image and the NAC PET image. HPE is suggestive of Anaplastic Ependymoma.

Figure 5

A 32 year old male postoperative, post-radiotherapy case of Anaplastic mixed oligoastrocytoma left thalamus, 3 year follow up MRI FDG PET axial images T2W (A) post-contrast T1 (B) Inverted DWI (C) DWI b2000 (D) ADC (E) NAC PET (F) show a postoperative cavity in the left parietal region. Anterior and posterior to this there is a heterogeneously enhancing lesion with elevated perfusion. The lesion shows DWI restriction with hypermetabolism on PET. This is suggestive of recurrence, but there is a large area of gyral enhancement due to SMART Syndrome. There is a false positive uptake on PET.

Figure 6

A 52 year old female with a headache for 1 year with recent onset of a seizure. MRI PET (F18 CHOLINE) axial images T2W (A) post-contrast TW (B) Inverted DWI (C) DWI b2000 (D) ADC (E) NAC PET (F) shows Ill-defined infiltrative heterogeneous lesion in the right frontal lobe with invasion to corpus callosum showing intense heterogeneous enhancement. The lesion shows DWI restriction with hypermetabolism on PET. There is a match on the inverted DWI image and the NAC PET image, which is suggestive of Glioblastoma.

Figure 7

A 59 year old female with Glioma, incidentally detected a lesion in follow up MRI C-11 Methionine PET axial images T2W (A) post-contrast T1 (B) Inverted DWI (C) DWI b2000 (D) ADC (E) NAC PET (F) shows a broad-based T2 hypointense intensely enhancing in the left inferior temporal convexity. The lesion shows no DWI restriction with hypermetabolism on PET. S/O meningioma. False-positive uptake of meningioma by methionine.

Figure 8

A 33 year old female postoperative, post-radiotherapy case of Embryonal tumor compatible (atypical teratoid rhabdoid tumor) 1 year follow up MRI C-11 Methionine PET axial images post-contrast T1 (A) ASL (B) Inverted DWI (C) DWI b2000 (D) ADC (E) NAC PET (F) showed Multiple enhancing dural based lesions are seen in bilateral frontal convexity and anterior falx with elevated perfusion. The lesion shows DWI restriction with hypermetabolism on PET. There is a match on the inverted DWI image and the NAC PET image, which is suggestive of recurrence.

Figure 9

A 34 year old female postoperative case of anaplastic clear cell Ependymoma, 7 year follow up MRI F-18 choline PET axial images SWI (B) postcontrast T1 (A) Inverted DWI (C) DWI b2000 (D) ADC (E) NAC PET (F) showed a Swiss cheese and nodular enhancement lesion in the right parietal region. The lesion shows DWI restriction with hypermetabolism on PET. There is a match on the inverted DWI image and the NAC PET image, which is suggestive of recurrence.