Whole-Body MRI and Whole Body 123I-MIBG scintigraphy: comparison in Lines and High Risk Neuroblastoma. A pilot study.


 Purpose: To assess agreement between 123I-metaiodobenzylguanidine (MIBG) and Whole Body Magnetic Resonance Imaging with diffusion-weighted whole-body imaging with background body signal suppression (WB MRI-DWIBS) in High and Low, Intermediate risk neuroblastoma, a retrospective review was performed on MIBG and DWIBS paired scans acquired at diagnosis, response-to-therapy steps, after-surgery, off therapy.Methods: 80 paired MIBG and DWIBS scans were acquired for 31 patients between June 2009 and June 2019 within 30 days, without intercurrent therapy. SIOPEN Semi-quantitative scoring systems for NB with 12 body sections was applied at whole body MIBG and WB MRI-DWIBS acquired to evaluate the disease extent. We evaluated specificity, sensitivity, overall accuracy, positive predictive value (PPV) and negative predictive value (NPV) of WB MRI-DWIBS respect MIBG scintigraphy considered as gold standard, and vice versa.Results: DWIBS and MIBG images were concordant in 890 out of the 960 analyzed segments, with high agreement between the two techniques (kendal =0.85 P<0.0001 and Chi 536.5975 p<0.0001). Considering MIBG as gold standard, WB MRI-DWIBS overall accuracy was 93%, sensitivity 78%, specificity 95%, PPV 77% and NPV 96%. Otherwise, MIBG overall accuracy was 93%; sensitivity 77%; specificity 97%; VPP 78%; VPN 95%, considering DWIBS as gold standard. MIBG and WB MRI-DWIBS SIOPEN scoring resulted superimposable (Rho Spearman = 0,88, p < 0,0001).Conclusions: DWIBS and MIBG images showed very high concordance. WB MRI may represent an alternative in weak-avid MIBG tumors and for follow up assessment. An integrated imaging model is proposed for HR, Low and Intermediate Risk protocols.


Introduction
Neuroblastoma (NB) is the most frequent extracranial solid tumor of childhood, representing 8 to 10 % of all cases of childhood cancer [1].
Overall survival for patients with low-and intermediate-risk neuroblastoma is excellent (greater than 90%), while overall survival for high-risk patients remains approximately 40% [2].
In recent years combined multi-treatments of High-Risk Neuroblastoma (HR-NB) and Low and Intermediate Risk Neuroblastoma (Lines) protocols have improved the prognosis and quality of life of patients.
About 80% of neuroblastoma are metastatic (stage IV) at the time of presentation and metastasis are most commonly present at cortical bone and bone marrow: at diagnosis is crucial the identi cation of metastatic sites to evaluate the good response to treatment-The speci city of 123 I-MetaIodoBenzylGuanidine (MIBG) for detecting primary and secondary neuroblastoma has always been estimated close to 100%, while the sensitivity is 90-95% [3]. More recently was found in neuroblastoma that 123I-MIBG has a sensitivity of 88%-93% and a speci city of 83%-92% [4,5].
So, the guidelines recommend the use of Whole Body (WB) MIBG scintigraphy to assess the extent of the disease and according to the International Neuroblastoma Risk Group Staging System (INRGSS) the scintigraphic uptake in the skeleton is a condition for considering a patient to be a stage M [6].
Radioiodine-labeled MIBG is used to detect primary tumors and is the test of choice for identi cation of metastatic sites [5,[7][8][9][10]. The addition of single photon emission computed tomography (SPECT) and SPECT/computed tomography to 123I-MIBG planar images can improve identi cation and characterization of sites of uptake [11].
Nevertheless, MIBG scintigraphy has some drawbacks as the radiation exposure, the weak or absent MIBG avidity in a 10% of neuroblastoma [4,5] and the suboptimal detection of small subcentimeter lesions [12,13].
Whole-body magnetic resonance imaging (WB MRI) has been used for evaluation of skeletal lesions, both for staging and follow-up in various oncologic diseasess, without the exposure of the patient to ionizing radiation [14].
To our knowledge, few series have been published about the diagnostic performance of WB-MRI in patients with neuroblastoma [15,16]
A total amount of 82 paired whole body and SPECT MIBG and WB-MRI/DWISB scans were acquired between June 2009 and June 2019 within 30 days, without intercurrent therapy. Two couple MIBG scintigraphy and WB MRI-DWIBS were rejected because of intercurrent CH-therapy: therefore, our data set included 80 paired WB MIBG scintigraphy-WB MRI-DWIBS. Two expert Nuclear Medicine Physicians (more than 10-20 year of activity) and two expert Radiologists (more than 5-10 year of activity) performed the readings of WB-scans on the basis of International Society of Pediatric Oncology Europe Neuroblastoma SIOPEN scoring system. This retrospective study had institutional review board approval; written informed consent was obtained from all Parents or Guardians.
Whole-Body 123I-MIBG scintigraphy All diagnostic MIBG scans were performed on the basis of 2002-2018 guidelines for scintigraphic examinations of NB [11,12,19]. Each patient received a 123 I-MIBG dose activity in accordance with European Association of Nuclear Medicine (EANM) dosage calculator [20,21], 5.18 MBq/kg was administered, with a maximum dose of 185 MBq (most of patients had a weight under 25 Kg, one has a weight of 38Kg with a maximum activity administered 236 MBq). All of them underwent to thyroid tissue iodine prophylaxis with Lugol's solution 5%, range 8-40 drops on the basis of weigh and age [19]. Whole Body vertex-feet and SPECT thoracic-abdominal tract images were acquired at about 24 hours, the rst performed with 5-7 cm/min. bed velocity or 400 Kcounts for each spot scans 128x128 matrix; the second with shoot and stop 3degrees projections 20-30 sec./step, according to EANM GL 2010 [20], 20 patients on a Picker Philips Medical System and 11 patients more recently on a SIEMENS ECAM Gamma-camera, both equipped with MEGP parallel hole collimator.
All scintigraphic scans were acquired after voiding and for younger than three years children after voiding and diaper change. No patient needed a catheterization, only one had a catheter for clinical reasons. No patients underwent sedo-analgesia procedure, in last two years some of younger and less compliant patients had premedication with 1-3 mg of melatonine per os one hour before scan to induce a transient para-physiological sleep or a more relaxed state. Melatonine was useful in our own experience but a wider feasibility should be yet assessed. Most of the other children performed scans asleep at the presence of parents with entertainment methods (tablet with cartoons or baby-songs).

SIOPEN Scoring System
According to the SIOPEN semiquantitative scoring method, the skeleton was divided into 12 anatomical body segments as follows: the skull, the thoracic cage, the proximal right upper limb, the distal right upper limb, the proximal left upper limb, the distal left upper limb, the spine, the pelvis, the proximal right lower limb, the distal right lower limb, the proximal left lower limb and the distal left lower limb. The extent and pattern of skeletal MIBG involvement was scored using a 0-6 scale to discriminate between focal discrete lesions and patterns of more diffuse in ltration [21][22][23]. As known this method de ne lesion extension with a 0-6 grade scoring: 0 no sites per segment, 1 one discrete site per segment, 2 two discrete sites per segment, 3 three discrete lesions, 4 more than three discrete foci or a single diffuse lesion involving <50% of the segment, 5 diffuse involvement of 50-95% of the segment, and 6 diffuse involvement of the entire segment ( Fig.1, Tab.1) [24]. SPECT acquisition is usually useful in evaluation of di cult to read body segments i.e. neck, abdomen and spine for physiological superimposing images (salivary glands, activated brown fat, intestinal and bladder content, hepatic or spleen physiological activity close to adrenals) [5]. So, this scan, always performed in thoracic-abdomen district, was used to con rm MIBG-WB metabolic alterations and for controversial founding.
Whole Body MRI with Diffusion-weighted imaging with background body signal suppression (WB MRI-

DWIBS)
MR examination was performed using a 1.5 or 3T scanner (Achieva and Achieva D-Stream, respectively; Philips Medical Systems, The Netherland) with patient in supine feet-rst position; 58 exams were performed on 1.5T scanner and 22 exams on 3T equipment. Whole-body images were obtained with three or more consecutive package acquisitions, depending on body height, using Q-body coil for signal receiving and transmitting. The imaging protocol consisted of a coronal T2-weighted short time inversionrecovery (T2W-STIR) and axial diffusion weighted imaging with background body signal suppression (DWIBS) sequence. DWIBS was acquired using a short TI inversion recovery echo-planar imaging (STIR-EPI) sequence under free breathing applying one b-value (800 and1000 s/mm2 respectively for 3T and 1,5T scanner) in 62 exams and four b-value (0, 100, 200 and 800 s/mm2) in 18 cases performed on 3T scanner.
Multiplanar reconstructions (MPR) images and high-resolution maximum intensity projection (MIP) images were reconstructed in all cases.
Total acquisition time for whole-body MRI was approximately 45-50 minutes.
Younger or uncooperative children underwent general inhalation anesthesia with maintenance of spontaneous breathing and monitoring of vital parameters (heart rate, respiratory rate, SpO 2, EtCO 2 ), during performing MR examinations, in the presence of the anesthetist.

WB MRI Image analysis
Whole-body MRI data sets were transferred to a Picture Archiving and Communications System (PACS).
Two independent radiologists with 10 and 5 years of WB MRI experience, respectively, blinded to 123I-MIBG scintigraphy, evaluated in consensus MR images. On MR images bone marrow involvement was considered positive if present abnormal and/or focal increase of DWIBS and/or STIR intensity not from normal anatomic structure; DWIBS was evaluated only visually, in comparison with signal intensity of skeletal muscle. Quantitative analysis of ADC value (ADC, apparent diffusion coe cient) was not performed in this study. In case of discrepancies between STIR and DWIBS images, we considered as "true" DWIBS results.
SIOPEN scoring System was also applied to all WB MRI-DWIBS scans using the same scintigraphic criteria.

Statistical analysis
Speci city, sensibility, overall accuracy, VPP and VPN of WB MRI were estimated respect MIBG considered as gold standard. We performed furthermore the same analysis taking WB MRI-DWIBS as gold standard. Chi-square, parametric and not-parametric correlations were used to assess agreement degree among total scoring value, number of lesions, mean of scoring for each segment. T di Student for coupled data and mean comparison were used to compare mean±SD and % of segments resulted site of lesions among 80 paired data. p < 0.05 is considered as signi cative. Comparison between means for scoring data in pathological segments was studied with the Kendal-coe cient concordance and the sign-test. Wilcoxon test was used to compare the % of segments resulted as pathological.  Fig. 4. We report another discordant case with weak not homogeneus MIBG uptake in thoracic primary tumor and a focal intense alteration on dorsal spine, not clearly visible detected at DWIBS images (Fig.5).

4)
Both parametric and not-parametric tests for paired data showed a very good concordance between MIBG and DWIBS: for mean scoring values was found a Pearson correlation R value of 0.81 and a Rho Spearman value of 0.97, p < 0.0001; for total number of lesions in whole population R 0.78 and Rho 0.97, p < 0.0001; only in pathologic segments, mean scoring value correlation had R 0.82 and Rho 0.97, p < 0.0001, and R 0.78 and Rho 0.96 p < 0.0001 for total number of lesions.
The comparison of paired data mean-scoring per-segment and % of segments, resulted site of disease, didn't show any signi cant difference: t = 0.62 with p = 0.54 for mean-scoring and t = 0.46 with p = 0.65 for % of pathologic segments. Non-parametric test, (Kendal-coe cient concordance) K= 0.76; sign-test =1. Wilcoxon test for % of pathologic segments p = 0,61 and for mean-scoring p = 0,66.

Discussion
MRI is an effective method for imaging neuroblastoma [25]. It shows high sensitivity in detecting bone marrow metastases, high intrinsic soft tissue contrast resolution, precise de nition of intraspinal tumor extension, good delineation of diaphragmatic involvement of thoracic tumors [26,19]. WB MRI may represent a radiation-free alternative in the assessment of patients with NB and its feasibility has already been demonstrated for the work-up of oncologic patients with various neoplastic diseases, (e.g., melanoma, breast, colorectal, prostate cancers) or for hematologic diseases with nodal or bone marrow involvement (lymphoma, multiple myeloma) [27,28].
WB MRI uses both conventional sequences which provide predominantly anatomical information, such STIR e T1 weighted sequences, and functional sequences, such DWI and/or DWIBS. As known, DWIBS is a particular DWI technique that provide functional information from entire body during free breathing, in high signal-to-noise ratio (SNR) images, leading to easy identi cation of small lesions and thereby helping to visualize the spread of the disease [29].
In particular, as regards neuroblastic tumors, DWI sequence, based on ADC maps, has been shown to be able to distinguish between benign and malignant neuroblastic tumors, and to be useful in evaluating the response to chemotherapy [30][31][32][33].
In the present study, we evaluated the diagnostic accuracy of WB MRI-DWIBS in the assessment of the burden of disease, compared to MIBG WB Scintigraphy considered as gold standard, applying SIOPEN scoring system to both methods. The SIOPEN scoring systems have been used in large international clinical trials, showing to provide important prognostic information that can be used to guide appropriate therapy [34].
Our study demonstrates a good concordance about diagnosis, response to therapy and stop therapy evaluation scored by SIOPEN system on MIBG WB Scintigraphy and WB MRI-DWIBS. The two diagnostic techniques showed a high agreement of 92.7% of segments evaluated (80,1% negative concordant sites and 12.6% positive concordant sites) and resulted discordant in only 7.2% of segments evaluated (3.5% DWIBS negative but MIBG positive sites and 3.7% DWIBS positive but MIBG negative sites). Both mean scoring values for positive segments and percentage of segments appear superimposable, with few light differences of performance and high Rho Spearman value.
The scoring evaluation shows in our court of segments about a 20% of metastatic involvement in bone marrow for skull, thorax, spine, pelvis, femur and tibia, less percentage for the other sites.
Most of few discordant results regards skull, thorax and pelvis (slightly more sensitivity of MIBG), spine and limbs (slightly more sensitivity of MRI). As for ribs and skull, the lower sensitivity of WB MRI might be explained by thin thickness of these bones; to overcome the weakness on this segment we could perform as additional sequence an axial STIR sequence with thin thickness.
Also, the mean value of scoring for each segment shows a light prevalence of WB MRI on WB MIBG because of the higher sensibility on smaller signal-alterations related to the different resolution of two diagnostic method: about 7 -10 mm for MIBG [13] and about 4 mm for MRI [28]. Our data con rm also the assessment that MIBG scintigraphy is the best established and most widely used scintigraphic technique in the evaluation of NB because of its high sensitivity (97%) and speci city (83%-92%) [26]. A combination of MRI and MIBG scintigraphy has been shown to achieve the best sensitivity and speci city in NB imaging [19].
However, scintigraphy exposes patients to ionizing radiation. This is a major concern in children, who are at higher risk because of their smaller body size, higher mitotic rate, and longer life expectancy [35], in particular for low and intermediate risk NB.
According to protocol HR-NB, at least 7 MIBG-scintigraphy are necessary during the different steps of therapy with a high number of diagnostic examinations, and increased risk of potential secondary malignancies [11,35]. Leverdiere et al. found that the cumulative incidence of second malignant neoplasms in long survivor of neuroblastoma was 3.5% at 25 years and 7.0% at 30 years after diagnosis.
Compared with the sibling cohort, survivors had an increased risk of selected chronic health conditions (risk ratio [RR] = 8.3; 95% CI = 7.1 to 9.7) with a 20-year cumulative incidence of 41.1%. Endocrine complications are prevalent in childhood cancer survivors, with 50% experiencing at least one hormonal disorder over the course of their lives [36,37]. Moreover, Mostou et al. demonstrated at least one (16.7%) at least two (8,6%) and three or more (6.6%) endocrinopathies in survivors of neuroblastoma (31.9%) [38].
At our knowledge no other published study exists designed to perform a systematic comparison of SIOPEN Scoring on WB MIBG scintigraphy and on WB MRI-DWIBS. This may represent an important innovation about diagnostic evaluation and semiquantitative scoring of HR-NB and Intermediate-Risk NB.
In our experience, the clinical introduction of WB MRI may be useful in diagnostic protocol of NB with very high accuracy in disease extension and functional complemental characterization of primary tumor and metastasis. This is even more important for those cases with weak or poor MIBG avidity, due to the degree of undifferentiation of tumor cells, as well as for neuroblastoma with loss of MIBG avidity at relapse, as demonstrated in two case of our series [15]. Also, in our experience, a combination of MRI and MIBG scintigraphy showed to achieve the best sensitivity and speci city in NB imaging.
As known, a limitation of WB MRI is the light overestimation of bone lesions, especially in postchemotherapy examinations. At the onset, the false-positive ndings at DWIBS sequences are often due to the high signal of the regions rich in red bone marrow in the normal developing skeleton, above all in lumbar spine and pelvic skeleton as reported by Muller et al [39]. Therefore, the radiologist experience is fundamental in the identi cation of these areas of physiological hyper-intensity.
WB MRI shows lightly less speci city compared to MIBG scintigraphy also during the evaluation of therapy response as it arises from our results, whose statistical analysis we have not reported because they are not reliable given the too small number of tests. This limit of DWIBS sequence can be explained in part by the so-called "T2 shine-through" phenomenon: high signal on diffusion-weighted images is not due to restricted diffusion, but rather to high T2 signal which 'shines through' to the DWI image. It can be overcome by evaluating the apparent diffusion coe cient (ADC), a value that measures the effect of diffusion independent of the in uence of T2 shine-through [40], but our study lacks a quantitative analysis. Nevertheless, there are no validated bone ADC criteria in the literature, and there is a poor reproducibility of ADC measurements especially if the regions examined are "small". Furthermore, it should be added that especially in the evaluation of bone marrow there is a need to consider how the different types of treatment (chemotherapy, radiotherapy, immunotherapy) can affect the modi cation of the bone marrow signal intensity, data to date not yet clearly known [41,42]. These could be other interesting items for further studies. An important limitation is given by the lack of a standardized technique in the execution of the WB MRI, with different protocols among the numerous published studies. Another weakness is the non-capillary diffusion of MRI instrumentation. Finally, the necessity of general inhalation anesthesia for less than four years old patients or for not collaborative ones, with the assistance of the pediatric anesthetist might be another limitation of MRI application. This is otherwise true also for scintigraphic acquisitions in particular for SPECT-CT modality.

Conclusions
WB MRI-DWIBS and WB MIBG scintigraphy can be considered as complementary tools in the evaluation of metastatic NB at the diagnosis and during the various steps of therapy. We propose an integrated diagnostic model where WB MRI-DWIBS could avoid the necessity or MIBG scan in some of multiple steps of HR and reduce thus the number of diagnostic MIBG scans in the course of HR and low and intermediate risk NB protocol. We usually perform both exams at staging, post-induction, post-surgery, before maintenance and at the end of treatment; in the steps post-high dose chemotherapy MIBG could be omitted in case of stable negativity of WB MRI-DWIBS. WB MRI assessment could be useful without any other diagnostic modality during the follow up: 123I-MIBG scan should be performed to con rm or exclude relapse, for the eventual restaging, and for metabolic typi cation of skeletal or soft tissue new lesions. Another possible employment of WB MRI imaging is relative to children with instable systemic onset of neuroblastoma, who need a staging assessment into a short time interval, WB MRI could allow both an evaluation of primary tumor with focused sequences and an evaluation of skeletal and extraskeletal metastases, in a single exam without radiation exposure. Thus, as already a rmed a good combination of MRI and MIBG scintigraphy allows to achieve the best sensitivity and speci city in NB imaging.

Declarations
Funding: this study wasn't funded.
Con ict of Interest: Author Catia Olianti declares that she has no con ict of interest. Author Anna Perrone declares that she has no con ict of interest. Author Emanuele Neri declares that he has no con ict of interest. Author Dania Cioni declares that she has no con ict of interest. Author Michela Allocca declares that she has no con ict of interest. Author Marco Di Maurizio declares that he has no con ict of interest. Author Federica Carra declares that she has no con ict of interest. Author Annalisa Tondo declares that she has no con ict of interest.
Availability of data and material (data transparency) : the Authors give their availability.
Ethics approval: All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.   High DWIBS -WB restricted diffusion on a large abdominal primary tumor with a few-avid MIBG abdominal uptake in a Lines NB at staging, arrows Tables.pdf