Comparison of ⁶⁸Ga-DOTATOC-PET/CT and PET/MRI hybrid systems in patients with cranial meningioma: Initial results

Abstract

Background

⁶⁸Ga-DOTATOC-PET/CT is a well-established method for detecting and targeting the volume definition of meningiomas prior to radiotherapy. Moreover, there is evidence that this method is able to detect meningiomas with higher sensitivity than the goldstandard MRI. Since the hybrid PET/MRI scanner became available in the past few years, the next stage of development could consequently evolve by evaluating the feasibility of a hybrid PET/MRI scanner using ⁶⁸Ga-DOTATOC for detecting meningiomas.

Methods

Fifteen patients received ⁶⁸Ga-DOTATOC-PET/CT (0.5 h post injection [p.i.]) followed by PET/MRI 2 hours p.i. Both investigations were analyzed separately and then compared with respect to image quality, detection of intracranial meningiomas, and radiotracer uptake values (RUVs). In addition, ratios between radiotracer uptake in meningiomas and pituitary glands were compared between both PET/CT and PET/MRI.

Results

Overall, 33 intracranial meningiomas were detected. All were visible with high contrast in both PET/CT and PET/MRI. ⁶⁸Ga-DOTATOC-PET/MRI provided flawless image quality without artefacts. Calculated RUV in meningiomas, as well as the ratios of RUVs in meningiomas to those of pituitary glands, were higher in PET/CT. As a result, meningiomas can be distinguished from pituitary glands better in early images.

Conclusions

⁶⁸Ga-DOTATOC-PET/MRI provided flawless image quality and presented an ideal combination of high sensitivity/specificity (PET) and the best possible morphological visualization of meningiomas (MRI). In addition, excellent detection of meningiomas is already possible at 0.5 hours p.i. Later images do not improve the distinction between pituitary gland and adjacent meningiomas. However, RUVs need to be carefully compared between both imaging modalities.

Meningiomas, the most common nonglial tumors of the brain, arise from the membranous layers surrounding the central nervous system. More than 90% of meningiomas are benign in nature and show a low proliferation index and predominance in females.¹ Many meningiomas are asymptomatic and require only periodic observation. Symptomatic tumors are usually treated by surgical resection, resulting in long-term control rates of 33%–60% (observations up to 15 years).^2–4 Radiation therapy can also be used as a primary treatment for tumors that are surgically unresectable. Other indications for radiotherapy are patients with residual meningioma following surgery or those who are inoperable for other medical reasons.

Meningiomas located at the skull base are particularly difficult to treat due to their limited surgical approach and their proximity to vital structures such as blood vessels, cranial nerves, or the brainstem. In such cases, a maximum level of treatment accuracy is imperative. Accurate diagnostic tools are an important prerequisite for such intricate procedures. In this context, PET/CT imaging with the somatostatin receptor analogue DOTA-D-Phe1-Tyr3-octreotide (DOTATOC) labelled with ⁶⁸Ga has increasingly become a method for detection and target volume definition of meningiomas prior to radiotherapy at our hospital. This imaging modality is based on the fact that almost all meningiomas intensely express the somatostatin receptor subtype 2 (SSTR 2), to which DOTATOC is able to bind with very high affinity.^5–7 In contrast to all conventional imaging modalities (including the gold standard, contrast enhanced MRI), ⁶⁸Ga-DOTATOC-PET/CT can clearly distinguish between vital meningioma tissue and other types of tissue such as postoperative scarring. In addition, DOTATOC is able to detect meningiomas with very high contrast because normal brain tissue does not express SSTR except for the pituitary gland. Moreover, there is evidence that this method is more sensitive in detecting meningiomas than the current gold standard, contrast-enhanced MRI.⁸

Following many years of complex development, hybrid PET/MRI scanners have finally become available. Two types of PET/MRI machines are on the market, however. One type is able to simultaneously acquire PET and MRI images, which allows for faster investigations with more accurate image fusion. The other type of PET/MRI acquires PET and MRI images consecutively. By using a PET/MRI, all investigations necessary for planning radiotherapy can be conducted in a single session. Initial reports of the hybrid PET/MRI system, which uses the most common radiotracer ¹⁸F-FDG, show it to be a promising method. However, recent studies report artefact-related limitations when ⁶⁸Ga-labelled tracers are applied.^9,10 The next step in development of the hybrid PET/MRI would consequently evolve from the feasibility and image quality using ⁶⁸Ga-DOTATOC for the detection of meningiomas. This new method could be an integral part of the clinical routine in the future and possibly enable detection and therapy of meningiomas with improved sensitivity and accuracy.

Materials and Methods

This study was approved by the ethics committee of the University of Heidelberg (S-485/2012). Patients participating in the present study provided written informed consent prior to receiving PET/MRI examinations and allowing scientific analysis of the obtained datasets.

Patients

Patient characteristics are summarized in Table 1. Fifteen consecutive meningioma patients underwent static PET/CT 30 minutes and PET/MRI 2 hours (124 ± 26 min) post injection (p.i.) of ⁶⁸Ga-labelled DOTATOC. Patients who were unable to provide informed consent or had metallic implants (not MR-compatible or unknown) were excluded from the study (n = 0). Due to potential aggravation of tinnitus symptoms by the MRI, those patients who were not willing to accept this risk would also have been excluded from this study (n = 0). The average patient’s' age was 48 years (±13y). The cohort consisted of 5 males and 10 females. The PET/CT was initiated by radiation oncologists in order to determine the gross tumor volume (GTV).

Table 1.

Characteristics of all 15 patients investigated in this study

Patient No.	Age (years)	Sex (m/f)	68Ga-DOTATOC (MBq)	Intracranial Meningiomas (n)	Previous Therapy
1	72	m	172	6	surgery + radiation
2	62	m	154	1	none
3	62	f	216	1	surgery
4	47	f	205	1	surgery
5	61	m	190	3	surgery
6	51	m	100	1	none
7	55	f	265	8	surgery + radiation
8	48	m	176	4	surgery + radiation
9	42	f	154	1	surgery
10	33	f	175	1	surgery
11	26	f	251	1	surgery + radiation
12	38	f	177	1	none
13	56	f	201	1	surgery + radiation
14	26	f	156	1	none
15	48	f	258	2	none

Tracer

For the PET/CT, DOTA0-D-Phe1-Tyr3-octreotide was produced as previously published.^{11 68}Ga (half-life, 68.3 min) was eluted from a ⁶⁸Ge/⁶⁸Ga radionuclide generator. Both components were coupled as described previously.¹² The ⁶⁸Ga-DOTATOC solution was administered to participants via an intravenous bolus (mean, 190 ± 43 MBq; range, 100–265 MBq). Variation of injected radiotracer activity was caused by the short half-life of ⁶⁸Ga and variable elution efficiencies obtained during the lifetime of the ⁶⁸Ge/⁶⁸Ga radionuclide generator. However, based on our previous experiences, all activities injected were sufficient to detect meningiomas.⁸ Targeted activity was 3 MBq/kg. Because binding of DOTATOC involves a specific receptor interaction that might be insufficient by the amount of peptide, the quantity of the tracer injected was chosen on a peptide basis, and all radiotracer preparations contained 12.5 µg DOTATOC.

Positron Emission Tomography/Computed Tomography

A noncontrast-enhanced CT scan of the head was performed ∼30 minutes after tracer injection using the following parameters: slice thickness of 5 mm; increment of 0.8 mm; soft tissue reconstruction kernel; 130 keV; and 80 mAs. Immediately after CT scanning, a PET scan of the head (one bed position) was acquired in 3D (matrix, 164 × 164). For one bed position (16.2 cm; overlapping scale, 4.2 cm), we used a 10-minute acquisition time. PET and CT were performed using the same protocol for every participant on a BIOGRAPH-6 PET/CT scanner (Siemens).

All findings with abnormal DOTATOC-uptake that visually matched characteristic appearances of meningiomas were counted. In addition, the localization and the standard uptake value (SUV_mean/max) of meningiomas and the pituitary gland were determined.

Positron Emission Tomography/Magnetic Resonance Imaging

All PET/MRI examinations were performed using a hybrid PET/MRI-system (Biograph mMR; Siemens Medical Solutions) capable of simultaneous PET and MR imaging during one examination (software, syngo MRB 18P).

As described previously, the PET/MRI-system consists of a 3.0-Tesla whole-body system (based on a Siemens Magnetom Verio) with a magnet length of 163 cm and a bore size of 60 cm.¹³ The MR scanner operates with a maximum gradient strength of 45 mT/m and a slew rate of 200 T/m/sec in all 3 directions. The head coil was used for homogeneous radiofrequency transmission; the same coil, when optimized for a minimal 511 keV photon attenuation, was used for signal detection.

The PET detector technology of whole-body hybrid PET/MR imaging relies on lutetium oxyorthosilicate scintillation crystals in combination with MR-compatible avalanche photodiodes instead of photomultiplier tubes. Each block detector consists of 64 crystal elements with a crystal size of 4 × 4 × 20 mm. Fifty-six lutetium oxyorthosilicate-avalanche photodiode block detectors form a detector ring, and 64 detector element rings are arranged on the z-axis. The entire PET scanner has a field of view (FOV) of about 25.8 cm in the z direction, an axial FOV of 59.4 cm, and an inner detector ring diameter of 65.6 cm.

Simultaneous PET and MR imaging data acquisition: PET and MR imaging were started ∼2 hours after administration of the tracer with 10 minutes of acquisition time for the bed position. Acquired PET data were reconstructed with an iterative 3D ordered-subset expectation maximization algorithm by using 2 iterations, 21 subsets, Gaussian filter of 4 mm, image matrix of 172, and extended mu-map FOV.

During each PET data acquisition, a series of MR sequences was performed as follows: after gradient echo localizers, a Dixon volume interpolated examination (VIBE) sequence (in-/opposed phase technique) for attenuation correction was conducted (repetition time [TR]/echo time [TE] 3.6/1.23 and 2.46; flip angle 10°; matrix size 256 × 192 × 120; FOV 500 × 328 mm; bandwidth, 965 Hz/pixel; and parallel imaging GRAPPA factor 2).

Protocol Head

T2-weighted axial TSE (TR/TE 4000/109 ms; turbofactor 17; FOV 220; inplane resolution 0.6 × 0.5 × 4.0 mm; parallel acquisition techniques [PAT] grappa factor 2; averages 2). T1-weighted 3D axial FLASH (TR/TE 16/4.92 ms; flip angel 20°; FOV 230; inplane resolution 0.9 × 0.9 × 3.0 mm; parallel acquisition techniques [PAT] none; averages 1). Axial epi (TR/TE 5000/77 ms; FOV 225; inplane resolution 1.5 × 1.5 × 5.0 mm; PAT GRAPPA factor 3; averages 4). T2-weighted axial fat suppressed (TR/TE 4000/91 ms; Turbofactor 17; FOV 220; inplane resolution 0.7 × 0.7 × 3.0 mm; PAT none; averages 2). FLAIR axial fat suppressed (TR/TE 8000/89 ms; Turbofactor 12; FOV 220; inplane resolution 1.1 × 0.9 × 3.0 mm; PAT none). T1-weighted MPR 3D flash after administration of weight-adjusted gadolinium contrast medium (TR/TE 3200/1,64 ms; flip angle 9°; FOV 300; inplane resolution 0.9 × 0.9 × 0.9 mm; PAT GRAPPA factor 2). Contrast-enhanced coronal and axial T1-weighted TSE fat suppressed (TR/TE 700/8,1 ms; Turbofactor 3; FOV 220; inplane resolution 0.9 × 0.7 × 3.0 mm; PAT none).

Image Analysis

Two board-certified specialists in nuclear medicine and radiology read all datasets independently. The analysis was performed using a workstation and Syngo software TrueD (Siemens Medical Systems). Lesions that were visually considered as meningioma were counted and analyzed with respect to their standardized uptake values (SUV_mean/max). The same analysis was performed with regard to the pituitary gland. All acquired MR images were used for further interpretation. For PET/MR imaging, T1 MPR 3D flash with contrast medium was used for image fusion.

Similar to our previous reports, SUVs in late images (PET/MRI) were defined as increasing, decreasing, or stable, with intensity changes of >10%, < −10%, or between −10% and +10%, respectively.¹⁰

For calculation of the SUV, circular regions of interest (ROI) were drawn around areas with focally increased uptake in transverse slices and automatically adapted to a 3-dimensional volume of interest at a 70% isocontour.

To determine whether distinction between meningiomas and pituitary glands is better in early or late images, the SUV of meningiomas was divided by the SUV of the pituitary glands. The resulting SUV ratios were then compared. The distinction between the 2 above-mentioned tissues is particularly relevant for external-beam radiation therapy when meningiomas are adjacent to the pituitary gland.

Statistical Analysis

For statistical analysis, Sigmaplot version 11 software (Systat Software) was used. Significance of differences was evaluated by 2-sided Wilcoxon signed rank tests for tumor uptake and contrast in both PET/CT methods. A P value <.05 was considered statistically significant.

Results

Image Quality

PET/CT and PET/MRI were feasible in all cases. Both PET and MRI of the PET/MRI-system provided diagnostic image quality without apparent image artefacts. Most lesions characteristic for meningioma demonstrated higher uptake and contrast in early images (PET/CT 30 min. p.i.). This is discussed in more detail in the section “Lesions Characteristic for Meningioma.” Moreover, having several different MRI sequences available with high resolution facilitated evaluation of the images provided by the PET/MRI system (Figs. 1 and 2).

Fig. 1.

⁶⁸Ga-DOTATOC-PET/MRI (A–C) and PET/CT (D–F) of patient 9 demonstrating a meningioma of the skull base (yellow arrows) adjacent to the pituitary gland (white arrows). Late images (PET/MRI) do not help to improve the distinction between the 2 types of tissues. (A) contrast enhanced T1-weighted MRI. (B) DOTATOC-PET 30 minutes p.i. (derived from the PET/CT). (C) fusion of a and b. (D) native CT. (E) DOTATOC-PET ∼2 hours p.i. (derived from the PET/MRI). (F) fusion of D and E.

Fig. 2.

⁶⁸Ga-DOTATOC-PET/MRI (A–C) and PET/CT (D–F) of patient 11. Extensive and inhomogeneous meningioma of the skull base infiltrating the nasal cavity. DOTATOC-PET can distinguish between vital meningioma and other tissues such as postoperative scarring or reactive tissue. (A) contrast-enhanced T1-weighted MRI. (B) DOTATOC-PET 30 minutes p.i. (derived from the PET/CT). (C) fusion of a and b. (D) native CT. (E) DOTATOC-PET ∼2 hours p.i. (derived from the PET/MRI). (F) fusion of D and E.

Pituitary Gland

Table 2 presents the mean uptake values of the 15 pituitary glands in PET/CT and PET/MRI, including standard deviation (SD), minimum, maximum, and median.

Table 2.

SUV_mean/max for all meningiomas and pituitary glands in both ⁶⁸Ga-DOTATOC-PET/CT (30 min. p.i.) and PET/MRI (2 h p.i.). Also listed is the ratio of the SUV in the meningiomas to that in pituitary glands.

	PET/CT (30 min. p.i.)			PET/MRI (2 h p.i.)
	SUVmean ± SD	Range	Median	SUVmean ± SD	Range	Median
Meningiomas (n = 33)	8.3 ± 5.9	2.7 − 28.9	5.8	6.0 ± 3.3	1.9 − 19.1	4.7
Pituitary glands (n = 15)	5.6 ± 1.4	3.7 − 8.3	5.1	5.3 ± 1.4	3.0 − 8.3	5.0
Ratio, meningoma/pituitary	1.7 ± 1.3	0.3 − 6.4	1.2	1.3 ± 0.7	0.4 − 3.6	1.1
	SUVmax ± SD	Range	Median	SUVmax ± SD	Range	Median
Meningiomas (n = 33)	16.5 ± 14.8	3.0 − 71.4	10.5	11.1 ± 7.6	1.9 − 29.4	8.3
Pituitary glands (n = 15)	8.9 ± 2.1	5.6 − 13.2	8.6	8.0 ± 1.9	3.8 − 10.9	8.6
Ratio, meningioma/pituitary	2.0 ± 1.9	0.2 − 9.2	1.4	1.6 ± 1.2	0.2 − 4.5	1.4

Abbreviations: p.i., post injection; SD, standard deviation; SUV, standard uptake value.

As demonstrated by Fig. S1 in supplementary data, SUV_mean increased clearly (>10%) in 2 pituitaries, decreased clearly (>10%) in 6 pituitaries, and remained stable (±10%) in 7 pituitaries between PET/CT and PET/MRI. SUV_max increased clearly (>10%) in 2 pituitaries, decreased clearly (>10%) in 8 pituitaries, and remained stable (±10%) in 5 pituitaries between PET/CT and PET/MRI.

In many cases, SUVs of the pituitary glands were higher in the early images (PET/CT) than the later images (PET/MRI), although this was not statistically significant (P = .542 for SUV_mean and P = .055 for SUV_max).

Lesions Characteristic for Meningioma

Among the 15 participants investigated by both imaging techniques, 33 lesions characteristic for intracranial meningioma were detected. All lesions were clearly detectable in both early (PET/CT) and late images (PET/MRI).

Average uptake values among the 33 representative meningiomas are also presented in Table 2.

As demonstrated by Fig. 3, SUV_mean increased clearly (>10%) in 4 lesions, decreased clearly (>10%) in 20 lesions, and remained stable (±10%) in 9 lesions between PET/CT and PET/MRI. SUV_max increased clearly (>10%) in 5 lesions, decreased clearly (>10%) in 23 lesions, and remained stable (±10%) in 5 lesions between PET/CT and PET/MRI.

Fig. 3.

Mean and maximum uptake values (SUV_mean/max) of the 33 meningiomas in ⁶⁸Ga-DOTATOC-PET/CT (30 min p.i.) and PET/MRI (2 h p.i.). In the majority of the cases, radiotracer uptake was higher in early images.

SUVs of the meningiomas were significantly higher in PET/CT (SUV_mean: P = .011 and SUV_max: P = .007).

Mean ratios of the uptake in meningiomas to those in pituitary glands are presented in Table 2 and Fig. 4.

Fig. 4.

Ratios between meningiomas and pituitary glands (hypophysis) in ⁶⁸Ga-DOTATOC-PET/CT (30 min p.i.) and PET/MRI (2 h p.i.). The majority of the ratios were higher in early images. Later scans therefore do not improve the distinction between meningiomas and adjacent pituitary glands.

Using SUV_mean ratios between meningiomas and pituitary gland increased clearly (>10%) in 4 cases, decreased clearly (>10%) in 17 cases, and remained stable (± 10%) in 12 cases between PET/CT and PET/MRI. With regard to SUV_max the same ratios increased clearly (>10%) in 5 cases, decreased clearly (>10%) in 16 cases, and remained stable (±10%) in 12 cases between PET/CT and PET/MRI.

In conclusion, ratios between meningiomas and pituitary glands were significantly higher in PET/CT (P = .003 for SUV_mean and P = .035 for SUV_max).

Discussion

⁶⁸Ga-DOTATOC-PET/CT is a highly effective method for detection of meningiomas and their distinction from other types of tissues such as postoperative scarring. In addition to the current diagnostic gold standard, contrast-enhanced MRI, it has become a useful diagnostic tool for accurately defining GTV prior to radiotherapy at our hospital.^7,14 There is also evidence that ⁶⁸Ga-DOTATOC-PET/CT is able to detect meningiomas with higher sensitivity than that of contrast-enhanced MRI.⁸ In particular, small lesions adjacent to the falx cerebri or located at the skull base are difficult for MRI to detect. Additional DOTATOC-PET analysis can improve detection of meningiomas and thereby influence treatment planning and follow-up, all of which are of potential clinical benefit to patients.⁸

Since hybrid PET/MRI scanners have become available, the next stage of development depends on the feasibility of using ⁶⁸Ga-DOTATOC to detect meningiomas. No systematic evaluation of ⁶⁸Ga-DOTATOC-PET/MRI exists, and only one case report has been published to date.¹⁵

Some experts argue that the development of hybrid PET/MRI scanners was futile because certain software already exists that can fuse separately acquired PET and MRI images. Similar arguments were voiced at the time of hybrid PET/CT scanner development. However, the ensuing years have clearly shown multiple advantages of PET/CT hybrid scanners. The image fusion was found to be more accurate compared with images that were reconstructed based on retroactive fusion of separately obtained PET and CT/MRI images. The development of hybrid PET/CT has enabled more accurate therapies, especially external radiation. Moreover, image fusion can be easily accomplished immediately after the scans, using the same control unit of the scanner. Because it does not require manipulation by either physicians or technical personnel, it prevents human error in the context of image fusion. As a result, image fusion saves time and resources. This is an important consideration for a modern health care system, which continuously pushes the boundaries of efficacy. Another consideration is that patients only have to undergo a single examination, thus increasing comfort and saving time. This also frees the single CT- or MRI-scanners for investigations of patients who do not require PET. Patients are also exposed to less radiation because CT can be omitted in most cases. Only in cases of calcifications within meningiomas, which cause extinction artefacts in MRI, is it useful to obtain an additional CT scan in order to improve GTV planning prior to radiation therapy. Due to the above-mentioned reasons, the authors believe that hybrid PET/MRI scanners will be an integral part of clinical routine in the future and possibly replace PET/CT. At this stage, a single ⁶⁸Ga-DOTATOC-PET/MRI at 30 minutes p.i. seems to be the best option for imaging meningiomas.

Our study demonstrated the feasibility of ⁶⁸Ga-DOTATOC-PET/MRI for imaging intracranial meningiomas. In all cases, the image quality was excellent and without artefacts; recent studies have reported severe artefacts in PET/MRI hybrid systems when specifically binding tracers were used.^9,10 However, whether PET/MRI is superior to PET/CT with regard to planning therapy for meningiomas will have to be investigated in future studies featuring a larger patient cohort. The authors are convinced that the present cohort of 15 patients is too small for a meaningful comparison.

One limitation of the ⁶⁸Ga-DOTATOC-PET in general is the physiological tracer uptake of the pituitary gland. In cases of meningiomas located at the skull base and adjacent to the pituitary gland, DOTATOC-PET cannot clearly distinguish between the margins of both tissues in early images (PET/CT). However, our results in this study demonstrated that late images 2 hours p.i. (PET/MRI) cannot improve the distinction between meningiomas and pituitary glands.

It is already known that meningiomas present with excellent contrast at 30 minutes p.i. and that their radiotracer uptake rises within the first phase p.i., reaching a plateau between 60–120 minutes p.i.^5,6,8 Our study, however, demonstrated that DOTATOC-uptake in meningiomas measured by the PET/MRI hybrid system 2 hours p.i. is lower compared with images conducted 30 minutes p.i. by PET/CT. Theoretically, the different PET detector techniques in the 2 methods could cause differences in uptake quantification. While in PET/CT the detector consists of a scintillating crystal and photomultiplier, a semiconductor technique is used in hybrid PET/MRI systems. Another explanation could be different algorithms of measurement between the 2 imaging methods or difficulties of the scatter correction of the PET/MRI system. The latter aspect has been reported for specific tracers such as the ⁶⁸Ga-PSMA-ligand HBED-CC, which is used for imaging prostate cancer.¹⁰ In summary, the SUV values determined by using ⁶⁸Ga-DOTATOC-PET/CT and PET/MRI systems need to be compared carefully (eg, when evaluating therapy response).

Despite the described differences in uptake quantification, the more important aspect is the clear presentation of meningiomas and the absence of artefacts by the PET/MRI system as demonstrated by our data. In addition, the ratio between uptake in meningioma and pituitary tissue is independent of quantification differences. In this context, our data could demonstrate that late images 2 hours p.i. cannot improve the distinction between these 2 tissues.

As presented above, data exist on the DOTATOC-uptake of meningiomas in late images. However, one must concede that it is still unclear if late images could further clarify other DOTATOC-positive nonmeningeal tissues such as esthesioneuroblastomas,¹⁶ accumulations of leucocytes in chronic inflammatory tissue,¹⁷ pituitary tumors or gliomas with impaired blood-brain barrier,¹⁸ fibrous dysplasia of the bone,¹⁹ Paget's disease,²⁰ and various cranial metastases of tumors such as breast cancer.²¹

Another limitation of this study is the fact that a histological confirmation was not conducted for every single lesion. However, in cases with difficult access, biopsy is neither medically indicated nor ethical. In addition, the above-mentioned different DOTATOC-positive tissues that are not meningiomas usually present with a significantly lower uptake as well as distinct morphology and localization that clearly differ from meningiomas. In particular, small meningiomas frequently present with excellent contrast due to their high tracer uptake as well as their typical localization adjacent to the meninges. In this context, none of the lesions examined for this study was unclear. They all were typical for meningiomas.

Conclusion

This study investigated the feasibility of a hybrid PET/MR system using ⁶⁸Ga-DOTATOC for detecting intracranial meningiomas and compared the results of the hybrid system with those of PET/CT. The images obtained from the PET/MRI scanner were flawless and without artefacts. However, radiotracer uptake values need to be carefully compared between both imaging systems. Our results also demonstrated that the contrast of meningiomas in DOTATOC-PET is already excellent at 30 minutes p.i. Later images do not help to improve the distinction between pituitary gland and adjacent meningiomas.

In our opinion, ⁶⁸Ga-DOTATOC-PET/MRI presents an ideal combination of high sensitivity and specificity and features the best possible morphological tumor visualization. Further studies are needed to evaluate if this new method can possibly enable detection and therapy of meningiomas with improved sensitivity and accuracy.

Supplementary material

Supplementary material is available online at Neuro-Oncology (http://neuro-oncology.oxfordjournals.org/).

Funding

There was no funding that supported the research.