[Potential of PET/MRI for diagnosis of prostate cancer]

CLINICAL/METHODICAL ISSUE

A present goal is to improve detection and staging of prostate cancer using innovative imaging technology such as PET/MRI.

STANDARD RADIOLOGICAL METHODS

The modality of choice for detection of prostate cancer is multiparametric MRI. Furthermore, PET/CT is used, in particular, for the detection and staging of distant metastases and recurrent disease. For assessment of bone metastases, the method most commonly used is bone scintigraphy.

METHODICAL INNOVATIONS

The development of a simultaneous hybrid PET/MRI system is the last great "fusion" of the known cross-sectional image modalities. In addition, synthesis of new, innovative tracers such as (18)F-FACBC or (68)Ga-PSMA allows more specific detection of prostate cancer.

PERFORMANCE

Hybrid PET/MRI imaging has the potential to replace conventional imaging techniques in the future.

ACHIEVEMENTS

The method is just starting the broad application. Clinical studies must be expanded in order to substantiate the additional value of the method.

PRACTICAL RECOMMENDATIONS

Currently, there is still a low distribution situation, since it is a new and cost-intensive method. At the same time, there is still no consistent solution for reimbursement. The importance in practice first rises by clarifying the payment situation and further demonstration of the method's benefit by larger studies.

Radiological monitoring of the treatment of solid tumors in practice

PURPOSE

Thanks to advances in cancer therapy, the diagnosis of "incurable cancer" is increasingly able to be changed to a chronic disease that is manageable over long periods, resulting in a change in the clinical management of cancer patients with solid tumors. New parameters are needed to measure the success of targeted therapy in clinical trials.

MATERIALS AND METHODS

Review article on the basis of selective literature research.

RESULTS

In order to assess how well solid tumors respond to treatment, size-based criteria called RECIST (Response Evaluation Criteria in Solid tumors) have been defined. These criteria have been validated in large oncology trials and are currently used most frequently. New molecular therapies often do not - or at least do not immediately - reduce the size of a tumor. Therefore, RECIST evaluation should be critically assessed especially in the case of modern therapies. Any additional available tumor biology information should be considered. In radiology new methods and developments of RECIST have been introduced to better assess the success of targeted therapy.

CONCLUSION

Assessment according to RECIST has been proven for the follow-up of classic tumor therapy. For the monitoring of targeted therapies, new parameters are often required. Therefore, some specific tumor- and therapy-adapted criteria have already been defined to better evaluate treatment success in clinical trials.

Multivariate regression approaches for surrogate-based diffeomorphic estimation of respiratory motion in radiation therapy

Breathing-induced location uncertainties of internal structures are still a relevant issue in the radiation therapy of thoracic and abdominal tumours. Motion compensation approaches like gating or tumour tracking are usually driven by low-dimensional breathing signals, which are acquired in real-time during the treatment. These signals are only surrogates of the internal motion of target structures and organs at risk, and, consequently, appropriate models are needed to establish correspondence between the acquired signals and the sought internal motion patterns. In this work, we present a diffeomorphic framework for correspondence modelling based on the Log-Euclidean framework and multivariate regression. Within the framework, we systematically compare standard and subspace regression approaches (principal component regression, partial least squares, canonical correlation analysis) for different types of common breathing signals (1D: spirometry, abdominal belt, diaphragm tracking; multi-dimensional: skin surface tracking). Experiments are based on 4D CT and 4D MRI data sets and cover intra- and inter-cycle as well as intra- and inter-session motion variations. Only small differences in internal motion estimation accuracy are observed between the 1D surrogates. Increasing the surrogate dimensionality, however, improved the accuracy significantly; this is shown for both 2D signals, which consist of a common 1D signal and its time derivative, and high-dimensional signals containing the motion of many skin surface points. Eventually, comparing the standard and subspace regression variants when applied to the high-dimensional breathing signals, only small differences in terms of motion estimation accuracy are found.

Comparison of PET/CT and PET/MRI hybrid systems using a 68Ga-labelled PSMA ligand for the diagnosis of recurrent prostate cancer: initial experience

PURPOSE

(68)Ga-labelled HBED-CC-PSMA is a highly promising tracer for imaging recurrent prostate cancer (PCa). The intention of this study was to evaluate the feasibility of PET/MRI with this tracer.

METHODS

Twenty patients underwent PET/CT 1 h after injection of the (68)Ga-PSMA ligand followed by PET/MRI 3 h after injection. Data from the two investigations were first analysed separately and then compared with respect to tumour detection rate and radiotracer uptake in various tissues. To evaluate the quantification accuracy of the PET/MRI system, differences in SUVs between PET/CT and corresponding PET/MRI were compared with differences in SUVs between PET/CT 1 h and 3 h after injection in another patient cohort. This cohort was investigated using the same PET/CT system.

RESULTS

With PET/MRI, different diagnostic sequences, higher contrast of lesions and higher resolution of MRI enabled a subjectively easier evaluation of the images. In addition, four unclear findings on PET/CT could be clarified as characteristic of PCa metastases by PET/MRI. However, in PET images of the PET/MRI, a reduced signal was observed at the level of the kidneys (in 11 patients) and around the urinary bladder (in 15 patients). This led to reduced SUVs in six lesions. SUVmean values provided by the PET/MRI system were different in muscles, blood pool, liver and spleen.

CONCLUSION

PCa was detected more easily and more accurately with Ga-PSMA PET/MRI than with PET/CT and with lower radiation exposure. Consequently, this new technique could clarify unclear findings on PET/CT. However, scatter correction was challenging when the specific (68)Ga-PSMA ligand was used. Moreover, direct comparison of SUVs from PET/CT and PET/MR needs to be conducted carefully.

[Organ toxicity of medicinal tumor therapy: morphological correlates]

CLINICAL/METHODOLOGICAL ISSUE: In antineoplastic chemotherapy classical cytostatic drugs are increasingly being supplemented by antibodies and so-called targeted therapies. In addition to the antineoplastic effect and general intolerance quite characteristic morphological changes can often be found and identified by the radiologist. The distinction between findings indicating side effects versus tumor progression or an infectious etiology is essential.

FACTS AND CIRCUMSTANCES

Classical antineoplastic chemotherapy interacts with DNA and RNA synthesis, DNA repair or the mitosis process. In contrast modern targeted anticancer therapies act at the level of signal transduction pathways.Localized, organ-related changes are related to the metabolic characteristics of organs or anatomical features such as the properties of the local blood-tissue barrier. Toxicity associated findings often resemble fulminant tumor progression.

EVALUATION

In new targeted anti-cancer therapies toxicity often occurs in a non-cumulative way; therefore, morphological changes are often precursors of the manifestation of clinical toxicity.

PRACTICAL RECOMMENDATIONS

Oncological radiology requires increasingly active interdisciplinary dialogue in order to delineate morphological correlates of organ toxicity against tumor progression and initiate appropriate therapeutic measures.

Evaluation of the ESUR PI-RADS scoring system for multiparametric MRI of the prostate with targeted MR/TRUS fusion-guided biopsy at 3.0 Tesla

OBJECTIVES

To evaluate the Prostate Imaging Reporting and Data System (PI-RADS) proposed by the European Society of Urogenital Radiology (ESUR) for detection of prostate cancer (PCa) by multiparametric magnetic resonance imaging (mpMRI) in a consecutive cohort of patients with magnetic resonance/transrectal ultrasound (MR/TRUS) fusion-guided biopsy.

METHODS

Suspicious lesions on mpMRI at 3.0 T were scored according to the PI-RADS system before MR/TRUS fusion-guided biopsy and correlated to histopathology results. Statistical correlation was obtained by a Mann-Whitney U test. Receiver operating characteristics (ROC) and optimal thresholds were calculated.

RESULTS

In 64 patients, 128/445 positive biopsy cores were obtained out of 95 suspicious regions of interest (ROIs). PCa was present in 27/64 (42%) of the patients. ROC results for the aggregated PI-RADS scores exhibited higher areas under the curve compared to those of the Likert score. Sensitivity/Specificity for the following thresholds were calculated: 85 %/73 % and 67 %/92 % for PI-RADS scores of 9 and 10, respectively; 85 %/60 % and 56 %/97 % for Likert scores of 3 and 4, respectively [corrected.

CONCLUSIONS

The standardised ESUR PI-RADS system is beneficial to indicate the likelihood of PCa of suspicious lesions on mpMRI. It is also valuable to identify locations to be targeted with biopsy. The aggregated PI-RADS score achieved better results compared to the single five-point Likert score.

KEY POINTS

• The ESUR PI-RADS scoring system was evaluated using multiparametric 3.0-T MRI. • To investigate suspicious findings, transperineal MR/TRUS fusion-guided biopsy was used. • PI-RADS can guide biopsy locations and improve detection of clinically significant cancer. • Biopsy procedures can be optimised, reducing unnecessary negative biopsies for patients. • The PI-RADS scoring system may contribute to more effective prostate MRI.

Whole-body-MR-diffusion weighted imaging in oncology

The clinical implementation of whole body diffusion weighted imaging (WB-DWI) for tumor-detection, -characterization and therapy monitoring is well underway. The method is fast, robust and combined with its wide availability on modern MRI scanners, it has a vast potential clinical impact. Owing to the high tumor to background contrast, its main application areas are simple detection of tumor suspicious lesions (primary tumor, recurrence, and metastasis), tumor grading and therapy monitoring.WB-DWI has a strong diagnostic potential regarding the evaluation of bone marrow and its diseases and as thus, tumor detection and therapy monitoring of bone metastasis is of particular interest. The assessment of a lymphatic tumor spreading is constricted. One of the major hurdles that still hamper the wide clinical application of WB-DWI is a lack of standardization of measurement parameters that limit the comparability. of current research results.

KEY POINTS

Owing to the high tumor to background contrast WB-DWI allows fast assessment of tumor distribution and total tumor burden. WB-DWI allows therapy monitoring. WB-DWI is widely available.

Whole-body-MR-diffusion weighted imaging in oncology

The clinical implementation of whole body diffusion weighted imaging (WB-DWI) for tumor-detection, -characterization and therapy monitoring is well underway. The method is fast, robust and combined with its wide availability on modern MRI scanners, it has a vast potential clinical impact. Owing to the high tumor to background contrast, its main application areas are simple detection of tumor suspicious lesions (primary tumor, recurrence, and metastasis), tumor grading and therapy monitoring. WB-DWI has a strong diagnostic potential regarding the evaluation of bone marrow and its diseases and as thus, tumor detection and therapy monitoring of bone metastasis is of particular interest. The assessment of a lymphatic tumor spreading is constricted. One of the major hurdles that still hamper the wide clinical application of WB-DWI is a lack of standardization of measurement parameters that limit the comparability of current research results.

KEY POINTS

▶ Owing to the high tumor to background contrast WB-DWI allows fast assessment of tumor distribution and total tumor burden. ▶ WB-DWI allows therapy monitoring. ▶ WB-DWI is widely available.

Inter-observer reproducibility of semi-automatic tumor diameter measurement and volumetric analysis in patients with lung cancer

OBJECTIVES

Therapy monitoring in oncologic patient requires precise measurement methods. In order to improve the precision of measurements, we used a semi-automated generic segmentation algorithm to measure the size of large lung cancer tumors. The reproducibility of computer-assisted measurements were assessed and compared with manual measurements.

METHODS

CT scans of 24 consecutive lung cancer patients who were referred to our hospital over a period of 6 months were analyzed. The tumor sizes were measured manually by 3 independent radiologists, according to World Health Organization (WHO) and the Revised Response Evaluation Criteria in Solid Tumors (RECIST) guidelines. At least 10 months later, measurements were repeated semi-automatically on the same scans by the same radiologists. The inter-observer reproducibility of all measurements was assessed and compared between manual and semi-automated measurements.

RESULTS

Manual measurements of the tumor longest diameter were significantly (p < 0.05) smaller compared with the semi-automated measurements. The intra-rater correlations coefficients were significantly higher for measurements of longest diameter (intra-class correlation coefficients: 0.998 vs. 0.986; p < 0.001) and area (0.995 vs. 0.988; p = 0.032) using semi-automated compared with manual method. The variation coefficient for manual measurement of the tumor area (WHO guideline, 15.7% vs. 7.3%) and the longest diameter (RECIST guideline, 7.7% vs. 2.7%) was 2-3 times that of semi-automated measurement.

CONCLUSIONS

By using computer-assisted size assessment in primary lung tumor, interobserver-variability can be reduced to about half to one-third compared to standard manual measurements. This indicates a high potential value for therapy monitoring in lung cancer patients.

Monitoring targeted therapy using dual-energy CT: semi-automatic RECIST plus supplementary functional information by quantifying iodine uptake of melanoma metastases

AIM

Supplementary functional information can contribute to assess response in targeted therapies. The aim of this study was to evaluate semi-automatic RECIST plus iodine uptake (IU) determination in melanoma metastases under BRAF inhibitor (vemurafenib) therapy using dual-energy computed tomography (DECT).

METHODS

Nine patients with stage IV melanoma treated with a BRAF inhibitor were included. Contrast-enhanced DECT was performed before and twice after treatment onset. Changes in tumor size were assessed according to RECIST. Quantification of IU (absolute value for total IU (mg) and volume-normalized IU (mg/ml)) was based on semi-automatic tumor volume segmentation. The decrease compared with baseline was calculated.

RESULTS

The mean change of RECIST diameter sum per patient was -47% at the first follow-up (FU), -56% at the second FU (P < 0.01). The mean normalized IU per patient was -21% at the first FU (P < 0.2) and -45% at the second FU (P < 0.01). Total IU per patient, combining both normalized IU and volume, showed the most pronounced decrease: -89% at the first FU and -90% at the second FU (P < 0.01).

CONCLUSION

Semi-automatic RECIST plus IU quantification in DECT enables objective, easy and fast parameterization of tumor size and contrast medium uptake, thus providing 2 complementary pieces of information for response monitoring applicable in daily routine.

[PI-RADS classification: structured reporting for MRI of the prostate]

PURPOSE

To flesh out the ESUR guidelines for the standardized interpretation of multiparametric magnetic resonance imaging (mMRI) for the detection of prostate cancer and to present a graphic reporting scheme for improved communication of findings to urologists.

MATERIALS AND METHODS

The ESUR has recently published a structured reporting system for mMRI of the prostate (PI-RADS). This system involves the use of 5-point Likert scales for grading the findings obtained with different MRI techniques. The mMRI includes T2-weighted MRI, diffusion-weighted imaging, dynamic contrast-enhanced MRI, and MR spectroscopy. In a first step, the fundamentals of technical implementation were determined by consensus, taking into account in particular the German-speaking community. Then, representative images were selected by consensus on the basis of examinations of the three institutions. In addition, scoring intervals for an aggregated PI-RADS score were determined in consensus.

RESULTS

The multiparametric methods were discussed critically with regard to implementation and the current status. Criteria used for grading mMRI findings with the PI-RADS classification were concretized by succinct examples. Using the consensus table for aggregated scoring in a clinical setting, a diagnosis of suspected prostate cancer should be made if the PI-RADS score is 4 or higher (≥ 10 points if 3 techniques are used or ≥ 13 points if 4 techniques are used). Finally, a graphic scheme was developed for communicating mMRI prostate findings.

CONCLUSION

Structured reporting according to the ESUR guidelines contributes to quality assurance by standardizing prostate mMRI, and it facilities the communication of findings to urologists.

Diffusion-weighted imaging in rectal carcinoma patients without and after chemoradiotherapy: a comparative study with histology

Diffusion-weighted imaging (DWI) can be used to quantitatively assess functional parameters in rectal carcinoma that are relevant for prognosis and treatment response assessment. However, there is no consensus on the histopathological background underlying the findings derived from DWI. The aim of this study was to perform a comparison of DWI and histologic parameters in two groups of rectal carcinoma patients without (n=12) and after (n=9) neoadjuvant chemoradiotherapy (CRT). The intravoxel incoherent motion (IVIM) model was used to calculate the diffusion coefficient D and the perfusion fraction f in rectal carcinoma, the adjacent rectum and fat in the two patient groups. Immunohistological analysis was performed to assess the cellularity, vascular area fraction and vessel diameter for comparison and correlation. Out of 36 correlations between parameters from DWI and histology, four were found to be significant. In rectal carcinoma of patients without CRT, the diffusion D and the perfusion f correlated with the vascular area fraction, respectively, which could not be found in the group of patients who received CRT. Further correlations were found for the rectum and fat. Histological evaluation revealed significant differences between the tissues on the microscopic level concerning the cellular and vascular environment that influence diffusion and perfusion. In conclusion, DWI produces valuable biomarkers for diffusion and perfusion in rectal carcinoma and adjacent tissues that are highly dependent of the underlying cellular microenvironment influenced by structural and functional changes as well as the administered treatment, and consequently can be beyond histological ascertainability.

Spin dephasing in a magnetic dipole field

Transverse relaxation by dephasing in an inhomogeneous field is a general mechanism in physics, for example, in semiconductor physics, muon spectroscopy, or nuclear magnetic resonance. In magnetic resonance imaging the transverse relaxation provides information on the properties of several biological tissues. Since the dipole field is the most important part of the multipole expansion of the local inhomogeneous field, dephasing in a dipole field is highly important in relaxation theory. However, there have been no analytical solutions which describe the dephasing in a magnetic dipole field. In this work we give a complete analytical solution for the dephasing in a magnetic dipole field which is valid over the whole dynamic range.