Katharina Erb-Eigner

Diffusion-weighted imaging of ocular melanoma.

ObjectivesDiffusion-weighted imaging (DWI) allows characterization of masses on the basis of their cellular density. We hypothesized that ocular melanoma has a marked diffusion restriction as seen in other malignant tumors. Furthermore, we aimed to assess whether DWI is useful to differentiate ocular melanoma from retinal detachment. Materials and MethodsThe institutional review board approved the prospective study on 44 patients investigated with ocular magnetic resonance imaging including DWI during a 9-month period. A region-of-interest analysis of diffusion-weighted images with b values of 0 and 1000 s/mm2 was performed to calculate the apparent diffusion coefficient (ADC) of the ocular melanoma and the retinal detachment. Three patients were excluded because DWI was nondiagnostic owing to severe artifacts; in 1 patient, the melanoma was too small for ADC calculation. Therefore, 40 patients were included in the final analysis. Ocular melanomas and detachments were compared with respect to their ADC values. The image quality of DWI was qualitatively scored by 2 readers in consensus on a 3-point scale from 1 (minor artifacts) to 3 (major artifacts). ResultsOcular melanomas showed a marked diffusion restriction, and the mean (SD) ADC was 891 (172) × 10−6 mm2/s. Twenty-nine patients (66%) had retinal detachment. The mean ADC of the ocular melanoma differed significantly (P < 0.001) from the mean ADC of the retinal detachment (1986 [375] × 10−6 mm2/s). The image quality of DWI was rated 1 in 38 patients, 2 in 3 patients, and 3 in 3 patients. ConclusionsOcular melanoma shows a marked diffusion restriction with an ADC of less than 1000 mm2/s, which is in concordance with other malignant tumor entities. Diffusion-weighted imaging helps differentiating ocular tumors from retinal detachment and should therefore be included in the ocular magnetic resonance imaging protocol if an ocular mass is suspected.

Characterization of orbital masses by multiparametric MRI.

OBJECTIVES DWI and dynamic contrast enhanced (DCE) MR imaging are techniques that allow insight to tumor vascularity and cellularity. We evaluated the diagnostic performance of multiparametric MRI (mp-MRI) in distinguishing benign from malignant orbital masses using standard anatomic imaging (sAI), DWI and DCE. MATERIALS AND METHODS This prospective IRB approved study with written informed consent included 65 patients. mp-MRI at 3 Tesla including DWI and DCE was performed in all patients. Parametric maps were generated for obtaining the perfusion parameters including K(trans), kep, ve and iAUC and time-signal intensity curves were recorded to determine the curve pattern. Two radiologists rated the likelihood of malignancy on a five-point scale in three separate, randomized reading sessions (initially only sAI, afterwards sAI+either DWI or DCE and finally sAI+DWI+DCE). Data was statistically analyzed. RESULTS 33 Patients had malignant orbital masses and 32 patients had benign orbital masses (reference standard histopathology in 35 cases and clinical follow-up in 30 patients). The mean ADC of malignant masses differed significantly from the mean (SD) ADC of benign masses (0.825 [0.437]×10(-3)mm(2)/s and 1.257 [0.576]×10(-3)mm(2)/s, respectively) (p=0.001). K(trans), kep and iAUC were significantly higher in malignant masses (p<0.01). The reading of sAI only resulted in a moderate specificity but poor sensitivity in differentiating benign from malignant lesions. Adding DWI and DCE images improved specificity and sensitivity considerably, being the highest for the combined reading of all sequences. CONCLUSION mp-MRI is a helpful tool in differentiating malignant orbital lesions from benign masses and should therefore be included in the routine diagnostic protocol for orbital imaging.

Impact of magnetic field strength and receiver coil in ocular MRI: a phantom and patient study.

PURPOSE Generally, high-resolution MRI of the eye is performed with small loop surface coils. The purpose of this phantom and patient study was to investigate the influence of magnetic field strength and receiver coils on image quality in ocular MRI. MATERIALS AND METHODS The eyeball and the complex geometry of the facial bone were simulated by a skull phantom with swine eyes. MR images were acquired with two small loop surface coils with diameters of 4 cm and 7 cm and with a multi-channel head coil at 1.5 and 3 Tesla, respectively. Furthermore, MRI of the eye was performed prospectively in 20 patients at 1.5 Tesla (7 cm loop surface coil) and 3 Tesla (head coil). These images were analysed qualitatively and quantitatively and statistical significance was tested using the Wilcoxon-signed-rank test (a p-value of less than 0.05 was considered to indicate statistical significance). RESULTS The analysis of the phantom images yielded the highest mean signal-to-noise ratio (SNR) at 3 Tesla with the use of the 4 cm loop surface coil. In the phantom experiment as well as in the patient studies the SNR was higher at 1.5 Tesla by applying the 7 cm surface coil than at 3 Tesla by applying the head coil. Concerning the delineation of anatomic structures no statistically significant differences were found. CONCLUSION Our results show that the influence of small loop surface coils on image quality (expressed in SNR) in ocular MRI is higher than the influence of the magnetic field strength. The similar visibility of detailed anatomy leads to the conclusion that the image quality of ocular MRI at 3 Tesla remains acceptable by applying the head coil as a receiver coil.

Magnetic resonance imaging based morphologic evaluation of the pineal gland for suspected pineoblastoma in retinoblastoma patients and age-matched controls☆

PURPOSE The purpose of this study was to evaluate the morphologic magnetic resonance imaging (MRI) characteristics of the pineal gland in retinoblastoma (Rb) patients without and with pineoblastoma in comparison to age-matched controls to improve early identification of pineoblastomas (trilateral retinoblastoma, TRb). METHODS AND MATERIALS 80 patients with retinoblastoma and 80 age-matched controls who had undergone brain MRI were included in this retrospective institutional review board approved cohort study. Two readers analyzed the following MR characteristics of the pineal gland: signal intensity on T1- and T2-weighted images, enhancement pattern, delineation of the gland, presence of cystic component, size of pineal gland and size of pineal cysts, respectively. A third reader assessed all images for the presence or absence of pineoblastoma. RESULTS 3 patients were positive (TRb cohort) and 77 negative for pineoblastoma (non-TRb cohort). The mean maximum diameter of the pineal gland was 6.4mm in Rb patients and 6.3mm in age-matched controls. The mean volume of the pineal gland in Rb patients was 93.1mm(3) and was 87.6mm(3) in age-matched controls. Considering all available MRI scans the mean maximum diameter of the pineal gland in TRb patients was 11.2mm and the mean volume in TRb patients was 453.3mm(3). The third reader identified pineoblastomas with a sensitivity of 100% (3 of 3) and a specificity of 94% (72 of 77). CONCLUSION Our non-TRb patients did not show significant differences in the size of the pineal gland and pineal gland cysts compared to age-matched controls. The presented data can serve as a reference for the volume of normal pineal glands and pineal cysts in the diagnostic work-up of Rb patients with suspected pineoblastoma.

Predicting Lens Diameter: Ocular Biometry With High-Resolution MRI.

PURPOSE The aim of this study was to correlate different biometric dimensions of the eye as measured from ocular magnetic resonance imaging (MRI) scans to predict the lens diameter. METHODS High-resolution ocular MRI scans of 100 eyes of 100 patients were reviewed. Various anatomical variables of the eye such as the axial length, the globe diameter, and the lens dimensions were measured. Also, the distances between the ciliary sulcus and angle-to-angle were measured. A partial least square (PLS) regression model was built to analyze which variables influence the model regarding the lens dimensions. RESULTS Sixty-two eyes of 62 patients were included in the final analysis. The lens diameter ratio (horizontal to vertical) was 0.93 (SD: 0.04; 0.83-1.00). The partial least square regression showed a significant connection (P < 0.001) between the horizontal and vertical diameter. The partial least square regression model that included the globe diameter and the axis length resulted in the best prediction for the horizontal lens diameter. Similar to the horizontal lens diameter, globe diameter was the best predictor for the vertical lens diameter followed by the distance of the ciliary sulcus. White-to-white distance, distance of the ciliary sulcus, and axial eye length were found to have a high influence on the angle-to-angle distance. CONCLUSIONS The introduced models may serve as tools to predict the capsular bag biometry in a preoperative setting for cataract surgery or lens refilling procedures.

Dynamic contrast-enhanced MRI of ocular melanoma.

Dynamic contrast-enhanced MRI is used for the assessment of microvasculature in several tumours. We aimed to assess the contrast signal enhancement characteristics of ocular melanoma. Forty patients with ocular melanoma were prospectively investigated with ocular MRI including dynamic contrast-enhanced sequences over a 13-month period. A region-of-interest analysis of the images was carried out to calculate signal enhancement characteristics after a contrast injection. Clinical follow-up data such as extraocular spread and development of liver metastasis were compared with the signal enhancement characteristics of the ocular melanoma. In 39 patients (98%), the ocular melanomas showed an early strong signal enhancement after contrast injection, resulting in a mean time of maximum enhancement of 49 s. Clinical follow-up was available in 28 patients (70%) and indicated that the peak signal intensity was significantly increased (P=0.039) in patients who developed extraocular spread or liver metastasis at a later stage. Ocular melanoma shows signal enhancement characteristics of hypervascular neoplasms. This study provides baseline curve pattern data that may be useful for assessing changes in vascularity, for example during therapy response. Furthermore, the study showed that a strong signal enhancement of the ocular melanoma might be linked to a less favourable prognosis.

Equilibrium‐phase MR angiography: Comparison of unspecific extracellular and protein‐binding gadolinium‐based contrast media with respect to image quality

The purpose of this study was to compare contrast and image quality of whole-body equilibrium-phase high-spatial-resolution MR angiography using a non-protein-binding unspecific extracellular gadolinium-based contrast medium with that of two contrast media with different protein-binding properties. 45 patients were examined using either 15 mL of gadobutrol (non-protein-binding, n = 15), 32 mL of gadobenate dimeglumine (weakly protein binding, n = 15) or 11 mL gadofosveset trisodium (protein binding, n = 15) followed by equilibrium-phase high-spatial-resolution MR-angiography of four consecutive anatomic regions. The time elapsed between the contrast injection and the beginning of the equilibrium-phase image acquisition in the respective region was measured and was up to 21 min. Signal intensity was measured in two vessels per region and in muscle tissue. Relative contrast (RC) values were calculated. Vessel contrast, artifacts and image quality were rated by two radiologists in consensus on a five-point scale. Compared with gadobutrol, gadofosveset trisodium revealed significantly higher RC values only when acquired later than 15 min after bolus injection. Otherwise, no significant differences between the three contrast media were found regarding vascular contrast and image quality. Equilibrium-phase high-spatial-resolution MR-angiography using a weakly protein-binding or even non-protein-binding contrast medium is equivalent to using a stronger protein-binding contrast medium when image acquisition is within the first 15 min after contrast injection, and allows depiction of the vasculature with high contrast and image quality. The protein-binding contrast medium was superior for imaging only later than 15 min after contrast medium injection.

DCE-MR imaging of orbital lesions: diagnostic performance of the tumor flow residence time τ calculated by a multi-compartmental pharmacokinetic tumor model based on individual factors

Background Differentiating benign from malignant orbital lesions by imaging and clinical presentation can be challenging. Purpose To differentiate benign from malignant orbital masses using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) based on tumor flow residence time τ calculated with the aid of a pharmacokinetic tumor model. Material and Methods Sixty patients with orbital masses were investigated by 3-T MRI including dynamic sequences. The signal intensity-time curve after i.v. contrast medium administration within lesions was approximated by Gd-concentration profiles on the basis of model calculations where the tumor is embedded in a whole-body kinetic model. One output of the model was tumor flow residence time τ, defined as the ratio of the tumor volume and the tumor blood flow rate. Receiver operating characteristic (ROC) curves were used to analyze the diagnostic performance of τ. The results were compared with those of Ktrans, kep, ve, iAUC, and ADC. Results Thirty-one benign and 29 malignant orbital masses were identified (reference standard: histopathology, clinical characteristics). Mean τ was significantly longer for benign masses (94 ± 48 s) than for malignant masses (21 ± 19 s, P < 0.001). ROC analysis revealed the highest area under the curve (AUC = 0.94) for τ in orbital masses compared to standard methods. Conclusion Tumor flow residence times τ of benign and malignant orbital masses are valuable in the diagnostic work-up of orbital tumors. Measures of diagnostic accuracy were superior for τ compared to ADC, Ktrans, ve, and iAUC.

A headset communication system for interventional radiology training.

What problem was addressed? Practical training of radiology trainees in interventional procedures usually requires individual in-room instruction along with precise communication. Patients undergoing image-guided procedures such as interventions guided by angiography or computer tomography (CT) are often not under general anaesthesia and can hear what is spoken by medical staff in the room. The teaching situation during the procedure can cause stress for both the patient and the trainee carrying out the procedure (e.g. ‘Watch the tip of the needle, it is very close to the artery.’). Furthermore, radiation exposure is a major disadvantage of X-ray-based image-guided procedures. The general increase in radiation exposure of medical staff, especially in CT-guided procedures, has raised concern. The total radiation dose used varies widely with the complexity of a procedure and the experience of the radiologist performing it. What was tried? We introduced a simple headset communication system for educational purposes in CT-guided interventions at our hospital, a large academic training institution. Headset communication systems are widely used in the non-medical world, particularly for training purposes (e.g. motorcycle drivers, actors and dancers). This DECT (digital enhanced cordless communication)-based device (Plantronics C053A system, Plantronics, Inc., Santa Cruz, CA, USA) allows the supervisor to provide continuous support and communicate with the in-training radiologist without being in the scanner room. That way, the CT-guided procedure (and what is most important, the tip of the needle) can be monitored from outside via the scanner control screens. Also, the supervisor’s instructions are not heard by the patient. After the headset communication system had been available for 18 months, two independent questionnaires were sent out to our radiologists, asking about the experience with the system and how often the headset was used when available. What lessons were learned? All radiologists using the headset communication system (n = 12) rated their experience with the system to be very good (n = 10; 83.3%) or good (n = 2; 16.7%). The survey shows that most of the radiologists think it is advantageous when the patient is less aware of the educational situation. The supervisor can give straightforward instructions without being heard by the patient. Comments suggest that the system may also promote independence of the in-training radiologist. This may be of particular importance for the training model widely used in interventional radiology, which is based on the principle of gradual reduction in supervision as the trainee’s competence increases. However, a major advantage revealed by the survey is that the supervisors’ radiation exposure decreases because they are in the scanner room less often. The results of the survey indicate that the headset was used in 57% of all (n = 100, educational and non-educational) CT-guided procedures and was considered to be very helpful in 71.9% and helpful in 22.8%. Radiologists not having access to the system were also surveyed and stated that they could imagine using the system in the future (n = 28; 93.3%). In summary, our experience suggests that the use of a headset communication system is beneficial for training in CT-guided procedures and welcomed by supervisors and in-training radiologists alike. The system may also be useful in other medical educational settings, such as angiography or surgical procedures.