Objective
To perform preliminary tests in vitro and with healthy volunteers to determine the 3-T MRI compatibility of a cochlear implant with a non-removable magnet.
Methods
In the in vitro phase, we ...tested six implants for temperature changes and internal malfunctioning. We measured the demagnetisation of 65 internal magnets with different tilt angles between the implant’s magnetic field (bi) and the main magnetic field (b0). In the in vivo phase, we tested 28 operational implants attached to the scalps of volunteers with the head in three different positions.
Results
The study did not find significant temperature changes or electronic malfunction in the implants tested in vitro. We found considerable demagnetisation of the cochlear implant magnets in the in vitro and in vivo testing influenced by the position of the magnet in the main magnetic field. We found that if the bi/b0 angle is <90°, there is no demagnetisation; if the bi/b0 angle is >90°, there is demagnetisation in almost 60 % of the cases. When the angle is around 90°, the risk of demagnetisation is low (6.6 %).
Conclusion
The preliminary results on cochlear implants with non-removable magnets indicate the need to maintain the contraindication of passage through 3-T MRI.
Key Points
•
Magnetic resonance imaging can affect cochlear implants and vice versa.
•
Demagnetisation of cochlear implant correlates with the angle between bi and b0.
•
The position of the head in the MRI influences the demagnetisation.
•
Three-Tesla MRI for cochlear implants is still contraindicated.
•
However some future solutions are discussed.
Purpose
To evaluate utility of diffusion-weighted magnetic resonance imaging (DWI) to detect and predict the histological characteristics of upper urinary tract urothelial carcinomas (UTUCs).
...Materials and methods
We retrospectively evaluated 20 suspicious lesions from 19 patients. MRI study included conventional sequences and DWI with apparent diffusion coefficient (ADC) maps calculated between
b
= 0 and
b
= 1,000. ADC values were measured within two different regions of interest (ROI): a small identical ROI placed in the most restrictive part of the tumour and a larger ROI covering two-thirds of the mass surface. The mean ADC values of the tumours were compared with that of normal renal parenchyma using an unpaired Student’s
t
test. Association between ADC values and histological features was tested using non-parametric tests.
Results
Overall, 18 tumours were confirmed histologically as UTUCs. DWI failed to detect two cases of UTUCs (one CIS and one small tumour of 5 mm). There was no statistically significant difference in ADC values measured with the small or large ROI (
p
= 0.134). The mean ADC value of UTUC was significantly lower than that of the normal renal parenchyma (
p
< 0.001). No statistical association was found between ADC values and pathological features (location,
p
= 0.35; grade,
p
= 0.98; muscle-invasive disease,
p
= 0.76 and locally advanced stage,
p
= 0.57).
Conclusion
DWI may be interesting tool for detecting UTUCs regarding the difference of ADC values between the tumours and surrounding healthy tissues. In regard to low frequency of UTUCs, the association of ADC values and histological characteristics need further investigations in a large prospective multi-institutional study.
Abstract Multiparametric MRI (mp-MRI) of the prostate currently provides stable and reproducible performances. The usefulness of dynamic contrast-enhanced (DCE) sequences is currently challenged, as ...they sometimes only confirm what has already been observed on diffusion-weighted imaging (DWI) and require the additional purchase of a contrast agent. Eliminating these sequences may help accelerate the use of MRI in addition to, or in lieu of, prostate biopsies in selected patients. However, many studies show that these sequences can detect lesions invisible on T2-weighted and diffusion-weighted images, better assess cancer extension and aggressiveness, and finally help detecting recurrence after treatment. We present the various applications of dynamic MRI and discuss the possible consequences of its omission from the current protocol.
Abstract Multiparametric MRI of the prostate is an essential examination for the diagnosis, preoperative evaluation and planning of treatment for prostate cancer. This examination can accurately ...detect cancer foci in the gland so that the most appropriate management can be offered, reduce the risk of over-treatment and also ensure that certain aggressive lesions or unusual locations, which might affect the prognosis, are not ignored. We present here its main indications, focusing on the techniques for interpreting MRI, its performance and its limitations, as well as the recent European recommendations underlining the need for international harmonisation.
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