Short tau inversion recovery in breast diffusion-weighted imaging: signal-to-noise ratio and apparent diffusion coefficients using a breast phantom in comparison with spectral attenuated inversion recovery

Vendor-Specific Correction Software for Apparent Diffusion Coefficient Bias Due to Gradient Nonlinearity in Breast Diffusion-Weighted Imaging Using Ice-Water Phantom

OBJECTIVE

This study aimed to evaluate a vendor-specific correction software for apparent diffusion coefficient (ADC) bias due to gradient nonlinearity in breast diffusion-weighted magnetic resonance imaging using an ice-water phantom.

METHODS

The phantom consists of 5 plastic tubes with a length of 100 mm and a diameter of 15 mm, filled with distilled water and immersed in an ice-water bath. Diffusion-weighted images were acquired by echo-planar imaging sequence on a 3.0-T scanner. ADC maps with and without correction were calculated using 4 b-values (0, 100, 600, and 800 s/mm2). The mean ADCs were measured using a rectangular profile with 5 × 40 pixels in the anterior-posterior (AP) and a square region of interest with 5 × 5 pixels in the right-left (RL) and superior-inferior (SI) directions on the ADC map. ADC was compared with and without correction using a paired t test. Additionally, ADC of the ice-water phantom was measured at the magnet isocenter.

RESULTS

ADC increased in the AP and RL directions and decreased in the SI direction with increasing distance from the isocenter before correction. After the correction, ADC at the off-center positions in the AP, RL, and SI directions was reduced to within 5% of the expected value. There were significant differences in the ADC at the off-center positions without and with correction (P < 0.001); however, ADC at the magnet isocenter did not vary after correction (1.08 ± 0.02 × 10-3 mm2/s).

CONCLUSIONS

The vendor-specific software corrected the ADC bias due to gradient nonlinearity at the off-center positions in the AP, RL, and SI directions. Therefore, the software will contribute to the accurate ADC assessment in breast DWI.

MR relaxation properties of tissue-mimicking phantoms

High quality tissue-mimicking phantoms (TMPs) have a critical role in the preclinical testing of emerging modalities for diagnosis and therapy. TMPs capable of accurately mimicking real tissue in Magnetic Resonance guided Focused Ultrasound (MRgFUS) applications should be fabricated with precise T1 and T2 relaxation times. Given the current popularity of the MRgFUS technology, we herein performed a systematic review on the MR relaxation properties of different phantoms types. Polyacrylamide (PAA) and agar based phantoms were proven capable of accurately replicating critical thermal, acoustical, and MR relaxation properties of various body tissues. Although gelatin phantoms were also proven factional in this regard, they lack the capacity to withstand ablation temperatures, and thus, are only recommended for hyperthermia applications. Other gelling agents identified in the literature are Poly-vinyl alcohol (PVA), Polyvinyl Chloride (PVC), silicone, and TX-150/ TX-151; however, their efficacy in thermal studies is yet to be established. PAA gels are favorable in that they offer optical transparency enabling direct visualization of coagulative lesions. On the other hand, agar phantoms have lower preparation costs and were proven very promising for use with the MRgFUS technology, without the toxicity issues related to the preparation and storage of PAA materials. Remarkably, agar turned out to be the prominent modifier of the T2 relaxation time even for phantoms containing other types of gelling agents instead of agar. This review could be useful in manufacturing realistic MRgFUS phantoms while simultaneously indicating an opportunity for further research in the field with a particular focus on the MR behavior of agar-based TMPs.

Apparent diffusion coefficient measurement using thin-slice diffusion-weighted magnetic resonance imaging: assessment of measurement errors and repeatability

We investigated the measurement error and repeatability of the apparent diffusion coefficient (ADC) obtained using thin-slice imaging. Diffusion-weighted images of an ice-water phantom were acquired using 1.5-T and 3.0-T scanners with 1-, 3-, and 5-mm thickness. ADC maps were generated at b = 0 and 1000 mm²/s using five consecutive scans. Measurement errors were assessed with accuracy and precision. Repeatability was assessed using the within-subject coefficient of variation. The ADC accuracy of both scanners agreed with the ADC of water at 0 °C. At 1-mm, precisions were 2.9% and 8.4% for the 3.0-T and 1.5-T scanners, respectively. The repeatabilities of 1-mm thickness were 1.3% and 3.4% in the 3.0-T and 1.5-T scanners, respectively. The 3.0-T scanner showed acceptable measurement errors and moderate repeatability compared with Quantitative Imaging Biomarkers Alliance recommendation. A 3.0-T scanner can be used for reliable ADC measurement, even with a 1-mm thickness at a reasonable scan time.

Apparent diffusion coefficient magnetic resonance imaging (ADC-MRI) in the axillary breast cancer lymph node metastasis detection: a narrative review

The presence of axillary lymph nodes metastases in breast cancer is the most significant prognostic factor, with a great impact on morbidity, disease-related survival and management of oncological therapies; for this reason, adequate imaging evaluation is strictly necessary. Physical examination is not enough sensitive to assess breast cancer nodal status; axillary ultrasonography (US) is commonly used to detect suspected or occult nodal metastasis, providing exclusively morphological evaluation, with low sensitivity and positive predictive value. Currently, sentinel lymph node biopsy (SLNB) and/or axillary dissection are the milestone for the diagnostic assessment of axillary lymph node metastases, although its related morbidity. The impact of magnetic resonance imaging (MRI) in the detection of nodal metastases has been widely investigated, as it continues to represent the most promising imaging modality in the breast cancer management. In particular, diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) values represent additional reliable non-contrast sequences, able to improve the diagnostic accuracy of breast cancer MRI evaluation. Several studies largely demonstrated the usefulness of implementing DWI/ADC MRI in the characterization of breast lesions. Herein, in the light of our clinical experience, we perform a review of the literature regarding the diagnostic performance and accuracy of ADC value as potential pre-operative tool to define metastatic involvement of nodal structures in breast cancer patients. For the purpose of this review, PubMed, Web of Science, and SCOPUS electronic databases were searched with different combinations of "axillary lymph node", "breast cancer", "MRI/ADC", "breast MRI" keywords. All original articles, reviews and metanalyses were included.

Dual energy CT in gland tumors: a comprehensive narrative review and differential diagnosis

Dual energy CT (DECT)with image acquisition at two different photon X-ray levels allows the characterization of a specific tissue or material/elements, the extrapolation of virtual unenhanced and monoenergetic images, and the quantification of iodine uptake; such special capabilities make the DECT the perfect technique to support oncological imaging for tumor detection and characterization and treatment monitoring, while concurrently reducing the dose of radiation and iodine and improving the metal artifact reduction. Even though its potential in the field of oncology has not been fully explored yet, DECT is already widely used today thanks to the availability of different CT technologies, such as dual-source, single-source rapid-switching, single-source sequential, single-source twin-beam and dual-layer technologies. Moreover DECT technology represents the future of the imaging innovation and it is subject to ongoing development that increase according its clinical potentiality, in particular in the field of oncology. This review points out recent state-of-the-art in DECT applications in gland tumors, with special focus on its potential uses in the field of oncological imaging of endocrine and exocrine glands.

Image Quality and ADC Assessment in Turbo Spin-Echo and Echo-Planar Diffusion-Weighted MR Imaging of Tumors of the Head and Neck

RATIONALE AND OBJECTIVES

We aimed to compare the distortion ratio (DR), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) between turbo spin-echo (TSE)-diffusion-weighted imaging (DWI) and echo-planar imaging (EPI)-DWI of the orofacial region and prove the usefulness of TSE-DWI for the differential diagnosis of orofacial lesions.

MATERIALS AND METHODS

The DR, SNR, and CNR of both sequences were compared in 42 cases. Then, the apparent diffusion coefficient (ADC) of various orofacial lesions obtained by TSE-DWI was investigated in 143 lesions.

RESULTS

In the first study, 38 of 42 cases were analyzed. TSE-DWI showed a significantly lower DR (p < 0.05) and higher SNR and CNR than EPI-DWI (p < 0.05), indicating the superiority of TSE-DWI. In the second study, 114 cases (79.3%) were successfully analyzed. When lesions were divided into cysts, benign tumors, squamous cell carcinoma, malignant lymphoma, and other malignant tumors (OT), significant differences were observed in all pairs of lesions (p < 0.05) except squamous cell carcinoma and OT (p = 0.877). The area under the curve for distinguishing benign from malignant tumors was 0.80 with a cutoff ADC of 1.29 × 10^-3 mm²/s.

CONCLUSION

TSE-DWI produced better quality images than EPI-DWI. TSE-DWI yields the high possibility of obtaining ADC in the orofacial region, and this value was considered useful for the differential diagnosis of orofacial lesions.