Evaluation of a free-breathing respiratory-triggered (Navigator) 3-D T1-weighted (T1W) gradient recalled echo sequence (LAVA) for detection of enhancement in cystic and solid renal masses

Effects of Breathing Patterns on Amide Proton Transfer MRI in the Kidney: A Preliminary Comparative Study in Healthy Volunteers and Patients With Tumors

BACKGROUND

The amide proton transfer-weighted (APTw) imaging for kidney diseases is important. However, the breathing patterns on APTw imaging remains unexplored.

PURPOSE

This study aimed to investigate the effects of intermittent breath-hold (IBH) and free breathing (FB) on renal 3D-APTw imaging.

STUDY TYPE

Healthy volunteers were enrolled prospectively, and renal clear cell carcinoma (RCCC) patients were included retrospectively.

POPULATION

58 healthy volunteers and 10 RCCC patients.

FIELD STRENGTH/SEQUENCE

3-T, turbo spin echo, and fast field echo.

ASSESSMENT

3D-APTw imaging was scanned using the IBH and FB methods in volunteers and using the IBH method in RCCC patients. The image quality was evaluated by three observers according to the 5-point Likert scale. Optimal images rated at three points or higher were used to measure the APT values.

STATISTICAL ANALYSIS

The measurement repeatability was assessed using the intraclass correlation coefficient (ICC) and the Bland-Altman plot. The APT values were analyzed using McNemar's test, one-way analysis of variance, and t test.

RESULTS

50 healthy volunteers and 8 RCCC patients were enrolled. Renal 3D-APTw imaging using the IBH method revealed a higher success rate (88% vs 78%). The ICCs were excellent in the IBH group (ICCs > 0.74) and were good in the FB group (ICCs < 0.74). No significant differences in the APT values among various zones using the IBH (P = 0.263) or FB method (P = 0.506). The mean APT value using the IBH method (2.091% ± 0.388%) was slightly lower than the FB method (2.176% ± 0.292%), but no significant difference (P = 0.233). The APT value of RCCC (4.832% ± 1.361%) was considerably higher than normal renal using the IBH method.

CONCLUSIONS

The study demonstrated that the IBH method substantially increased the image quality of renal 3D-APTw imaging. Furthermore, APT values may vary between normal and tumor tissues.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 2.

Comparison of image quality and depiction of microscopic fat at 2-D and 3-D T1-Weighted (T1W) chemical shift (dual-echo) MRI for evaluation of adrenal adenomas

OBJECTIVE

To compare image quality and detection of microscopic fat in adrenal adenomas imaged with 2-D and 3-D chemical shift imaging (CSI) and, to derive parameters which best match 2-D and 3-D-CSI.

METHODS

This two-phase, retrospective, and phantom + prospective study was IRB approved. First, a retrospective assessment of 50 consecutive adrenal adenomas imaged at 1.5 T with 2-D (TR minimum, Flip Angle [FA] 70°, TE 2.2/4.4 ms.) and 3-D (TR minimum, FA 10°, TE 2.2/4.4 ms.] CSI was performed. Second, phantom (varied fat: water concentration) experiments guided a prospective assessment of 12 consecutive adrenal adenomas imaged at 1.5 T with 3-D CSI (FA 10°, 18°). Two blinded radiologists independently evaluated: image quality, signal intensity (SI) cancellation (5-point Likert scale), and CSI-index ([SI.In.Phase-SI.Opposed.Phase/SI.In.Phase]*100).

RESULTS

2-D-CSI yielded higher image quality (p < 0.001) and, subjectively (p < 0.001) and quantitatively (p < 0.001) had more SI cancellation from microscopic fat. Proportion of adenomas with no detectable microscopic fat (3-D; 26-36% subjectively, 18-24% quantitatively [CSI-index < 16.5%] versus 2-D; 20-22% subjectively, 6-8% quantitatively) differed (p = 0.008-0.08 subjectively, 0.008-0.03 quantitatively) by CSI technique. Phantom experiments indicated 18°FA 3-D-CSI compared favorably to 70° 2-D-CSI for fat detection between 5% and 50%. In vivo, there was no differences in subjective or quantitative SI cancellation comparing 18°3D-CSI and 2D-CSI (p = 0.16-0.56 and 0.73-0.60). Greater SI cancellation occurred with 18°3D compared to 10°3D-CSI evaluated subjectively (p = 0.003-0.01).

CONCLUSION

2-D CSI has subjectively higher image quality and shows more signal intensity loss from microscopic fat in adrenal adenomas compared to 10° flip angle 3-D-CSI. Increasing the 3-D flip angle to 18° more closely matches depiction of microscopic fat to 2-D-CSI at 1.5 T.

Bosniak classification of cystic renal masses, version 2019: interpretation pitfalls and recommendations to avoid misclassification

The purpose of this review is to describe the potential sources of variability or discrepancy in interpretation of cystic renal masses under the Bosniak v2019 classification system. Strategies to avoid these pitfalls and clinical examples of diagnostic approaches are also presented. Potential pitfalls in the application of Bosniak v2019 are divided into three categories: interpretative, technical, and mass related. An organized, comprehensive review of possible discrepancies in interpreting Bosniak v2019 cystic masses is presented with pictorial examples of difficult clinical cases and proposed solutions. The scheme provided can guide readers to consistent, precise application of the classification system. Radiologists should be aware of the possible sources of misinterpretation of cystic renal masses when applying Bosniak v2019. Knowing which features and types of cystic masses are prone to interpretive errors, in addition to the inherent trade-offs between the CT and MR techniques used to characterize them, can help radiologists avoid these pitfalls.

Clinical Evaluation of MR-Gated Respiratory Motion Correction in Simultaneous PET/MRI

PURPOSE

The recently available gated T1-weighted imaging with the Dixon technique enables the synchronized gating signal for both MR acquisition and PET reconstruction. Herein, we evaluated the clinical value of this MR-gated PET reconstruction in the thoracic-abdominal PET/MRI compared with non-MR-gated method.

METHODS

Twenty patients (28 hypermetabolic target lesions) underwent PET/MRI. Four types of PET images were reconstructed: non-MR-gating + gated attenuation correction (AC) (group A), MR-gating + gated AC (group B), non-MR-gating + breath-hold (BH) AC (group C), and MR-gating + BH AC (group D). A 4-point objective scale (from well match to obvious mismatch was scored from 3 to 0) was proposed to evaluate the mismatch. The detection rate and quantitative metrics were also evaluated.

RESULTS

In the patient-based analysis, for groups A through D, the detection rates were 90%, 100%, 85%, and 90% as well as 95%, 100%, 85%, and 85%, assessed by readers 1 and 2, respectively, and significant difference of mismatch score was observed with the highest proportion of 3 points in group B (85%, 90%, 35%, and 40%, and 80%, 90%, 35%, and 20%, assessed by readers 1 and 2, respectively). The lesion-based analysis demonstrated significant differences in quantitative metrics for groups A through D (all P's < 0.05), with the highest quantitative metrics in group B (SUVmax: 7.49 ± 3.37, 8.45 ± 3.82, 6.90 ± 3.24, and 7.69 ± 3.50; SUVmean: 3.90 ± 1.60, 4.34 ± 1.84, 3.67 ± 1.61, and 4.03 ± 1.81; SUVpeak: 5.60 ± 2.50, 6.10 ± 2.80, 5.22 ± 2.40, and 5.65 ± 2.68; signal-to-noise ratio: 136.06 ± 90.58, 136.24 ± 81.63, 99.52 ± 53.16, and 107.57 ± 69.05).

CONCLUSIONS

The MR-gated reconstruction using gated AC reduced the mismatch between MR and PET images and improved the thoracic-abdominal PET image quality in simultaneous PET/MRI systems.

Update on MRI of Cystic Renal Masses Including Bosniak Version 2019

Incidental cystic renal masses are common, usually benign, and almost always indolent. Since 1986, the Bosniak classification has been used to express the risk of malignancy in a cystic renal mass detected at imaging. Historically, magnetic resonance imaging (MRI) was not included in that classification. The proposed Bosniak v.2019 update has formally incorporated MRI, included definitions of imaging terms designed to improve interobserver agreement and specificity for malignancy, and incorporated a variety of masses that were incompletely defined or not included in the original classification. For example, at unenhanced MRI, homogeneous masses markedly hyperintense at T₂ -weighted imaging (similar to cerebrospinal fluid) and homogeneous masses markedly hyperintense at fat suppressed T₁ -weighted imaging (approximately ≥2.5 times more intense than adjacent renal parenchyma) are classified as Bosniak II and may be safely ignored, even when they have not been imaged with a complete renal mass MRI protocol. MRI has specific advantages and is recommended to evaluate masses that at computed tomography (CT) 1) have abundant thick or nodular calcifications; 2) are homogeneous, hyperattenuating, ≥3 cm, and nonenhancing; or 3) are heterogeneous and nonenhancing. Although MRI is generally excellent for characterizing cystic renal masses, there are unique weaknesses of MRI that bear consideration. These details and others related to MRI of cystic renal masses are described in this review, with an emphasis on Bosniak v.2019. A website (https://bosniak-calculator.herokuapp.com/) and mobile phone apps named "Bosniak Calculator" have been developed for ease of assignment of Bosniak classes. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY STAGE: 3.

Primary and secondary diseases of the perinephric space: an approach to imaging diagnosis with emphasis on MRI

The perinephric space is the middle compartment of the retroperitoneum, containing the kidneys and adrenal glands. Differential considerations for diseases involving primarily the perinephric space differ from those arising from the kidney itself, show variant imaging features, and require identification and characterisation by interpreting radiologists-an imaging diagnosis can be suggested in many cases. Lymphangiomas are congenital cystic lesions that may contain lipid-laden chyle, which may be detectable on magnetic resonance imaging (MRI). Retroperitoneal fibrosis, Erdheim-Chester disease, and lymphoma may present as a perinephric soft tissue rind. Osseous findings favour Erdheim-Chester, ureteric obstruction favours retroperitoneal fibrosis, and associated lymphadenopathy with mass-effect, but without invasion of adjacent structures favours lymphoma. Extramedullary haematopoiesis and brown fat stimulation are both characterised by signal drop on opposed-phase T1-weighted (W) images, the former resulting from severe anaemia and the latter in the context of elevated serum catecholamines, especially in the setting of phaeochromocytoma. Liposarcoma is the most common primary sarcoma of the retroperitoneum. Metastases are uncommon; however, they can be seen in melanoma, among other primary malignancies. Increased T1W signal hyperintensity is typical of melanoma metastases and haematomas. Abscesses show non-enhancing fluid centrally with marked diffusion restriction. This article presents a review of the perinephric space, pathological conditions of the perinephric space, and an approach towards imaging and diagnosis using cross-sectional imaging, with emphasis on MRI. MRI provides better tissue characterisation, assessment of enhancement kinetics, and detection of intralesional fat in comparison to CT. Clinical and laboratory correlation or tissue sampling may be required for definitive diagnosis in some cases.

Longitudinal phenotype development in a minipig model of neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is a rare, autosomal dominant disease with variable clinical presentations. Large animal models are useful to help dissect molecular mechanisms, determine relevant biomarkers, and develop effective therapeutics. Here, we studied a NF1 minipig model (NF1+/ex42del) for the first 12 months of life to evaluate phenotype development, track disease progression, and provide a comparison to human subjects. Through systematic evaluation, we have shown that compared to littermate controls, the NF1 model develops phenotypic characteristics of human NF1: [1] café-au-lait macules, [2] axillary/inguinal freckling, [3] shortened stature, [4] tibial bone curvature, and [5] neurofibroma. At 4 months, full body computed tomography imaging detected significantly smaller long bones in NF1+/ex42del minipigs compared to controls, indicative of shorter stature. We found quantitative evidence of tibial bowing in a subpopulation of NF1 minipigs. By 8 months, an NF1+/ex42del boar developed a large diffuse shoulder neurofibroma, visualized on magnetic resonance imaging, which subsequently grew in size and depth as the animal aged up to 20 months. The NF1+/ex42del minipig model progressively demonstrates signature attributes that parallel clinical manifestations seen in humans and provides a viable tool for future translational NF1 research.