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Background Prior imaging studies characterizing lumbar arachnoiditis have been based on small sample numbers and have reported inconsistent results. Purpose To review the different imaging patterns of lumbosacral arachnoiditis, their significance, and clinical implications. Study type Retrospective. Population A total of 96 patients (43 women; average age 61.3 years) with imaging findings of arachnoiditis (postsurgical: N = 49; degenerative: N = 29; vertebral fracture: N = 6; epidural and subdural hemorrhage: N = 3, infectious: N= 1; other: N = 8) from January 2009 to April 2018. Field strength/Sequence Sagittal and axial T2‐weighted Turbo Spin Echo at 1.5 T and 3 T. Assessment Chart review was performed to assess the cause of arachnoiditis, and imaging was reviewed by two musculoskeletal and three neurology radiologists, blinded to the clinical data and to each other's imaging interpretation. Previous classification included a three‐group system based on the appearance of the nerve roots on T2‐weighted images. A fourth group was added in our review as “nonspecified” and was proposed for indeterminate imaging findings that did not fall into the classical groups. The presence/absence of synechiae/fibrous bands that distort the nerve roots and of spinal canal stenosis was also assessed. Statistical tests The kappa score was used to assess agreement between readers for both classification type and presence/absence of synechiae. Results Postsurgical (51%) and degenerative changes (30%) were the most common etiologies. About 7%–55% of arachnoiditis were classified as group 4. There was very poor classification agreement between readers (kappa score 0.051). There was also poor interreader agreement for determining the presence of synechiae (kappa 0.18) with, however, strong interreader agreement for the presence of synechia obtained between the most experienced readers (kappa 0.89). Data Conclusion This study demonstrated the lack of consensus and clarity in the classification system of lumbar arachnoiditis. The presence of synechia has high interreader agreement only among most experienced readers and promises to be a useful tool in assessing arachnoiditis. Evidence Level 3 Technical Efficacy Stage 2

The aim of this study was to investigate the value of pharmacokinetic modeling for quantifying C-choline uptake in patients with recurrent prostate cancer. In total, 194 patients with clinically suspected recurrence of prostate cancer underwent C-choline dynamic PET over the pelvic region (0-8 min), followed by a 6-min static acquisition at about 25 min after injection. Regions of interest were drawn over sites of disease identified by a radiologist with experience in nuclear medicine.C-choline uptake and pharmacokinetics were evaluated by SUV, graphical analysis (Patlak plot; ), and 1- and 2-compartment pharmacokinetic models ( , / , , , and the macro parameter ). Twenty-four local recurrences, 65 metastatic lymph nodes, 19 osseous metastases, and 60 inflammatory lymph nodes were included in the analysis, which was subsequently repeated for regions of interest placed over the gluteus maximus muscle and adipose tissue as a control. SUV and were 3.60 ± 2.16 and 0.28 ± 0.22 min in lesions, compared with 2.11 ± 1.33 and 0.15 ± 0.10 min in muscle and 0.26 ± 0.07 and 0.02 ± 0.01 min in adipose tissue. According to the Akaike information criterion, the 2-compartment irreversible model was most appropriate in 85% of lesions and resulted in a of 0.79 ± 0.98 min (range, 0.11-7.17 min), a / of 2.92 ± 3.52 (range, 0.31-20.00), a of 0.36 ± 0.30 min (range, 0.00-1.00 min) and a of 0.28 ± 0.22 min (range, 0.00-1.33 min). The Spearman ρ between SUV and , between SUV and , and between and was 0.94, 0.91, and 0.97, respectively, and that between SUV and , between SUV and / , and between SUV and was 0.70, 0.44, and 0.33, respectively. Malignant lymph nodes exhibited a higher SUV, , and than benign lymph nodes. Although C-choline pharmacokinetic modeling has potential to uncouple the contributions of different processes leading to intracellular entrapment ofC-choline, the high correlation between SUV and both and supports the use of simpler SUV methods to evaluate changes inC-choline uptake and metabolism for treatment monitoring.

HR detected primary breast lesions and metastatic LNs missed on SR, which led to change in staging and management. In addition, HR images provided higher SUVmax, which enabled a more comfortable localization, especially when SR presented borderline values. Finally, HR images decreased the number of gray zone lesions, especially in axillary LN detection.