Although diagnosing gout generally is straightforward, atypical disease may present a challenge if it is associated with unusual symptoms or sites, discordant serum urate level, or mimics of gout. Dual-energy computed tomography (CT) may be used to differentiate urate crystals from calcium by using specific attenuation characteristics, which may help diagnose gout. In patients with known tophaceous gout, dual-energy CT may be used for serial volumetric quantification of subclinical tophi to evaluate response to treatment. Given the utility of dual-energy CT in challenging cases and its ability to provide an objective outcomes measure in patients with tophaceous gout, dual-energy CT promises to be a unique and clinically relevant modality in the diagnosis and management of gout.

Soft-tissue sarcoma requires aggressive treatment, often with a combination of radiation therapy, chemotherapy, and surgical resection. Even after multimodality treatment, local recurrence is common, and regular follow-up imaging at short intervals is required. Interpretation of posttreatment magnetic resonance (MR) images may be complicated by changes in the surgical bed or treatment field. The challenge of distinguishing posttreatment change from recurrent tumor may be minimized by using an organized, systematic approach to imaging, with emphasis on the patient's clinical and surgical history and a review of pretreatment images. Common changes that result from radiation therapy include soft-tissue trabeculation, increased fatty marrow, and focal marrow abnormalities. Rarely, radiation-induced malignancies may develop within the treatment field. Chemotherapy also influences posttreatment imaging appearance. Occasionally, it causes a substantial increase in tumor size that is a result of chemotherapy-induced hemorrhage. Although myocutaneous flaps used in reconstructive surgery may mimic a mass, they demonstrate time-dependent changes in size, signal intensity, and enhancement on MR images. Recurrent tumor is characterized by the presence of a discrete nodule or mass with signal characteristics that typically mirror those of the original tumor. MR imaging sequences such as unenhanced T1-weighted fat-suppressed and gradient-echo sequences may help differentiate posttreatment hemorrhage from local tumor recurrence. A consistent imaging approach combined with a detailed knowledge of the patient's history, familiarity with pretreatment images, and an understanding of the various posttreatment changes enables optimal monitoring of the treatment bed and maximizes accuracy in the detection of recurrence.

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We confirmed that attenuation values of L1 trabecular bone, unlike attenuation values of fat, fluid, or soft tissue, vary at different CT x-ray tube voltages. Therefore, standard reference attenuation values for trabecular bone seen at 120 kV cannot be applied to other single-energy settings, DECT, or CT examinations where dose modulation software automatically raises or lowers the tube voltage from 120 kV. Knowledge of the specific energy spectra used is essential before performing opportunistic CT evaluation for osteoporosis.

Mass-like extramedullary hematopoiesis most commonly presents as multiple, fat-containing lesions localized to the axial skeleton. When these imaging features are identified, extramedullary hematopoiesis should be strongly considered, particularly when occurring in the setting of a predisposing medical condition.

A 51-year-old man presented to his orthopedic surgeon with a 2-week history of pain and swelling in his right knee. The patient reported that 2 weeks before he had repeatedly kneeled and squatted while gardening in his yard. Physical examination revealed a large, right knee joint effusion and a painful active range of motion. The patient underwent radiography and magnetic resonance (MR) imaging for further evaluation. Imaging Findings A lateral radiograph of the right knee showed a large joint effusion (Fig 1). Subsequent multisequence, multiplanar MR images showed a large effusion and synovial proliferation. The synovium demonstrated low signal intensity on both T1-weighted (650/14-repetition time msec/echo time msec) and T2-weighted (4610/87) images (Fig 2). The synovium also demonstrated magnetic susceptibility artifact with disproportionately lower signal intensity ("blooming") on

The purpose of this article is to present algorithms for the diagnostic management of solitary bone lesions incidentally encountered on computed tomography (CT) and magnetic resonance (MRI) in adults. Based on review of the current literature and expert opinion, the Practice Guidelines and Technical Standards Committee of the Society of Skeletal Radiology (SSR) proposes a bone reporting and data system (Bone-RADS) for incidentally encountered solitary bone lesions on CT and MRI with four possible diagnostic management recommendations (Bone-RADS1, leave alone; Bone-RADS2, perform different imaging modality; Bone-RADS3, perform follow-up imaging; Bone-RADS4, biopsy and/or oncologic referral). Two algorithms for CT based on lesion density (lucent or sclerotic/mixed) and two for MRI allow the user to arrive at a specific Bone-RADS management recommendation. Representative cases are provided to illustrate the usability of the algorithms.

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