The use of multiparametric magnetic resonance (MR) imaging in prostate cancer therapy is increasing, as newer treatment methods and management approaches emerge. The mainstays of therapy-radiation and surgery-are being supplemented (and even replaced) by novel focal therapy methods. Laser and ultrasonographic ablation, photodynamic therapy, electroporation, and cryoablation are the most common focal therapies, each with its own imaging findings. Typical ablation zones have a central focus of enhancement with peripheral rim enhancement; thus, dynamic contrast material-enhanced (DCE) MR imaging is the most important sequence for evaluation of treatment in the immediate posttherapeutic setting. Detection of recurrence can initiate salvage therapy, but recurrence can be difficult to detect on T2-weighted images, again necessitating DCE MR imaging and also diffusion-weighted imaging. Furthermore, the location of recurrence can vary depending on the therapy. With radiation therapy, the most common site of recurrence is the prior tumor site, whereas after prostatectomy, the recurrence usually occurs around the vesicoureteral anastomosis. Regarding management, there is an increased emphasis on watchful waiting and active surveillance, for which MR imaging has a critical role in both selection and follow-up of patients who undergo active surveillance. As MR imaging is being increasingly used for imaging suspected recurrence, it is important for radiologists to be familiar with the normal posttreatment findings and patterns and MR imaging findings of recurrence. RSNA, 2018.

3 J. Magn. Reson. Imaging 2017;45:917-925.

Benign prostatic hyperplasia (BPH) is a histologic diagnosis showing glandular and stromal hyperplasia in the prostate. Its symptoms usually occur after the age of 40, and its prevalence reaches 50%-60% by the age of 60 (1). About 50% of men who have a histologic diagnosis of BPH have lower urinary tract symptoms including storage and voiding symptoms (2). Imaging plays an important role in evaluation of enlargement locations and nodules, estimation of prostatic volumes, and management of BPH patients. Ultrasonography (US) and magnetic resonance imaging (MRI) are used in evaluation of the prostate. US is the most common imaging modality in BPH patients, because it is relatively inexpensive and provides important information in most patients. Recently, MRI has been more commonly used in management of prostate cancer (3). Wasserman (4) described the US classification of BPH using findings on sagittal and axial images of transrectal US based on the pathologic classification (5). Following this, Wasserman et al. (6) implemented this classification to MRI. The classification for detecting BPH types is important, as patients with different BPH types may have different symptoms and treatment options.In this paper, we retrospectively evaluated MRI scans of BPH patients who were histologically diagnosed as BPH and presented the different types of BPH on T2-weighted MRI, since the prostatic parenchyma is best evaluated on T2-weighted images (6, 7). Additionally, the sagittal and axial images that are important for the classification of BPH were only available on T2-weighted images. In our practice, we perform prostate MRI on a 3.0 T scanner (AchievaTX; Philips) using an endorectal coil (Prostate eCoil, Medrad). Anatomy of the prostateIn previous studies (4,8), the anatomy of the prostate has been reviewed. There are three main glandular zones (central, transition, peripheral) and one stromal zone (anterior fibromuscular stroma). There is also a subsphincteric periurethral gland (PUG) region, which is a fraction of the size of the transition zone (TZ) (9). BPH mostly involves PUGs, TZ, and stromal ABSTRACTBenign prostatic hyperplasia (BPH) is a common condition in middle-aged and older men and negatively affects the quality of life. An ultrasound classification for BPH based on a previous pathologic classification was reported, and the types of BPH were classified according to different enlargement locations in the prostate. Afterwards, this classification was demonstrated using magnetic resonance imaging (MRI). The classification of BPH is important, as patients with different types of BPH can have different symptoms and treatment options. BPH types on MRI are as follows: type 0, an equal to or less than 25 cm 3 prostate showing little or no zonal enlargements; type 1, bilateral transition zone (TZ) enlargement; type 2, retrourethral enlargement; type 3, bilateral TZ and retrourethral enlargement; type 4, pedunculated enlargement; type 5, pedunculated with bilateral TZ and/or retrourethral enlargement; type 6, subtrigon...

1Computed tomography (CT) colonography is a screening modality used to detect colonic polyps before they progress to colorectal cancer. Computer-aided detection (CAD) is designed to decrease errors of detection by finding and displaying polyp candidates for evaluation by the reader. CT colonography CAD false-positive results are common and have numerous causes. The relative frequency of CAD false-positive results and their effect on reader performance on the basis of a 19-reader, 100-case trial shows that the vast majority of CAD false-positive results were dismissed by readers. Many CAD false-positive results are easily disregarded, including those that result from coarse mucosa, reconstruction, peristalsis, motion, streak artifacts, diverticulum, rectal tubes, and lipomas. CAD false-positive results caused by haustral folds, extracolonic candidates, diminutive lesions (<6 mm), anal papillae, internal hemorrhoids, varices, extrinsic compression, and flexural pseudotumors are almost always recognized and disregarded. The ileocecal valve and tagged stool are common sources of CAD falsepositive results associated with reader false-positive results. Nondismissable CAD soft-tissue polyp candidates larger than 6 mm are another common cause of reader false-positive results that may lead to further evaluation with follow-up CT colonography or optical colonoscopy. Strategies for correctly evaluating CAD polyp candidates are important to avoid pitfalls from common sources of CAD false-positive results.

CT colonography (CTC) is a colorectal cancer screening modality which is becoming more widely implemented and has shown polyp detection rates comparable to those of optical colonoscopy. CTC has the potential to improve population screening rates due to its minimal invasiveness, no sedation requirement, potential for reduced cathartic examination, faster patient throughput, and cost-effectiveness. Proper implementation of a CTC screening program requires careful attention to numerous factors, including patient preparation prior to the examination, the technical aspects of image acquisition, and post-processing of the acquired data. A CTC workstation with dedicated software is required with integrated CTC-specific display features. Many workstations include computer-aided detection software which is designed to decrease errors of detection by detecting and displaying polyp-candidates to the reader for evaluation. There are several pitfalls which may result in false-negative and false-positive reader interpretation. We present an overview of the potential errors in CTC and a systematic approach to avoid them.