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PURPOSE The purpose of this study was to evaluate the mid-term results of posterior medial meniscal root tear (PMMRT) repair through assessment of functional outcome scores and magnetic resonance imaging (MRI). METHODS This was a single-center, retrospective study evaluating patients that had undergone a PMMRT. This was a follow-up to a previously published 2-year outcome study (all original patients were invited to participate). Clinical outcomes included pre- and postoperative International Knee Documentation Committee (IKDC) and Lysholm scores. Root healing, meniscal extrusion, and cartilage degeneration via International Cartilage Repair Society Scale (ICRS) grades were assessed on MRI by two musculoskeletal fellowship-trained radiologists. RESULTS 10 of the original study's 18 patients were able to participate. Mean age and BMI was 48.4 ± 12.0 years and 29.5 ± 4.5, respectively, with mean follow-up 65.5 ± 8.3 months (range 52.0-75.8) (60% female). The IKDC significantly increased from 43 ± 13 preoperatively to 75 ± 16 at 5-year follow-up (p 3 mm of extrusion on preoperative MRI had

There is a paucity of literature describing MRI patterns of high ankle sprains in pediatric patients. Radiologists should understand MRI patterns of these injuries in both adults and children. To describe normal MRI appearance of pediatric syndesmotic ligaments and compare MRI patterns of high ankle sprains in children versus adults. We reviewed consecutive ankle MRIs performed over 3 years and divided them into three cohorts: a normal pediatric (≤16 years) cohort, and pediatric and adult cohorts with acute/subacute ankle syndesmosis injuries. Our retrospective review assessed interobserver agreement (Cohen kappa coefficient) and normal pediatric syndesmotic anatomy. We compared patterns of high ankle sprains (Fisher exact test) including ligament tears, periosteal stripping, avulsions and fractures. Of the 582 ankle MRIs, we included 25 in the normal pediatric cohort, 20 in the pediatric injury cohort and 23 in the adult injury cohort. The anterior and posterior tibiofibular ligaments all attached to cortex or cartilaginous precursor, while the interosseous ligament/membrane complex attached to the fibrous periosteum in 22/25 (88%) normal pediatric cases. Tibial periosteal stripping at the interosseous ligament/membrane complex attachment occurred in 7/20 (35%) pediatric and 1/23 (4%) adult injury cases (P=0.02). No other statistically significant differences were found. Interobserver agreement ranged from kappa=0.46 to kappa=0.82 (ligament tears), 0.38 to 0.45 (avulsions) and 0.69 to 0.77 (periosteal stripping). The normal interosseous ligament/membrane complex typically attaches to fibrous periosteum rather than bony cortex. Tibial periosteal stripping, usually without tibial fracture, is significantly more common among pediatric high ankle sprains. MRI patterns of high ankle sprains are otherwise not significantly different between children and adults.

OBJECTIVE: Deep learning (DL) image reconstruction has the potential to disrupt the current state of MRI by significantly decreasing the time required for MRI examinations. Our goal was to use DL to accelerate MRI to allow a 5-minute comprehensive examination of the knee without compromising image quality or diagnostic accuracy. MATERIALS AND METHODS. A DL model for image reconstruction using a variational network was optimized. The model was trained using dedicated multisequence training, in which a single reconstruction model was trained with data from multiple sequences with different contrast and orientations. After training, data from 108 patients were retrospectively undersampled in a manner that would correspond with a net 3.49-fold acceleration of fully sampled data acquisition and a 1.88-fold acceleration compared with our standard twofold accelerated parallel acquisition. An interchangeability study was performed, in which the ability of six readers to detect internal derangement of the knee was compared for clinical and DL-accelerated images. RESULTS. We found a high degree of interchangeability between standard and DL-accelerated images. In particular, results showed that interchanging the sequences would produce discordant clinical opinions no more than 4% of the time for any feature evaluated. Moreover, the accelerated sequence was judged by all six readers to have better quality than the clinical sequence. CONCLUSION. An optimized DL model allowed acceleration of knee images that performed interchangeably with standard images for detection of internal derangement of the knee. Importantly, readers preferred the quality of accelerated images to that of standard clinical images.

Rationale and Objectives The medial plantar proper digital nerve, also called Joplin's nerve, arises from the medial plantar nerve, courses along the medial hallux metatarsophalangeal joint, and can be a source of neuropathic pain due to various etiologies, following acute injury including bunion surgery and repetitive microtrauma. We describe our clinical experience with diagnostic ultrasound assessment of Joplin's neuropathy and technique for ultrasound-guided therapeutic intervention including both injection and cryoablation over a 6-year period. Materials and Methods Retrospective review of all diagnostic studies performed for Joplin's neuropathy and therapeutic Joplin's nerve ultrasound-guided injections and cryoablations between 2012 and 2018 was performed. Indications for therapeutic injection and cryoablation, were recorded. Studies were assessed for sonographic abnormalities related to the nerve and perineural soft tissues. Post-treatment outcomes including immediate pain scores, clinical follow-up, and periprocedural complications were documented. Results Twenty-four ultrasound-guided procedures were performed, including 15 perineural injections and nine cryoablations. With respect to sonographic abnormalities, nerve thickening (33%) and perineural hypoechoic scar tissue (27%) were the most common findings. The mean pain severity score prior to the therapeutic injection was 6.4/10 (range 4–10) and 0.25/10 (range 0–2) following the procedure; mean follow-up was 26.2 months (range 3–63 months). All of the cryoablation patients experienced sustained pain relief with a mean length follow-up of 3.75 months (range 0.2–10 months). Conclusion Therapeutic injection of Joplin's nerve is a safe and easily performed procedure under ultrasound guidance, with high rates of immediate symptom improvement. For those experiencing a relapse or recurrent symptoms, cryoablation offers an effective secondary potential treatment option.

PURPOSE To describe our experience using ultrasound (US) to evaluate postoperative complications in the presence of in situ shoulder arthroplasty. METHODS Review of patients who underwent US evaluation following total shoulder arthroplasty (TSA), reverse total shoulder arthroplasty (RTSA) or hemiarthroplasty from 2007 to 2020. All studies were reviewed independently by two musculoskeletal radiologists to assess for joint effusion, periarticular collection, and characterization of associated rotator cuff tears. Tendon tears were assessed with respect to (1) thickness: low grade ( 50% thickness), full thickness; (2) morphology (focal vs. diffuse) and location (insertion vs. critical zone). Inter-reader agreements were determined using Cohen's kappa test. RESULTS Ninety-seven studies were performed in 72 patients following TSA, RTSA, or hemiarthroplasty. Thirty-seven exams were solely for diagnostic purposes, and 59 were for guiding joint or periarticular collection aspiration. Twenty-eight studies assessed the cuff tendons post TSA. The mean time between surgery and US examination was 29.2 months. Complete or high-grade tears were identified in 8/28 (28.6%) diagnostic exams. The most commonly torn tendon among TSA patients was the subscapularis, with 13/28 (46.4%) demonstrating at least partial tearing. Inter-reader agreement was excellent for presence of effusion (k = 0.79, p

PURPOSE: We aimed to retrospectively correlate (18)F-fluorodeoxyglucose ((18)F-FDG) metabolic activity with lumbar spine magnetic resonance imaging (MRI) findings and epidural steroid injection sites in patients with symptomatic degenerative disease of the lumbar spine. METHODS: A database search was conducted for patients receiving epidural injections

Osteoarthritis (OA) is the most common joint disease in the United States. The prevalence of OA is rising due to an aging population and increasing rates of obesity. Magnetic resonance imaging (MRI) allows an incomparable noninvasive assessment of all joint structures. Irreversible and progressive degradation of the articular cartilage remains the hallmark feature of OA. To date, attempts at developing disease-modifying drugs or biomechanical interventions for treating OA have proven unsuccessful. MRI-based cartilage imaging techniques have continued to advance, however, and will likely play a central role in the development of these joint preservation methods of the future. In this narrative review, we describe clinical MR image acquisition and assessment of cartilage. We discuss the semiquantitative cartilage scoring methods used in research. Lastly, we review the quantitative MRI techniques that allow assessment of changes in the biochemical composition of cartilage, even before the morphological changes are evident.

Objective The purpose of this study is to determine the most accurate imaging techniques to measure glenoid bone loss in anterior glenohumeral instability through a systematic review of existing literature. Materials and methods We performed a comprehensive literature search of five databases for original research measuring glenoid bone loss at radiography, CT, or MRI, using prospective or retrospective cohort, case-control, or cadaveric study designs up to January 2018. The Quality Assessment of Diagnostic Accuracy Studies-2 tool aided qualitative assessment of the methods. Data extraction included results, index test interobserver agreement, and accuracy analysis. Results Twenty-seven studies (evaluating 1425 shoulders) met inclusion criteria after full-text review by two independent readers. Glenoid bone loss was assessed, comparing several index tests to nonimaging (n = 18 studies) and imaging (n = 11) reference standards. Compared with arthroscopic or cadaveric measurements, 2D CT was accurate in six of seven studies (86%), 3D CT was accurate in eight of 10 studies (80%), 2D MRI was accurate in five of seven studies (71%), 3D MRI was accurate in four of four studies (100%), and radiographs were accurate in zero of four studies (0%). Best-fit circle methods (glenoid width or Pico surface area) were the most common and both were accurate (86-90% and 75-100%, respectively) using CT and MRI. Studies had good external validity (78%). Most risk for bias arose from patient selection and reference standards. Only two studies reported sensitivity and specificity, both comparing CT to arthroscopy using different bone loss thresholds (20% and 25%). Conclusion CT and MRI (2D or 3D) accurately measure glenoid bone loss in anterior shoulder instability, but radiographs do not. Best-fit circle measurement techniques are reliable and accurate. Current literature about glenoid bone loss is heterogeneous, and future studies should focus on diagnosis of clinically relevant glenoid bone loss.

Ultrasound-guided hookwire localization was initially introduced to facilitate the excision of nonpalpable breast lesions by guiding surgical exploration, thereby reducing operative time and morbidity. The same technique has since found utility in a range of other applications outside breast and can be useful within the musculoskeletal system. Despite this, there remains limited literature with respect to its technical aspects and practical utility. We describe our technique and a series of preoperative ultrasound-guided wire localizations in the musculoskeletal system to assist surgical excision of 4 soft tissue masses.

Normal skeletal development in the pediatric ankle is dynamic and often produces variable imaging appearances that are subject to misinterpretation. Radiologists must understand the underlying developmental phenomena, such as endochondral and membranous ossification and physeal fusion, and be familiar with their common and uncommon imaging manifestations unique to the pediatric ankle. This is especially true as the use of MRI in the evaluation of musculoskeletal trauma expands among younger populations. The authors focus on MRI evaluation of the skeletally maturing pediatric ankle and present pearls for accurately distinguishing normal findings and imaging pitfalls from true pathologic findings. The normal but often variable imaging findings of preossification, secondary ossification, and multiple ossification centers, as well as the range of bone marrow signal intensities that can be visualized within ossification centers, are described, along with tips to help differentiate these from true pathologic findings such as contusion, fracture, or tumor. The authors also review dynamic periosteal and physeal contributions to bone growth to highlight helpful distinguishing features and avoid misdiagnosis of common subperiosteal and periphyseal abnormalities. For example, the normal trilaminar appearance of the immature cortex and periosteum should not be mistaken for periosteal reaction, traumatic stripping, or subperiosteal hematoma. In addition, the physis can have several confusing but normal appearances, including normal physeal undulations (eg, Kump bump) or focal periphyseal edema, which should not be mistaken for pathologic findings such as physeal fracture, infection, or bar. ©RSNA, 2020.

Please see the Editorial Comment by Lauren Ladd discussing this article. BACKGROUND. Tearing of the superior peroneal retinaculum is a known cause of peroneal tendon subluxation-dislocation. Howeve...

The aims of this study are to assess the diagnostic yield of image-guided biopsy for discitis-osteomyelitis (DO), identify factors associated with biopsy yield (laboratory, pre-defined MRI findings, and biopsy technique), and impact of biopsy on management of patients appropriately selected according to the Infectious Disease Society of America guidelines (IDSA). This is a retrospective review of patients who underwent biopsy for suspected DO from 2011 to 2019. Reference standards to establish diagnosis of DO in order were histopathology/microbiology from biopsy or subsequent surgical sampling, positive blood culture or serology, and imaging/clinical follow-up. Laboratory markers, pre-biopsy antibiotics and MRI features, procedural-related variables, and impact of biopsy on management were assessed. Multivariable logistic regression was also performed. Out of 97 included patients, 78 were diagnosed with DO. Overall sensitivity of biopsy for detecting DO was 41.0% (32/78), including 10 patients with positive histopathology only, 14 with positive biopsy culture only, and 8 with both. Elevated ESR (p < 0.001) and epidural collection on MRI (p = 0.008) were associated with higher biopsy yield (63.6% and 68.6%, respectively) in a multivariable model. Procedural variables were not associated with yield. Biopsy results impacted the management in 19/77 (24.7%) patients, of whom 15/19 (78.9%) had treatment de-escalation and 4/19 (21.0%) had treatment escalation including starting new anti-tuberculous and anti-fungal regimens. Sensitivity of biopsy for detecting DO was 41.0%. When IDSA guidelines are followed, biopsy provided impactful information that changed the management in 24.7% of patients. Evaluation for elevated ESR and epidural collection can help improve yield and patient selection for biopsy.

BACKGROUND. Literature on glenohumeral dislocations has focused on younger patient populations because of high recurrence rates. However, the spectrum of injuries sustained in younger versus older ...

Purpose : To assess the utility of a 2D dynamic HASTE sequence in assessment of cervical spine flexion-extension, specifically (1) comparing dynamic spondylolisthesis to radiographs and (2) assessing dynamic contact upon or deformity of the cord. Methods : Patients with a dynamic flexion-extension sagittal 2D HASTE sequence in addition to routine cervical spine sequences were identified. Static and dynamic listhesis was first determined on flexion-extension radiographs reviewed in consensus. Blinded assessment of the dynamic HASTE sequence was independently performed by 2 radiologists for (1) listhesis and translation during flexion-extension and (2) dynamic spinal cord impingement (cord contact or deformity between neutral, flexion and extension). Results 32 scans in 32 patients (9 males, 23 females) met inclusion criteria acquired on 1.5 T (n = 15) and 3 T (n = 17) scanners. The mean acquisition time was 51.8 s (range 20–95 seconds). Dynamic translation was seen in 14 patients on flexion-extension radiographs compared to 12 (reader 1) and 13 (reader 2) patients on HASTE, with 90.6 % agreement (K = 0.83; p = 0.789). In all cases dynamic listhesis was ≤3 mm translation with one patient showing dynamic listhesis in the range 4−6 mm. Four cases (13 %) demonstrated deformity of the cord between flexion-extension, not present in the neutral position. For cord impingement there was strong inter-reader agreement (K = 0.93) and the paired sample Wilcoxon signed rank test found no significant difference between the impingement scores of the two readers (p = 0.787). Conclusions : A sagittal dynamic flexion-extension HASTE sequence provides a rapid addition to standard MRI cervical spine protocols, which may useful for assessment of dynamic spondylolisthesis and cord deformity.

To evaluate change in patient-reported outcomes following image-guided intra-articular therapeutic steroid hip injections for pain and assess correlations of outcomes with patient- and injection-specific factors. We retrospectively reviewed consecutive patients treated for hip pain who completed outcomes assessments from October 2011 to September 2017 at an outpatient orthopedic surgery clinic. Only patients with radiographic hip osteoarthritis (Tonnis grade ≥ 1) who underwent steroid hip injections were included. Outcomes assessments included EuroQol-5 domain (EQ5D), EQ5D-visual analog scale (VAS), and hip disability and osteoarthritis outcome score (HOOS), obtained before and within 1–6 months post-injection. Among 113 patients who completed surveys, the mean age was 59 years (±13.7 years), including 77 women (68%) and 36 men (32%). Time to repeat injection or arthroplasty was recorded. Exact Wilcoxon signed rank test assessed score differences and Spearman correlation, Kruskal–Wallis, and Mann–Whitney tests assessed correlations. Of 113 patients, 34 had outcomes measured at

The objective of this article is to review the normal anatomy and posttraumatic findings of the Chopart joint complex. Key imaging features of the normal ligaments and patterns of ligamentous and osseous injuries are discussed.Traumatic midtarsal injuries, particularly midtarsal sprain, are often overlooked clinically and on imaging but are relatively common and typically are associated with inversion ankle injuries. Radiologists should be familiar with Chopart joint anatomy and the imaging features of midtarsal injuries because early diagnosis may help optimize clinical management.

To correlate patterns of 18F-FDG uptake on whole-body PET-CT with MR findings and compare the degree of FDG activity between symptomatic and asymptomatic knees. Retrospective database query was performed using codes for knee MRI as well as whole-body PET-CT. Patients with malignant disease involving the knee or hardware were excluded. Patients who had both studies performed within 1 year between 2012 and 2017 were included for analysis. Knee joint osteoarthrosis, meniscal and ligamentous integrity, presence of joint effusion, and synovitis were assessed and recorded. Bone marrow edema lesions (BMELs) were identified, segmented, and analyzed using volumetric analysis. SUVmax was assessed over the suprapatellar joint space, intercondylar notch and Hoffa’s fat pad. Symptomatic and asymptomatic knees were compared in patients with unilateral symptoms. Twenty-two cases (20 patients) with mean age 63.3 years (range, 36–91 years) were included. Two patients had bilateral pain. The most FDG avid regions in both symptomatic and asymptomatic knees were the intercondylar notch (SUVmax = 1.84 vs. 1.51), followed by suprapatellar pouch (SUVmax = 1.74 vs. 1.29) and Hoffa’s fat pad (SUVmax = 1.01 vs. 0.87). SUVmax was significantly associated with cartilage loss (mean modified Outerbridge score) (r = 0.60, p = 0.003) and degree of synovitis (r = 0.48, p = 0023). Overall, mean SUVmax was significantly higher in the presence of a meniscal tear (1.83 ± 0.67 vs. 1.22 ± 0.40, p = 0.030). Nine patients had BMELs (volume: range = 0.6–27.8, mean = 7.79) however there was no significant association between BMEL volume and SUVmax. Higher FDG activity correlates with intra-articular derangement and the intercondylar notch represents the most metabolically active region of the knee.

Injuries at the calcaneocuboid and talonavicular joint have been described as two distinct, unrelated entities in the radiology literature. Our purpose was to assess the coexistence of these injuries using radiography and MRI and to correlate our findings with radiologic and clinical diagnoses.Twenty-one patients with injury at the anterior calcaneal process on radiographs or MR images were retrospectively assessed for concomitant injury at the talonavicular joint. Radiologic and clinical diagnoses and treatment were documented. McNemar and kappa statistics were calculated; p values0.05 were considered statistically significant.Radiographic and MRI rates of detection of injuries across the Chopart joint were statistically different. Calcaneocuboid avulsion fractures were evident on 48% of radiographs and 100% of MR images (p = 0.001). Talonavicular joint injuries were evident on 38% of radiographs and 76% of MR images (p = 0.008). Concomitant injury at both joints was evident on 14% of radiographs and 76% of MR images (p0.0001). Interrater agreement was 0.488-0.637 and 0.286-0.364 for talonavicular and 0.144-0.538 and 0.976-1 for calcaneocuboid injuries on radiography and MRI, respectively. Sixty percent of calcaneocuboid fractures were prospectively missed on radiography (none on MRI), whereas 38% and 25% of talonavicular findings were missed on radiography and MRI, respectively. Sixty percent of injuries were clinically misdiagnosed as ankle sprains. Chopart joint injury was never mentioned in prospective clinical or imaging diagnoses.Calcaneocuboid and talonavicular injuries commonly coexist. Radiographs underestimate severity of injury; MR images show more subtle abnormalities. Lack of mention of Chopart joint injury clinically and on imaging reports underlies the need for greater familiarity with this entity.

To review the MRI appearance of medial patellofemoral capsuloligamentous plication (also known as reefing or imbrication) for proximal patellar realignment in patients with patellofemoral instability. Retrospective analysis of our surgical and PACS databases identified cases of medial plication performed between June 2011 and July 2016. Pre- and postoperative MRI characteristics were reviewed. Correlation was made with operative reports and clinical records to define postoperative appearances on MRI. Forty-one patients underwent medial plication during the study period; 29 were excluded owing to a lack of postoperative imaging. Ultimately, 12 knees were included in 11 patients who had postoperative MRI studies available (8 women and 3 men, mean age 27.3 ± 10.2 years). Ten (83%) of the surgeries were performed open and 2 (17%) arthroscopically. There were differences in the post-surgical MRI appearance of medial plications carried out after surgery using the open and arthroscopic techniques. The open technique produces a “heaped up” distal vastus medialis obliquus (VMO) with centralized patellar insertion (100%), which was absent in the case of arthroscopic plication, where subtle medial retinaculum thickening was demonstrated without alteration of its patellar insertion. The mean postoperative lateral patellar and patellofemoral congruence angles measured 2.5° ± 5.6° and 12.4° ± 19.9° respectively. A significant association was found regarding change in patellofemoral alignment (p = 0.018 and p = 0.004 respectively). The MRI appearance of medial plication is not well described in the radiology literature; radiologists should be familiar with anticipated post-plication findings to avoid potential confusion for pathology and allow more accurate interpretation of postoperative imaging findings from this common surgery.

We describe an easily constructed, customizable phantom for magnetic resonance imaging-ultrasound fusion imaging and demonstrate its role as a learning tool to initiate clinical use of this emerging modality. Magnetic resonance imaging-ultrasound fusion can prove unwieldy to integrate into routine practice. We demonstrate real-time fusion with single-sequence magnetic resonance imaging uploaded to the ultrasound console. Phantom training sessions allow radiologists and sonographers to practice fiducial marker selection and improve efficiency with the fusion hardware and software interfaces. Such a tool is useful when the modality is first introduced to a practice and in settings of sporadic use, in which intermittent training may be useful.

Purpose To correlate shoulder ultrasound and radiography with F-FDG PET-CT to establish FDG uptake and therefore range of metabolic activity, as defined by SUV analysis, in various symptomatic shoulder pathologies. Methods Retrospective database query was performed for shoulder ultrasound and PET-CT scans between January 2012 and January 2017. Patients who had both studies within 1 year were included. Age- and sex-matched control patients with PET-CT scans only were also included. Retrospective image review determined shoulder pathology, and F-FDG SUVmax was measured using regions of interest placed at the glenohumeral joint, rotator cuff/bursa, and bicipital groove. Glenohumeral and acromioclavicular osteoarthrosis was assessed by radiography using the Kellgren-Lawrence classification system. Results Thirty-three patients had both imaging studies within 1 year. Ten patients (11 cases) were included, ranging in age from 56 to 90 years (mean, 67.9 years). Control subjects were selected among patients receiving PET-CT within 1 week of symptomatic patients. Glenohumeral osteoarthrosis was mild in 3 (27%), moderate in 2 (18%), and severe in 2 (18%). Six full-thickness rotator cuff tears (55%) were identified. SUVmax means were compared between the pathologic and control groups and were significantly higher in the former: glenohumeral joint (1.96 vs 1.32; P = 0.016), rotator cuff/bursa (2.80 vs 2.0; P = 0.005), and bicipital groove (2.19 vs 1.48; P = 0.007). The highest values were seen in full-thickness rotator cuff tear and severe biceps tenosynovitis. Conclusions Increased metabolic activity about the shoulder is associated with a spectrum of rotator cuff, glenohumeral joint, and other soft tissue pathology that can be correlated with diagnostic ultrasound findings.

To describe a 4-year clinical experience with ultrasound-guided therapeutic perineural injections of peripheral nerves about the foot and ankle. Retrospective analysis of foot and ankle perineural injections performed between January 2012 and August 2016. Demographics, clinical indications, presence of structural pathology, immediate and interval pain relief, as well as complications were recorded. Fifty-nine therapeutic injections were performed among 46 patients, accounting for multiple injections in a single visit or multiple visits [mean age = 43 years (range 18–75), 31 female (67%) and 15 male (33%)]. Most commonly, perineural injections involved the hallux branch of the medial plantar nerve (n = 17, 22%). Least commonly, perineural injections involved the saphenous nerve (n = 3, 4%). Other injections in our series include sural (10), superficial (11) and deep (7) peroneal, medial (5) and lateral (3) plantar nerves, and the posterior tibial nerve (3). Ultrasound evaluation revealed structural abnormality associated with the nerve in 30 cases (51%)—most commonly thickening with perineural scarring (n = 14). Of 45 injections with complete documentation, immediate relief of symptoms was reported in 43 (96%) cases. Interval symptom relief was achieved in 23 injections [short term (n = 12), intermediate (n = 6), and long term (n = 5)] out of 38 for which follow-up was available (61%). Complications are rare, occurring in only one case. Ultrasound-guided perineural injections about the foot and ankle are safe and provide lasting symptomatic relief for many indications. Concomitant sonographic evaluation identifies structural abnormalities that may contribute to neuropathic symptoms, allowing targeting of injection or clinical therapy.

Background The MRI manifestations of subspine impingement (SSI) other than morphologic features of anterior inferior iliac spine (AIIS) have not been extensively explored and validated. Purpose To determine the MRI findings associated with SSI, including AIIS morphologic features, femoral distal cam, and associated soft-tissue injuries. Materials and Methods This is a retrospective study of symptomatic patients who underwent arthroscopic treatment for femoroacetabular impingement between December 2014 and March 2017, with preoperative MRI within 6 months before surgery. The SSI group included patients with clinical and intraoperative findings of SSI; the remaining patients comprised the non-SSI group. Preoperative MRI findings were independently assessed by two radiologists who were blinded to clinical information. Interreader agreement was assessed, and multivariable logistic regression was also used. Results A total of 62 patients (mean age ± standard deviation, 42.1 years ± 11.9; 38 women) were included. SSI was diagnosed in 20 of the 62 patients (32%) (mean age, 43 years ± 12); 42 patients (68%) did not have SSI (mean age, 41 years ± 10). Reader 1 detected distal cam in 16 of the 20 patients with SSI (80%) and eight of the 42 patients without SSI (19%), and reader 2 detected distal cam in 15 of the 20 patients with SSI (75%) and eight of the 42 patients without SSI (19%) (P < .001 for both). Reader 1 detected signs of impingement on the distal femoral neck (IDFN) in 18 of the 20 patients with SSI (90%) and seven of the 42 patients without SSI (16%), and reader 2 detected signs of IDFN in 13 of the 20 patients with SSI (65%) and nine of the 42 patients without SSI (21%) (P < .001 and P = .001, respectively). Reader 1 detected superior capsular edema in 15 of 20 patients with SSI (75%) and three of 42 patients without SSI (7%), and reader 2 detected superior capsular edema in 17 of 20 patients with SSI (85%) and 22 of 42 patients without SSI (52%) (P < .001 and P = .02, respectively). Distal cam was a predictor of SSI after adjustment for IDFN. Interreader agreement was substantial for distal cam (κ = 0.80) and moderate for IDFN (κ = 0.50). Conclusion Soft-tissue injuries and osseous findings other than morphologic features of the anterior inferior iliac spine were associated with subspine impingement. © RSNA, 2019 See also the editorial by Guermazi in this issue.

The purpose of this study was to describe clinical experience with ultrasound-guided therapeutic procedures and associated pathologic conditions involving the peripheral nerves of the upper extremity over 5 years at a large academic institution.A retrospective database search of procedure codes was performed for all ultrasound-guided upper extremity peripheral nerve procedures between 2012 and 2017. Retrospective review of the electronic medical record for patient demographics, indications, interval follow-up pain relief, and complications was undertaken. Retrospective review of ultrasound and other correlative imaging findings was performed to assess for neural and perineural abnormalities.In total, 242 procedures performed on a cohort of 183 patients (53% women, 47% men; mean age, 53 years; range, 15-97 years) were reviewed. Nine patients underwent multifocal injections in a single encounter, and 39 underwent repeat injections of previously documented symptom generators. Perineural injections included ulnar (n = 109), median (n = 81), posterior interosseous-deep radial (n = 39), sensory branch of the radial (n = 7), anterior interosseous (n = 2), axillary (n = 2), suprascapular (n = 1), and digital (n = 1) nerves. Structural or dynamic abnormality seen either during the procedure or at preprocedural imaging included loss of normal morphologic features (n = 148), nerve subluxation (n = 8), ganglion cyst (n = 4), and neuroma (n = 7). Forty-four patients reported immediate pain relief after the procedure. Of the 89 patients with documented clinical follow-up, 52 reported a period of symptom relief (mean, 125 days), and six reported complete resolution of symptoms. Subsequent surgical procedures were performed on 32 patients, a combination of those who did (n = 12) and did not (n = 20) experience a period of symptom relief from the perineural injection. There were no complications with regard to the site or distribution of perineural injections. Three episodes of vasovagal reaction were reported.Ultrasound-guided percutaneous interventions for upper extremity neural abnormalities can be safely performed for a variety of indications. Real-time ultra-sound evaluation during the procedure allows assessment for neural and perineural abnormalities and tailoring of the procedure to potentially symptomatic structural abnormalities.

The midtarsal (Chopart) joint complex consists of the talonavicular and calcaneocuboid joints and their stabilizing ligaments. Detailed assessment of this complex at MRI can be challenging owing to frequent anatomic variation and the small size of the structures involved. Nevertheless, a wide spectrum of pathologic conditions affect the joint complex, and its imaging evaluation deserves more thorough consideration. This review focuses on MRI evaluation of normal ligamentous anatomy and common variations about the Chopart joint, presenting practical imaging tips and potential diagnostic pitfalls. Imaging findings across a spectrum of traumatic Chopart joint injuries are also reviewed, from midtarsal sprains to Chopart fracture-dislocations. Midtarsal sprains-commonly associated with ankle inversion injuries-are emphasized, along with their often predictable radiographic and MRI injury patterns. Online DICOM image stacks are available for this article. ©RSNA, 2018.

To compare femoroacetabular motion in a series of consecutive symptomatic patients with hip pain throughout the range of motion of the hip using a real-time radial gradient echo (GRE) sequence in addition to the routine hip protocol sequences for magnetic resonance (MR) arthrographic assessment of patients with and without clinical femoroacetabular impingement (FAI) syndrome. In particular, we sought to assess whether the additional dynamic sequence could differentiate between patients with and without a positive physical exam maneuver for FAI syndrome.Patients with hip pain referred for conventional hip MR arthrogram including those with and without a positive physical exam maneuver for FAI syndrome were imaged using routine hip MR arthrogram protocol and an additional real-time radial 2-dimensional GRE acquisition at 3 Tesla in an axial oblique plane with continuous scanning of a 9 mm thick slice through the center of the femoral head-neck axis. Patients who were unable to move through the range of motion were excluded (n = 3). Patients with acetabular dysplasia (defined by a lateral center-edge angle [CEA] of 20°) were also excluded, as were patients had Kellgren and Lawrence scores of0. The real-time cine sequence was acquired with the patient actively moving through neutral, flexion, flexion-abduction external-rotation, and flexion-adduction internal rotation (FADIR) positions aiming for 40° of abduction, then 25° of adduction at 80° to 90° flexion. Due to the placement of the coil over the hip, a true FADIR was precluded. Images were evaluated independently by 2 musculoskeletal radiologists measuring the joint space in the anterior, central, and posterior positions at each point during range of motion for femoroacetabular cortical space (FACS). Anterior FACS narrowing was calculated as the ratio of joint space in FADIR:neutral position, with lower ratios indicating greater narrowing. Static metrics including alpha angle, CEA, grade of cartilage loss according the Outerbridge classification, and patient demographics were also recorded.Twenty-two painful hips in 22 patients (11 males and 11 females) with mean age 36 years (range, 15-67) were included. Twelve patients had a positive physical exam maneuver for FAI syndrome. The time to perform the dynamic sequence was 3 to 6 minutes. Interobserver agreement was strong, with intraclass correlation 0.91 and concordance correlation 0.90. According to results from both readers, patients with impingement on clinical exam had significantly lower anterior FACS ratios compared with those without clinical impingement (reader 1: 0.39 ± 0.10 vs 0.69 ± 0.20, P = .001; reader 2: 0.36 ± 0.07 vs 0.70 ± 0.17, P.001). Decreased anterior FACS ratio was found to be significantly correlated to increased alpha angle by both readers (reader 1: R = -0.63, P = .002; reader 2: R = -0.67, P = .001) but not significantly correlated to CEA (reader 1: R = 0.13, P = .561; reader 2: R = 0.20, P = .378) or cartilage loss (reader 1: R = 0.03, P = .885; reader 2: R = -0.06, P = .784). Both readers found patients with an anterior FACS ratio of 1/2 to have significantly higher mean alpha angle (reader 1: 62.88 vs 52.79, P = .038; reader 2: 63.50 vs 50.58, P = .006); however, there were no significant differences in cartilage loss (reader 1: P = .133; reader 2: P = .882) or CEA (reader 1: P = .340; reader 2: P = .307).A dynamic radial 2-dimensional-GRE sequence can be added to standard hip MR arthrogram protocols in6 minutes, allowing assessment of dynamic femoroacetabular motion with strong interreader agreement. Patients with impingement on clinical exam had significantly lower anterior FACS ratios between FADIR and neutral positions, compared with those without clinical impingement.Level III, comparative diagnostic investigation.

Piriformis syndrome is a common cause of lumbar, gluteal, and thigh pain, frequently associated with sciatic nerve symptoms. Potential etiologies include muscle injury or chronic muscle stretching associated with gait disturbances. There is a common pathological end pathway involving hypertrophy, spasm, contracture, inflammation, and scarring of the piriformis muscle, leading to impingement of the sciatic nerve. Ultrasound-guided piriformis injections are frequently used in the treatment of these pain syndromes, with most of the published literature describing injection of the muscle. We describe a safe, effective ultrasound-guided injection technique for the treatment of piriformis syndrome using targeted sciatic perineural hydrodissection followed by therapeutic corticosteroid injection.

Purpose Retained surgical items result in substantial morbidity, health care-related expense, and legal liability. This study determines the performance of a protocol for locating surgical items after a miscount, in which intraoperative radiography included a radiograph of the unaccounted for item. Methods Institutional review board approval was obtained. In 20,820 operations performed between January 1, 2011 and April 1, 2013, a total of 183 consecutive surgical miscounts occurred, involving 180 patients (97 male, 83 female; median age: 55 years). Departmental protocol mandated that a radiograph of an example of the potentially retained item be taken simultaneously with each patient intraoperative radiograph. Three board-certified radiologists retrospectively reviewed these radiographs and follow-up imaging, achieving consensus on interpretation. Adherence to institutional protocol was assessed. Demographic data, surgical documentation, and clinical follow-up data were recorded. Results The incidence of surgical miscounts was 0.9% (183 of 20,820). Only 9% (17 of 183) were resolved by discovery: outside the patient (8 cases); on intraoperative radiographs (5 cases); incidentally on follow-up radiographs (2 cases); and on retrospective review (2 cases). The false-negative rate was 44% (4 of 9). Neither of the 2 retained needles discovered postoperatively was removed. The procedures most prone to miscounts were: esophagogastrectomy (33%; 2 of 6); liver transplant (18%; 12 of 66); and Whipple procedure (16%; 7 of 44). Needles (65%) and sponges (9%) were the items that were overlooked most often. Adherence to the protocol of imaging an example of a potentially retained item was 91% (167 of 183). Conclusions Despite good adherence to a protocol of imaging the potentially retained items, small needles often were not visualized on intraoperative radiographs and were not subsequently removed, without known adverse events. This finding suggests that intraoperative radiography for small needles may be unnecessary, but further study is required.

This study determined the frequency and MRI appearance of osseous and ligamentous injuries in midtarsal (Chopart) sprains and their association with ankle sprains after acute ankle injuries. Prospective diagnosis of and interobserver agreement regarding midtarsal injury among musculoskeletal radiologists were also assessed.Two cohorts with ankle MRI were identified via a digital PACS search: patients who had undergone MRI within 8 weeks after ankle injury and control subjects who had not sustained ankle trauma. Studies were retrospectively reviewed in consensus as well as independently, assessing ligamentous and osseous injury to the Chopart joint (calcaneocuboid and talonavicular joints) and associated lateral collateral and deltoid ligamentous injury. Interobserver agreement was calculated, and prospective radiology reports were reviewed to determine the musculoskeletal radiologist's familiarity with Chopart joint injury.MR images of control subjects (n = 16) and patients with ankle injury (n = 47) were reviewed. The normal dorsal calcaneocuboid and calcaneocuboid component of bifurcate ligaments were variably visualized; the remaining normal ligaments were always seen. Eleven patients (23%) had midtarsal ligamentous and osseous injury consistent with midtarsal sprain (eight acute or subacute, one probable, and two old). Six (75%) of eight acute or subacute cases had coexisting lateral collateral ligament injury. Eighty-nine percent of osseous injuries were reported prospectively, but 83% of ligamentous injuries were missed. Substantial interobserver agreement was achieved regarding diagnosis of midtarsal sprain.Midtarsal sprains are commonly associated with acute ankle injury and with ankle sprains. Presently, midtarsal sprains may be underrecognized by radiologists; thus, greater familiarity with the MRI spectrum of ligamentous and osseous injuries at the Chopart joint is important for accurate diagnosis and clinical management.

The aim of this study is to demonstrate the usefulness of adding 3-dimensional (3D) ultrasound in evaluation of renal transplant vasculature compared to 2-dimensional (2D) Duplex ultrasound.One hundred thirteen consecutive renal transplant 2D and 3D ultrasound examinations were performed and retrospectively reviewed by 2 board-certified radiologists and a radiology resident individually; each reviewed 2D and then 3D images, including color and spectral Doppler. They recorded ability to visualize the surgical anastomosis and rated visualization on a subjective scale. Interobserver agreement was evaluated. Variant anastomosis anatomy was recorded. Tortuosity or stenosis was evaluated if localized Doppler velocity elevation was present.The reviewers directly visualized the anastomosis more often with 3D ultrasound ((Equation is included in full-text article.)=97.5%) compared with 2D ((Equation is included in full-text article.)=54.5%) [difference in means (DM) = 43% (95% confidence interval (CI) = 36%-50%) (P0.001)]. The reviewers visualized the anastomosis more clearly with 3D ultrasound (P0.001) [difference in medians = 0.5, 1.0, and 1.0, (95% CI = 0.5-1.0, 0.5-1.0, and 1.0-1.5)]. Detection of variant anatomy improved with 3D ultrasound by 2 reviewers [DM = 7.1% and 8.9% (95% CI = 1%-13% and 4%-14%, respectively) (P0.05)]. There was high interobserver agreement [(Equation is included in full-text article.)= 95.3%, (95% CI = 91.9%-98.7%) regarding anastomosis visualization among reviewers with wide-ranging experience.Direct visualization of the entire anastomosis was improved with 3D ultrasound. Three-dimensional evaluation improved detection of anatomic variants and identified tortuosity as the likely cause of borderline localized elevation in Doppler velocity. The data added by 3D ultrasound may obviate confirmatory testing with magnetic resonance angiography or computed tomographic angiography after equivocal 2D ultrasound results.

In this study, we investigate the 14 September 1988 U.S.–Soviet Joint Verification Experiment nuclear test at the Semipalatinsk test site in eastern Kazakhstan and two nuclear explosions conducted less than 10 years later at the Chinese Lop Nor test site. These events were very sparsely recorded by stations located within 1600 km, and in each case only three or four stations were available in the regional distance range. We have utilized a regional distance seismic waveform method fitting long‐period, complete, three‐component waveforms jointly with first‐motion observations from regional stations and teleseismic arrays. The combination of long‐period waveforms and first‐motion observations provides a unique discrimination of these sparsely recorded events in the context of the Hudson et al. (1989) source‐type diagram. We demonstrate through a series of jackknife tests and sensitivity analyses that the source type of the explosions is well constrained. One event, a 1996 Lop Nor shaft explosion, displays large Love waves and possibly reversed Rayleigh waves at one station, indicative of a large F ‐factor. We show the combination of long‐period waveforms and P ‐wave first motions are able to discriminate this event as explosion‐like and distinct from earthquakes and collapses. We further demonstrate the behavior of network sensitivity solutions for models of tectonic release and spall‐based tensile damage over a range of F ‐factors and K ‐factors.

Purpose To describe the successful implementation of a structured reporting initiative in a large urban academic radiology department. Methods We describe our process, compromises, and top 10 lessons learned in overhauling traditional reporting practices and comprehensively implementing structured reporting at our institution. To achieve our goals, we took deliberate steps toward consensus building, undertook multistep template refinement, and achieved close collaboration with the technical staff, department coders, and hospital information technologists. Following institutional review board exemption, we audited radiologist compliance by evaluating 100 consecutive cases of 12 common examination types. Fisher exact test was applied to determine significance of association between trainee initial report drafting and template compliance. Results We produced and implemented structured reporting templates for 95% of all departmental computed tomography, magnetic resonance, and ultrasound examinations. Structured templates include specialized reports adhering to the American College of Radiologyʼs Reporting and Data Systems (ACRʼs RADS) recommendations (eg, Lung-RADS and Li-RADS). We attained 94% radiologist compliance within 2 years, without any financial incentives. Conclusions We provide a blueprint of how to successfully achieve structured reporting using a collaborative multistep approach.

Well-resolved moment-tensor solutions reveal information about the sources of seismic waves. In this paper, we introduce a new way of assessing confidence in the regional full moment-tensor inversion via the introduction of the network sensitivity solution (NSS). The NSS takes into account the unique station distribution, frequency band, and signal-to-noise ratio of a given event scenario. The NSS compares both a hypothetical pure source (for example, an explosion or an earthquake) and the actual data with several thousand sets of synthetic data from a uniform distribution of all possible sources. The comparison with a hypothetical pure source provides the theoretically best-constrained source-type distribution for a given set of stations; and with it, one can determine whether further analysis with the data is warranted. The NSS that employs the actual data gives a direct comparison of all other source types with the best-fit source. In this way, one can choose a threshold level of fit in which the solution is comfortably constrained. The method is tested for the well-recorded nuclear test, JUNCTION, at the Nevada Test Site. Sources that fit comparably well to a hypothetical pure explosion recorded with no noise at the JUNCTION data stations have a large volumetric component and are not described well by a double-couple (DC) source. The NSS using the real data from JUNCTION is even more tightly constrained to an explosion because the data contain some energy that precludes fitting with any type of deviatoric source. We also calculate the NSS for the October 2006 North Korea test and a nearby earthquake, where the station coverage is poor and the event magnitude is small. The earthquake solution is very well fit by a DC source, and the best-fit solution to the nuclear test ( M w 4.1) is dominantly explosion.

The past 10 years have brought rapid growth in the development and use of three-dimensional (3D) seismic models of Earth structure at crustal, regional, and global scales. In order to explore the potential for 3D seismic models to contribute to important societal applications, Lawrence Livermore National Laboratory (LLNL) hosted a Workshop on Multi-Resolution 3D Earth Models to Predict Key Observables in Seismic Monitoring and Related Fields on 6–7 June 2007, in Berkeley, California. The workshop brought together academic, government, and industry leaders in research programs developing 3D seismic models and methods for nuclear explosion monitoring and seismic ground-motion hazard assessment. The workshop was designed to assess the current state of 3D seismology and to discuss a path forward for 3D Earth models and techniques— how can they be used to achieve measurable increases in our capabilities for monitoring underground nuclear explosions and characterizing seismic ground-motion hazards? This paper highlights some of the presentations, issues, and discussions at the workshop and proposes two specific paths by which to begin quantifying the potential contribution of progressively refined 3D seismic models in critical applied arenas. Seismic monitoring agencies are tasked with detection, location, and characterization of seismic activity in near real time. In the case of nuclear explosion monitoring or seismic hazard, decisions to further investigate a suspect event or to launch disaster relief efforts may rely heavily on real-time analysis and results. Because these are weighty decisions, monitoring agencies are regularly called upon to meticulously document and justify every aspect of their monitoring system. To meet this level of scrutiny and maintain operational robustness, only mature technologies are considered for operational monitoring systems, so operational technology necessarily lags contemporary research. Current monitoring practice is to use relatively simple Earth models that generally afford analytical prediction of seismic observables (see “Examples of Current …

On August 6, 2007 a local magnitude 3.9 seismic event occurred at 08:48:40 UTC in central Utah. The epicenter is within the boundaries of the Crandall Canyon coal mine (c.f. Pechmann et al., this volume). We performed a moment tensor analysis with complete, three-component seismic recordings from stations operated by the USGS, the University of Utah, and EarthScope. The analysis method inverts the seismic records to retrieve the full seismic moment tensor, which allows for interpretation of both shearing (e.g., earthquakes) and volume-changing (e.g., explosions and collapses) seismic events. The results show that most of the recorded seismic wave energy is consistent with an underground collapse in the mine. We contrast the waveforms and moment tensor results of the Crandall Canyon Mine seismic event to a similar sized tectonic earthquake about 200 km away near Tremonton, Utah, that occurred on September 1, 2007. Our study does not address the actual cause of the mine collapse.

Purpose The aim of this study was to compare the accuracy of coronary atherosclerosis reporting before and after the implementation of a structured reporting chest CT template. Methods A noncardiac, noncontrast chest CT structured reporting template was developed and mandated for department-wide use at a large academic center. The template included the statement "There are no coronary artery calcifications." All noncardiac, noncontrast chest CT examinations reported over 3 days, 1 month after template implementation (structured template group), and from a 3-day period 1 year prior (control group) were retrospectively collected. Final radiology reports were reviewed and designated positive or negative for coronary calcifications. CT images were reviewed in consensus by 2 radiologists, who scored each case for the presence or absence of coronary calcifications, blinded to the original report. Statistical analysis was performed using Pearson χ 2 and Fisher exact tests. Results Sixty-five percent (69 of 106) of structured template group and 58% (62 of 106) of control group cases had coronary calcifications. Reports from the structured template group were more likely to correctly state the presence or absence of coronary atherosclerosis compared with those from the control group (96.2% vs 85.8%; odds ratio, 4.2; 95% confidence interval, 1.3–13.1; P = .008). Structured template group reports were less likely to be falsely negative compared with control group reports (3.8% vs 11.7%; odds ratio, 3.4; 95% confidence interval, 1.0–10.8; P = .03). Conclusions Implementing a structured reporting template improves reporting accuracy of coronary calcifications.

Small underground nuclear explosions need to be confidently detected, identified, and characterized in regions of the world where they have never before occurred. We develop a parametric model of the nuclear explosion seismic source spectrum derived from regional phases that is compatible with earthquake-based geometrical spreading and attenuation. Earthquake spectra are fit with a generalized version of the Brune spectrum, which is a three-parameter model that describes the long-period level, corner-frequency, and spectral slope at high-frequencies. Explosion spectra can be fit with similar spectral models whose parameters are then correlated with near-source geology and containment conditions. We observe a correlation of high gas-porosity (low-strength) with increased spectral slope. The relationship between the parametric equations and the geologic and containment conditions will assist in our physical understanding of the nuclear explosion source.

The last ten years have brought rapid growth in the development and use of three-dimensional (3D) seismic models of earth structure at crustal, regional and global scales. In order to explore the potential for 3D seismic models to contribute to important societal applications, Lawrence Livermore National Laboratory (LLNL) hosted a 'Workshop on Multi-Resolution 3D Earth Models to Predict Key Observables in Seismic Monitoring and Related Fields' on June 6 and 7, 2007 in Berkeley, California. The workshop brought together academic, government and industry leaders in the research programs developing 3D seismic models and methods for the nuclear explosion monitoring and seismic ground motion hazard communities. The workshop was designed to assess the current state of work in 3D seismology and to discuss a path forward for determining if and how 3D earth models and techniques can be used to achieve measurable increases in our capabilities for monitoring underground nuclear explosions and characterizing seismic ground motion hazards. This paper highlights some of the presentations, issues, and discussions at the workshop and proposes a path by which to begin quantifying the potential contribution of progressively refined 3D seismic models in critical applied arenas.

The Arizona Source Phenomenology Experiments (SPE) have resulted in an important dataset for the nuclear monitoring community. The 19 dedicated single-fired explosions and multiple delay-fired mining explosions were recorded by one of the most densely instrumented accelerometer and seismometer arrays ever fielded, and the data have already proven useful in quantifying confinement and excitation effects for the sources. It is very interesting to note that we have observed differences in the phenomenology of these two series of explosions resulting from the differences between the relatively slow (limestone) and fast (granodiorite) media. We observed differences at the two SPE sites in the way the rock failed during the explosions, how the S-waves were generated, and the amplitude behavior as a function of confinement. Our consortium's goal is to use the synergy of the multiple datasets collected during this experiment to unravel the phenomenological differences between the two emplacement media. The data suggest that the main difference between single-fired chemical and delay-fired mining explosion seismograms at regional distances is the increased surface wave energy for the latter source type. The effect of the delay-firing is to decrease the high-frequency P-wave amplitudes while increasing the surface wave energy because of the longer source duration and spall components. The results suggest that the single-fired explosions are surrogates for nuclear explosions in higher frequency bands (e.g., 6-8 Hz Pg/Lg discriminants). We have shown that the SPE shots, together with the mining explosions, are efficient sources of S-wave energy, and our next research stage is to postulate the possible sources contributing to the shear-wave energy.

The basic results from the U.S. Department of Energy’s (DOE’s) Non-Proliferation Experiment (NPE) for seismic signal generation are that the source function for a chemical explosion is equivalent to that of a nuclear explosion of about twice the yield and that the seismic moment measurements are consistent between freefield, local, and regional measurements. In addition, evidence was found that Pn in the Basin and Range province of the western United States is a turning ray and is simply proportional to the source function while the transfer functions for Pg and Lg are low-pass in nature.