On the connection between uniqueness from samples and stability in Gabor phase retrieval.

Gabor phase retrieval is the problem of reconstructing a signal from only the magnitudes of its Gabor transform. Previous findings suggest a possible link between unique solvability of the discrete problem (recovery from measurements on a lattice) and stability of the continuous problem (recovery from measurements on an open subset of R2). In this paper, we close this gap by proving that such a link cannot be made. More precisely, we establish the existence of functions which break uniqueness from samples without affecting stability of the continuous problem. Furthermore, we prove the novel result that counterexamples to unique recovery from samples are dense in L2(R). Finally, we develop an intuitive argument on the connection between directions of instability in phase retrieval and certain Laplacian eigenfunctions associated to small eigenvalues.

Hamstring tendon autografts do not show complete graft maturity 6 months postoperatively after anterior cruciate ligament reconstruction.

PURPOSE: In this prospective, double-center cohort study, we aim to assess how the anterior cruciate ligament (ACL) signal intensity on magnetic resonance imaging (MRI) potentially varies between a group of patients with anatomic ACL reconstruction using autogenous hamstring grafts 6 months postoperatively and a healthy ACL control group, and how MRI-based graft signal intensity is related to knee laxity. METHODS: Sixty-two consecutive patients who underwent ACL reconstruction using quadrupled hamstring tendon autograft were prospectively invited to participate in this study, and they were evaluated with MRI after 6 months of follow-up. 50 patients with an MRI of their healthy ACL (Clinica Luganese, Lugano, Switzerland) and 12 patients of their contralateral healthy knee (Department of Orthopaedic and Trauma Surgery, Medical University of Vienna, Austria) served as the control group. To evaluate graft maturity, the signal-to-noise quotient (SNQ) was measured in three regions of interest (ROIs) of the proximal, mid-substance and distal ACL graft and the healthy ACL. KT-1000 findings were obtained 6 months postoperatively in the ACL reconstruction group. Statistical analysis was independently performed to outline the differences in the two groups regarding ACL intensity and the correlation between SNQ and KT-1000 values. RESULTS: There was a significant difference in the mean SNQ between the reconstructed ACL grafts and the healthy ACLs in the proximal and mid-substance regions (p = 0.001 and p = 0.004). The distal region of the reconstructed ACL showed a mean SNQ similar to the native ACL (n.s). Patients with a KT-1000 between 0 and 1 mm showed a mean SNQ of 0.1; however, a poor correlation was found between the mean SNQ and KT-1000 findings, probably due to the small sample size of patients with higher laxity. CONCLUSION: After 6 months of follow-up, hamstring tendon autografts for anatomic ACL reconstruction do not show equal MRI signal intensity compared to a healthy ACL and should therefore be considered immature or at least not completely healed even if clinical laxity measurement provides good results. However, in the case of a competitive athlete, who is clinically stable and wants to return to sports at 6 months, performing an MRI to confirm the stage of graft healing might be an option. LEVEL OF EVIDENCE: Prospective, comparative study II.

Conventional versus Smart Wireless Navigation in Total Knee Replacement: Similar Outcomes in a Randomized Prospective Study.

Purpose The development of new computer-assisted navigation technologies in total knee arthroplasty (TKA) has attracted great interest; however, the debate remains open as to the real reliability of these systems. We compared conventional TKA with last generation computer-navigated TKA to find out if navigation can reach better radiographic and clinical outcomes. Methods Twenty patients with tricompartmental knee osteoarthritis were prospectively selected for conventional TKA ( n = 10) or last generation computer-navigated TKA ( n = 10). Data regarding age, gender, operated side, and previous surgery were collected. All 20 patients received the same cemented posterior-stabilized TKA. The same surgical instrumentation, including alignment and cutting guides, was used for both the techniques. A single radiologist assessed mechanical alignment and tibial slope before and after surgery. A single orthopaedic surgeon performed clinical evaluation at 1 year after the surgery. Wilcoxon's test was used to compare the outcomes of the two groups. Statistical significance was set at p < 0.05. Results No significant differences in mechanical axis or tibial slope was found between the two groups. The clinical outcome was equally good with both techniques. At a mean follow-up of 15.5 months (range, 13-25 months), all patients from both groups were generally satisfied with a full return to daily activities and without a significance difference between them. Conclusion Our data showed that clinical and radiological outcomes of TKA were not improved by the use of computer-assisted instruments, and that the elevated costs of the system are not warranted. Level of Evidence This is a Level II, randomized clinical trial.

Gemella morbillorum deep brain abscess successfully treated with combined stereotactic, medical, and imaging approach.

A rare case of brain abscess due to Gemella morbillorum, a normal inhabitant of the oral cavity, is presented. The aim of this report is to draw the attention of radiology literature readers to this little known pathogen, which caused a potentially life-threatening condition in an immunocompetent young man, and to emphasise the usefulness of a combined stereotactic, medical, and imaging approach to deep-located brain abscesses.

Diagnosis of hepatocellular carcinoma complicating liver cirrhosis: utility of repeat ultrasound-guided biopsy after unsuccessful first sampling.

PURPOSE: To evaluate the utility of a second ultrasound-guided fine-needle biopsy of liver nodules thought to be hepatocellular carcinoma when the original biopsy has failed to provide a reliable diagnosis. METHODS: Thirty-seven cirrhotic patients underwent ultrasound-guided fine-needle biopsy of liver nodules that were subsequently diagnosed as hepatocellular carcinoma. Each biopsy involved a single puncture with a 20 G cutting needle, which yielded pathologic material used both for cytologic and histologic studies. In 23 cases (mean diameter of nodules 48 mm) the biopsy furnished exclusively necrotic material (non-diagnostic subgroup); in the other 14 cases (mean diameter 26 mm) the biopsy yielded no neoplastic elements (false-negative subgroup). All 37 nodules were subjected to repeat biopsies performed in the same manner. RESULTS: The repeat biopsies provided a diagnosis of hepatocellular carcinoma in six of the 23 patients from the non-diagnostic subgroup and in seven of the 14 in the false-negative subgroup. Overall, repeat biopsy produced a diagnostic gain of 35.1%. CONCLUSION: The chance of success with repeat biopsy of hepatocellular carcinoma is limited and may depend to some extent on the characteristics of the lesions (i.e., areas of necrosis in large nodules, well-differentiated cellular populations in small ones).

Diagnosis of liver nodules observed in chronic liver disease patients during ultrasound screening for early detection of hepatocellular carcinoma.

OBJECTIVES: The aim of our study was to evaluate the nature of focal liver lesions detected during the ultrasound follow-up of a population (prevalently anti-hepatitis C virus [anti-HCV] positive) with chronic liver disease. METHODS: The study population consisted of 1827 consecutive newly diagnosed chronic liver disease cases without liver nodules at enrollment. Patients were screened at 4-month intervals by ultrasound and serum alpha-fetoprotein assessment. All lesions detected on imaging studies (except those accompanied by diagnostic a-fetoprotein levels) were subjected to biopsy (histology and cytology). RESULTS: During the 7-yr follow-up period (mean = 43.1 months), one or more solid focal lesions were found in 287 patients. a-Fetoprotein was diagnostic for hepatocellular carcinoma in 51 patients. Ultrasound-guided fine-needle biopsy was performed in the remaining 236 patients, yielding a diagnosis in 214: 198 hepatocellular carcinomas, 11 dysplastic nodules, and five B-cell non-Hodgkin's lymphomas (all confined to the liver and all in patients with chronic HCV infection). Twenty-two patients with nondiagnostic biopsies received diagnoses of hepatocellular carcinoma (20) or dysplastic nodules (two) based on arteriography or surgical biopsy. CONCLUSIONS: Focal lesions arising in patients with HCV-related chronic liver disease can be other than hepatocellular carcinoma, and ultrasound-guided fine-needle biopsy plays an important role in their diagnosis. The prevalence of non-Hodgkin's lymphoma in this selected population was 0.31%. The fact that all five lymphoma patients had cirrhosis related to hepatitis C strengthens the hypothesis of an etiological correlation between the latter infection and B-cell lymphoproliferative disorders.