Mark D. Price

EXPERIMENTAL QUANTUM ERROR CORRECTION

Quantum error correction is required to compensate for the fragility of the state of a quantum computer. We report the first experimental implementations of quantum error correction and confirm the expected state stabilization. A precise analysis of the decay behavior is performed in alanine and a full implementation of the error correction procedure is realized in trichloroethylene. In NMR computing, however, a net improvement in the signal to noise would require very high polarization. The experiment implemented the three-bit code for phase errors using liquid state NMR.

Nuclear magnetic resonance spectroscopy: an experimentally accessible paradigm for quantum computing

Abstract We present experimental results which demonstrate that nuclear magnetic resonance spectroscopy is capable of emulating many of the capabilities of quantum computers, including unitary evolution and coherent superpositions, but without attendant wave-function collapse. This emulation is made possible by two facts. The first is that the spin active nuclei in each molecule of a liquid sample are largely isolated from the spins in all other molecules, so that each molecule is effectively an independent quantum computer. The second is the existence of a manifold of statistical spin states, called pseudo-pure states, whose transformation properties are identical to those of true pure states. These facts enable us to operate on coherent superpositions over the spins in each molecule using full quantum parallelism, and to combine the results into deterministic macroscopic observables via thermodynamic averaging. We call a device based on these principles an ensemble quantum computer . Our results show that it is indeed possible to prepare a pseudo-pure state in a macroscopic liquid sample under ambient conditions, to transform it into a coherent superposition, to apply elementary quantum logic gates to this superposition, and to convert it into the equivalent of an entangled state. Specifically, we have: • - implemented the quantum XOR gate in two different ways, one using Pound-Overhauser double resonance, and the other using a spin-coherence double resonance pulse sequence; • - demonstrated that the square root of the Pound-Overhauser XOR corresponds to a conditional rotation, thus confirming that NMR spectroscopy provides a universal set of gates; • - devised a spin-coherence implementation of the Toffoli gate, and confirmed that it transforms the equilibrium state of a four-spin system as expected; • - used standard gradient-pulse techniques in NMR to equalize all but one of the populations in a two-spin system, thus obtaining the basic pseudo-pure state that corresponds to |00〉; • - validated that one can identify which basic pseudo-pure state is present by transforming it into one-spin superpositions, whose associated spectra jointly characterize the state; • - applied the spin-coherence XOR gate to a one-spin superposition to create an entangled state, and confirmed its existence by detecting the associated double-quantum coherence via gradient-echo methods.

Self-calibrating parallel imaging with automatic coil sensitivity extraction.

Calibration of the spatial sensitivity functions of coil arrays is a crucial element in parallel magnetic resonance imaging (PMRI). The most common approach has been to measure coil sensitivities directly using one or more low‐resolution images acquired before or after accelerated data acquisition. However, since it is difficult to ensure that the patient and coil array will be in exactly the same positions during both calibration scans and accelerated imaging, this approach can introduce sensitivity miscalibration errors into PMRI reconstructions. This work shows that it is possible to extract sensitivity calibration images directly from a fully sampled central region of a variable‐density k‐space acquisition. These images have all the features of traditional PMRI sensitivity calibrations and therefore may be used for any PMRI reconstruction technique without modification. Because these calibration data are acquired simultaneously with the data to be reconstructed, errors due to sensitivity miscalibration are eliminated. In vivo implementations of self‐calibrating parallel imaging using a flexible coil array are demonstrated in abdominal imaging and in real‐time cardiac imaging studies. Magn Reson Med 47:529–538, 2002.

Recent advances in image reconstruction, coil sensitivity calibration, and coil array design for SMASH and generalized parallel MRI

Parallel magnetic resonance imaging (MRI) techniques use spatial information from arrays of radiofrequency (RF) detector coils to accelerate imaging. A number of parallel MRI techniques have been described in recent years, and numerous clinical applications are currently being explored. The advent of practical parallel imaging presents various challenges for image reconstruction and RF system design. Recent advances in tailored SiMultaneous Acquisition of Spatial Harmonics (SMASH) image reconstructions are summarized. These advances enable robust SMASH imaging in arbitrary image planes with a wide range of coil array geometries. A generalized formalism is described which may be used to understand the relations between SMASH and SENSE, to derive typical implementations of each as special cases, and to form hybrid techniques combining some of the advantages of both. Accurate knowledge of coil sensitivities is crucial for parallel MRI, and errors in calibration represent one of the most common and the most pernicious sources of error in parallel image reconstructions. As one example, motion of the patient and or the coil array between the sensitivity reference scan and the accelerated acquisition can lead to calibration errors and reconstruction artifacts. Self-calibrating parallel MRI approaches that address this problem by eliminating the need for external sensitivity references are reviewed. The ultimate achievable signal-to-noise ratio (SNR) for parallel MRI studies is closely tied to the geometry and sensitivity patterns of the coil arrays used for spatial encoding. Several parallel imaging array designs that depart from the traditional model of overlapped adjacent loop elements are described.

Coil-by-coil image reconstruction with SMASH

The SiMultaneous Acquisition of Spatial Harmonics (SMASH) technique uses linear combinations of undersampled datasets from the component coils of an RF coil array to reconstruct fully sampled composite datasets in reduced imaging times. In previously reported implementations, SMASH reconstructions were designed to reproduce the images that would otherwise be obtained by simple sums of fully gradient encoded component coil images. This strategy has left SMASH images vulnerable to phase cancellation artifacts when the sensitivities of RF coil array elements are not suitably phase‐aligned. In fully gradient encoded imaging schemes these artifacts can be eliminated using a variety of methods for combining the individual coil images, including matched filter combinations as well as sum of squares combinations. Until now, these reconstruction schemes have been unavailable to SMASH reconstructions as SMASH produced a final composite image directly from the raw component coil k‐space datasets. This article demonstrates a modification to SMASH that allows reconstruction of a full set of accelerated individual component coil images by fitting component coil sensitivity functions to a complete set of spatial harmonics tailored for each coil in the array. Standard component coil combinations applied to the individual reconstructed images produce final composite images free of phase cancellation artifacts. Magn Reson Med 46:619–623, 2001.

Effect of timing of ACL reconstruction in surgery and development of meniscal and chondral lesions.

Abstract Purpose: To investigate whether a delay in the timing of surgery of > 6 months compared with performing the surgery > 6 months after the anterior cruciate ligament (ACL) injury leads to an increased risk of injuries or degenerative changes in the ACL-deficient knee. Methods: Patients who underwent primary ACL reconstruction at an academic tertiary care center, and had preoperative magnetic resonance imaging (MRI) performed within 2 months of the time of the ACL injury were included. The prevalence of degenerative changes at the time of surgery was assessed and related to the timing of ACL surgery, with “early reconstruction” defined as a surgery performed ≤ 6 months and “delayed reconstruction” defined as surgery performed > 6 months after ACL injury. “New” meniscal tears were defined as lesions detected at the time of surgery that were not detected by MRI. Results: Of 195 patients who were selected based on inclusion criteria, 171 patients underwent surgery ⩽ 6 months after their ACL injury, and 24 patients underwent surgery > 6 months after their ACL injury. The prevalence of new medial meniscal tears in the early reconstruction group was 4.1%, while in the delayed reconstruction group, the prevalence was 16.7% (P = 0.012). Conclusion: A delay in the timing of ACL reconstruction from ≤ 6 months to > 6 months following injury is associated with a significant increase in the prevalence of medial meniscal tears (P = 0.012), with a relative risk of 4.07 (CI, 1.29-12.88). Conclusion: A delay in the timing of ACL reconstruction from > 6 months to < 6 months following injury is associated with a significant increase in the prevalence of medial meniscal tears (P = 0.012), with a relative risk of 4.07 (CI, 1.29.12.88).

Management of complications after reverse shoulder arthroplasty

Reverse total shoulder arthroplasty (RTSA) has become the treatment of choice for patients with rotator cuff arthropathy. Complication rate after RTSA has been reported to be three to five times that of conventional total shoulder arthroplasty. Intraoperative and postoperative complications include neurological injury, infection, dislocation or instability, acromial or scapular spine fracture, hematoma, and scapular notching. Knowledge of optimal component placement along with preoperative planning and recognition of risk factors are essential in optimizing patient outcome. The purpose of this review article is to identify the most common and serious complications associated with the RTSA and discuss the current methods of management. Complications after RTSA pose a significant challenge for healthcare providers and economic burden to society. Therefore, it is essential to make the proper diagnosis and develop and implement early management plans to improve patient outcome and satisfaction.

Gender differences in osteoarthritis

G olda Meir’s quip that Bwhether women are better than men I cannot sayVbut I can say they are certainly no worse,[ is certainly true in many aspects of life but seems to be less and less true when it comes to orthopedic disease and injury. Gender has been made a culprit in a wide array of orthopedic diseases including osteoarthritis (OA), osteoporosis, and knee ligament injuries, to name but a few. Although research continues into developing a better understanding of the relationship between genetics, gender, and OA, several key features have already emerged. It is known that articular cartilage has estrogen receptors, that OA heritability is greater in women than men, that certain genes may be responsible for the development of OA in women, and that biomechanical differences between the sexes play some role in the development of OA. With the preponderance of the emerging literature, the notion that existed as recently as 15 years ago that women are simply Blittle men[ has been firmly put to rest. This issue of gender difference is of particular concern when it comes to the development of OA as it continues to be diagnosed more frequently in women than men and will likely continue to grow as the population increases in both age and weight. Cartilage defects have been shown to lead to the development of OA in a rabbit articular cartilage model, and the presence of such defects in humans is known to correlate with magnetic resonance imaging signs of osteoarthrosis and osteophyte formation in persons with OA. The severity of these defects correlate well with other hallmarks of OA such as decreased cartilage volume and increased type II collagen breakdown. However, there are currently few data that can shed light on the question as to whether these defects lead to OA or are a result of it. The few existing studies that have analyzed the progression of known cartilage lesions have found the progression of some lesions to more severe lesions over time and an association between this progression and gender. In the current issue of the journal, Hanna et al seek to further define this relationship. Like previous studies, they used magnetic resonance imaging (MRI) to quantify cartilage defects in the knee and study their change over time. However, unlike previous studies, they took a sample of the population presumably without documented evidence of OA. Participants were excluded on the basis of a previous clinical diagnosis of OA, knee pain for more than 24 hours at any time in the last 5 years, previous knee injury that required nonweight bearing for more than 24 hours, or prior surgery. Participants were imaged at baseline and then an average of 2.3 years later so that the amount of cartilage loss and the progression of cartilage defects could be tracked. Annual percentage loss of both tibial and patella cartilage, when adjusted for age, height, weight, and baseline tibial bone area, was significantly greater in women. Moreover, the progression of tibiofemoral cartilage defects was significantly correlated with female gender. Interesting to note, however, was that the progression of patellofemoral cartilage defects, after adjusting for confounders, was not associated with gender. This work represents a key next step in understanding the pathogenesis of OA, and well-designed natural history studies remain as useful and important as they are rare. There are some points about the current study that deserve a mention. The authors did not make note of other possible abnormalities often seen in the knee at the time of MRI, presumably owing to the fact that a limited set of imaging sequences were performed. However, it is well known that anterior cruciate ligament tears or meniscal injuries can predispose to the development of OA in a manner that may be gender neutral. At the very least, the presence of such injuries would serve as a potential confounder. In addition, a 5-year history of freedom from knee injury may not be enough because the development of OA can be seen much later. Finally, there is some concern surrounding the lack of a significant difference in the progression of patellofemoral cartilage defects. This result was unexpected because it has been shown that the contact forces across the patellofemoral joint are different between men and women and that there is more patellofemoral arthritis in women. Some of these concerns raise the question as to whether a single MRI scan at two time points is adequate to tell the whole story. It may be that more sensitive MRI techniques for measuring cartilage degeneration are necessary to clarify these issues. Ultimately, it is likely that the interplay of several factors will dictate the course of one’s ultimate cartilage health. Studies such as this one serve as an important reminder that the development of these injuries is both multifactorial and insidious. An injury to the knee in the remote past in a person with a particular genetic framework and particular body habitus will be predisposed to developing OA in a particular location, whereas a similar set of circumstances may have a completely different effect in another person. The basic understanding that these cartilage lesions are progressive, positional, and gender dependent serves as an important node in the web of genetics, biomechanics, and lifestyle that determines who is going to get OA.

The Latarjet Procedure at the National Football League Scouting Combine: An Imaging and Performance Analysis

Background: The Latarjet procedure is commonly performed in the setting of glenoid bone loss for treatment of recurrent anterior shoulder instability; however, little is known regarding the outcomes of this procedure in elite American football players. Purpose: (1) Determine the prevalence, clinical features, and imaging findings of elite college football athletes who present to the National Football League (NFL) Combine with a previous Latarjet procedure and (2) describe these athletes’ performance in the NFL in terms of draft status and initial playing time. Study Design: Case series; Level of evidence, 4. Methods: After review of all football players who participated in the NFL Combine from 2009 to 2016, any player with a previous Latarjet procedure was included in this study. Medical records, position on the field, and draft position were recorded for each player. In addition, imaging studies were reviewed to determine fixation type, hardware complications, and status of the bone block. For those players who were ultimately drafted, performance was assessed based on games played and started, total snaps, and percentage of eligible snaps in which the player participated during his rookie season. Results: Overall, 13 of 2617 (<1%) players at the combine were identified with a previous Latarjet procedure. Radiographically, 8 of 13 (61%) showed 2-screw fixation, while 5 of 13 (39%) had 1 screw. Of the 13 players, 6 (46%) players demonstrated hardware complications. All players had evidence of degenerative changes on plain radiographs, with 10 (77%) graded as mild, 1 (8%) as moderate, and 2 (15%) as severe according to the Samilson Prieto classification. Six of the 13 (46%) players went undrafted, while the remaining 7 (54%) were drafted; however, no player participated in more than half of the plays for which he was eligible during his rookie season. Conclusion: Only a small percentage of players at the NFL Combine (<1%) had undergone a Latarjet procedure. High rates of postoperative complications and radiographically confirmed degenerative change were observed. Athletes who had undergone a Latarjet procedure demonstrated a variable amount of playing time, but none participated in more than half of their eligible plays during their rookie season.

Total Elbow Arthroplasty in the United States: Evaluation of Cost, Patient Demographics, and Complication Rates.

Total elbow arthroplasty (TEA) is utilized in the treatment of rheumatoid and post-traumatic elbow arthritis. TEA is a relatively low volume surgery in comparison to other types of arthroplasty and therefore little is known about current surgical utilization, patient demographics and complication rates in the United States. The purpose of our study is to evaluate the current practice trends and associated in-patient complications of TEA at academic centers in the United States. We queried the University Health Systems Consortium administrative database from 2007 to 2011 for patients who underwent an elective TEA. A descriptive analysis of demographics was performed which included patient age, sex, race, and insurance status. We also evaluated the following patient clinical benchmarks: hospital length of stay (LOS), hospital direct cost, in-hospital mortality, complications, and 30-day readmission rates. Our cohort consisted of 3146 adult patients (36.5% male and 63.5% female) with an average age of 58 years who underwent a total elbow arthroplasty (159 academic medical centers) in the United States. The racial demographics included 2334 (74%) Caucasian, 285 (9%) black, 236 (7.5%) Hispanic, 16 (0.5%) Asian, and 283 (9%) other patients. The mean LOS was 4.2±5 days and the mean total direct cost for the hospital was 16,300±4000 US Dollars per case. The overall inpatient complication rate was 3.1% and included mortality <1%, DVT (0.8%), re-operation (0.5%), and infection (0.4%). The 30-day readmission rate was 4.4%. TEA is a relatively uncommon surgery in comparison to other forms of arthroplasty but is associated with low in-patient and 30-day perioperative complication rate. Additionally, the 30-day readmission rate and overall hospital costs are comparable to the traditional total hip and knee arthroplasty surgeries.