The neural cell adhesion molecule (NCAM) as a regulator of cell-cell interactions

The neural cell adhesion molecule (NCAM) can influence a number of diverse intercellular events, including junctional communication, the association of axons with pathways and targets, and signals that alter levels of neurotransmitter enzymes. These pleiotropic effects appear to reflect the ability of NCAM to regulate membrane-membrane contact required to initiate specific interactions between other molecules. Such regulation can occur through changes in either NCAM expression or the molecule's content of polysialic acid (PSA). When NCAM with a low PSA content is expressed, adhesion is increased and contact-dependent events are triggered. In contrast, the large excluded volume of NCAM PSA can inhibit cell-cell interactions through hindrance of overall membrane apposition.

MR Fingerprinting of Adult Brain Tumors: Initial Experience

BACKGROUND AND PURPOSE

MR fingerprinting allows rapid simultaneous quantification of T1 and T2 relaxation times. This study assessed the utility of MR fingerprinting in differentiating common types of adult intra-axial brain tumors.

MATERIALS AND METHODS

MR fingerprinting acquisition was performed in 31 patients with untreated intra-axial brain tumors: 17 glioblastomas, 6 World Health Organization grade II lower grade gliomas, and 8 metastases. T1, T2 of the solid tumor, immediate peritumoral white matter, and contralateral white matter were summarized within each ROI. Statistical comparisons on mean, SD, skewness, and kurtosis were performed by using the univariate Wilcoxon rank sum test across various tumor types. Bonferroni correction was used to correct for multiple-comparison testing. Multivariable logistic regression analysis was performed for discrimination between glioblastomas and metastases, and area under the receiver operator curve was calculated.

RESULTS

Mean T2 values could differentiate solid tumor regions of lower grade gliomas from metastases (mean, 172 ± 53 ms, and 105 ± 27 ms, respectively; P = .004, significant after Bonferroni correction). The mean T1 of peritumoral white matter surrounding lower grade gliomas differed from peritumoral white matter around glioblastomas (mean, 1066 ± 218 ms, and 1578 ± 331 ms, respectively; P = .004, significant after Bonferroni correction). Logistic regression analysis revealed that the mean T2 of solid tumor offered the best separation between glioblastomas and metastases with an area under the curve of 0.86 (95% CI, 0.69-1.00; P < .0001).

CONCLUSIONS

MR fingerprinting allows rapid simultaneous T1 and T2 measurement in brain tumors and surrounding tissues. MR fingerprinting-based relaxometry can identify quantitative differences between solid tumor regions of lower grade gliomas and metastases and between peritumoral regions of glioblastomas and lower grade gliomas.

Positron emission tomography and breast masses: comparison with clinical, mammographic, and pathological findings

BACKGROUND

Positron emission tomography (PET) is a means of imaging tissue based upon its metabolic activity. Initial studies in the field of oncology suggest that PET may be useful for diagnosis, staging, and treatment of various tumors.

METHODS

Twenty-eight patients with 37 breast lesions were studied with PET using [fluorine-18] 2-deoxy-2-fluoro-D-glucose (FDG) to assess which clinicopathological characteristics relate to FDG accumulation by the primary tumor.

RESULTS

PET-FDG was found to successfully discriminate malignant from benign breast lesions (p = 0.02) and identify axillary lymph node metastases. FDG uptake by the primary tumor was found to be independent of age, menopausal status, race, tumor size, laterality, histologic differentiation, ploidy, DNA index, estrogen or progesterone receptor value, pathologic stage, and serum glucose. Higher tumor nuclear grade and S-phase were associated with more FDG accumulation by the primary tumor compared with normal breast tissue. PET-FDG correctly identified five malignant lesions that were indeterminant for cancer both on clinical breast examination and mammography and identified one occult cancer that was neither palpable nor apparent mammographically. PET-FDG correctly identified clinical occult axillary metastatic cancer in five patients.

CONCLUSIONS

This study shows that PET-FDG imaging can distinguish malignant from benign breast lesions among a diverse group of patients and suggests that PET-FDG may not only allow for preoperative staging of patients but also provide information about prognosis. This study provides impetus for continued research into PET-FDG imaging of breast lesions, which could have a major impact on the treatment of breast cancer.

Changes in neural cell adhesion molecule (NCAM) structure during vertebrate neural development

Changes in carbohydrate and polypeptide form of the neural cell adhesion molecule (NCAM) have been documented during the development of central nervous system tissue in both chicken and frog. The carbohydrate variations reflect a high and low content of polysialic acid, and for the two vertebrates examined the expression of these forms is similar. At very early stages of neural development NCAM with a low content of polysialic acid is present, during histogenesis of the central nervous system NCAM with a high content of polysialic acid dominates, and there is a gradual return to NCAM with a low content of polysialic acid as the animals approach maturity. In contrast, the order of expression of the major NCAM polypeptide forms is different in the chicken and frog. These findings suggest that changes in sialic acid are a fundamental aspect of the function of NCAM in development, whereas NCAM polypeptide differences may affect events associated with a particular vertebrate. Studies have demonstrated that a decreased sialic acid content enhances the adhesion properties of NCAM. On this basis, we propose that NCAM with a low content of polysialic acid functions both to maintain integrity of neuroepithelium during morphogenesis of the early embryo and to stabilize differentiated structures in the adult, while the decreased adhesive function of NCAM with a high content of polysialic acid provides more plasticity in cell interactions during cell migration, axon outgrowth, and formation of neural circuits.

Neural cell adhesion molecule expression in Xenopus embryos

The spatiotemporal pattern of expression of the neural cell adhesion molecule NCAM was mapped immunohistochemically in embryos of the frog Xenopus, from blastula to early swimming stages, using a polyclonal antibody that recognizes Xenopus NCAM. The neural plate stage was the earliest at which NCAM could be detected. The initial sites of NCAM immunoreactivity were neural ectoderm, somitic mesoderm, and chordamesoderm. During formation of the neural tube, NCAM immunoreactivity became restricted to the neuroectoderm and its derivatives. During closure of the neural tube and for 2-4 hr thereafter, NCAM was expressed in a distinctive radial pattern in coronal sections of the neural tube. NCAM was observed in neural crest cells before migration and after formation of cranial and spinal ganglia. During the period of initial neurite outgrowth, NCAM became concentrated in the developing central nerve fiber pathways. NCAM was seen on peripheral nerves from the time of their initial outgrowth and it was strongly expressed at neuromuscular junctions during the period of their formation. These results show that NCAM is expressed after neural induction and functions during morphogenesis of the neural plate and tube, some neural crest derivatives, development of nerve fiber tracts, and formation of neuromuscular connections.

The effect of imaging guidelines on the number and quality of outpatient radiographic examinations

OBJECTIVE

A significant percentage of outpatient diagnostic radiology is performed by nonradiologists. Studies have shown nonradiologists have higher utilization and cost, as well as quality problems. We sought to determine if, in a managed care environment, a set of guidelines limiting imaging privileges of nonradiologist physicians could decrease imaging costs while ensuring that equipment and personnel providing imaging were of the highest quality.

MATERIALS AND METHODS

We determined the number and type of radiographic imaging studies performed the year after these guidelines were set in place (1997) and compared these findings with those of the year before the guidelines were established (1995) and with preguideline trends. We established quality criteria and, based thereon, inspected imaging offices.

RESULTS

The number of radiographic examinations per 1000 enrollees decreased 20-25% from the previous trend. Nonradiologists' share of the total fell from 39% to 15%. No deficiencies were found in the inspection of five radiologists' offices, whereas significant deficiencies of equipment, equipment maintenance, or documentation of the examinations performed were found in 78% of nonradiologists' offices. None of the quality indicators monitored by the health plan showed significant change.

CONCLUSION

Specific guidelines can effect change in the location and number of radiologic examinations performed, with an improvement in the quality of the studies and a decrease in radiation dose and cost. No decline in quality of care appears to result, despite claims by opponents to such changes that widespread serious quality impairment would occur.

The job market in diagnostic radiology 1999: updated findings from a help wanted index of job advertisements

OBJECTIVE

The purpose of this article is to report 1999 data on the job market in diagnostic radiology detected using a help wanted index of job advertisements and to profile trends in practice type, location, and subspecialty using our previously published data as a basis for comparison.

MATERIALS AND METHODS

Each advertised job for a diagnostic radiologist in the American Journal of Roentgenology and RADIOLOGY: between January 1991 and December 1999 was coded by practice type, location, and subspecialty.

RESULTS

In 1999, 3926 positions were advertised for diagnostic radiologists, representing a 75% increase from 1998. Private practice jobs, which represented 53% of advertisements from 1991 through 1994 and 64% of ads from 1995 through 1998, increased to 66% of ads in 1999. Geographic trends in 1999 were characterized by a relative increase of jobs in the Midwest and California and a decrease in percentage (but increase in total number of ads) in the Northeast and Southwest. The demand for subspecialists continued in 1999, with only 34% of ads placed for general radiologists. A relative increase in demand for neuroradiologists, mammographers, and abdominal imagers was also seen in 1999 in comparison with previously published data from 1995 through 1998.

CONCLUSION

The demand for diagnostic radiologists continues to rise, with more ads placed in 1999 than any other year from 1991 through 1998. Using a help wanted index of job advertisements, we have created an indicator of changes in the diagnostic radiology job market with specific reference to practice type, geographic location, and subspecialty training.

Hiring of diagnostic radiologists in 1998

OBJECTIVE

We sought to determine the 1998 hiring activities of physician practices with respect to diagnostic radiologists.

MATERIALS AND METHODS

A survey was mailed to a sample of 970 radiology practices in the spring through fall of 1999; 73.0% responded. Responses were weighted to represent all practices in the United States providing diagnostic radiology services. Findings were compared with results of similar surveys from previous years.

RESULTS

In 1998, multiradiologist groups sought to hire 2299 (+/-148 [standard error]) diagnostic radiologists, an increase of 20% from 1977. Positions offered in 1998 were split almost equally between expansion positions and replacements for those who had left a practice. Another 422 (+/-58) positions had been vacated that practices did not seek to refill. In 1998, 621 (+/-57) diagnostic radiologists left active practice, which is more than the usual number of approximately 400 annually but less than the approximately 800 of 1996 and 1997. There was no significant association between hiring activity and the self-perceived effect of managed care on a group.

CONCLUSION

The pace of hiring and turnover of diagnostic radiologists increased in 1998. Positions available continue to exceed radiologists available to fill them; the excess was approximately 330 positions, which is not significantly different from the excess reported for 1997, but is higher than the (not statistically significant) net shortfall of 51 positions estimated for 1996.

The job market for radiology residents and fellows graduating in 1994

OBJECTIVE

In response to anecdotal reports of grave deterioration in the job market for graduates of radiology training programs, the American College of Radiology undertook a systematic appraisal of this job market for 1994.

MATERIALS AND METHODS

Between mid-April and mid-May 1994, the American College of Radiology surveyed 40 directors of randomly chosen diagnostic radiology training programs and 20 directors of randomly chosen radiation oncology training programs. We achieved a response rate of 80% or more in both categories. The survey asked, among other questions, the number of graduates, how many had jobs, the number of offers received by graduates this year and last, and how difficult the job market was relative to recent years.

RESULTS

Directors reported that 96% of graduating residents and 86% of graduating diagnostic fellows had commitments for positions. Of those with commitments, 94% of residents and 84% of diagnostic fellows were reported to have jobs that reasonably matched their training and job goals. Program directors estimated that the average graduate received two job offers but, on average, rated the job market as somewhat more difficult than was typical of recent years and reported that 1993 graduates had received more job offers. Plans to change size were reported for one fourth of programs, but the job market situation was not an important reason for these planned changes.

CONCLUSION

Although the overwhelming majority of 1994 graduates obtained jobs, and these overwhelmingly were jobs of interest, program directors reported that the job market was weakening. Given the changes in the socioeconomic environment--managed care, for example--and the changing job market, training programs should give more attention to the job market in planning for changes in size.

Expression and function of neural cell adhesion molecule during limb regeneration

The neural cell adhesion molecule (NCAM) has been detected in regenerating limb bud of adult newts in addition to brain and peripheral nerves. In the regenerating tissue, NCAM was found primarily on mesenchymal cells and also in wound epidermis. Infusion of Fab fragments of antibodies to NCAM into limb buds at the early blastema stage delayed the regenerative process. Previous studies have indicated that NCAM serves as a homophilic ligand for adhesion among cells that express this molecule and, in doing so, can influence the interaction of nerves with their environment. The expression of NCAM in regenerating limb and the effects of antibody infusion are therefore consistent with the observation that limb regeneration requires interactions among axons and mesenchymal cells.

Do interventional radiologists pose a significant threat to the practice of vascular surgery?

PURPOSE

Vascular surgeons have become concerned recently about perceived threats to their practices posed by the growth of interventional radiology. The authors studied nationwide 1996 Medicare Part B procedure data to determine the seriousness of these threats.

MATERIALS AND METHODS

The national Health Care Financing Administration (HCFA) Physician/Supplier Procedure Summary Master File for 1996 was searched. Two hundred thirteen distinct Current Procedural Terminology (CPT-4) codes were identified for therapeutic surgical and percutaneous interventional procedures performed to treat noncardiac vascular diseases. For each code, determination was made of total volume, specialty of the physician providers, and Medicare Part B reimbursement dollars paid to the providers as professional fees. In view of the conflicts among various specialties over peripheral vascular interventions, the authors also determined the percentages of these procedures performed by radiologists, surgeons, cardiologists, and other physicians.

RESULTS

A total of 759,548 noncardiac therapeutic vascular procedures (operations or percutaneous interventions) were performed during 1996 in patients receiving Medicare benefits. Radiologists performed 135,103 (17.8%) of these procedures but received only 10.4% of professional reimbursements. By contrast, surgeons performed 510,871 (67.3%) procedures, but received 78.0% of professional reimbursements. Cardiologists performed 4.7% of procedures and other specialists performed the remaining 10.3%. Radiologists performed 75.5% of percutaneous transluminal angioplasties, the majority of thrombolysis procedures, stent placements, and portal decompression procedures, and approximately half of inferior vena cava interruptions. Cardiologists performed 12.6% of percutaneous transluminal angioplasties, surgeons performed 6.3%, and other specialists performed 5.6%.

CONCLUSIONS

In terms of overall physician workload and professional reimbursements paid for invasive treatment of all types of noncardiac vascular disease, surgeons predominate and do not appear to be seriously threatened by interventional radiologists. Radiologists perform three-fourths of noncardiac percutaneous transluminal angioplasties and a majority of other percutaneous interventional therapies for vascular disease, but some inroads have been made by cardiologists and surgeons, particularly the former.

Impact of MR imaging on nationwide health care costs and comparison with other imaging procedures

OBJECTIVE

We wished to determine the extent to which MR imaging contributes to the overall costs of imaging in the United States and to compare MR imaging costs with other imaging techniques.

MATERIALS AND METHODS

All 23 current procedural terminology, version 4 (CPT-4) codes for MR imaging were extracted from the national 1993 Part B Medicare annual data reimbursement file. For each code, we calculated total Medicare physician reimbursements. Aggregate reimbursement for all MR imaging was compared with aggregate reimbursement for all 659 imaging-related current procedural terminology, version 4 codes and also with comparable figures for echocardiography and other categories of cardiovascular imaging.

RESULTS

Within the 23 MR imaging codes, 1,449,911 examinations were performed on Medicare patients in 1993, for which physicians were reimbursed $370 million. Medicare reimbursement of physicians for all 659 imaging-related procedures was $5.3 billion. Thus, MR imaging accounted for only 7% of all imaging costs. By comparison, a group of just 10 imaging codes, which are primarily cardiovascular in nature, accounted for $1.67 billion, or 32% of the entire Part B costs for imaging. Reimbursements for echocardiography alone are more than twice those for MR imaging.

CONCLUSION

From the national perspective, MR imaging does not appear to warrant its reputation as a costly procedure. The costs of echocardiography and other imaging related to the cardiovascular system are considerably higher.

Hiring preferences of diagnostic radiology groups: results of a 1994 survey

RATIONALE AND OBJECTIVES

We surveyed diagnostic radiology group preferences and considerations in hiring radiologists and compared these findings with those of a survey performed in 1990. We sought to identify changes in hiring practices that might have occurred because of socioeconomic changes. We also sought to identify features of job candidates that make them more attractive to hiring groups.

METHODS

One hundred surveys were mailed to a stratified random sample of diagnostic radiology groups identified by the American College of Radiology. We solicited information on the importance of various attributes and the level of experience of a candidate, the fellowship training considered most desirable, and the effect of changes in the health care socioeconomic environment. The responses were weighted by group size and geographic location to estimate what results might have been obtained if we had surveyed all groups in the United States.

RESULTS

Seventy-five groups returned the survey. The two most important factors in choosing a candidate were motivation and radiologic knowledge. The fellowships that groups that were hiring considered to be the most desirable were body imaging, neuroradiology, and angiography/interventional radiology. Groups overwhelmingly preferred recent training over long experience.

CONCLUSION

Fellowship training increases a candidate's marketability, but the two factors that hiring groups consider the most important are motivation and radiologic knowledge.

Basic characteristics of radiology groups in the United States: results of a 1991-1992 census

OBJECTIVE

The American College of Radiology (ACR), the principal professional organization of United States radiologists, receives numerous requests for information on the characteristics of radiology groups. This report describes the basic characteristics of radiology groups in the United States. We defined radiology groups as any practice with two or more radiologists or radiation oncologists, including academic departments, units in multispecialty groups, and staff of government facilities.

MATERIALS AND METHODS

To collect basic information on radiology groups, the ACR conducted a mail census of all identified radiology groups in the United States during late 1991 and early 1992. Follow-up was conducted by mail and telephone. To make the responses accurately representative of all radiology groups, we weighted the approximately 2000 responses to correspond to known control totals for the number of groups of each of seven size categories in each of the four census regions (Northeast, Midwest, South, and West). These control totals were obtained from the ACR's 1990 Manpower Survey, which showed a total of approximately 3200 radiology groups.

RESULTS

Approximately one fourth of all groups have two radiologists, one fourth have three or four radiologists, one fourth have five to seven radiologists, and one fourth have eight or more radiologists. Academic groups were relatively large; almost 50% had 11 or more radiologists. Nonmetropolitan areas had very few large groups, and metropolitan center cities had relatively few small groups. Ninety-two percent of all groups practiced at hospitals, and 73% of all groups practiced at nonhospital offices or centers. The median number of practice sites for all groups was three, including both hospital and nonhospital sites. Eighty-eight percent of all groups provided diagnostic radiology services, 23% provided radiation oncology, 12% offered both, and 11% were oncology-only groups. Relatively many academic groups (25%) were oncology-only groups; very few radiology groups (2%) in multispecialty practices were oncology-only groups. The diagnostic radiology techniques available from the largest percentages of groups were general radiography (plain film), sonography, mammography, and CT. One eighth of academic groups that provided diagnostic services did not report providing mammography, compared with only a few percent of all groups in the United States that provided diagnostic services.

CONCLUSION

Half of all groups have two to four radiologists, and this has not changed since at least 1986. A substantial percentage of groups that perform diagnostic radiology do not provide MR, interventional, or nuclear medicine services. This is particularly true of relatively small groups. These characteristics may become the source of some problems as managed care becomes more prominent and larger groups, offering a full range of services and practicing at several sites, are favored by managed care organizations that seek to contract with one group for all their radiology services.

Percutaneous abdominal abscess drainage. Portland area experience

After reviewing 21 patients who have had percutaneous abdominal abscess drainage, we believe that the procedure should be considered for those abscesses that are unilocular without septations, with safe access being a key variable dictating the use of percutaneous abdominal abscess drainage rather than surgery. A computerized tomographic scan of the abdomen should be employed at some stage of the percutaneous abdominal abscess drainage procedure to facilitate safe access to the abscess and to distinguish a synchronous abscess where present. In addition, we believe that percutaneous abdominal abscess drainage should be considered for postsurgical abscesses only and not those that are spontaneous in nature or where the original abnormality cannot be accurately surmised. With regard to catheter management, frequent irrigation of the catheter must be carried out at least every 4 to 6 hours, with high levels of antibiotics present in the blood before irrigation. This must be done to obviate the most frequent and potentially lethal complication of the procedure, namely sepsis. Percutaneous abdominal abscess drainage, although safe for the most part, is capable of inducing considerable morbidity. Our data suggest that percutaneous abdominal abscess drainage is not as efficacious as previous reports have suggested. Traditional surgical drainage techniques are best utilized for those abscesses that are multiple, highly viscous, inaccessible, spontaneous, or unresponsive to percutaneous abdominal abscess drainage.

Radiology practices and their contracts with hospitals, 1989-1990: a representative sample survey

Because of concern about pressures from hospitals for changes in their contracts with radiology practices, the American College of Radiology undertook a stratified sample survey of radiology practices and their contracts with hospitals in late 1989 and early 1990. After three remailings, the survey obtained 904 valid responses for a 64% response rate. It found (weighting data to represent all radiology practices in the nation) that 91% of radiology practices provide services in hospitals. There are contracts at 57% of these hospital sites, and hospitals use tax-exempt bond financing in 54% of the sites with contracts. One year is the most common duration of contracts, and 90 days is the most common cancellation period (89% of contracts can be canceled during the contract's term). Eighty-six percent of contracts are exclusive; 73% are automatically renewable ("evergreen"). Separate billing exists in well over 90% of hospitals with contracts. Two percent of contracts require radiologists to provide equipment; 4% require them to provide support staff. There are fixed-fee arrangements in 9% of contracts and percent compensation arrangements in 3%. Hospitals share in radiologists' fees as a charge for contractual privileges in 5% of contracts. Twenty-seven percent of contracts require hospital approval for radiologists' fee increases; 19% require radiologists to participate with Blue Shield or Medicare. If a contract characteristic is predominant nationally, it is predominant in every region, for solo, small, medium, and large practices, and whether or not hospitals use tax-exempt bond financing. There is, however, some modest variation in frequency of contract provisions. Multivariate analysis shows that most such variation reflects true effects of region and other variables, not statistical artifacts. Region was a statistically significant determinant of 11 of 17 contract characteristics studied. Practice size was a statistically significant determinant of only about half as many characteristics. The survey found some interference in the independence of radiology practices (e.g., required hospital approval of fee increases), questionable clauses (e.g., mandated provision of equipment), and even illegal ones (hospitals charging a fee for contract privileges). Knowledge of the survey findings can make individual radiology practices more effective in negotiations with hospitals and assist the profession in forming a strategy to oppose disadvantageous and illegal provisions.

Changes in the job market for interventional radiology as detected through a help-wanted index of job advertisements

RATIONALE AND OBJECTIVES

The purpose of this study was to study trends in the job market in interventional radiology.

MATERIALS AND METHODS

Each job advertisement for a diagnostic radiologist in the American Journal of Roentgenology and Radiology between January 1991 and December 1999 was coded by practice type (academic vs private), location, and subspecialty. Positions for interventional radiologists were compared with positions for noninterventional radiologists. Data from the first 48 months (January 1991 through December 1994) were compared with data from the second 48 months (January 1995 through December 1998). Data from 1999 were grouped separately.

RESULTS

The nadir for all noninterventional and interventional radiology positions was seen in July 1995, and both areas have experienced great recovery since then. In December 1999, the last month of data collection, the absolute peak number of advertisements for interventional radiologists was reached. In fact, during the last half of the decade, an increasing percentage of jobs advertised for diagnostic radiologists was specifically for interventional radiologists. Statistically significant trends also occurred toward the private sector and toward positions in the Midwest and California.

CONCLUSION

With a help-wanted index, dramatic shifts toward the private sector and toward jobs in the Midwest and California were demonstrated in the interventional radiology job market.

Evidence for multi-fragmentation and mass shedding of boulders on rubble-pile binary asteroid system (65803) Didymos

Asteroids smaller than 10 km are thought to be rubble piles formed from the reaccumulation of fragments produced in the catastrophic disruption of parent bodies. Ground-based observations reveal that some of these asteroids are today binary systems, in which a smaller secondary orbits a larger primary asteroid. However, how these asteroids became binary systems remains unclear. Here, we report the analysis of boulders on the surface of the stony asteroid (65803) Didymos and its moonlet, Dimorphos, from data collected by the NASA DART mission. The size-frequency distribution of boulders larger than 5 m on Dimorphos and larger than 22.8 m on Didymos confirms that both asteroids are piles of fragments produced in the catastrophic disruption of their progenitors. Dimorphos boulders smaller than 5 m have size best-fit by a Weibull distribution, which we attribute to a multi-phase fragmentation process either occurring during coalescence or during surface evolution. The density per km2 of Dimorphos boulders ≥1 m is 2.3x with respect to the one obtained for (101955) Bennu, while it is 3.0x with respect to (162173) Ryugu. Such values increase once Dimorphos boulders ≥5 m are compared with Bennu (3.5x), Ryugu (3.9x) and (25143) Itokawa (5.1x). This is of interest in the context of asteroid studies because it means that contrarily to the single bodies visited so far, binary systems might be affected by subsequential fragmentation processes that largely increase their block density per km2. Direct comparison between the surface distribution and shapes of the boulders on Didymos and Dimorphos suggest that the latter inherited its material from the former. This finding supports the hypothesis that some asteroid binary systems form through the spin up and mass shedding of a fraction of the primary asteroid.

MRI efficacy and effectiveness research: who needs it and who pays for it?

Health care reform has made quality efficacy research in MRI important to an increasing number of audiences. Historically, the deficit of quality outcomes research in MRI was due to difficulties in study design, lack of funding, disincentives for researches and funding sources, and poor coordination. These issues would be best addressed by the formation of an MRI implementation group that would coordinate funding, planning, and dissemination of the outcomes research efforts.