Time-Resolved Noncontrast Magnetic Resonance Perfusion Imaging of Paraspinal Muscles.

BACKGROUND: While evaluation of blood perfusion in lumbar paraspinal muscles is of interest in low back pain, it has not been performed using noncontrast magnetic resonance (MR) techniques. PURPOSE: To introduce a novel application of a time-resolved, noncontrast MR perfusion technique for paraspinal muscles and demonstrate effect of exercise on perfusion parameters. STUDY TYPE: Longitudinal. SUBJECTS: Six healthy subjects (27-48 years old, two females) and two subjects with acute low back pain (46 and 65 years old females, one with diabetes/obesity). FIELD STRENGTH/SEQUENCE: 3-T, MR perfusion sequence. ASSESSMENT: Lumbar spines of healthy subjects were imaged axially at L3 level with a tag-on and tag-off alternating inversion recovery arterial spin labeling technique that suppresses background signal and acquires signal increase ratio (SIR) from the in-flow blood at varying inversion times (TI) from 0.12 seconds to 3.5 seconds. SIR vs. TI data were fit to determine the perfusion metrics of peak height (PH), time to peak (TTP), mean transit time, apparent muscle blood volume (MBV), and apparent muscle blood flow (MBF) in iliocostal, longissimus, and multifidus. Imaging was repeated immediately after healthy subjects performed a 20-minute walk, to determine the effect of exercise. STATISTICAL TESTS: Repeated measures analysis of variance. RESULTS: SIR vs. TI data showed well-defined leading and trailing edges, with sharply increasing SIR to TI of approximately 500 msec subsiding quickly to near zero around TI of 1500 msec. After exercise, the mean SIR at every TI increased markedly, resulting in significantly higher PH, MBV, and MBF (each P < 0.001 and F > 28.9), and a lower TTP (P < 0.05, F = 4.5), regardless of the muscle. MBF increased 2- to 2.5-fold after exercise, similar to the expected increase in cardiac output, given the intensity of the exercise. DATA CONCLUSIONS: Feasibility of an MR perfusion technique for muscle perfusion imaging was demonstrated, successfully detecting significantly increased perfusion after exercise. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 1.

A comparison of unguided vs guided case-based instruction on the surgery clerkship.

BACKGROUND: Guided case-based instruction is an effective and efficient means of learning for third year medical students on the surgery clerkship. Compared with an unguided format for teaching biliary disease, we observed greater student satisfaction as well as a more efficient utilization of student as well as faculty time with the guided instruction. OBJECTIVE: While case-based instruction (CBI) has become an extremely popular teaching modality during the first 2 years of medical school, there has been little published regarding its utilization during the clinical years of medical school. The purpose of our study was to compare guided CBI (G-CBI) to unguided CBI (UG-CBI) during the surgery clerkship. DESIGN: From July 2007 to July 2008, we utilized a UG-CBI format to teach biliary disease, formerly taught by a standard lecture. The unguided style is used by our institution for the first 2 years of medical school education, where the role of the facilitator is minimal. From July 2008 to December 2010, we changed to a G-CBI format where 5 different clinical scenarios were presented that all dealt with some form of biliary disease. A Likert-like scale was used to analyze student opinion comparing guided to the traditional unguided format. Questions regarding biliary disease contained in the National Board of Medical Examiners (NBME) shelf examination, given to all students at the end of the rotation, were also compared between the 2 groups. Cohen's d statistic was used to assess effect size. SETTING: The study took place at the University of Arizona College of Medicine. PARTICIPANTS: There were 88 students in the UG-CBI group and 146 in the G-CBI group. RESULTS: Ninety-six percent of the students preferred G-CBI over the unguided format utilized during the basic science years. Eighty-two percent felt that the guided format sessions were a more efficient method of instruction and 91% of students agreed or strongly agreed that time was more efficiently utilized in preparing for the case discussion during the guided format. Shelf examination scores analyzing biliary disease questions (2-4 per examination) showed a moderate size effect favoring the G-CBI, although the numbers were too small to draw definite conclusions in this regard. CONCLUSIONS: G-CBI is more suited for the surgery clerkship than the UG-CBI utilized during the first 2 years of medical school. Lack of a clinical knowledge base among the students rotating on the surgery clerkship as well as time limitations for both the student and clinical faculty favor this more efficient means of learning.

The use of a lightly preserved cadaver and full thickness pig skin to teach technical skills on the surgery clerkship--a response to the economic pressures facing academic medicine today.

BACKGROUND: In response to declining instruction in technical skills, the authors instituted a novel method to teach basic procedural skills to medical students beginning the surgery clerkship. METHODS: Sixty-three medical students participated in a skills training laboratory. The first part of the laboratory taught basic suturing skills, and the second involved a cadaver with pig skin grafted to different anatomic locations. Clinical scenarios were simulated, and students performed essential procedural skills. RESULTS: Students learned most of their suturing skills in the laboratory skills sessions, compared with the emergency room or the operating room (P = .01). Students reported that the laboratory allowed them greater opportunity to participate in the emergency room and operating room. Students also felt that the suture laboratory contributed greatly to their skills in wound closure. Finally, 90% of students had never received instruction on suturing, and only 12% had performed any procedural skills before beginning the surgery rotation. CONCLUSIONS: The laboratory described is an effective way of insuring that necessary technical skills are imparted during the surgery rotation.

Autosomal resequence data reveal Late Stone Age signals of population expansion in sub-Saharan African foraging and farming populations.

BACKGROUND: A major unanswered question in the evolution of Homo sapiens is when anatomically modern human populations began to expand: was demographic growth associated with the invention of particular technologies or behavioral innovations by hunter-gatherers in the Late Pleistocene, or with the acquisition of farming in the Neolithic? METHODOLOGY/PRINCIPAL FINDINGS: We investigate the timing of human population expansion by performing a multilocus analysis of > or = 20 unlinked autosomal noncoding regions, each consisting of approximately 6 kilobases, resequenced in approximately 184 individuals from 7 human populations. We test the hypothesis that the autosomal polymorphism data fit a simple two-phase growth model, and when the hypothesis is not rejected, we fit parameters of this model to our data using approximate Bayesian computation. CONCLUSIONS/SIGNIFICANCE: The data from the three surveyed non-African populations (French Basque, Chinese Han, and Melanesians) are inconsistent with the simple growth model, presumably because they reflect more complex demographic histories. In contrast, data from all four sub-Saharan African populations fit the two-phase growth model, and a range of onset times and growth rates is inferred for each population. Interestingly, both hunter-gatherers (San and Biaka) and food-producers (Mandenka and Yorubans) best fit models with population growth beginning in the Late Pleistocene. Moreover, our hunter-gatherer populations show a tendency towards slightly older and stronger growth (approximately 41 thousand years ago, approximately 13-fold) than our food-producing populations (approximately 31 thousand years ago, approximately 7-fold). These dates are concurrent with the appearance of the Late Stone Age in Africa, supporting the hypothesis that population growth played a significant role in the evolution of Late Pleistocene human cultures.