FDG PET Imaging of Extremities in Rheumatoid Arthritis.

BACKGROUND: The primary objective of this study was to evaluate the utility of fluorodeoxyglucose positive emission tomography imaging in assessing the degree of joint inflammation and response to therapy in patients with rheumatoid arthritis using standard PET parameters. METHODS: Five subjects with newly diagnosed RA were enrolled in this IRB-approved prospective study. After standard conventional workup that included clinical and laboratory evaluation and disease activity score (DAS3v) calculation, subjects underwent baseline FDG PET scans of their hands and feet prior to initiation of treatment and after six months of standard treatment. The uptake of FDG in involved joints was assessed qualitatively (visual evaluation) as well as semi quantitatively using standardized uptake value (SUV). Findings from the FDG PET scans were correlated with clinical and laboratory parameters including DAS and ESR. RESULTS: In all five patients, increased FDG uptake was noted in various joints affected by RA. The intensity of uptake varied from mild to intense (SUVmax values from 3.10 to 6.0). Overall, these correlated well with the clinical evaluation of involved joints. FDG PET imaging provided additional information by showing involvement in joints that were difficult to evaluate clinically (e.g. mid foot joints). The PET data also provided a distribution of joint involvement with varying degrees of severity in the same subject. On objective analysis using Spearman rank correlation coefficient for statistical analysis, no significant correlations were observed (p>0.05) between DAS, ESR, and the different PET parameters at baseline (before treatment) despite large calculated positive correlation coefficients. This was due to the small sample size (n=5). At post-treatment, the significant correlations were those between DAS and Maximum metabolic disease burden (MDB max) (RS=0.9, p=0.04) and between ESR and MDB max (RS=0.9, p=0.04). The positive correlations between total metabolic disease burden (Total MDB) and DAS (RS=0.7) and between Total MDB and ESR were also large (RS=0.7) but not significant. The non-significance was due to the small sample size. CONCLUSIONS: FDG PET imaging provides a unique noninvasive quantitative method in assessing disease status and response to therapy and can serve as a useful adjunct to clinical evaluation in management of patients with rheumatoid arthritis.

Photographic art in exam rooms may reduce white coat hypertension.

INTRODUCTION: Blood pressure (BP) elevation in medical office settings in patients who are normotensive in nonmedical settings is an effect known as 'white coat hypertension'. This phenomenon is thought to be due to situational anxiety caused by the experience of visiting a doctor and the anxiety-inducing nature of the medical office. Our study was designed to determine if carefully selected photographic art could counter the anxiety that causes white coat hypertension and lead to lower BP recordings in some patients. METHODS: 117 adults, non-pregnant patients from the Louisiana State University Health Sciences Center Family Medicine Resident Clinic participated in this study. After the triage nurse measured the BP, the patients were randomly placed in either an exam room with standard medical posters (control room) or in an exam room with photographic art (photo room). The BP was measured in the exam room. After the medical visit, the patients switched rooms and the BP was measured a third time. The patients were asked to fill out a questionnaire to identify room preference. RESULTS: On average, the BP obtained in the control rooms was higher than that obtained in the photo rooms. There was a statistically significant difference between the mean arterial pressure, systolic BP and diastolic BP between the control room and the photo room. CONCLUSIONS: Landscape photographic art may have the beneficial effect of reducing BP in medical office examination rooms.

Graftula: a composite access consisting of a graft used to repair a dysfunctional hemodialysis fistula.

Nonmaturing or dysfunctional hemodialysis fistulas are often repaired with interposition grafts placed either within the fistula (fistula-to-fistula configuration), or connected to another vein (fistula-to-vein configuration). The goal of this study was to compare the survival and usefulness of the composite accesses thus created, which we call "graftulas," with upperarm grafts. This was a retrospective study wherein we determined the survival and thrombosis rates of graftulas (n=24) and upper arm grafts (n=31) placed 1/1/07 through 12/31/09 and followed through 11/30/10. Graftulas resembled grafts as most (96%) were successfully cannulated in 65 ± 43 days. Survival of graftulas was also similar to grafts (58%, 47%, and 32% vs. 56%, 47%, and 39% at 1, 2, and 3 years respectively, p=0.60). However, graftulas had a lower thrombosis rate than grafts (0.5 vs. 1.2 per patient year, p=0.04), and in the fistula-to-fistula configuration, a 2-year thrombosis-free survival of 78%. Total survival of the access site (fistula+graftula) was 92%, 73%, and 42% at 1, 3, and 5 years, respectively. Graftulas possess certain beneficial properties of fistulas and grafts that allows for continued use of the original access site.

Pleural ultrasonography versus chest radiography for the diagnosis of pneumothorax: review of the literature and meta-analysis.

INTRODUCTION: Ultrasonography is being increasingly utilized in acute care settings with expanding applications. Pneumothorax evaluation by ultrasonography is a fast, safe, easy and inexpensive alternative to chest radiographs. In this review, we provide a comprehensive analysis of the current literature comparing ultrasonography and chest radiography for the diagnosis of pneumothorax. METHODS: We searched English-language articles in MEDLINE, EMBASE and Cochrane Library dealing with both ultrasonography and chest radiography for diagnosis of pneumothorax. In eligible studies that met strict inclusion criteria, we conducted a meta-analysis to evaluate the diagnostic accuracy of pleural ultrasonography in comparison with chest radiography for the diagnosis of pneumothorax. RESULTS: We reviewed 601 articles and selected 25 original research articles for detailed review. Only 13 articles met all of our inclusion criteria and were included in the final analysis. One study used lung sliding sign alone, 12 studies used lung sliding and comet tail signs, and 6 studies searched for lung point in addition to the other two signs. Ultrasonography had a pooled sensitivity of 78.6% (95% CI, 68.1 to 98.1) and a specificity of 98.4% (95% CI, 97.3 to 99.5). Chest radiography had a pooled sensitivity of 39.8% (95% CI, 29.4 to 50.3) and a specificity of 99.3% (95% CI, 98.4 to 100). Our meta-regression and subgroup analyses indicate that consecutive sampling of patients compared to convenience sampling provided higher sensitivity results for both ultrasonography and chest radiography. Consecutive versus nonconsecutive sampling and trauma versus nontrauma settings were significant sources of heterogeneity. In addition, subgroup analysis showed significant variations related to operator and type of probe used. CONCLUSIONS: Our study indicates that ultrasonography is more accurate than chest radiography for detection of pneumothorax. The results support the previous investigations in this field, add new valuable information obtained from subgroup analysis, and provide accurate estimates for the performance parameters of both bedside ultrasonography and chest radiography for pneumothorax evaluation.

A home telemonitoring program reduced exacerbation and healthcare utilization rates in COPD patients with frequent exacerbations.

RATIONALE: As the impact of home telemonitoring on patients with chronic obstructive pulmonary disease (COPD) is not fully understood and reduction in healthcare utilization is not proven, we attempt to evaluate the effects of home telemonitoring on healthcare utilization in patients with COPD. SUBJECTS AND METHODS: We conducted a retrospective cohort study using the Veterans Health Administration database of COPD patients enrolled in the Care Coordination Home Telehealth (CCHT) program. We evaluated the effects of monitoring through this program in patients with moderate to severe COPD and frequent exacerbations. Numbers of emergency department (ED) visits, urgent care (UC) visits, and hospitalizations were all evaluated before and after enrollment. The differences in average pre-enrollment and during-enrollment numbers of hospital admissions, ED/UC visits, and exacerbations were tested for significance among all patients enrolled in the program who had one or more exacerbations at pre-enrollment; results were expressed on a per-year basis. RESULTS: Data were available on a total of 1,133 patients with COPD enrolled in the CCHT program between 2005 and 2009. Given the objectives of our study, we only included 369 patients who had at least one exacerbation per year in the year prior to enrollment. Of these, 71.5% had a reduction in numbers of ED visits and exacerbations requiring hospitalizations after enrollment in the program. The average number of hospital admissions, ED visits, and total exacerbations were all reduced (0.41 ± 1.68, 0.15 ± 1.65, and 0.56 ± 2.3, respectively; all with p<0.01). The pre-enrollment number of exacerbations was the only factor observed to be significantly associated with the reduction in number of exacerbations. CONCLUSIONS: In patients with COPD and frequent exacerbations, enrollment in a home telemonitoring program may decrease healthcare utilization.

Chemoradiotherapy for unresectable stage IVB head and neck cancer.

OBJECTIVE: As the occurrence of unresectable stage IVB head and neck cancer is expected to continue, we present our experience over the last 17 years with chemoradiotherapy management of 14 cases to clarify the effectiveness and safety of this treatment scheme. METHOD: Of the 1,267 individuals who were diagnosed with carcinoma of the upper aerodigestive tract between 1992 to 2008, 14 patients were treated by induction chemotherapy followed by concurrent chemoradiation or simultaneous chemoradiotherapy for stage IVB disease. The median follow-up time was 54.5 months. RESULTS: The complete objective response rate was 79%. Six individuals remained disease-free during a followup period ranging from 24 to 149 months. The disease-free survival rate at five years was 68%. Local, regional, and distant failure rates were 21%,14%, and 7% respectively. Most of the patients (79%) experienced transient mucositis during treatment. Significant late complications consisted of dental caries or osteoradionecrosis (14%) and esophageal stricture (7%). CONCLUSION: Definitive chemoradiotherapy administered for unresectable stage IVB head and neck cancer has the potential of achieving long-term disease-free survival in up to two-thirds of the patients with a low risk of complications.

Ventriculoperitoneal shunt complications in hydrocephalus patients with intracranial tumors: an analysis of relevant risk factors.

Patients with intracranial tumors are predisposed to persistent hydrocephalus, often requiring a permanent CSF diversion procedure with shunts. This study reviews the long-term experience with ventriculoperitoneal shunts for the management of hydrocephalus in patients with intracranial tumors. Patients with intracranial tumors who underwent ventriculoperitoneal shunt placement for hydrocephalus from October 1990 to October 2009 were included in this study. During the 19-year period, medical charts, operative reports, imaging studies, and clinical follow- up evaluations were reviewed and analyzed retrospectively for all patients. A total of 187 intracranial tumor patients with hydrocephalus were included. The median follow up was 391 days. Malignant tumors were present in 40% of the patients. Overall shunt failure was 27.8%. Single shunt revision occurred in 13% of the patients and 14% had multiple shunt revision. Tumor histology, age and a procedure prior to shunt placement (ventriculostomy/Ommaya reservoirs) were significantly associated with the shunt revisions. Shunt system replacement and proximal shunt complication were significantly attributed to multiple shunt revisions. The overall shunt revision within 3 months, 6 months, 1 year and 5 years was 17.7%, 18.7%, 19.8% and 24.1%, respectively. The results of the study demonstrate that VP shunting is an effective for the management of hydrocephalus in patients with intracranial tumors. The overall incidence of shunt revision was 27.8%. Age, tumor histology, and a procedure prior to shunt placement (ventriculostomy/Ommaya reservoirs) were significantly associated with the shunt revisions. Additional studies using minimally invasive techniques are being explored for the management of hydrocephalus in patients with intracranial tumors.

Protected carotid artery stenting in patients at high risk for carotid endarterectomy.

OBJECTIVES: To compare the 30-day, six-month, and one-year outcomes of carotid artery stenting (CAS) and carotid endarterectomy (CEA) in male veterans, and to identify any predictors of adverse outcomes. CAS has been shown to be non-inferior to CEA in patients at high-risk for CEA. The outcome of CAS compared to low-risk CEA is less clear. METHODS: Retrospective analysis of 96 consecutive patients who underwent CAS (N = 31) or CEA (N = 65). The cumulative 30-day, six-month, and one-year incidence of ipsilateral transient ischemic attack (TIA) or stroke, restenosis or reocclusion, need for target vessel revascularization, non-fatal myocardial infarction (MI), and death were compared. RESULTS: All patients in the CAS group were at high risk for CEA. Among the CEA group, 50 (76.9%) were at high risk and the remaining 15 (23.1%) were considered to be at low risk. The cumulative incidence of adverse outcomes with CAS and CEA, respectively, at 30 days (3.2% vs 9.2%, P = ns), six months (3.2 vs 18.5%, P = 0.047), and one year (9.7% vs 18.5%, P = ns) favored CAS. This difference was primarily due to adverse events in the high-risk CEA patients. There was no significant difference in outcome between the CAS and low-risk CEA groups. The independent significant predictors for adverse outcomes within six months were the group (P = 0.047) and number of risk factors (P = 0.01). Interestingly, the use of angiotensin-converting enzyme inhibitors (ACE-I) predicted adverse outcomes within one year (P = 0.01). CONCLUSION: CAS may be superior to high-risk CEA with better six-month outcomes. The outcomes with CAS were not significantly different compared to low-risk CEA, suggesting that CAS may be non-inferior to low-risk CEA.

A contemporary experience of open aortic reconstruction in patients with chronic atherosclerotic occlusion of the abdominal aorta.

OBJECTIVE: To examine and report surgical results from a contemporary experience of open abdominal aortic reconstruction in patients with chronic atherosclerotic abdominal aortic occlusion (CAAAO). METHODS: Between January 1999 through May 2010, 54 patients with CAAAO were identified and retrospectively reviewed. CAAAOs were categorized into infrarenal aortic occlusions (IRAOs) and juxtarenal aortic occlusions (JRAOs) based on superior extension of thrombus and requirement for supra-renal aortic clamping to repair. Morbidity, mortality, hospital stay, and operative variables were assessed. The χ2 or Fisher test and the Wilcoxon rank sum test were used to compare demographic and operative variables between two aortic occlusion groups (IRAO and JRAO). Univariate and multivariate analyses were performed to assess factors associated with surgical outcomes and hospital stay. The Kaplan-Meier method was used to calculate survival and patency rates. RESULTS: Fifty patients underwent aortic reconstructions with aorto-bifemoral or iliac bypass, and three underwent a remote axillo-femoral bypass procedure. There were 35 (64.8%) males, and 19 (35.2%) females. Median age was 51.9 years (range, 32-72 years). Of the two CAAAO groups, there were 20 IRAOs and 33 JRAOs. Aorto-renal thromboendartectomy was performed in 26 (49.1%) patients; 26 (75.8%) among JRAOs versus 1 (5%) of IRAOs (P<.01). Proximal aortic clamps were required in 28 (85%) of JRAOs and 3 (15%) of IRAOs (P<.01). Thirty-day and in-hospital mortality was zero. Median length of hospital stay was 7 days (range, 4 to 66 days), and median intensive care unit length of stay was 3 days (range, 1-22 days). Complications included cardiopulmonary dysfunction in four (8%), postoperative renal insufficiency in 10 (18.9%), and other postoperative complications in 15 (28.3%). All 10 with renal insufficiency recovered renal function to baseline creatinine or a creatinine value<1.1 mg/dL. Mean increases in right and left ankle-brachial indicess were 0.54±0.25 and 0.59±0.22, respectively. On univariate analysis, coronary artery disease and African American race were predictors of postoperative complications (P=.048). Age was significantly associated with total complications. Patients with postoperative complications and/or renal insufficiency were older than those without such complications (P=.02) Independent predictors of prolonged hospital stay were intraoperative blood replacement (P=.003), postoperative complications (P<.01), and postoperative renal insufficiency (P<.01). Prolonged intensive care unit stay was predicted by JRAO (P=.04), postoperative complications (P=.02), and postoperative renal insufficiency (P=.013). Survival at 3, 5, and 7 years were 86.6%, 76.5% and 50.9%, respectively. The reduced survival rates were predicted by previous myocardial infarction and existing coronary artery disease (P<.01). CONCLUSION: Abdominal aortic reconstruction is a safe method for treating CAAAO with low associated morbidity and mortality. Aorto-renal thromboendartectomy with supra-renal aortic clamping and aortic replacement remains an effective treatment for those with significant pararenal aortic disease, and can be performed without significant renal impairment.

Clinical sobriety assessment by emergency physicians in blunt trauma patients with acute alcohol exposure.

BACKGROUND: Alcohol use increases injury risk and severity. However, few studies have evaluated the ability of emergency physicians (EPs) to accurately determine sobriety. OBJECTIVES: To determine the predictive value of clinical sobriety assessment by EPs in blunt trauma patients with acute alcohol use. MATERIALS AND METHODS: Blunt trauma patients, aged 18-65 years with suspected acute alcohol use, were prospectively enrolled in the study. EPs assessed study subjects before sample collection for blood alcohol level (BAL) and urine drug screen measurement. Alcohol exposure was considered significant if BAL was ≥ 80 mg/dL. Sobriety (non-significant alcohol exposure) was defined as a BAL < 80 mg/dL. EP sobriety assessment was compared to measured BAL and predictive values were calculated. Agreement on significance of alcohol exposure occurred if EP-estimated BAL > 80 mg/dL agreed with measured BAL > 80 mg/dL, or estimated BAL < 80 mg/dL agreed with measured BAL < 80 mg/dL. Chi-squared analysis was used to compare the proportion of correct physician assessments among patients with sobriety and those with significant alcohol exposure. RESULTS: Of 158 enrolled subjects, 153 completed clinical assessment. EP assessment had a predictive value of 83% (95% confidence interval [CI] 77-90%) for significant alcohol exposure and 69% (95% CI 60-78%) for sobriety. Agreement on the significance of alcohol exposure was 82% (125/153; 95% CI 76-88%). EPs identified 32% (11/34; 95% CI 17-48%) of sober patients, but identified 96% (114/119; 95% CI 92-99%) of patients with significant alcohol exposure. EP assessment was significantly less accurate in identifying sober patients (p < 0.01). CONCLUSIONS: Emergency physicians identified significant recent alcohol exposure in blunt trauma patients 96% of the time. However, clinical assessment by EPs in blunt trauma patients with recent alcohol use had only moderate predictive value for significant alcohol exposure. Sober patients were frequently misidentified as having significant alcohol exposure.

Association of sexually-transmitted infection and African-American race with Streptococcus agalactiae colonization in pregnancy.

BACKGROUND: Group B Streptococcus (GBS) remains a significant cause of neonatal infection, but the maternal risk factors for GBS colonization remain poorly defined. We hypothesized that there may be an association between antibiotic exposure during pregnancy and GBS colonization and/or the presence of inducible clindamycin resistance (iCLI-R) in GBS isolates from GBS-colonized pregnant women. METHODS: A retrospective cohort study was performed at Louisiana State University Health Sciences Center - Shreveport including demographic and clinical data from 1513 pregnant women who were screened for GBS between July 1, 2009 and December 31, 2010. RESULTS: Among 526 (34.8%) women who screened positive for GBS, 124 (23.6%) carried GBS strains with iCLI-R (GBS-iCLI-R). While antibiotic exposure, race, sexually-transmitted infection (STI) in pregnancy, GBS colonization in prior pregnancy and BMI were identified as risk factors for GBS colonization in univariate analyses, the only independent risk factors for GBS colonization were African-American race (AOR = 2.142; 95% CI = 2.092-3.861) and STI during pregnancy (AOR = 1.309; 95% CI = 1.035-1.653). Independent risk factors for GBS-iCLI-R among women colonized with GBS were non-African-American race (AOR = 2.13; 95% CI = 1.20-3.78) and younger age (AOR = 0.94; 95% CI = 0.91-0.98). Among GBS-colonized women with an STI in the current pregnancy, the only independent risk factor for iCLI-R was Chlamydia trachomatis infection (AOR = 4.31; 95% CI = 1.78-10.41). CONCLUSIONS: This study identified novel associations for GBS colonization and colonization with GBS-iCLI-R. Prospective studies will improve our understanding of the epidemiology of GBS colonization during pregnancy and the role of antibiotic exposure in alterations of the maternal microbiome.

Poor outcome of indigent patients with peripartum cardiomyopathy in the United States.

OBJECTIVE: Peripartum cardiomyopathy (PPCM) patients from Haiti and South Africa have poor survival and poor left ventricular (LV) function recovery compared with patients from the United States. There are no reported studies of PPCM among the African American population in the United States. We evaluated the prognosis of PPCM in a mostly African American population. STUDY DESIGN: We analyzed the clinical and echocardiographic data of 44 (39 African American) patients with PPCM over an 11 year period (1992-2003). RESULTS: Thirty-nine patients were indigent and 5 had health insurance. During a mean follow-up of 24.0 (range, 0.1-264) months, 7 (15.9%) patients died and LV function returned to normal in 14 (35%). CONCLUSION: LV function recovery and survival rates of PPCM patients observed in our study are similar to those reported from Haiti and South Africa and different from what is generally accepted in the United States.

Does the negative node count affect disease-free survival in early-stage oral cavity cancer?

PURPOSE: We performed a retrospective study to determine whether there is a relationship between disease-free survival and negative lymph node count in patients with resected early-stage oral cavity cancers. MATERIALS AND METHODS: Of the 526 individuals diagnosed with carcinoma of the oral cavity between 1998 and 2005, 52 had undergone primary tumor resection and lymph node dissection of the neck for stage I or II disease. With a mean count of 27 examined negative nodes, these 52 patients were separated into groups with fewer than 27 or > or = 27 uninvolved lymph nodes and compared for disease-free survival. RESULTS: The tumor recurred or progressed in 10 patients (19%) during a median follow-up of 27 months. The 2-year disease-free survival rates were 75% and 78% in individuals with fewer than 27 and > or = 27 uninvolved node counts, respectively (P > .78). CONCLUSION: The removal of a greater number of regional, uninvolved cervical lymph nodes does not correlate with disease-free survival in this particular cohort of patients.

Gamma knife radiosurgery for arteriovenous malformations located in eloquent regions of the brain.

BACKGROUND: Stereotactic radiosurgery is an effective treatment strategy for selected group of patients with cerebral arteriovenous malformations (AVMs). AIM: The aim of this study was to evaluate the obliteration rates, complications, and patient outcomes after Gamma knife radiosurgery for cerebral arteriovenous malformations (AVMs) located in eloquent regions of the brain with an emphasis on neurological morbidity. MATERIALS AND METHODS: Between 2000 and December 2005, 37 patients with AVMs in eloquent locations (sensory, motor, speech, visual cortex, basal ganglia, and brain stem) underwent stereotactic radiosurgery. We retrospectively reviewed the clinical data of these patients to asses the outcomes. Of the 37 patients, only two patients had prior embolization. Three underwent prospective staged volume radiosurgery. Two patients needed redo-radiosurgery for residual AVM. Mean target volume was 9.1 cc. Three lesions had nidus volume more than 20 cc. Average marginal dose was 18.75 Gy. The median duration of follow-up was 23 months (range, 6-60 months). 15 patients had follow-up of more than 36 months. RESULTS: A total of 15 patients had follow-up of more than 36 months, thus available for evaluation of angiographic obliteration rates. Complete angiographic obliteration was documented in seven patients (46.7%). Four patients experienced hemorrhage during the latency period. One patient who had subsequent hemorrhage on follow-up developed worsening of neurological deficit. One patient developed significant sensory symptoms which resolved after steroids. No additional clinical deterioration related to treatment was noted in rest of the patients. CONCLUSIONS: AVMs located in eloquent and in deep locations can be treated safely with stereotactic radiosurgery with acceptable obliteration rates and minimal morbidity.

Mammalian target of rapamycin inhibitors as possible adjuvant therapy for microscopic residual disease in head and neck squamous cell cancer.

Molecular therapeutics identifies an aberration in tumors to select patients that benefit from molecular targeted therapy. Overexpression of eIF4E in histologically "tumor-free" surgical margins of head and neck squamous cell cancer (HNSCC) patients is an independent predictor of recurrence and is functionally activated through the Akt/mammalian target of rapamycin (mTOR) pathway. Although mTOR inhibitors are cytostatic agents, best used in combination therapy, we hypothesize that they can be used as long-term single agents in an HNSCC model of minimal residual disease (MRD). CCI-779, an mTOR inhibitor, arrested growth of a phosphatase and tensin homologue deleted on chromosome 10 (PTEN) abnormal HNSCC cell line FaDu, inhibiting phosphorylation of 4E-binding protein 1, resulting in increased association with eIF4E and inhibition of basic fibroblast growth factor and vascular endothelial growth factor. Fluorescence in situ hybridization detected PTEN abnormalities in 68% of patient tumors and 35% of tumor-free margins. CCI-779 inhibited growth of established tumors in nude mice. However, in the MRD model, there were significant differences in the tumor-free rate between the control (4%) and the treatment group (50%), and the median tumor-free time was 7 versus 18 days, respectively (P < 0.0001). In those animals that formed tumors, CCI-779 caused a significant decrease in the tumor volume. The Kaplan-Meier curve showed that CCI-779 significantly increased survival (P < 0.0001). The mTOR pathway was inhibited in peripheral blood mononuclear cells potential surrogate markers of response to therapy. Stable transfection of FaDu with luciferase allowed us to monitor the effects of CCI-779 with bioluminescence imaging in the MRD model. These results pave the way for a clinical trial using targeted molecular therapy with CCI-779 as a single agent for mTOR-activated residual cells.