External anal sphincter defects: correlation between pre-operative anal endosonography and intraoperative findings

Short- and long-term outcomes of sphincteroplasty for anal incontinence related to obstetric injury: a systematic review

Anal incontinence is a frequent pathological condition with devastating impact on quality of life. The prevalence is approximately 15% of the population, with higher incidence reported in the elderly and multiparous women, and several factors have a major role in its pathogenesis, such as anatomical sphincter defects (Glasgow and Lowry in Dis Colon Rectum 55(4): 482-490, 2012), delivery injuries, and colorectal, uro-gynecological, and perineal surgery. The direct surgical approach is the gold standard treatment for fecal incontinence, especially through anterior sphincteroplasty, although a permanent defect of continence persists over time. The aim of our study is to evaluate, throughout a systematic review of the literature, the short- and long-term outcomes of sphincteroplasty performed for obstetric injuries anal incontinence. A systematic review of the studies published in the literature from January 2000 to December 2021 was performed in accordance with the PRISMA guidelines. Of the 2543 studies extrapolated, only eight fulfilled the inclusion criteria and were admitted represented by retrospective and prospective studies. The data analyzed from the included studies were number and mean age of the female population, and incontinence improvement with preoperative and postoperative short- and long-term outcomes, as reported by QoL questionaries and incontinence scores. Overall 355 patients with obstetric sphincter damage underwent sphincteroplasty with an anterior external sphincter overlapping procedure. A consistent improvement in fecal incontinence at short-term follow-up with relative improvement in QoL was reported. In 7 of 8 studies, the authors found a progressive worsening of the incontinence symptoms on the long-term follow-up. However, it is not clear whether the decrease in long-term continence results is parallel to a simultaneous decrease in QoL scores. Nevertheless, compared to the preoperative findings, the improvement was maintained in the long-term follow-up. Despite the limited data in the literature, a properly performed sphincteroplasty can guarantee a consistent improvement of the continence in short term with encouraging outcomes, especially for solid stool continence, in long time. We believe that anterior sphincteroplasty, as a low cost, feasible, and safe procedure, still has a role in the treatment of fecal incontinence for obstetric injury. Further large cohort randomized clinical trials are necessary to validate these results.

Accuracy of clinical diagnosis of anal sphincter defect: clinical evaluation versus 3D-transperineal ultrasound

BACKGROUND

Obstetric anal sphincter injuries (OASIS) are common and an important factor in the etiology of anal incontinence. The objective of this study was to evaluate, classify and compare the agreement of clinically diagnosed third-degree sphincter tears with 3D-transperineal ultrasound (3D-TPUS) realized within 3-7 days post-delivery.

METHODS

This is a retrospective observational study were 119 patients with third-degree obstetric anal sphincter tears were diagnosed and treated, 85 of those underwent a 3D-TPUS examination 3-7 days postpartum. We compared the proportion of third-degree perineal tears, classified with the clinical examination as grade 3a+b and grade 3c, with the 3D-TPUS.

RESULTS

In 16 patients with clinically diagnosed third-degree perineal tears grade a and b, the ultrasound examination confirmed the lesion of the external anal sphincter (EAS) muscle, but in nine patients (56% of the cases) we found a lesion of the internal anal sphincter (IAS) muscle, missed by clinical examination. In the remaining 69 patients with the third-degree perineal tears grade c, the ultrasound examination confirmed both lesions (EAS and IAS muscles) in 56 women, but in 13 patients (19% of the cases) defects of the IAS muscle could not be confirmed by the ultrasound.

CONCLUSIONS

There was moderate agreement regarding diagnosis of grade 3a+b and grade c perineal tears between ultrasound and clinical examination, so a combined use of clinical and ultrasound knowledge can improve the possibility to find a gold standard in the diagnosis of OASIS.

Diagnosis and treatment of faecal incontinence: Consensus statement of the Italian Society of Colorectal Surgery and the Italian Association of Hospital Gastroenterologists

Faecal incontinence is a common and disturbing condition, which leads to impaired quality of life and huge social and economic costs. Although recent studies have identified novel diagnostic modalities and therapeutic options, the best diagnostic and therapeutic approach is not yet completely known and shared among experts in this field. The Italian Society of Colorectal Surgery and the Italian Association of Hospital Gastroenterologists selected a pool of experts to constitute a joint committee on the basis of their experience in treating pelvic floor disorders. The aim was to develop a position paper on the diagnostic and therapeutic aspects of faecal incontinence, to provide practical recommendations for a cost-effective diagnostic work-up and a tailored treatment strategy. The recommendations were defined and graded on the basis of levels of evidence in accordance with the criteria of the Oxford Centre for Evidence-Based Medicine, and were based on currently published scientific evidence. Each statement was drafted through constant communication and evaluation conducted both online and during face-to-face working meetings. A brief recommendation at the end of each paragraph allows clinicians to find concise responses to each diagnostic and therapeutic issue.

Residual defects of the external anal sphincter following primary repair: an observational study using transperineal ultrasound

OBJECTIVES

Obstetric anal sphincter tears are common and an important factor in the etiology of anal incontinence. The objective of the study was to evaluate the prevalence of residual defects of the external anal sphincter (EAS) after primary repair of obstetric anal sphincter injury using four-dimensional (4D) transperineal ultrasound and to correlate sonographic findings of residual defects and levator avulsion with significant symptoms of anal incontinence, defined as St Mark's fecal incontinence score (SMIS) of ≥ 5.

METHODS

This was a retrospective observational study. One-hundred and forty women were seen after primary repair of obstetric anal sphincter tears in a dedicated perineal clinic at a tertiary hospital in Australia. They all underwent a standardized interview, and physical and 4D transperineal ultrasound examination.

RESULTS

Mean follow-up interval was 1.9 months after delivery. Eighty-nine (64%) women had a 3a/3b tear, 28 (20%) a 3c/4(th) degree tear and 23 (16%) an unclassified 3(rd) degree tear. Thirty-five (25%) patients reported symptoms of anal incontinence. Nine had an SMIS of ≥ 5. A residual defect was found in 56 (40%) cases and levator avulsion in 27 (19%). On multivariate logistic regression, residual defects (P = 0.03; odds ratio (OR) = 6.38; 95% CI, 1.23-33.0) and levator avulsion (P = 0.047; OR = 4.38; 95% CI, 1.02-18.77) were found to be independent risk factors for anal incontinence.

CONCLUSIONS

Residual defects of the EAS were found on transperineal ultrasound in 40% of women after primary repair of obstetric anal sphincter injuries. Although most were asymptomatic, residual anal sphincter defects and levator avulsion were associated with significant symptoms of anal incontinence as quantified using the SMIS.

Accuracy of the digital anal examination in women with fecal incontinence

INTRODUCTION AND HYPOTHESIS

This study aims to determine the accuracy of digital rectal examination (DRE) to detect anal sphincter defects when compared to endoanal ultrasound (US) in women with fecal incontinence (FI).

METHODS

Seventy-four patients identified by retrospective chart review who presented with complaints of bothersome FI who underwent endoanal US are the subjects of this analysis. Sensitivity, specificity, and positive and negative likelihood ratios were calculated for the ability of the DRE to detect anal sphincter defects.

RESULTS

Anal sphincter defect was suspected on DRE in 75%. At endoanal US, external sphincter defects were noted in all three segments in 41% (complete defect) while partial defects were noted in 30%. DRE demonstrated a sensitivity of 82%, specificity of 32%, +likelihood ratio 1.2 (95% confidence interval (CI), 0.95-1.16) and -likelihood ratio of 0.6 (95% CI, 0.2-1.24) for detecting a complete EAS defect on endoanal US.

CONCLUSION

DRE has poor specificity for detecting anal sphincter defects seen on endoanal US.

Three-dimensional endoanal ultrasonography in daily proctological practice

Three-dimensional endoanal ultrasonography (3D-EAUS) provides unequalled quality in terms of the anatomical image of the anal canal and sphincter complex. In less than one minute it produces a three-dimensional "cube" that can be manipulated in all spatial dimensions, then archived. In just a few years it has become a new gold standard exploration in proctology. In addition to image quality, 3D-EAUS has the advantage of being easily and rapidly performed, well-tolerated and moderate in cost. For anal incontinence, 3D-EAUS contributes to the identification of sphincter defects. The anatomy of the sphincters can be evaluated spatially. Simple scoring systems with good reproducibility and readily applicable in routine practice can be used to evaluate the "damaged" sphincter volume. For the management of anoperineal suppurations, 3D-EAUS provides information on the fistulous track(s) and on potential collections. These data are crucial as the choice of treatment and its efficacy depend on accurate topographic assessment of the suppuration and the state of the sphincter apparatus.

Perineum compression during EAUS enhances visualization of anterior anal sphincter defects

OBJECTIVE

Endo-anal ultrasound (EAUS) can detect anal sphincter injuries. However, anterior external anal sphincter (EAS) defects can be difficult to define. We assessed different EAUS techniques to determine if any particular method improved defect identification.

METHOD

Ninety females with faecal incontinence were prospectively studied. Wexner faecal incontinence scores were obtained. All patients underwent anorectal manometry and EAUS using three different techniques: standard, digit-assisted (gloved finger pressing on posterior vaginal wall) and balloon-assisted (standard balloon inflated into the vagina). The three techniques were assessed by comparing defect characteristics (detection, angle, edges and scar tissue), and perineal body thickness. All measurements were performed at the mid anal canal level.

RESULTS

are expressed as medians (IQR). Results Standard EAUS (S-EAUS) identified a sphincter defect in 54 patients. Digit assisted EAUS (D-EAUS) and balloon-assisted EAUS (B-EAUS) ultrasound revealed a sphincter defect in additional 11 and 9 patients respectively compared to S-EAUS. Correlation of maximum squeeze pressure with EAUS findings improved on D-EAUS and B-EAUS. The defect angle was significantly wider with D-EAUS and B-EAUS [S-EAUS 90 degrees (63-97), D-EAUS 100 degrees (81-101.5), B-EAUS 100 degrees (80-105), P = 0.0005]. The perineal body was significantly thicker when measured with B-EAUS [D-EAUS 9 mm (7-10) vs B-EAUS 10 mm (8-11), P = 0.0005]. Inter-observer agreement was comparable [S-EAUS (K) = 0.677, D-EAUS (K) = 0.658, B-EAUS (K) = 0.601].

CONCLUSION

EAS anterior defect detection and definition on EAUS may be improved by the demarcation and gentle pressure on the posterior vaginal wall.

Endoanal ultrasound in benign anorectal disorders: clinical relevance and possibilities

Endoanal ultrasound is a well-established technique used to evaluate benign anorectal disorders. The technique is easy to perform, has a short learning curve and causes very little discomfort. Reconstruction of 3D images is possible. The clinical indications for endoanal ultrasound in benign anorectal diseases are fecal incontinence and peri-anal fistula. Sphincter defects can be depicted with precision and correlate perfectly with surgical findings. Furthermore, an impression of sphincter atrophy can be established. With perianal fistula the tracts can be visualized. Introducing hydrogen peroxide via the external fistula opening improves imaging. Endoanal ultrasound and MRI have comparable results in diagnosing anorectal disorders.

Diagnostic precision of endoanal MRI in the detection of anal sphincter pathology: a meta-analysis

OBJECTIVE

This study aims to evaluate the diagnostic precision of endoanal magnetic resonance imaging in identifying anal sphincter injury and/or atrophy when compared with either endoanal ultrasound or surgical diagnosis.

MATERIALS AND METHODS

Quantitative meta-analysis was performed on nine studies, comparing endoanal MRI with endoanal ultrasound or surgical diagnosis in 157 patients. Sensitivity, specificity, and diagnostic odds ratio were calculated for each study. Summary receiver operating characteristic curves (SROC) and subgroup analysis were undertaken.

RESULTS

The overall sensitivity and specificity of endoanal MRI for external sphincter injury was 0.78 (95%CI: 0.66-0.84) and 0.66 (95%CI: 0.51-0.79), respectively. For internal sphincter injury detection, this was 0.63 (95%CI: 0.50-0.74) and 0.71 (95%CI: 0.60-0.81), respectively. For detection of atrophy, this was 0.86 (95%CI: 0.71-0.95) and 0.82 (95%CI: 0.65-0.93), respectively. The area under the SROC curve and diagnostic odds ratio were 0.84 (SE = 0.07) and 6.14 (95%CI: 2.17-17.4) for external sphincter injury, 0.79 (SE = 0.07) and 4.60 (95%CI: 1.75-12.15) for internal sphincter injury, and 0.92 (SE = 0.08) and 21.49 (95%CI: 2.87-160.64) for sphincter atrophy.

CONCLUSION

Endoanal MRI was sensitive and specific for the detection of external sphincter injury and especially sphincter atrophy. It may be useful as an alternative to endoanal ultrasound in patients presenting with fecal incontinence, although further clinical studies are needed to identify its best application in clinical practice.

Anal inspection and digital rectal examination compared to anorectal physiology tests and endoanal ultrasonography in evaluating fecal incontinence

BACKGROUND

Anal inspection and digital rectal examination are routinely performed in fecal incontinent patients but it is not clear to what extent they contribute to the diagnostic work-up. We examined if and how findings of anal inspection and rectal examination are associated with anorectal function tests and endoanal ultrasonography.

METHODS

A cohort of fecal incontinent patients (n=312, 90% females; mean age 59) prospectively underwent anal inspection and rectal examination. Findings were compared with results of anorectal function tests and endoanal ultrasonography.

RESULTS

Absent, decreased and normal resting and squeeze pressures at rectal examination correlated to some extent with mean (+/-SD) manometric findings: mean resting pressure 41.3 (+/-20), 43.8 (+/-20) and 61.6 (+/-23) Hg (p<0.001); incremental squeeze pressure 20.6 (+/-20), 38.4 (+/-31) and 62.4 (+/-34) Hg (p<0.001). External anal sphincter defects at rectal examination were confirmed with endoanal ultrasonography for defects <90 degrees in 36% (37/103); for defects between 90-150 degrees in 61% (20/33); for defects between 150-270 degrees in 100% (6/6). Patients with anal scar tissue at anal inspection had lower incremental squeeze pressures (p=0.04); patients with a gaping anus had lower resting pressures (p=0.013) at anorectal manometry. All other findings were not related to any anorectal function test or endoanal ultrasonography.

CONCLUSIONS

Anal inspection and digital rectal examination can give accurate information about internal and external anal sphincter function but are inaccurate for determining external anal sphincter defects <90 degrees. Therefore, a sufficient diagnostic work-up should comprise at least rectal examination, anal inspection and endoanal ultrasonography.

Endoanal ultrasound compared to anorectal manometry for the evaluation of fecal incontinence: a study of the effect these tests have on clinical outcome

Tests for evaluating incontinence include endoanal ultrasound (EUS) and anorectal manometry. We hypothesized that EUS would be superior to anorectal manometry in identifying the subset of patients with surgically correctable sphincter defects leading to an improvement in clinical outcome in these patients. The purpose of this study was to compare these 2 techniques to determine which is more predictive of outcome for fecal incontinence. Thirty-five unselected patients with fecal incontinence were prospectively studied with EUS and anorectal manometry to evaluate the internal anal sphincter (IAS) and external anal sphincter (EAS). EUS was performed with Olympus GFUM20 echoendoscope and a hypoechoic defect in the EAS or IAS was considered a positive test. Anorectal manometry was performed with a standard water-perfused catheter system. A peak voluntary squeeze pressure of < 60 mm Hg in women and 120 mm Hg in men was considered a positive test. All patients were administered the Cleveland Clinic Continence Grading Scale at baseline and at follow-up. Improvement in fecal control was defined as a 25% or greater decrease in continence score. EUS versus manometry were compared with subsequent surgical treatment and outcome. P-values were calculated using Fisher's exact test. Patients (n = 32; 31 females) were followed for a mean 25 months (range 13-46). Sixteen patients had improved symptoms (50%). There was no correlation between EUS or anorectal manometry sphincter findings and outcome. Seven of 14 (50%) patients who subsequently underwent surgery versus 9 of 18 (50%) without surgery improved (P = .578). In long-term follow-up, approximately half of patients improve regardless of the results of EUS or anorectal manometry, or whether surgery is performed.

Endosonography in anorectal disease: an overview

Anorectal endosonography (AE), which was introduced 20 years ago, derives from the study of urology. It was first used to evaluate rectal tumours and later also to investigate benign disorders of the anal sphincters and pelvic floor. The technique is easy to perform, it has a short learning curve and causes no more discomfort than a routine digital examination. A rotating probe with a 360 degrees radius and a frequency between 5 and 16 MHz is introduced to the rectum and then slowly withdrawn so that the pelvic floor and subsequently the sphincter complex are seen. Recently, it has become possible to reconstruct three-dimensional images. AE has been used for almost every possible disorder in the anal region and has increased our insight into anal pathology. The clinical indications for AE are: 1. Faecal incontinence in patients when surgery is an option. AE can show sphincter defects with excellent precision. There is a perfect correlation with surgical findings. Studies comparing AE with endoanal magnetic resonance imaging (MRI) have shown that both methods are equally good for demonstrating defects in the external anal sphincter; the internal anal sphincter is better visualized with AE. After sphincter repair, the effect is directly related to the decrease in the sphincter defect. 2. Perianal fistulae. AE has been shown to be accurate in staging perianal cryptoglandular fistulae and fistulae in Crohn's disease. When there is an external fistula opening, H2O2 can be introduced with a plastic infusion catheter. The tract then becomes visible as a hyperechoic lesion ("white"). It has been shown that this corresponds well with surgical findings. It is equally sensitive as endoanal MRI. Since recurrent cryptoglandular fistulae are complex in 50% and Crohn's fistula in 75%, it is mandatory to perform AE preoperatively in these patients to avoid missed tracts during surgery and subsequent recurrences. 3. Rectal tumors. In low tubulovillous adenomas or malignant polyps considered removable locally, confirming the local resectability (T0 or T1) is mandatory. Although larger rectal and more advanced tumours can be evaluated with AE, MRI is more sensitive in staging nodal involvement. 4. Anal carcinoma for staging. AE has been shown to stage better than the classical TNM classification for both local extension and prognosis. In conclusion, AE images the internal and external anal sphincter with high accuracy. It is easy to perform and is of particular value in the diagnosis of anal incontinence and perianal fistulae. It is excellent in staging anal carcinoma and can also be used in staging rectal carcinoma, especially very low large malignant polyps.

Informed consent and birth: protecting the pelvic floor and ourselves

The controversy over elective cesarean versus vaginal birth with regard to pelvic floor trauma has left many caregivers and patients confused. With the growing evidence to support the development of fecal incontinence as a result of childbirth, we believe that it is imperative to reevaluate modern obstetric practices both for the patient's benefit and for our medical-legal protection. Our attention and energy need to be focused on good informed consent regarding these risks along with improved postpartum surveillance for injury.

Endosonography of anal canal diseases

Anal endosonography became a valuable imaging method for diagnosis of anal diseases because of its accessibility, relative simplicity of performance, and low cost. It is used most often to detect anal sphincter defects, to classify anal fistulas and perianal abscesses, and to stage anal tumors. This review presents a normal anatomy of the anal canal, examination technique, and normal endosonographic anatomy of anal sphincters. The endosonographic findings of anal sepsis, malignancy, trauma, abnormalities in Crohn disease, and ulcerative colitis, as well as the role for anal endosonography among other imaging modalities, are discussed.

Measurement of anal sphincter muscles: endoanal US, endoanal MR imaging, or phased-array MR imaging? A study with healthy volunteers

PURPOSE

To compare endoanal ultrasonography (US), endoanal magnetic resonance (MR) imaging, and phased-array MR imaging for anal sphincter muscle measurement.

MATERIALS AND METHODS

Sixty healthy volunteers underwent 1.5-T phased-array MR, endoanal MR, and endoanal US examinations. Sphincter muscle thicknesses were measured. Measurement reliability was analyzed, and correlations among the imaging methods were calculated. Multivariate analysis was performed to assess the influence of age, weight, height, sex, parity, and obstetric trauma on sphincter dimensions.

RESULTS

Both MR methods had good reliability for measurements of all sphincter components, whereas endoanal US was reliable for internal sphincter measurement only. There was little correlation between the techniques, except between the two MR techniques, with a strong correlation for total sphincter and perineal body thickness. The internal sphincter thickened significantly (P =.002) with age at endoanal US and endoanal MR imaging but not at phased-array MR imaging. There were small sex-based differences in sphincter muscle measurements at phased-array MR imaging only.

CONCLUSION

Endoanal US enables reliable measurement of only internal sphincter thickness, whereas both MR imaging methods enable reliable measurement of all sphincter components. Sphincter measurement with phased-array MR imaging is as reliable as that with endoanal MR imaging.

Endosonography for assessment of anorectal changes in patients with fecal incontinence

Our aim was to evaluate the anorectal changes in patients with fecal incontinence by using different endoultrasound techniques. Eighteen females with fecal incontinence and 14 healthy controls (females) were examined. Rigid linear transducer and 10 MHz radial scanning miniprobe were used. Statistically significant difference was found in the mean percentage of decreasing of the anorectal angle during contraction between healthy subjects (21.4%) and incontinent patients (7.5%). The mean percentage of shortening of the puborectal muscle length during squeezing was significantly lower in patients (9.6%) than in controls (17.9%). By means of miniprobe the anal sphincter defects were clearly demonstrated. Endosonography with a radial scanning miniprobe and rigid linear transducer ensures complex morphological and functional assessment of the anorectal region.

Long-term results of overlapping anterior anal-sphincter repair for obstetric trauma

BACKGROUND

Anterior structural damage to the anal sphincter occurs in up to a third of women at first vaginal delivery, and of these a third have new bowel symptoms. The standard treatment for such structural damage is anterior overlapping anal-sphincter repair. We aimed to assess the long-term results of this operation.

METHODS

We assessed the long-term results in 55 consecutive patients who had had repair a minimum of 5 years (median 77 months [range 60-96]) previously. Questionnaire and telephone interview assessed current bowel function and continence, restriction in activities related to bowel control, and overall satisfaction with the results of surgery. 42 of these patients had been continent of solid and liquid stool at a median of 15 months after the repair.

FINDINGS

We were able to contact 47 (86%) of the 55 patients. One of these patients had required a proctectomy and end ileostomy for Crohn's disease. Of the remaining 46 patients, 27 reported improved bowel control without the need for further surgery, and 23 rated their symptom improvement as 50% or greater. Seven patients had undergone further surgery for incontinence and one patient had not had a covering stoma closed. Thus, the long-term functional outcome of the sphincter repair alone could be assessed in 38 patients. Of these patients, none was fully continent to both stool and flatus; only four were totally continent to solid and liquid stool; six had no faecal urgency; and eight had no passive soiling. Of the 38 patients, 20 still wore a pad for incontinence and 25 reported lifestyle restriction. 14 reported the onset of a new evacuation disorder after sphincter repair. 23 of the 46 patients contacted had a successful long-term outcome (defined as no further surgery and urge faecal incontinence monthly or less).

INTERPRETATION

The results of overlapping sphincter repair for obstetric anal-sphincter damage seem to deteriorate with time. Preoperative counselling should emphasise that although most patients will improve after the procedure, continence is rarely perfect, many have residual symptoms, and some may develop new evacuation disorders.

Perineal body measurement improves evaluation of anterior sphincter lesions during endoanal ultrasonography

Endoanal ultrasonography has become an important tool in the evaluation of patients with anal incontinence. However, the extent of anterior defects is sometimes difficult to quantitate during endoanal ultrasonography.

PURPOSE

This study was designed to evaluate perineal body measurement during endoanal ultrasonography in assessing patients with obstetric anal sphincter injuries.

METHODS

Forty-two patients with anal incontinence because of obstetric sphincter injuries and 13 asymptomatic subjects were investigated with endoanal ultrasonography. Sphincter muscle thickness, sphincter defects, and perineal body were measured. Perineal body measurement was performed by inserting a finger, held gently against the posterior vaginal wall, into the vagina and measuring the distance between the inner surface of the internal sphincter and the ultrasonographic reflection of the finger.

RESULTS

All patients had anterior sphincter lesions of varying extent. Mean size of internal sphincter lesions was 146 degrees, and mean size of external sphincter lesions was 107 degrees (P < 0.001). Perineal body measurement was performed without difficulty in all patients and subjects. Perineal body measurement (mean +/- standard deviation) was 6 +/- 2 mm in patients and 12 +/- 3 mm in asymptomatic subjects (P < 0.001). Ninety-three percent of patients had perineal body measurement < or = 10 mm, and 70 percent of asymptomatic subjects had perineal body measurement > 10 mm. Digital delineation of the perineal body during endoanal ultrasonography improved the visualization of sphincter lesions in 74 percent of patients.

CONCLUSIONS

Digital delineation of the perineal body during endoanal ultrasonography improved the visualization of sphincter lesions in the majority of patients. Perineal body measurement is performed without difficulty and is a good predictor of anterior sphincter lesions. Use of this technique improves visualization of sphincter lesions.

Physical performance measures of radiographic imaging systems

New systems and technologies for dental radiographic imaging are being introduced at an increasing rate. Established methods of physical measurement allow the imaging performance of these systems to be quantified. These quantitative measures are important when comparing the imaging performance of competing systems. This review presents an overview of the main concepts in the assessment of the physical performance of imaging systems including signal transfer, as described by both the characteristic curve and modulation transfer function (MTF), and image noise, as described by the Noise Power Spectra. These measures can be combined to produce signal-to-noise ratio descriptors such as Noise Equivalent Quanta and Detective Quantum Efficiency which give an overall description of imaging system performance. Subjective means of measuring image quality, which naturally include the performance of the image display system and the observer, are also considered as a gauge of system performance.