Integrative radiomics expression predicts molecular subtypes of primary clear cell renal cell carcinoma.

AIM: To identify combined positron-emission tomography (PET)/magnetic resonance imaging (MRI)-based radiomics as a surrogate biomarker of intratumour disease risk for molecular subtype ccA and ccB in patients with primary clear cell renal cell carcinoma (ccRCC). MATERIALS AND METHODS: PET/MRI data were analysed retrospectively from eight patients. One hundred and sixty-eight radiomics features for each tumour sampling based on the regionally sampled tumours with 23 specimens were extracted. Sparse partial least squares discriminant analysis (SPLS-DA) was applied to feature screening on high-throughput radiomics features and project the selected features to low-dimensional intrinsic latent components as radiomics signatures. In addition, multilevel omics datasets were leveraged to explore the complementing information and elevate the discriminative ability. RESULTS: The correct classification rate (CCR) for molecular subtype classification by SPLS-DA using only radiomics features was 86.96% with permutation test p=7×10-4. When multi-omics datasets including mRNA, microvascular density, and clinical parameters from each specimen were combined with radiomics features to refine the model of SPLS-DA, the best CCR was 95.65% with permutation test, p<10-4; however, even in the case of generating the classification based on transcription features, which is the reference standard, there is roughly 10% classification ambiguity. Thus, this classification level (86.96-95.65%) of the proposed method represents the discriminating level that is consistent with reality. CONCLUSION: Featured with high accuracy, an integrated multi-omics model of PET/MRI-based radiomics could be the first non-invasive investigation for disease risk stratification and guidance of treatment in patients with primary ccRCC.

Perineal body length as a risk factor for ultrasound-diagnosed anal sphincter tear at first delivery.

INTRODUCTION AND HYPOTHESIS: Shortened perineal body (PB) is associated with an increased risk of ultrasound-detected obstetric anal sphincter tear. The objective was to determine if shortened perineal body length (<3 cm) is a risk factor for ultrasound-detected anal sphincter tear at first delivery. METHODS: Pregnant nulliparous women were recruited over 18 months. At 35-37 weeks' gestation and 6 weeks' postpartum perineal body length (PB) was measured and subjects completed quality of life questionnaires. Primary outcome was ultrasound-diagnosed anal sphincter tear at 6 weeks postpartum. Secondary outcomes were also assessed. A priori power analysis determined that 70 subjects were needed to detect a difference in anal sphincter tear based on a PB cut-off of 3 cm. RESULTS: Seventy-three subjects completed the study. Mode of delivery was 69.9% spontaneous vaginal, 15.1% operative vaginal, and 15.1% labored cesarean. There were 25 anal sphincter abnormalities (34.2%) seen on ultrasound: 11 (15.1%) internal or external sphincter tears, 3 (4.1%) internal sphincter atrophy, 6 (8.2%) external sphincter thinning, and 7 (9.6%) external sphincter scarring. Only the 11 sphincter tears qualified as abnormal for the primary outcome. In the vaginal delivery group 16.4% (10 out of 61) had a sphincter tear, compared with 8.3% (1 out of 12) in the labored cesarean group (p = 0.68). Women with PB < 3 had a significantly higher rate of ultrasound-diagnosed anal sphincter tear (40.0% vs 11.1%, p = 0.038). When comparing women with and without sphincter tear, there was a significant difference in mean antepartum PB (3.1 vs 3.7 cm, p = 0.043). CONCLUSIONS: A shortened perineal body length in primiparous women is associated with an increased risk of anal sphincter tear at the time of first delivery.

Double cervix and vagina with septate uterus: an uncommon müllerian malformation.

BACKGROUND: The case of an unusual müllerian anomaly is described. CASE: A nulligravida was found to have a septate uterus with double cervix and a vagina with partial longitudinal vaginal septum. The anomaly presented symptomatically, was suggested by clinical examination, and confirmed by magnetic resonance imaging and intraoperative visualization. Visualization of the anomaly was enhanced by magnetic resonance-based three-dimensional reconstruction techniques. CONCLUSION: Description of double cervix and vagina in the setting of an anatomically normal or simple septate uterus is uncommon. This anomaly is inconsistent with the generally accepted understanding of müllerian development but fits with an alternative hypothesis. Magnetic resonance imaging and magnetic resonance-based three-dimensional reconstruction was useful in aiding visualization of the anomaly.

Bayesian regression methodology for estimating a receiver operating characteristic curve with two radiologic applications: prostate biopsy and spiral CT of ureteral stones.

RATIONALE AND OBJECTIVES: The authors evaluated two Bayesian regression models for receiver operating characteristic (ROC) curve analysis of continuous diagnostic outcome data with covariates. MATERIALS AND METHODS: Full and partial Bayesian regression models were applied to data from two studies (n = 180 and 100, respectively): (a) The diagnostic value of prostate-specific antigen (PSA) levels (outcome variable) for predicting disease after radical prostatectomy (gold standard) was evaluated for three risk groups (covariates) based on Gleason scores. (b) Spiral computed tomography was performed on patients with proved obstructing ureteral stones. The predictive value of stone size (outcome) was evaluated along with two treatment options (gold standard), as well as stone location (in or not in the ureterovesical junction [UVJ]) and patient age (covariates). Summary ROC measures were reported, and various prior distributions of the regression coefficients were investigated. RESULTS: (a) In the PSA example, the ROC areas under the full model were 0.667, 0.769, and 0.703, respectively, for the low-, intermediate-, and high-risk groups. Under the partial model, the area beneath the ROC curve was 0.706. (b) The ROC areas for patients with ureteral stones in the UVJ decreased dramatically with age but otherwise were close to that under the partial model (ie, 0.774). The prior distribution had greater influence in the second example. CONCLUSION: The diagnostic tests were accurate in both examples. PSA levels were most accurate for staging prostate cancer among intermediate-risk patients. Stone size was predictive of treatment option for all patients other than those 40 years or older and with a stone in the UVJ.

Variations in levator ani volume and geometry in women: the application of MR based 3D reconstruction in evaluating pelvic floor dysfunction.

OBJECTIVE: We report on the comparative 3-dimensional (3D) living female pelvic floor geometry in five women, comparing the volume, morphology, and integrity of the levator sling, and pelvic anatomic relationships among study subjects. METHODS: Five women of varying ages, parity, continence, and prolapse status were studied. Two-dimensional (2D) imaging of the pelvic floor organs was performed on each subject in the supine position. Manual segmentation techniques and solid modeling software was used to build 3D models of each patient's pelvic floor structures, which could then be viewed and measured on the computer screen. We measured levator muscle volume, posterior urethro-vesical angle, distance from the urethra to pubo-coccygeal line, and the levator plate angle. The integrity of pubo-coccygeal attachments was also recorded. RESULTS: Levator muscle volume ranged from 68 ml in the nulliparous female, to 26 ml in the grand multipara with severe prolapse and mild genuine stress incontinence (GSI). The second lowest volume (30 ml) was in the multipara with GSI. Volumes in the parous subjects without stress urinary incontinence or pelvic organ prolapse were 36 and 39 ml. Pubo-coccygeal attachments were found to be torn in the 2 symptomatic subjects, and were intact in all 3 asymptomatic subjects. CONCLUSION: MR based 3D modeling is feasible and can be used in a research setting to evaluate complex anatomic relationships which may accompany pelvic floor dysfunction. The technique can also be used to evaluate levator muscle morphology and volume, as well as pelvic floor support integrity and its possible role in GSI and prolapse. We are currently conducting a larger study to validate our technique, and to better define the relationship between pelvic floor geometry and pelvic floor dysfunction.

Two- and 3-dimensional MRI comparison of levator ani structure, volume, and integrity in women with stress incontinence and prolapse.

OBJECTIVE: The aim of this study was to identify imaging markers for genuine stress incontinence and pelvic organ prolapse by using magnetic resonance imaging and reconstructed 3-dimensional models. STUDY DESIGN: Thirty women were studied, 10 with prolapse, 10 with genuine stress incontinence, and 10 asymptomatic volunteers. Axial and sagittal T1 and T2 weighted pelvic magnetic resonance scans were obtained with the patient in the supine position. Source images were measured to determine levator hiatus height, bladder neck to pubococcygeal line, levator plate angle, and perineal descent at rest and maximum Valsalva. Manual segmentation and surface modeling was applied to build 3-dimensional models of the organs. The 3-dimensional models were measured to determine levator muscle volume, shape and hiatus width, distance between symphysis and levator sling muscle, posterior urethrovesical angle, bladder neck descent, and levator plate angle. RESULTS: The 3 groups of subjects were comparable in age, parity, and body mass index. In the control, genuine stress incontinence, and prolapse groups, the menopausal rate was 40%, 60%, and 55% (P =.7). In the same order, significant mean 2-dimensional measures were: resting bladder neck descent of 24, 17, and 3 mm (P <.005), straining levator plate angle of -4.3, -11.5, and -31 degrees (P =.01), straining levator hiatus height of 48.5, 51.1, and 65.3 mm (P <.005), and straining perineal descent of 17.2, 22.5, 27.2 mm (P =.02). Similarly ordered mean 3-dimensional parameters showed levator volumes of 32.2, 23.3, and 18.4 cm(3) (P <.005); hiatus widths of 25.7, 34.7, and 40.3 mm (P <.005); left levator sling muscle gaps of 15.6, 20.3, and 23.8 mm (P =.03), right levator sling muscle gaps of 15.6, 22.5, and 30.8 mm, (P = 0.003), and levator shape (90%, 40%, and 20% dome shaped; P <.005). CONCLUSION: Both 2-dimensional magnetic resonance images and 3-dimensional models yield findings that differ among asymptomatic subjects compared with those with genuine stress incontinence and prolapse. Our 3-dimensional data demonstrate a statistically significant continuum in levator volume, shape, and integrity across groups of asymptomatic, genuine stress incontinence, and prolapse subjects.

A detailed audit of reimbursement for abdominal CT in an academic practice.

RATIONALE AND OBJECTIVES: Declining fee schedules, decreasing operating margins, and increasingly stringent compliance regulations create a need for intense scrutiny and optimization of a radiology organization's billing and collection procedures. The authors' goal was to analyze the effectiveness of departmental professional billing procedures, identify controllable factors, and intervene when they could be improved. MATERIALS AND METHODS: A detailed audit of professional claims and payments was performed for all patients who underwent abdominal-pelvic computed tomography (CT) during July 1999 (n = 717). The adequacy of indication for the CT examination as given by the referring physician and modified by the radiology staff, the time required for claim generation, and the status of reimbursement within 120 days were assessed by an interdisciplinary team. After an intervention was performed to improve adequacy of the available clinical indication, the audit was repeated in December 1999 (n = 710). RESULTS: Despite a significant (P < .05) improvement in wording of clinical indications for billing purposes between July (68%) and December (85%), there was no significant change in reimbursement against gross charges. The vast majority of claims (97% in July, 99% in December) were generated in less than 30 days. At 120 days after the date of service, payments had been received that amounted to only 66% and 54% of discounted professional fees for July and December, respectively. For examinations performed in December, payment was delayed beyond contracted time periods in 138 cases (19%). CONCLUSION: Optimum billing and collection for imaging studies is an increasingly complex task. Even when substantial efforts are devoted to eliciting the proper indication for the study, reimbursement remains low primarily because of payer delays.

Volume assessment of the normal female cervix with MR imaging: comparison of the segmentation technique and two geometric formula.

RATIONALE AND OBJECTIVES: The purpose of this study was to determine the volume of the normal female cervix and to determine the geometric formula that yields the best estimate. MATERIALS AND METHODS: Magnetic resonance images of the pelvis in 30 young women were reviewed retrospectively. The volume of the cervix was estimated by using the formulas for an ellipse and a cylinder. Manual labeling and segmentation of the cervix were also performed, and the volume was calculated on the basis of the number and size of the voxels. Comparison of these methods was then performed by using a two-tailed Student t test. RESULTS: No statistically significant difference was found (P = .7) between the volume calculated with the segmentation technique (25.3 mL) and that estimated with the formula for a cylinder (24.8 mL). A statistically significant difference (P < .05) was found between the volume calculated with the segmentation technique and that estimated with the formula for an ellipse (16.4 mL). CONCLUSION: The normal volume of the cervix in this population of young women was approximately 25 mL. The volume of the cervix should be estimated with the formula for a cylinder.

Virtual CT cystoscopy: color mapping of bladder wall thickness.

RATIONALE AND OBJECTIVES: To improve the conspicuity of bladder tumors in a virtual environment, we developed an algorithm for color mapping the thickness of the bladder wall. The purpose of this study was to demonstrate the feasibility of this algorithm as a component of virtual CT cystoscopy. METHODS: Five subjects with a history of superficial transitional-cell carcinoma of the bladder underwent helical CT scanning after insufflation of the bladder with air. Source images were transformed into three-dimensional models, and the thickness of the bladder wall was demarcated by using a new computer algorithm and a fixed color scale. Results were compared with those obtained by conventional cystoscopy. RESULTS: Three tumors, one site of benign wall thickening, and normal wall thickness were correctly identified by using axial source images and virtual cystoscopy with color mapping. CONCLUSIONS: Color mapping of bladder wall thickness is feasible and demonstrates both normal and thickened urothelium. Its value in identification of small or sessile tumors will require further trials.

Voiding cystourethrography findings in elderly women with urge incontinence.

PURPOSE: We report voiding cystourethrography findings associated with urge incontinence in elderly women. MATERIALS AND METHODS: Two observers jointly reviewed voiding cystourethrograms of 50 cognitively intact and mobile elderly female participants in a drug trial for urge incontinence and 19 continent volunteers. Multichannel urodynamic testing was performed in all subjects. Bladder wall trabeculation and diverticula, cystocele and vesicoureteral reflux were noted. Maximal bladder capacity, post-void residual, and history of bladder suspension and hysterectomy were obtained from clinical records. RESULTS: Of the incontinent women 35 (70%) had trabeculation, which was mild in 30 (60%) and moderate in 5 (10%), and 41 (82%) had cystocele, which was mild in 23 (46%), moderate in 15 (30%) and severe in 3 (6%). Maximal bladder capacity ranged from less than 100 to more than 900 cc, and was greater than 500 in 37 incontinent women (74%). Of the continent women 16 (84%) had smooth bladders, 2 had mild (11%) and 1 had moderate (5%) trabeculation, and 11 (58%) had cystocele, which was mild in 8 (42%) and moderate in 3 (16%). In 7 continent women maximal bladder capacity was greater than 500 cc (37%). Differences between the 2 groups in regard to bladder wall trabeculation, maximal bladder capacity and presence of cystocele were significant at p<0.05. CONCLUSIONS: Large bladder capacity, bladder wall trabeculation and small to moderate cystocele on voiding cystourethrography are associated with urge incontinence in the elderly female population.

MR-based three-dimensional modeling of the normal pelvic floor in women: quantification of muscle mass.

OBJECTIVE: Our objective was to use a combination of axial MR source images and three-dimensional (3D) models to describe the anatomy of the normal pelvic floor in young nulliparous women and to measure the volume of the levator ani. SUBJECTS AND METHODS: Ten healthy nulliparous female volunteers (average age, 27 years) underwent T2-weighted MR imaging of the pelvis. Three-dimensional color-coded models of the pelvic bones and organs and the three major components of the levator ani--puborectalis, iliococcygeus, and coccygeus--were created. Source images were used to measure muscle width and signal intensity and to identify ligamentous structures. Using 3D models, we measured the volume of the levator ani, the angle of the levator plate, the posterior urethrovesical angle, and the distance of the bladder neck from the symphysis pubis and the pubococcygeal line. RESULTS: In all volunteers, the signal intensity of the puborectalis exceeded that of the obturator externus. The average volume of the levator ani was 46.6 ml, the average width of the levator hiatus was 41.7 mm, and the average posterior urethrovesical angle was 143.5 degrees. Vaginal shape in the volunteers followed no recognizable pattern. CONCLUSION: Muscle morphology, signal intensity, and volume is relatively uniform among healthy young women.

Helical CT of the urinary tract.

The advent of helical CT has changed the practice of uroradiology and has significantly benefited patients. Painful, obstructing ureteral stones can be diagnosed with certainty in less than 1 min without contrast medium. Radiologists can now thoroughly evaluate and characterize small renal masses without fear of skip areas caused by respiratory misregistration. Radiologic evaluation of living potential renal donors, formerly a two- or three-stage procedure, can now be performed in a single visit. Finally, three-dimensional reconstructions allow use of the same data both to diagnose tumors and to plan their resection. Axial or three-dimensional images generated using helical CT will likely be increasingly important in detecting and staging cancer, determining stone composition and appropriate therapy, and evaluating renal artery stenosis.

CT and ultrasound features of metanephric adenoma in adults with pathologic correlation.

PURPOSE: The purpose of this work was to correlate the CT, ultrasound, and pathologic features of metanephric adenoma, a rare benign renal tumor in adults. METHOD: Retrospective review of medical records (1990-1997) revealed three adult female patients who had both preoperative imaging and nephrectomy with pathologic diagnosis of metanephric adenoma performed at our institution. CT (n = 3) and ultrasound (n = 2) features were reviewed in consensus by two radiologists and correlated with pathologic findings. RESULTS: In all three cases, the metanephric adenoma was of increased attenuation relative to adjacent renal parenchyma on unenhanced CT scans. No septa or calcifications were seen. Ultrasound images showed both tumors to be hyperechoic with enhanced through-transmission. CONCLUSION: The CT and ultrasound findings correlate with the pathologic features of a high nuclear-to-cytoplasmic ratio and psammomatous calcifications. In the adult population, it is unlikely that metanephric adenoma can be prospectively differentiated from renal cell carcinoma based on imaging features.

Staging of 119 patients with renal cell carcinoma: the yield and cost-effectiveness of pelvic CT.

OBJECTIVE: The goal of this study was to determine the yield and cost-effectiveness of pelvic CT in staging renal cell carcinoma. MATERIALS AND METHODS: The records of 119 patients who underwent preoperative CT of the abdomen and pelvis during a 6-year interval and then underwent partial or radical nephrectomy for renal cell carcinoma were reviewed for CT findings and pathologic stage. Pelvic CT findings were divided into three categories: benign and likely insignificant, benign and likely significant, and probably malignant. The effect of CT findings on further testing and the scheduling of surgery was assessed. An estimate of the cost of pelvic CT scans and other radiologic tests was made using 1997 Medicare reimbursement rates. RESULTS: Total estimated cost of the 119 CT examinations of the pelvis was $40,698 ($342 each). No findings of probable malignancy were identified. In 27 patients, CT showed benign findings; these results did not cause planned surgery to be delayed. Three of these 27 patients underwent further radiologic tests at an estimated total cost of $243. CONCLUSION: CT of the pelvis has a negligible yield in the staging of renal cell carcinoma and should not be routinely performed. The findings on CT of the pelvis did not generate a significant number of other tests.

MR imaging of pelvic floor continence mechanisms in the supine and sitting positions.

OBJECTIVE: Our goal was to determine the anatomic differences in pelvic floor anatomy for continent women and women with stress incontinence using MR imaging and to assess whether these anatomic differences depend on the position of the subject during imaging. SUBJECTS AND METHODS: Eight continent volunteers and eight women with stress incontinence underwent MR imaging in the supine and sitting positions. For imaging, we used an open-configuration 0.5-T magnet. T2-weighted images were obtained in the midline sagittal plane with subjects at rest and at maximal pelvic floor strain in 5 sec using a modified fast spin-echo sequence. In the axial plane, thin-section T2-weighted images were obtained with subjects at rest using a standard fast spin-echo technique. Images were evaluated for mobility of the urethra and bladder neck and for integrity of the vagina, levator ani, and supporting fascia. RESULTS: Pelvic floor laxity and abnormalities of the supporting fascia were more common in incontinent women than in continent women. Both descent of the bladder neck when subjects strained and the posterior urethrovesical angle were not significantly greater when subjects were measured in the sitting position (p < .1). CONCLUSION: Changes of pelvic floor laxity related to incontinence can be seen with subjects in both the supine and the sitting positions but are increased in the sitting position.

Original smooth receiver operating characteristic curve estimation from continuous data: statistical methods for analyzing the predictive value of spiral CT of ureteral stones.

RATIONALE AND OBJECTIVES: Diagnostic studies such as spiral computed tomography (CT) in patients with obstructing ureteral calculi often necessitate the analysis of continuous test data (e.g., stone sizes). The accuracy of a test can be summarized by using a receiver operating characteristic (ROC) curve. The authors developed and compared three methods for constructing a smooth ROC curve from continuous diagnostic data. MATERIALS AND METHODS: Nonparametric, semiparametric, and parametric smooth ROC curve analyses were applied to data from 100 unenhanced spiral CT scans of patients with proved obstructing ureteral stones. Accuracy in using stone size to predict the need for intervention was evaluated by means of these methods. Characteristics and summary measures of the resulting ROC curves were estimated. RESULTS: All methods fit the data well. The nonparametric method followed the details of the empiric data. The semiparametric and parametric methods yielded similar estimates of the ROC curve parameters. Areas under the ROC curves were 0.807, 0.821, and 0.814 for nonparametric, semiparametric, and parametric methods, respectively, in comparison with 0.811 for the empiric method. CONCLUSION: The parametric method is preferred for constructing a smooth ROC curve with available stone-size data derived from spiral CT. The analyses confirm the predictive value of stone size in determining the need for intervention.

Unenhanced helical CT of ureteral stones: a replacement for excretory urography in planning treatment.

OBJECTIVE: The purpose of this study was to determine whether unenhanced helical CT alone can be used for diagnosis and treatment planning of patients with obstructing ureteral stones. MATERIALS AND METHODS: Medical records of 100 patients with ureteral stones and a clearly discernible clinical outcome who had undergone unenhanced helical CT were reviewed to determine the number of urography procedures and results of excretory urograms performed within 72 hr of helical CT. CT scans were then reviewed by two radiologists for six findings: in-plane stone diameter, z-axis stone diameter, location of stone, periureteral stranding, hydronephrosis, and perinephric fluid. Seventy-one patients passed stones spontaneously, and 29 patients required intervention including basket retrieval, extracorporeal shock-wave lithotripsy, laser lithotripsy, or a combination of the three treatments. Data were analyzed to determine those findings that correlated with the need for intervention. RESULTS: Five excretory urograms were obtained, all of which agreed with findings revealed by CT. Excretory urography added no information. CT findings of in-plane diameter (p < .001), z -axis diameter (p < .001), and location of stone (p = .003) all significantly correlated with the need for intervention. CONCLUSION: Helical CT can be used in place of excretory urography to plan treatment of patients with flank pain caused by obstructing ureteral stones. Stones that are larger than 5 mm, located within the proximal two thirds of the ureter, and seen on two or more consecutive CT images are more likely to require endoscopic removal, lithotripsy, or both.

Open-configuration MR imaging, intervention, and surgery of the urinary tract.

The open-configuration MR imaging system provides new applications both in diagnosis and in therapy of conditions in the urinary tract. In addition to conventional imaging, the open configuration permits MR imaging of patients in many positions. This has already been shown to be useful in imaging the pelvis during voiding, where a sitting position allows urodynamic evaluation. The lithotomy position can be used for imaging the prostate, which also permits procedural access. The ultimate purpose of the interventional MR imaging suite is to integrate therapeutic tools and techniques with MR imaging. From surgical planning through specialized imaging systems with minimally invasive surgical applications, new methods are being developed and implemented. This new field of image-guided therapy will require extensive clinical development and evaluation for applications in the urinary tract. This will require a large concentrated interdisciplinary effort of surgeons, radiologists, computer scientists, engineers, and physicists. Successful integration of basic research and clinical work will result in a number of cutting-edge technologies with direct clinical application in the urinary tract. Initial projects have included biopsies, endoscopies, and real-time procedural control of high-temperature and cryogenic ablations. It is anticipated that the current surge in image-guided interventions will motivate even more research activity in this field, and will ultimately define the role of MR imaging guidance in urologic intervention and surgery.

Transitional cell carcinoma of the fossa navicularis.

We report a case of transitional cell carcinoma of the fossa navicularis in an elderly white male. The patient presented in urinary retention, with a large exophytic mass at the external urethral meatus. Both the pathogenesis and natural history of this highly unusual tumor are unclear. Treatment depends on grade and stage of disease. Transurethral resection and fulguration have been successfully used to treat superficial lesions. Segmental resection and partial penectomy, with or without inguinal lymph node dissection, form the mainstay of treatment for invasive disease. The role of chemotherapy for advanced disease is unknown.

Magnetic resonance imaging of the lower urinary tract.

Magnetic resonance imaging with its excellent contrast resolution and direct multiplanar imaging capacity, has become a valuable tool to improve understanding of lower urinary tract function and pelvic floor physiology. Review of the current English language literature shows that the domain of magnetic resonance imaging is research. In comparison with other imaging techniques, magnetic resonance imaging has been shown to yield better soft tissue differentiation and anatomic resolution. Newer techniques also allow some form of dynamic imaging.