Fourier and factorial analysis: an objective and comparative evaluation on a cardiac phantom

Orthogonal and oblique factor analysis represent an alternative to Fourier analysis in the evaluation of cardiac dynamic behaviour in gated blood pool studies. In order to estimate their respective places, orthogonal factor analysis (OFA), factor analysis of dynamic structures (FADS) and Fourier analysis (FA) are tested on a dynamic and periodical phantom with well known and reproducible kinetics. The phantom data are acquired under standard conditions by varying the counting rates and the temporal frequency sampling. To compare the results of the three methods with maximal objectivity, the relative contribution of each component is calculated. With standard acquisition conditions, FA and OFA give very close results. Only a minor advantage in evaluation of small phase differences is observed with OFA. FADS solutions are effectively related to the dynamic behaviour of the phantom, but their interpretation is more complicated and the quality of the oblique factors is reduced as the number of calculated factors increases. The influence of the counting statistics on FA, OFA and FADS is very similar. However, in cases of undersampling, robustness is demonstrated with the factorial technics.     

Fourier and factorial analysis: An objective and comparative evaluation on a cardiac phantom

Orthogonal and oblique factor analysis represent an alternative to Fourier analysis in the evaluation of cardiac dynamic behaviour in gated blood pool studies. In order to estimate their respective places, orthogonal factor analysis (OFA), factor analysis of dynamic structures (FADS) and Fourier analysis (FA) are tested on a dynamic and periodical phantom with well known and reproducible kinetics. The phantom data are acquired under standard conditions by varying the counting rates and the temporal frequency sampling. To compare the results of the three methods with maximal objectivity, the relative contribution of each component is calculated. With standard acquisition conditions, FA and OFA give very close results. Only a minor advantage in evaluation of small phase differences is observed with OFA. FADS solutions are effectively related to the dynamic behaviour of the phantom, but their interpretation is more complicated and the quality of the oblique factors is reduced as the number of calculated factors increases. The influence of the counting statistics on FA, OFA and FADS is very similar. However, in cases of undersampling, robustness is demonstrated with the factorial technics.     

Perfusion MRI of infarcted and noninfarcted brain tissue in stroke: a comparison of conventional hemodynamic imaging and factor analysis of dynamic studies

RATIONALE AND OBJECTIVES: To investigate the hemodynamics of infarcted and noninfarcted regions of the brain in patients with stroke secondary to a complete middle cerebral artery occlusion. Also, to compare factor analysis, a novel method of analyzing perfusion-weighted images, with more conventional techniques. METHODS: Twenty-two patients with complete unilateral occlusion of the middle cerebral artery were examined by T1-weighted, contrast-enhanced, perfusion-weighted imaging, diffusion-weighted imaging, and magnetic resonance angiography. Quantitative cerebral blood volume (CBV), cerebral blood flow (CBF), and time-to-peak-intensity (TTP) images were generated. Factor analysis of dynamic studies (FADS) was used to generate "early" and "late" images. The hemodynamic parameters for the infarcted and noninfarcted regions of the occluded territory were compared with those for the brain territory on the nonoccluded side. RESULTS: Three regions were shown: (1) Normal tissue on the unaffected side; (2) an infarcted region, which was characterized by reduced CBV, CBF, and early FADS values with increased TTP values; and (3) a noninfarcted region with reduced early FADS and increased late FADS and TTP values compared with the normal region. Cerebral blood volume and CBF values were not reduced significantly in the noninfarcted region. CONCLUSIONS: The differences in parameters such as TTP, CBV, and CBF are significant, and it is necessary to use more than one parameter when interpreting magnetic resonance imaging perfusion data. Factor analysis of dynamic studies provides additional information to conventional methods of analyzing perfusion data.     

Noise removal using factor analysis of dynamic structures: application to cardiac gated studies.

Factor analysis of dynamic structures (FADS) facilitates the extraction of relevant data, usually with physiologic meaning, from a dynamic set of images. The result of this process is a set of factor images and curves plus some residual activity. The set of factor images and curves can be used to retrieve the original data with reduced noise using an inverse factor analysis process (iFADS). This improvement in image quality is expected because the inverse process does not use the residual activity, assumed to be made of noise. The goal of this work is to quantitate and assess the efficiency of this method on gated cardiac images. METHODS: A computer simulation of a planar cardiac gated study was performed. The simulated images were added with noise and processed by the FADS-iFADS program. The signal-to-noise ratios (SNRs) were compared between original and processed data. Planar gated cardiac studies from 10 patients were tested. The data processed by FADS-iFADS were subtracted to the original data. The result of the substraction was studied to evaluate its noisy nature. RESULTS: The SNR is about five times greater after the FADS-iFADS process. The difference between original and processed data is noise only, i.e., processed data equals original data minus some white noise. CONCLUSION: The FADS-iFADS process is successful in the removal of an important part of the noise and therefore is a tool to improve the image quality of cardiac images. This tool does not decrease the spatial resolution (compared with smoothing filters) and does not lose details (compared with frequential filters). Once the number of factors is chosen, this method is not operator dependent.     

Comparison of phase analysis with factor analysis in equilibrium gated radionuclide angiography

This study is the intercomparison of phase analysis (PA), factor analysis of dynamic structures (FADS) and Karhunen-Loeve analysis (KLA) in the diagnosis of regional wall motion abnormalities, RWMA, of the LV. One hundred and twenty eight patients with proven or suspected CAD have been investigated by both X-ray angiography and radionuclide equilibrium angiography performed in the LOA view. FADS and KLA are performed twice, once on the whole-image (WI-FADS, WI-KLA), and once on the LV ROI (LV-FADS, LV-KLA) as suggested by Pavel. Resulting images and factors are interpreted by a well trained observer. In an attempt to quantify LV-FADS images, two numeric parameters, P1 and P2, are defined. They measure the relative weight of the so-called ventricular factor for 2 and 3 factor analysis, respectively. A ROC curve is calculated for each method, taking X-ray angiography as the gold-standard. The areas under the ROC curves are estimated by the maximum likelihood method and are compared using a test described by Hanley which takes into account the correlation between the responses. The areas are: 0.90 for PA, 0.84 for WI-FADS, 0.86 for LV-FADS, 0.83 for WI-KLA, 0.86 for LV-KLA, 0.65 for P1 and 0.72 for P2. The observed differences are significant (at 5% level) between PA and WI-FADS and between FA and WI-KLA; whereas they are not between PA and LV-FADS, between PA and LV-KLA and between LV-FADS and LV-KLA. The diagnostic value of the two numeric parameters is poor.(ABSTRACT TRUNCATED AT 250 WORDS)     

Factor analysis of 81mKr lung ventilation studies

Factor analysis of dynamic structures (FADS) summarizes data depending on time and space in a few elementary components. Each of them associates a time-activity curve (factor) and the spatial distribution of the corresponding events. The aim was to evaluate the patterns, the number of components, and their possible link to physiology when FADS was applied to scintigraphic images representing a composite of a 81mKr ventilation cycle. In a study of 26 patients (10 normal, 16 pathologic), components were found that represent: (1) a rapid and steeply changing ventilation factor, corresponding mainly to bases in normal subjects and whole lung fields in patients, (2) a slower expiration and shorter inspiration ventilation factor distributed throughout both lung fields in all patients, (3) a constant activity curve, with an inspiratory activity peak distributed over both lung fields and the large airways, and (4) a factor including a phase shift with respect to the first; this was found significantly more often in patients with pathology.     

Factor analysis as a means of determining response to chemotherapy in patients with osteogenic sarcoma

The prognosis of localized osteogenic sarcoma (OS) has improved considerably since the introduction of neoadjuvant chemotherapy. However, there is a subset of patients who do not show full benefit from neoadjuvant chemotherapy because of chemoresistance. The early identification of poor responders to chemotherapy during neoadjuvant therapy remains difficult. In order to evaluate the role of bone scintigraphy we report our experience of dynamic technetium-99m hydroxymethylene diphosphonate bone scintigraphy in 19 cases of paediatric osteogenic sarcomas. Before the beginning of chemotherapy, a dynamic scan was recorded during 30 min followed by static images at 3 h. The procedure was repeated halfway through the course of chemotherapy (6th week). Histological grading of the response to chemotherapy was carried out in the 12th week, showing nine good responses and ten poor responses. Factor analysis of dynamic structures (FADS) applied to dynamic scans allowed us to identify three factors termed vascular, soft tissue and osseous factors. The effect of chemotherapy on each factor was evaluated. Using FADS we were able to detect all the poor histological responders with the combination of vascular and osseous factors. Six out of nine good histological responders were also classified as scintigraphic responders. FADS applied to dynamic bone scans allowed us to identify at an early stage all the poor histological responders to neoadjuvant chemotherapy. This method may have clinical relevance for the therapeutic strategy in patients with OS.     

Factor analysis of dynamic structures (FADS) in the diagnosis of renal disease

Factor analysis of dynamic structures (FADS) has been used in the interpretation of dynamic scintigraphic studies since the technique was described by Bazin et al. (1980). This study was designed to analyse to what extent, if any, does physiological factor analysis of dynamic renal data really help the clinician and by how much the method improves the diagnostic accuracy when compared to deconvolution analysis and parenchymal transit time (PTT) measurements. One hundred and fifty patients who were clinically, biochemically and radiologically investigated for renal disease were included in the study. Fifty of these were found to have no clinical evidence of renal disease, 50 were diagnosed as having non obstructive kidney disease and 50 had evidence of renal obstruction. Data obtained from ^99mTc-DTPA renography were processed using deconvolution (with PTTs) and physiological factor analysis and the results compared by ROC analysis. Clinically the information gained from factor analysis was superior to that obtained from deconvolution with PTT measurements in that a more accurate differentiation between an obstructive nephropathy and an obstructive uropathy was obtained. It is considered that physiological factor analysis enhanced the clinical information obtained from renography, increases diagnostic accuracy and obviates the need for diuresis renography.     

Factor analysis of dynamic structures (FADS) in the diagnosis of renal disease

Factor analysis of dynamic structures (FADS) has been used in the interpretation of dynamic scintigraphic studies since the technique was described by Bazin et al. (1980). This study was designed to analyse to what extent, if any, does physiological factor analysis of dynamic renal data really help the clinician and by how much the method improves the diagnostic accuracy when compared to deconvolution analysis and parenchymal transit time (PTT) measurements. One hundred and fifty patients who were clinically, biochemically and radiologically investigated for renal disease were included in the study. Fifty of these were found to have no clinical evidence of renal disease, 50 were diagnosed as having non obstructive kidney disease and 50 had evidence of renal obstruction. Data obtained from 99mTc-DTPA renography were processed using deconvolution (with PTTs) and physiological factor analysis and the results compared by ROC analysis. Clinically the information gained from factor analysis was superior to that obtained from deconvolution with PTT measurements in that a more accurate differentiation between an obstructive nephropathy and an obstructive uropathy was obtained. It is considered that physiological factor analysis enhanced the clinical information obtained from renography, increases diagnostic accuracy and obviates the need for diuresis renography.     

Clinical assessment of uneven ventilation by factor analysis of Xe-133 washout scintigram

Factor analysis (FA) was applied to 50 consecutive Xe-133 washout lung scintigrams, and its findings were compared with dynamic scintigrams of Xe-133 washout (DSW). Mean transit time (MTT) of radioactive xenon measured by FA also was compared with that measured by height/area (H/A) or two-compartment analysis (2CA). In 12 patients with normal DSW, FA separated and located two factors: one represented background activity, and the other uniform washout from the lung. In 31 out of 38 patients (82%) with abnormal DSW, FA separated the same areas where the washout was delayed on DSW. In 5 (13%) patients, FA diagnosed more areas of delayed washout than DSW. FA failed in 2 (5%) patients, but this failure was due to small number of counts of pixels. Diagnosis by FA was seemed easier than diagnosis by DSW in 95% of all patients by the authors' impression. MTT by FA (y) correlated with MTT by 2CA (x) in small groups of patients: in 9 patients in whom only one MTT was obtainable by FA (r = 0.75, p = 0.02, y = 4.2x + 1.9), and in 8 patients of normal DSW in whom two MTT's were obtainable by FA (r = 0.77, p = 0.02, y = 0.69x + 6.2, y; shorter MTT by FA between the two). MTT by FA did not correlate with MTT by H/A. In conclusion, FA is useful for diagnosing uneven Xe-133 washout from the lung.     

Calculation of cerebral perfusion parameters using regional arterial input functions identified by factor analysis

PURPOSE: To calculate regional cerebral blood volume (rCBV), regional cerebral blood flow (rCBF), and regional mean transit time (rMTT) accurately, an arterial input function (AIF) is required. In this study we identified a number of AIFs using factor analysis of dynamic studies (FADS), and performed the cerebral perfusion calculation pixel by pixel using the AIF that was located geometrically closest to a certain voxel. MATERIALS AND METHODS: To verify the robustness of the method, simulated images were generated in which dispersion or delay was added in some arteries and in the corresponding cerebral gray matter (GM), white matter (WM), and ischemic tissue. Thereafter, AIFs were determined using the FADS method and simulations were performed using different signal-to-noise ratios (SNRs). Simulations were also carried out using an AIF from a single pixel that was manually selected. In vivo results were obtained from normal volunteers and patients. RESULTS: The FADS method reduced the underestimation of rCBF due to dispersion or delay that often occurs when only one AIF represents the entire brain. CONCLUSION: This study indicates that the use of FADS and the nearest-AIF method is preferable to manual selection of one single AIF.     

Factor analysis of multigated cardiac blood pool scintigram for the measurement of left ventricular ejection fraction

Left ventricular ejection fraction (EF) was measured by factor analysis (FA) of multigated cardiac blood pool scintigram in 38 consecutive patients, and compared with that measured by the variable ROI method (EFVROI) with automated left ventricular contour detection. FA was automatically performed without operator intervention with a success rate of 100%. The correlation of EF with EFVROI was significant in the group of 22 patients with normal wall motion (r = 0.65, p less than 0.001), and the entire group of patients (r = 0.70, p less than 0.001), but not significant (p = 0.19) in the group of 16 patients with abnormal wall motion. In conclusion, left ventricular ejection fraction can be estimated by factor analysis of MUGA in patients with normal wall motion.     

Diffusion tensor tractography-based analysis of the cingulum: clinical utility and findings in traumatic brain injury with chronic sequels

Introduction

To evaluate the clinical utility of quantitative diffusion tensor tractography (DTT) and tractography-based core analysis (TBCA) of the cingulum by defining the reproducibility, normal values, and findings in traumatic brain injury (TBI).

Methods

Eighty patients with TBI and normal routine MRI and 78 controls underwent MRI at 3T. To determine reproducibility, 12 subjects were scanned twice. Superior (SC) and inferior (IC) cingulum were analyzed separately by DTT (fractional anisotropy (FA) thresholds 0.15 and 0.30). TBCA was performed from volumes defined by tractography with gradually changed FA thresholds. FA values were correlated with clinical and neuropsychological data.

Results

The lowest coefficient of variation was obtained at DTT threshold 0.30 (2.0 and 2.4 % for SC and IC, respectively), but in proportion to standard deviations of normal controls, the reproducibility of TBCA was better in SC and similar to that of DTT in IC. In patients with TBI, volume reduction with loss of peripheral fibers was relatively common; mean FA was mostly normal in these tractograms. The frequency of FA reductions (>2 SD) was in DTT smaller than in TBCA, in which FA decrease was present in 42 (13.1 %) of the 320 measurements. Central FA values in SC predicted visuoperceptual ability, and those in left IC predicted cognitive speed, language, and communication ability (p?Conclusion Tractography-based measurements have sufficient reproducibility for demonstration of severe abnormalities of the cingulum. TBCA is preferential for clinical FA analysis, because it measures corresponding areas in patients and controls without inaccuracies due to trauma-induced structural changes.     

MR-derived cerebral blood volume maps: issues regarding histological validation and assessment of tumor angiogenesis.

In an effort to develop MRI methods for the evaluation of tumor angiogenesis (new blood vessel formation), MRI-derived cerebral blood volume (CBV) information has been compared to histologic measures of microvessel density (MVD). Although MVD is a standard marker of angiogenesis, it is not a direct correlate of the volume measurements made with MRI, and therefore inappropriate for the development and validation of the MR techniques. Therefore, the goal of this study was to develop an approach by which MR measurements of CBV can be directly correlated. To this end, dynamic susceptibility contrast (DSC) MRI experiments were performed in six Fisher rats implanted with 9L gliosarcoma brain tumors. Subsequently, the circulation was perfused with a latex compound (Microfil), after which 50-microm tissue sections were analyzed for vessel count, diameter, and the fraction of area comprised of vessels. The results demonstrate that while fractional area (FA) does not provide a good measure of CBV, FA corrected for section thickness effects does. Whereas the FA in normal brain was found to be 13.03 +/- 1.83% the corrected FA, or fractional volume (FV), was 1.89 +/- 0.39%, a value in agreement with those reported in the literature for normal brain. Furthermore, while no significant difference was found between normal brain and tumor FA (P = 0.55), the difference was significant for FV (P = 0.036), as would be expected. And only with FV does a correlation with the MRI-derived CBV become apparent (r(S) = 0.74). There was strong correlation (r(s) = 0.886) between the tumor / normal blood volume ratios as estimated by each technique, although the MR-ratio (1.56 +/- 0.29) underestimated the histologic-ratio (2.35 +/- 0.75). Thus, the correlation of MRI CBV methods requires a measurement of fractional vessel area and correction of this area for section thickness effects. This new independent correlative measure should enable efficient and accurate progress in the development of MRI methods to evaluate tumor angiogenesis.     

颅内肿瘤DTI及DTT应用价值初探

目的 初步探讨MR扩散张量成像(DTI)在显示颅内肿瘤与周围白质关系的价值及其在鉴别诊断中的作用．通过扩散张量纤维束成像(DTT)重建双侧皮质脊髓束,评价其临床应用价值。资料与方法 对9例高级别胶质瘤、11例转移瘤、14例脑膜瘤患者进行常规MRI及DTI检查,测量患侧感兴趣区Dcavg、FA、1—VR、RA值,部分求出与对侧相应部位兴趣区比值,行组间统计学分析;三维重建双侧皮质脊髓束并与肿瘤图像融合．探讨患侧皮质脊髓束形态与肌力之间的相关性。结果 肿瘤实性部分、瘤周水肿、水肿周围“正常”白质的Dcavg、FA、1—VR、RA值及各参数比值组间比较部分存在显著性差异;肌力与皮质脊髓束形态具有良好的相关性。结论 DTI较常规MRI可更好地观察肿瘤与周围脑白质的关系,为肿瘤的鉴别诊断提供补充信息,而DTT具有良好的应用前景。     

Haemodynamic effects of dual-chamber pacing versus ventricular pacing during a walk test in patients with depressed or normal left ventricular function

Purpose Dual-chamber rate-modulated pacing provides haemodynamic benefits compared with ventricular pacing at rest, but it is unclear whether this also holds true during physical exercise in patients with heart failure. This study assessed the haemodynamic response to a walk test during dual-chamber pacing and ventricular pacing in patients with depressed or normal left ventricular (LV) function.Methods Twelve patients with an LV ejection fraction <50% and 11 patients with an LV ejection fraction 50% underwent two randomised 6-min walk tests under dual-chamber rate-modulated pacing and ventricular pacing at a fixed rate of 70 beats/min. All patients had a dual-chamber pacemaker implanted for complete heart block. LV function was monitored by a radionuclide ambulatory system.Results In patients with depressed LV function, the change from dual-chamber pacing to ventricular pacing induced a decrease in end-systolic volume at the peak of the walk test (P<0.05), with no difference in end-diastolic volume. As a consequence, higher increases in LV ejection fraction (P<0.0001) and stroke volume (P<0.01) were observed during ventricular pacing. No difference in cardiac output was found between the two pacing modes. In patients with normal LV function, the change from dual-chamber pacing to ventricular pacing induced a significant decrease in cardiac output (P<0.005 at rest and P<0.05 at the peak of the walk test).Conclusion Compared with dual-chamber rate-modulated pacing, ventricular pacing improves cardiac function and does not affect cardiac output during physical activity in patients with depressed LV function, whereas it impairs cardiac output in those with normal function.     

Diffusion tensor imaging and tractography of the kidneys: assessment of chronic parenchymal diseases

Objective

To assess renal dysfunction in chronic kidney diseases using diffusion tensor imaging (DTI).

Methods

Forty-seven patients with impaired renal function (study group) and 17 patients without renal diseases (control group) were examined using DTI sequences. Cortical and medullary regions of interest (ROIs) were located to obtain the corresponding values of the apparent diffusion coefficient (ADC) and the fractional anisotropy (FA). The mean values of the ADC and FA, for each ROI site, were obtained in each group and were compared. Furthermore, the correlations between the diffusion parameters and the estimated glomerular filtration rate (eGFR) were determined.

Results

In both the normal and affected kidneys, we obtained the cortico-medullary difference of the ADC and the FA values. The FA value in the medulla was significantly lower (P?=?0.0149) in patients with renal function impairment as compared to patients with normal renal function. A direct correlation between DTI parameters and the eGFR was not found. Tractography visualised disruption of the regular arrangement of the tracts in patient with renal function alteration.

Conclusion

DTI could be a useful tool in the evaluation of chronic kidney disease and, in particular, the medullary FA value seems to be the main parameter for assessing renal damage.

Key Points

? Magnetic resonance diffusion tensor imaging (MRDTI) provides new information about renal problems. ? DTI allows non-invasive repeatable evaluation of the renal parenchyma, without contrast media. ? DTI could become useful in the management of chronic parenchymal disease. ? DTI seems more appropriate for renal evaluation than diffusion-weighted imaging.