Paul Summers

Diffusion-weighted MR imaging in assessing cervical tumour response to nonsurgical therapy.

PurposeThis study was undertaken to assess whether there is a correlation between the response of cervical tumours to nonsurgical therapy (chemo- and/or radiotherapy) and apparent diffusion coefficient (ADC) values.Patients and methodsSeventeen consecutive patients prospectively underwent pelvic magnetic resonance (MR) imaging including diffusion-weighted imaging (DWI) sequences before and after nonsurgical therapy for cervical cancer. A control group of 17 patients without cervical pathology was matched to the study group. Differences in baseline ADC maps between the two groups and within the study group before and after therapy were assessed by nonparametric tests.ResultsThe diameter and volume of cervical cancers decreased after therapy in 14/17 lesions (responders) and increased in 3/17 lesions (nonresponders). The ADC values of responders increased significantly (p=0.0009). Percent changes in ADC values before and after therapy were higher in responders than nonresponders (p=0.04). There was no significant difference in ADC values between responders and nonresponders at the staging MR examination (p=0.09) and no significant correlation between pretreatment ADC values and percentage of tumour reduction. Tumours with higher percent ADC value increase showed higher tumour reduction volume, but this was not significant (p=0.12).ConclusionsADC values of cervical cancer after therapy showed significant differences compared with pretherapy values, particularly for responders.RiassuntoObiettivoScopo del nostro lavoro è stato valutare se esiste una correlazione tra la risposta dei tumori della cervice uterina alle terapie non chirurgiche (chemio- e/o radioterapia) e i valori di coefficiente di diffusione apparente (ADC).Pazienti e metodiDiciassette pazienti consecutive sono state prospetticamente sottoposte ad esami di risonanza magnetica (RM) della pelvi, comprendenti sequenze pesate in diffusione (DWI), prima e dopo terapie non chirurgiche per tumore della cervice uterina. A questo gruppo di studio è stato associato un gruppo di controllo (stesso numero di soggetti, senza patologia della cervice). Le differenze dei valori delle mappe ADC tra i due gruppi alla baseline, e nel gruppo di studio prima e dopo terapia sono state valutate con test non parametrici.RisultatiDiametro e volume dei tumori cervicali si sono ridotti dopo le terapie in 14/17 lesioni (rispondenti), sono invece aumentati in 3/17 lesioni (non rispondenti). I valori ADC dei rispondenti sono aumentati significativamente (p=0,0009). Le variazioni percentuali dei valori ADC prima e dopo terapia erano superiori nei rispondenti rispetto ai non rispondenti (p=0,04). Non si sono riscontrate differenze significative nei valori di ADC alla RM basale tra rispondenti e non rispondenti (p=0,09), né tra valori ADC basali e percentuale di riduzione del tumore. I tumori con più alto incremento percentuale di valori di ADC hanno mostrato più elevata riduzione del volume tumorale, ma questo non è risultato significativo (p=0,12).ConclusioniI valori di ADC del tumore della cervice uterina hanno mostrato significativo incremento dopo terapia rispetto ai valori pre-terapia, particolarmente per i tumori rispondenti.

Liver 4DMRI: A retrospective image-based sorting method.

PURPOSE Four-dimensional magnetic resonance imaging (4DMRI) is an emerging technique in radiotherapy treatment planning for organ motion quantification. In this paper, the authors present a novel 4DMRI retrospective image-based sorting method, providing reduced motion artifacts than using a standard monodimensional external respiratory surrogate. METHODS Serial interleaved 2D multislice MRI data were acquired from 24 liver cases (6 volunteers + 18 patients) to test the proposed 4DMRI sorting. Image similarity based on mutual information was applied to automatically identify a stable reference phase and sort the image sequence retrospectively, without the use of additional image or surrogate data to describe breathing motion. RESULTS The image-based 4DMRI provided a smoother liver profile than that obtained from standard resorting based on an external surrogate. Reduced motion artifacts were observed in image-based 4DMRI datasets with a fitting error of the liver profile measuring 1.2 ± 0.9 mm (median ± interquartile range) vs 2.1 ± 1.7 mm of the standard method. CONCLUSIONS The authors present a novel methodology to derive a patient-specific 4DMRI model to describe organ motion due to breathing, with improved image quality in 4D reconstruction.

Intra- and interobserver agreement and impact of arterial input selection in perfusion CT measurements performed in squamous cell carcinoma of the upper aerodigestive tract.

BACKGROUND AND PURPOSE: CT Perfusion (CTP) has shown potential for assessing head and neck tumors. Our purposes were to assess the inter- and intraobserver agreement of CTP measurements and to investigate whether the selection of arterial input, ipsilateral versus contralateral to the tumor or left-versus-right external carotid artery (ECA), may affect CTP measurements in patients with squamous cell carcinoma (SCCA) of the upper aerodigestive tract. MATERIALS AND METHODS: Twenty-six patients with SCCA were enrolled in this prospective study and underwent CTP. Data were analyzed by 2 expert readers and by an inexperienced reader for interobserver agreement and by the 2 expert readers for intraobserver agreement assessment, by using the ECA ipsilateral to tumor site as arterial input. All 3 readers repeated their analysis by using the ECA contralateral to tumor site as arterial input. Inter- and intraobserver agreement was assessed by using the Bland-Altman approach; CTP measurements by using ipsilateral-versus-contralateral or left-versus-right ECA were compared by using the Wilcoxon signed rank test. RESULTS: The geometric mean of the ratios (95% limits of agreement) for inter- and intraobserver agreement ranged from 0.96 (0.75–1.23) to 1.00 (0.92–1.10) for blood flow (BF), from 0.88 (0.63–1.21) to 1.00 (0.88–1.14) for blood volume (BV), from 0.96 (0.64–1.44) to 0.98 (0.76–1.27) for mean transit time (MTT), and from 0.85 (0.41–1.76) to 1.14 (0.70–1.86) for permeability surface area product (PS). Significantly higher tumor PS and MTT for 2 readers and lower tumor BF for 1 of 3 readers were observed when the arterial input was placed in the left ECA. CONCLUSIONS: BF, BV, and MTT demonstrated higher inter- and intraobserver agreement than PS. The selection of arterial input, right-versus-left ECA, may determine changes in CTP measurements in patients with SCCA of the upper aerodigestive tract.

Breast MR with special focus on DW-MRI and DCE-MRI

Abstract The use of magnetic resonance imaging (MRI) for the assessment of breast lesions was first described in the 1970s; however, its wide application in clinical routine is relatively recent. The basic principles for diagnosis of a breast lesion rely on the evaluation of signal intensity in T2-weighted sequences, on morphologic assessment and on the evaluation of contrast enhancement behaviour. The quantification of dynamic contrast behaviour by dynamic contrast-enhanced (DCE) MRI and evaluation of the diffusivity of water molecules by means of diffusion-weighted MRI (DW-MRI) have shown promise in the work-up of breast lesions. Therefore, breast MRI has gained a role for all indications that could benefit from its high sensitivity, such as detection of multifocal lesions, detection of contralateral carcinoma and in patients with familial disposition. Breast MRI has been shown to have a role in monitoring of neoadjuvant chemotherapy, for the evaluation of therapeutic results during the course of therapy. Breast MRI can improve the determination of the remaining tumour size at the end of therapy in patients with a minor response. DCE-MRI and DW-MRI have shown potential for improving the early assessment of tumour response to therapy and the assessment of residual tumour after the end of therapy. Breast MRI is important in the postoperative work-up of breast cancers. High sensitivity and specificity have been reported for the diagnosis of recurrence; however, pitfalls such as liponecrosis and changes after radiation therapy have to be carefully considered.

Magnetic Resonance Imaging–Guided versus Surrogate-Based Motion Tracking in Liver Radiation Therapy: A Prospective Comparative Study

PURPOSE This study applied automatic feature detection on cine-magnetic resonance imaging (MRI) liver images in order to provide a prospective comparison between MRI-guided and surrogate-based tracking methods for motion-compensated liver radiation therapy. METHODS AND MATERIALS In a population of 30 subjects (5 volunteers plus 25 patients), 2 oblique sagittal slices were acquired across the liver at high temporal resolution. An algorithm based on scale invariant feature transform (SIFT) was used to extract and track multiple features throughout the image sequence. The position of abdominal markers was also measured directly from the image series, and the internal motion of each feature was quantified through multiparametric analysis. Surrogate-based tumor tracking with a state-of-the-art external/internal correlation model was simulated. The geometrical tracking error was measured, and its correlation with external motion parameters was also investigated. Finally, the potential gain in tracking accuracy relying on MRI guidance was quantified as a function of the maximum allowed tracking error. RESULTS An average of 45 features was extracted for each subject across the whole liver. The multi-parametric motion analysis reported relevant inter- and intrasubject variability, highlighting the value of patient-specific and spatially-distributed measurements. Surrogate-based tracking errors (relative to the motion amplitude) were were in the range 7% to 23% (1.02-3.57 mm) and were significantly influenced by external motion parameters. The gain of MRI guidance compared to surrogate-based motion tracking was larger than 30% in 50% of the subjects when considering a 1.5-mm tracking error tolerance. CONCLUSIONS Automatic feature detection applied to cine-MRI allows detailed liver motion description to be obtained. Such information was used to quantify the performance of surrogate-based tracking methods and to provide a prospective comparison with respect to MRI-guided radiation therapy, which could support the definition of patient-specific optimal treatment strategies.

Quantification of variability in breath-hold perfusion CT of hepatocellular carcinoma: A step toward clinical use

PURPOSE To assess the variability of breath-hold perfusion computed tomography (CT) parameters and to investigate whether these measurements are affected by a commercial software upgrade in patients with hepatocellular carcinoma (HCC). MATERIALS AND METHODS Written informed consent was obtained from all participants in this institutional ethics committee-approved study. Perfusion CT examinations in HCC patients were prospectively analyzed by three readers. Two readers repeated their analysis after an interval of at least 4 weeks. Inter- and intraobserver agreement, as well as intersoftware agreement, were assessed with intraclass correlation coefficients (ICCs) and Bland-Altman limits of agreement (LoA), with adjustment for correlation between repeated measures. RESULTS Ninety-three breath-hold perfusion CT examinations were included from 23 HCC patients. The ICC between readers was very high (>0.91) for blood flow (BF), high (>0.84) for blood volume (BV), and lower (>0.30 and >0.39) for mean transit time (MTT) and permeability surface area product (PS), respectively, while ICC between readings was high (>0.80) for BF and BV, good (>0.75) for PS, and lower (>0.38) for MTT, irrespective of software version. By using the current software, the clinically relevant percentage of LoA between readers for BF were -33%; for BV, -39%; for MTT, 55%; and for PS, -93%. Between readings by the most expert reader, the clinically relevant LoA were -35% for BF,-43% for BV, 33% for MTT, and -79% for PS. BF, BV, and PS values were significantly higher and MTT values were significantly lower (P<.01) with the current software version relative to the previous version. CONCLUSION With the current CT perfusion software, only decreases between scans of HCC lesions of more than 35% for BF and 43% for BV, or an increase of more than 55% for MTT, could be considered beyond the analysis variability. The perfusion parameters obtained with the current and previous software versions were not exchangeable. The results of this study are specific for breath-hold perfusion CT of HCC and may not apply to different acquisition protocols and tumors.

Intraobserver and interobserver variability in the calculation of apparent diffusion coefficient (ADC) from diffusion-weighted magnetic resonance imaging (DW-MRI) of breast tumours

PurposeThis study evaluated intraobserver and interobserver variability in the measurement of apparent diffusion coefficient (ADC) values in breast carcinomas.Materials and methodsTwenty-eight patients with solid breast lesions >10 mm underwent conventional contrast-enhanced magnetic resonance imaging (MRI) and diffusion-weighted MRI (DW-MRI). Two observers (expert and trainee) segmented the lesion from the surrounding breast tissue on DW images with high b-value (1,000 s/mm2). This analysis was repeated by the expert reader after 6 months. Volumes were analysed to obtain mean, median and standard deviation (SD) of the ADC values. Interobserver and intraobserver variation was analysed using the Bland-Altman graph.ResultsAll lesions were breast carcinomas, with a mean ADC value of 1.07 × 10−3 mm2/s. The mean of the differences was 0.012 × 10−3 mm2/s, corresponding to an intraobserver variability of 1.1% (limits of agreement: −5%/+8%). The mean interobserver difference was 0.022 × 10−3 mm2/s, corresponding to an interobserver variability of 2% (limits of agreement: −9%/+14%).ConclusionsWe found a low intraobserver and interobserver variability in calculating ADC in breast carcinomas, which supports its potential use in routine clinical practice.RiassuntoObiettivoObiettivo del nostro lavoro è stato determinare la variabilità intra-osservatore e inter-osservatore nel calcolo del coefficiente di diffusione apparente (ADC) nei carcinomi mammari (CM).Materiali e metodiVentotto pazienti con lesioni mammarie solide >10 mm sono state sottoposte a risonanza magnetica (RM) convenzionale con mezzo di contrasto e a RM pesata in diffusione (RM-DW). Due osservatori hanno isolato la lesione dal tessuto mammario circostante nelle sequenze con elevata pesatura in diffusione (b-value=1000 s/mm2); tale analisi è stata ripetuta da un osservatore dopo 6 mesi. Per i volumi ottenuti sono state calcolate media, mediana e deviazione standard dell’ADC. La variabilità intra-osservatore e la variabilità inter-osservatore sono state valutate tramite il metodo di Bland e Altman.RisultatiTutte le lesioni sono risultate CM, con un valore medio di ADC di 1,07×10−3 mm2/s. è stata calcolata una media delle differenze di 0,012×10−3 mm2/s, corrispondente ad una variabilità intra-osservatore di 1,1% (limiti di accordo −5%/+8%). È stata calcolata una media delle differenze di 0,022×10−3 mm2/s, corrispondente ad una variabilità inter-osservatore di 2% (limiti di accordo di −9%/+14%).ConclusioniÈ stata osservata una bassa variabilità intraosservatore e inter-osservatore per il calcolo dell’ADC nei CM, la quale supporta un suo possibile utilizzo nella routine clinica.

Dielectric Properties Characterization From 0.5 to 50 GHz of Breast Cancer Tissues

Knowledge of the dielectric properties of human tissues is important for several biomedical applications, including imaging and hyperthermia treatment, as well as for determining safety thresholds in policy making. Breast tissues, both normal and tumorous, are of particular interest because of the medical and social impact of breast cancers. While experimental data is available up to 20 GHz, for higher frequencies, this information is missing, or has been extrapolated from models based on lower-frequency data. Emerging technologies and applications in the millimeter-wave region would benefit from experimental data that bridge this gap. This paper presents the characterization of dielectric properties of breast tissues for the frequency range from 0.5 to 50 GHz. Cole–Cole models are derived for normal and tumorous tissues based on experimental measurements on more than 220 tissue samples obtained at surgery (ex vivo) from a population exceeding 50 patients, covering a wide span of normal and tumorous tissues, from patients ranging in age from 28 to 85 years, with a time from excision to measurements under 3.5 h. This paper also presents a comprehensive analysis of the differences between normal and tumorous breast tissues at different frequencies in terms of sensitivity and specificity.

Scale Invariant Feature Transform as feature tracking method in 4D imaging: A feasibility study

We propose the use of Scale Invariant Feature Transform (SIFT) as a method able to extract stable landmarks from 4D images and to quantify internal motion. We present a preliminary validation of the SIFT method relying on expert user identification of landmarks and then apply it to 4D lung CT and liver MRI data. Results demonstrate SIFT capabilities as an operator-independent feature tracking method.

Robot-assisted Radical Prostatectomy: Multiparametric MR Imaging–directed Intraoperative Frozen-Section Analysis to Reduce the Rate of Positive Surgical Margins

PURPOSE To investigate whether use of multiparametric magnetic resonance (MR) imaging-directed intraoperative frozen-section (IFS) analysis during nerve-sparing robot-assisted radical prostatectomy reduces the rate of positive surgical margins. MATERIALS AND METHODS This retrospective analysis of prospectively acquired data was approved by an institutional ethics committee, and the requirement for informed consent was waived. Data were reviewed for 134 patients who underwent preoperative multiparametric MR imaging (T2 weighted, diffusion weighted, and dynamic contrast-material enhanced) and nerve-sparing robot-assisted radical prostatectomy, during which IFS analysis was used, and secondary resections were performed when IFS results were positive for cancer. Control patients (n = 134) matched for age, prostate-specific antigen level, and stage were selected from a pool of 322 patients who underwent nerve-sparing robot-assisted radical prostatectomy without multiparametric MR imaging and IFS analysis. Rates of positive surgical margins were compared by means of the McNemar test, and a multivariate conditional logistic regression model was used to estimate the odds ratio of positive surgical margins for patients who underwent MR imaging and IFS analysis compared with control subjects. RESULTS Eighteen patients who underwent MR imaging and IFS analysis underwent secondary resections, and 13 of these patients were found to have negative surgical margins at final pathologic examination. Positive surgical margins were found less frequently in the patients who underwent MR imaging and IFS analysis than in control patients (7.5% vs 18.7%, P = .01). When the differences in risk factors are taken into account, patients who underwent MR imaging and IFS had one-seventh the risk of having positive surgical margins relative to control patients (adjusted odds ratio: 0.15; 95% confidence interval: 0.04, 0.61). CONCLUSION The significantly lower rate of positive surgical margins compared with that in control patients provides preliminary evidence of the positive clinical effect of multiparametric MR imaging-directed IFS analysis for patients who undergo prostatectomy.