Unit of Medical Physics

Pisa, Italy

Unit of Medical Physics

Pisa, Italy
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Giannelli M.,Unit of Medical Physics | Belmonte G.,Unit of Medical Physics | Toschi N.,University of Rome Tor Vergata | Pesaresi I.,Unit of Medical Physics | And 5 more authors.
Medical Physics | Year: 2011

Purpose: Diffusion tensor imaging (DTI) is highly sensitive to noise and improvement of radiofrequency coil technology represents a straightforward way for augmenting signal-to-noise ratio (SNR) performance in magnetic resonance imaging (MRI) scanners. The aim of this study was to characterize the dependence of DTI measurements of fractional anisotropy (FA) and mean diffusivity (MD) on the choice of head coil, comparing two head coils with different functional designs and sensitivities. Methods: Fourteen healthy subjects underwent DTI acquisitions at 1.5 T. Every subject was scanned twice, using a standard quadrature birdcage head coil (coil-A) and an eight-channel array head coil (coil-B). FA and MD maps, estimated using both the linear least squares (LLS) and nonlinear least squares (NLLS) methods, were nonlinearly normalized into a standard space. Then, volumetric regions of interest encompassing typical white and gray matter structures splenium of the corpus callosum (SCC), internal capsule (IC), cerebral peduncles (CP), middle cerebellar peduncles (MCP), globus pallidus (GP), thalamus (TH), caudate (CA), and putamen (PU) were analyzed. Significant differences and trends of variation in DTI measurements were assessed by the Wilcoxon test for paired samples with and without Bonferroni correction for multiple comparisons, respectively. Results: The overall SNR of coil-B was ∼30 higher than that of coil-A. When comparing DTI measurements (coil-B versus coil-A), mean FA values (SCC, IC, and TH), mean MD values (IC, CP, GP, and TH), FA standard deviation (CP, MCP, GP, and CA), and MD standard deviation (IC, CP, TH, and PU) resulted decreased (significant difference, pcor 0.05, or trend of variation, puncor 0.05) in several gray and white matter regions of the human brain. With the exception of CP, the results in terms of revealed significant difference or trend of variation were independent of the method (LLS and NLLS) used for estimating the diffusion tensor. Conclusions: In various gray and white matter structures, the eight-channel array head coil yielded more precise and accurate measurements of DTI derived indices compared to the standard quadrature birdcage head coil. © 2011 American Association of Physicists in Medicine.


Giannelli M.,Unit of Medical Physics | Diciotti S.,University of Florence | Tessa C.,Versilia Hospital | Mascalchi M.,University of Florence
Journal of Applied Clinical Medical Physics | Year: 2010

In EPI-fMRI acquisitions, various readout bandwidth (BW) values are used as a function of gradients' characteristics of the MR scanner system. Echo spacing (ES) is another fundamental parameter of EPI-fMRI sequences, but the employed ES value is not usually reported in fMRI studies. Nyquist ghost is a typical EPI artifact that can degrade the overall quality of fMRI time series. In this work, the authors assessed the basic effect of BW and ES for two clinical 1.5 T MR scanner systems (scanner-A, scanner-B) on Nyquist ghost of gradient-echo EPI-fMRI sequences. BW range was: scanner-A, 1953-3906 Hz/pixel; scanner-B, 1220-2894 Hz/pixel. ES range was: scanner-A, scanner-B: 0.75-1.33 ms. The ghost-to-signal ratio of time series acquisition (GSRts) and drift of ghost-to-signal ratio (DRGSR) were measured in a water phantom. For both scanner-A (93% of variation) and scanner-B (102% of variation) the mean GSRts significantly increased with increasing BW. GSRts values of scanner-A did not significantly depended on ES. On the other hand, GSRts values of scanner-B significantly varied with ES, showing a downward trend (81% of variation) with increasing ES. In addition, a GSRts spike point at ES=1.05 ms indicating a potential resonant effect was revealed. For both scanners, no significant effect of ES on DRGSR was revealed. DRGSR values of scanner-B did not significantly vary with BW, whereas DRGSR values of scanner-A significantly depended on BW showing an upward trend from negative to positive values with increasing BW. GSRts and DRGSR can significantly vary with BW and ES, and the specific pattern of variation may depend on gradients performances, EPI sequence calibrations and functional design of radiofrequency coil. Thus, each MR scanner system should be separately characterized. In general, the employment of low BW values seems to reduce the intensity and temporal variation of Nyquist ghost in EPI-fMRI time series. On the other hand, the use of minimum ES value might not be entirely advantageous when the MR scanner is characterized by gradients with low performances and suboptimal EPI sequence calibration.


Tessa C.,Versilia Hospital | Lucetti C.,Versilia Hospital | Diciotti S.,University of Florence | Paoli L.,University of Florence | And 8 more authors.
Neuroradiology | Year: 2012

Introduction: Nuclear medicine studies in Parkinson's disease (PD) indicate that nigrostriatal damage causes a widespread cortical hypoactivity assumed to be due to reduced excitatory thalamic outflow. However, so far, functional MRI (fMRI) studies have provided controversial data about this "functional deafferentation" phenomenon. To further clarify this issue, we assessed, with fMRI, de novo drug-naive PD patients using a relatively complex motor task under strictly controlled conditions. Methods: Nineteen de novo PD patients with right-predominant or bilateral symptoms and 13 age-matched healthy volunteers performed continuous writing of "8" figures with the right-dominant hand using a MR-compatible device that enables identification of incorrectly performed tasks and measures the size and the frequency of the "8"s. The data were analyzed with FSL software and correlated with the clinical severity rated according to the Hoehn and Yahr (HY) staging system. Results: Fifteen (89%) of 19 PD patients and 12 (92%) of 13 controls correctly executed the task. PD patients showed significant hypoactivation of the left primary sensorimotor cortex (SM1) and cerebellum and no hyperactive areas as compared to controls. However, activation in SM1 and supplementary motor area bilaterally, in left supramarginal, parietal inferior, parietal superior and frontal superior gyri as well as in right parietal superior and angular gyri paralleled increasing disease severity as assessed with the HY stage. Conclusions: In line with the "deafferentation hypothesis", fMRI demonstrates hypoactivation of the SM1 in the early clinical stage of PD. © Springer-Verlag 2011.


Tessa C.,Versilia Hospital | Diciotti S.,University of Florence | Lucetti C.,Versilia Hospital | Baldacci F.,University of Pisa | And 4 more authors.
Parkinsonism and Related Disorders | Year: 2013

Background and purpose: Previous fMRI studies indicated a relationship between changes of the cortical activation pattern and disease severity in Parkinson's disease (PD). Early diagnosis of Parkinson's disease offers the opportunity to evaluate the putative neuroprotective and disease-modifying effects of drugs at a clinical stage when they might be more effective. The aim of this study was to assess motor cortex reorganization at the earliest clinically detectable stage of PD and the effects on it of chronic dopaminergic treatment. Methods: We evaluated with fMRI 11 de novo patients with right unilateral parkinsonism during execution of a controlled hand-tapping task by the unaffected left hand. In 7 of them fMRI examination with the same task was repeated after 6 months of ropinirole administration. Results: At baseline, as compared to control subjects, PD patients showed significant hypoactivation of right sensory-motor cortex (SM1) and hyperactivation of the left parietal superior and inferior gyri and frontal superior gyrus and of the right parietal superior gyrus and precuneus. Ropinirole treatment yielded a significant clinical improvement (mean UPDRS score subitem III 13.4 at baseline, 9.4 at follow-up; p < 0.001 at a paired t-test) which was combined with lower activation in the left parietal superior and inferior gyri and in right parietal and occipital superior gyri with respect to their baseline fMRI examination. Conclusions: Our results indicate that in PD patients changes in cortical activation precede the onset of motor symptoms in the clinically unaffected side and are partially reversed by chronic administration of long acting dopamine agonist ropinirole. © 2012 Elsevier Ltd.


Ginestroni A.,University of Florence | Diciotti S.,University of Florence | Cecchi P.,University of Pisa | Pesaresi I.,University of Pisa | And 12 more authors.
Human Brain Mapping | Year: 2012

Friedreich's ataxia (FRDA) is associated with a distributed pattern of neurodegeneration in the spinal cord and the brain secondary to selective neuronal loss. We used functional MR Imaging (fMRI) to explore brain activation in FRDA patients during two motor-sensory tasks of different complexity, i.e. continuous hand tapping and writing of "8" figure, with the right dominant hand and without visual feedback. Seventeen FRDA patients and two groups of age-matched healthy controls were recruited. Task execution was monitored and recorded using MR-compatible devices. Hand tapping was correctly performed by 11 (65%) patients and writing of the "8" by 7 (41%) patients. After correction for behavioral variables, FRDA patients showed in both tasks areas of significantly lower activation in the left primary sensory-motor cortex and right cerebellum. Also left thalamus and right dorsolateral prefrontal cortex showed hypo-activation during hand tapping. During writing of the "8" task FRDA patients showed areas of higher activation in the right parietal and precentral cortex, globus pallidus, and putamen. Activation of right parietal cortex, anterior cingulum, globus pallidus, and putamen during writing of the "8" increased with severity of the neurological deficit. In conclusion fMRI demonstrates in FRDA a mixed pattern constituted by areas of decreased activation and areas of increased activation. The decreased activation in the primary motor cortex and cerebellum presumably reflects a regional neuronal damage, the decreased activation of the left thalamus and primary sensory cortex could be secondary to deafferentation phenomena, and the increased activation of right parietal cortex and striatum might have a possible compensatory significance. © 2011 Wiley Periodicals, Inc.


Orlandi E.,Fondazione IRCCS Instituto Nazionale Dei Tumori | Giandini T.,Fondazione IRCCS Instituto Nazionale Dei Tumori | Iannacone E.,Fondazione IRCCS Instituto Nazionale Dei Tumori | De Ponti E.,Unit of Medical Physics | And 8 more authors.
Radiotherapy and Oncology | Year: 2014

Background and purpose To compare volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) plans for treatment of unresectable paranasal sinuses cancers (PNSCs) with different clinical presentations. Material and methods Four patients treated for primary target volume only (group 1), four requiring elective nodal irradiation (group 2) and four with positive nodes in macroscopic disease (group 3) were selected. For each patient were generated 7 fields IMRT, coplanar VMAT (c-VMAT) and non-coplanar VMAT (nc-VMAT) treatment plans. Total doses were 70 Gy and 54 Gy to high dose planning target volume (HD-PTV) and low-dose-PTV, respectively. Dose-volume histogram, conformity and homogeneity index (CI and HI), and monitor units (MUs) per Gy were evaluated. Results VMAT provided significantly better target coverage, in terms of V100% (Volume encompassed by the isodose 100%), than IMRT, in particular when nc-VMAT was used. In general, organ at risk sparing is similar with the three approaches, although nc-VMAT can allow a statistically significant reduction of dose to contralateral parotid gland and cochlea for all three groups. Conclusions VMAT can offer significant improvement of treatment for all unresectable PNSCs over existing IMRT techniques. In particular, nc-VMAT may be a further advantage for those patients with sinonasal cancers and involvement of the nodes in whom large volumes and complex/irregular shape have to be irradiated, even if clinical benefits should be established in the future. © 2014 Elsevier Ireland Ltd.


Giannelli M.,Unit of Medical Physics | Diciotti S.,University of Florence | Tessa C.,Versilia Hospital | Mascalchi M.,University of Florence
Medical Physics | Year: 2010

Purpose: Although in EPI-fMRI analyses typical acquisition parameters (TR, TE, matrix, slice thickness, etc.) are generally employed, various readout bandwidth (BW) values are used as a function of gradients characteristics of the MR scanner. Echo spacing (ES) is another fundamental parameter of EPI-fMRI acquisition sequences but the employed ES value is not usually reported in fMRI studies. In the present work, the authors investigated the effect of ES and BW on basic performances of EPI-fMRI sequences in terms of temporal stability and overall image quality of time series acquisition. Methods: EPI-fMRI acquisitions of the same water phantom were performed using two clinical MR scanner systems (scanners A and B) with different gradient characteristics and functional designs of radiofrequency coils. For both scanners, the employed ES values ranged from 0.75 to 1.33 ms. The used BW values ranged from 125.0 to 250.0 kHz/64pixels and from 78.1 to 185.2 kHz/64pixels for scanners A and B, respectively. The temporal stability of EPI-fMRI sequence was assessed measuring the signal-to-fluctuation noise ratio (SFNR) and signal drift (DR), while the overall image quality was assessed evaluating the signal-to-noise ratio (SNRts) and nonuniformity (NUts) of the time series acquisition. Results: For both scanners, no significant effect of ES and BW on signal drift was revealed. The SFNR, NUts and SNRts values of scanner A did not significantly vary with ES. On the other hand, the SFNR, NUts, and SNRts values of scanner B significantly varied with ES. SFNR (5.8%) and SNRts (5.9%) increased with increasing ES. SFNR (25% scanner A, 32% scanner B) and SNRts (26.2% scanner A, 30.1% scanner B) values of both scanners significantly decreased with increasing BW. NUts values of scanners A and B were less than 3% for all BW and ES values. Nonetheless, scanner A was characterized by a significant upward trend (3% percentage of variation) of time series nonuniformity with increasing BW while NUts of scanner B significantly increased (19% percentage of variation) with increasing ES. Conclusions: Temporal stability (SFNR and DR) and overall image quality (NUts and SNRts) of EPI-fMRI time series can significantly vary with echo spacing and readout bandwidth. The specific pattern of variation may depend on the performance of each single MR scanner system in terms of gradients characteristics, EPI sequence calibrations (eddy currents, shimming, etc.), and functional design of radiofrequency coil. Our results indicate that the employment of low BW improves not only the signal-to-noise ratio of EPI-fMRI time series but also the temporal stability of functional acquisitions. The use of minimum ES values is not entirely advantageous when the MR scanner system is characterized by gradients with low performances and suboptimal EPI sequence calibration. Since differences in basic performances of MR scanner system are potential source of variability for fMRI activation, phantom measurements of SFNR, DR, NUts, and SNR ts can be executed before subjects acquisitions to monitor the stability of MR scanner performances in clinical group comparison and longitudinal studies. © 2010 American Association of Physicists in Medicine.


Giannelli M.,Unit of Medical Physics
Journal of applied clinical medical physics / American College of Medical Physics | Year: 2010

In EPI-fMRI acquisitions, various readout bandwidth (BW) values are used as a function of gradients' characteristics of the MR scanner system. Echo spacing (ES) is another fundamental parameter of EPI-fMRI sequences, but the employed ES value is not usually reported in fMRI studies. Nyquist ghost is a typical EPI artifact that can degrade the overall quality of fMRI time series. In this work, the authors assessed the basic effect of BW and ES for two clinical 1.5 T MR scanner systems (scanner-A, scanner-B) on Nyquist ghost of gradient-echo EPI-fMRI sequences. BW range was: scanner-A, 1953-3906 Hz/pixel; scanner-B, 1220-2894 Hz/pixel. ES range was: scanner-A, scanner-B: 0.75-1.33 ms. The ghost-to-signal ratio of time series acquisition (GSRts) and drift of ghost-to-signal ratio (DRGSR) were measured in a water phantom. For both scanner-A (93% of variation) and scanner-B (102% of variation) the mean GSRts significantly increased with increasing BW. GSRts values of scanner-A did not significantly depended on ES. On the other hand, GSRts values of scanner-B significantly varied with ES, showing a downward trend (81% of variation) with increasing ES. In addition, a GSRts spike point at ES = 1.05 ms indicating a potential resonant effect was revealed. For both scanners, no significant effect of ES on DRGSR was revealed. DRGSR values of scanner-B did not significantly vary with BW, whereas DRGSR values of scanner-A significantly depended on BW showing an upward trend from negative to positive values with increasing BW. GSRts and DRGSR can significantly vary with BW and ES, and the specific pattern of variation may depend on gradients performances, EPI sequence calibrations and functional design of radiofrequency coil. Thus, each MR scanner system should be separately characterized. In general, the employment of low BW values seems to reduce the intensity and temporal variation of Nyquist ghost in EPI-fMRI time series. On the other hand, the use of minimum ES value might not be entirely advantageous when the MR scanner is characterized by gradients with low performances and suboptimal EPI sequence calibration.


Giannelli M.,Unit of Medical Physics
Journal of applied clinical medical physics / American College of Medical Physics | Year: 2010

The rotational variance dependence of diffusion tensor imaging (DTI) derived parameters on the number of diffusion weighting directions (N) has been investigated by several Monte Carlo simulation studies. However, the dependence of fractional anisotropy (FA) and mean diffusivity (MD) maps on N, in terms of accuracy and contrast between different anatomical structures, has not been assessed in detail. This experimental study further investigated in vivo the effect of the number of diffusion weighting directions on DTI maps of FA and MD. Human brain FA and MD maps of six healthy subjects were acquired at 1.5T with varying N (6, 11, 19, 27, 55). Then, FA and MD mean values in high (FAH, MDH) and low (FAL, MDL) anisotropy segmented brain regions were measured. Moreover, the contrast-to-signal variance ratio (CVRFA, CVRMD) between the main white matter and the surrounding regions was calculated. Analysis of variance showed that FAL, FAH and CVRFA significantly (p < 0.05) depend on N. In particular, FAL decreased (6%-11%) with N, whereas FAH (1.6%-2.5%) and CVRFA (4%-6.5%) increased with N. MDL, MDH and CVRMD did not significantly (p>0.05) depend on N. Unlike MD values, FA values significantly vary with N. It is noteworthy that the observed variation is opposite in low and high anisotropic regions. In clinical studies, the effect of N may represent a confounding variable for anisotropy measurements and the employment of DTI acquisition schemes with high N (> 20) allows an increased CVR and a better visualization of white matter structures in FA maps.


Iacconi C.,Azienda Ospedaliero Universitaria Pisana | Giannelli M.,Unit of Medical Physics | Marini C.,Azienda Ospedaliero Universitaria Pisana | Cilotti A.,Azienda Ospedaliero Universitaria Pisana | And 5 more authors.
European Radiology | Year: 2010

Objective: To evaluate the role of mean diffusivity (MD) as a predictive index of the response to chemotherapy in locally advanced breast cancer. Methods: Twenty-one women referred to our institution with a diagnosis of locally advanced breast cancer underwent magnetic resonance imaging (MRI) studies at 1.5 T before beginning and after completing combined neoadjuvant chemotherapy. The examination protocol included an EPI sequence sensitised to diffusion (b-value 1,000 s/mm2) and three-dimensional (3D) coronal T1 sequences before and after intravenous contrast medium. Tumours were delineated by using dynamic MR acquisition before and after chemotherapy. The percentage of tumour volume reduction (PVR) and pre-(MDpre) and post-therapy (MDpost) MD values were computed for each lesion. Results: PVR ≥ 65% was observed in 17/21 patients (responders). MDpre of responders (0.99± 0.27 10-3 mm2/s) was significantly (p=0.025) lower than MDpre of non-responders (1.46±0.33 10-3 mm2/s). Moreover, in patients as a whole PVR significantly correlated (p=0.01, r=-0.54) with MDpre. MDpost (1.26± 0.39 10-3 mm2/s) of responders was significantly(p=0.024) higher than MDpre (0.99±0.27 mm 2 10-3 mm2/s), whereas non-responders MD post(1.00±0.14 10-3 mm2/s) did not increase compared with MDpre(1.46±0.33 10-3 mm 2/s). Conclusions: This preliminary study seems to indicate that low values of pre-chemotherapyMDmay identify, before starting treatment, the patients with higher probability of response in terms of percentage of volume reduction of the lesion. MD may represent a complementary parameter useful to correctly select patients for neoadjuvant chemotherapy. © European Society of Radiology 2009.

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