Aringhieri, Giacomo

Caramella, Davide

Rossi, Piercarlo

Vitali, Saverio

English

Archivio della Ricerca - Università di Pisa

G. ARINGHIERI1, Radiologist and Researcher S. VITALI1, Radiologist and Researcher P. ROSSI1, MD, Radiology Resident D. CARAMELLA1, Radiology Professor  Please address correspondence to: Dr Giacomo Aringhieri, Via Leonardo da Vinci 31, 50050 Cerreto Guidi (FI), Italy. E-mail: g.aringhieri@gmail.com  Competing interests: none declared.  Received on October 16, 2017; accepted in revised form on October 27, 2017.  The new frontier of imaging: the micron  Sirs, Radiology is starting to explore micron- sized anatomical structures. The technologi- cal breakthroughs which allowed to achieve these previously unreachable results in terms of spatial resolution are the introduction of very high-frequency ultrasound (VHFUS) with advanced probes up to 70 MHz and ul- tra high magnetic fields up to 7 T in magnetic resonance imaging (UHF-MRI). Concerning rheumatologic applications, we focused on the depiction of fine anatomical cartilage al- terations both at VHFUS and at UHF-MRI. A recent feasibility study was performed in- volving the examination of metacarpophalan- geal joint (MPJ) cartilage in ten healthy male volunteers, who were divided into two groups: Group A (five subjects, mean age 32, range 29–33) and Group B (five subjects, mean age 63, range 57–68). We compared the measurements obtained using VHFUS probes (70 MHz). We analysed the MPJ of the sec- ond and third finger of the non-dominant hand and then measured the thickness of the cartilage with the flexed finger. Our results show a difference between the average thick- nesses obtained in the two groups (Fig. 1a-b). In fact, such difference is in the order of hun- dreds of microns. For the MPJ of the second finger, we found a median thickness of 800 micron in group A and 356 micron in group B (p=0.008 – Wil- coxon rank sum test). For the MPJ of the third finger, we found a median thickness of 656 micron in group A and 308 micron in group B (p=0.07 – Wilcoxon rank sum test). These values identify a statistically significant trend that warrants further investigation with a larger sample size. Furthermore, small cal- cifications of the cartilage profile have been identified in Group B. These results indicate a promising role of this imaging modality in the early evaluation of cartilage alterations, both in osteoarthritis and other forms of arthritis. Concerning MRI, medium and high-field MRI (between 1 T and 3 T) has been recog- nised as the standard imaging technique for cartilage evaluation due to its capability to directly visualise the cartilage with sufficient contrast, assessing its morphological appear- ance. However, innovations in therapeutic strategies require more detailed information such as quantification of the volume and the analysis of cartilage’s biochemical composi- tion, in order to diagnose and manage disease at the earliest stages (1). However, medium and high-field-MRI is unable to precisely evaluate the changes that occur in cartilage physiology prior to morphological changes. Recently, the introduction of the UHF-MRI allowed achieving a significantly higher Signal-to-Noise Ratio and Contrast-to-Noise Ratio, which allows us to reach a very high spatial resolution and to obtain more accurate volume quantification with sophisticated bio- chemical analysis of cartilage (2-5). We re- cently optimised a dedicated UHF-MRI pro- tocol to accurately evaluate the morphology, quantify the volume and generate specific highly accurate T2 and T2* maps to perform biochemical analysis of cartilage. This non- invasive technique has the potential to sub- stitute histology in defining early cartilage changes (age-related or disease-specific) with spatial resolution up to 100 micron (Fig. 1c-h, shows the comparison between 1.5 T, 3 T and 7 T). Furthermore, UHF-MRI permits to esti- mate cartilage content of water, proteoglycan and collagen. It can be anticipated that Rheumatology will greatly benefit from these advantages in high-resolution imaging: the accurate depiction of micron-sized alterations at the very early stages of disease will improve the therapeutic management of patients, and possibly change the natural history of many rheumatologic diseases. Future studies should be aimed at evaluating arthritic patients to identify imaging param- eters that can be used as early diagnostic signs in different arthritic pathologies. VHFUS and UHF-MRI may be particularly useful when conventional US and MRI examinations are insufficient to obtain an accurate diagnosis and a higher resolution of the joints is required.  References 1. LINK TM, STAHL R, WOERTLER K: Cartilage imaging: motivation, techniques, current and future significance. Eur Radiol 2007; 17: 1135-46.  2. WELSCH GH, JURAS V, SZOMOLANYI P et al.: Magnetic resonance imaging of the knee at 3 and 7 tesla: a comparison using dedicated multi-chan- nel coils and optimised 2D and 3D protocols. Eur Radiol 2012; 22: 1852-9.  3. MOSER E: Ultra-high-field magnetic resonance: Why and when? World J Radiol 2010; 2: 37-40. 4. STAHL R, KRUG R, KELLEY DA et al.: Assessment of cartilage-dedicated sequences at ultra-high-field MRI: comparison of imaging performance and di- agnostic confidence between 3.0 and 7.0 T with re- spect to osteoarthritis-induced changes at the knee joint. Skeletal Radiol 2009; 38: 771-83.  5. MATZAT SJ, van TIEL J, GOLD GE, OEI EH: Quantitative MRI techniques of cartilage composi- tion. Quant Imaging Med Surg 2013; 3: 162-74.    Fig. 1. a-b: A comparison between articular cartilage of metacarpophalangeal joints of the first finger is shown. We can observe the thinned cartilage (*) of a 66-year-old male (b) compared to a younger subject 34 years old (a). Images c-e show medium field MRI 1.5 T (c), high field MRI 3 T (d), and UHF-MRI 7 T (e) of the knee cartilage in the same 31-year-old male. Comparing the images acquired at increasing field strength, we can observe an improve- ment in spatial resolution and image detail. Images f-h focus on the patellar cartilage (#) and show a better definition of the borders and a higher spatial resolution obtained at 7 T, with a pixel size of 130 micron (h), in comparison with 1.5 T (f) and 3 T MRI (g).  

The new frontier of imaging: the micron

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The new frontier of imaging: the micron

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Archivio della Ricerca - Università di Pisa