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Signal vs Time Curves in Follow-Up Studies

After surgery and/or radiation therapy, precise discrimination between scar tissue and recurrent/persistent tumor is often a hard task. An easy and reliable guide for differential diagnosis may be obtained by comparing signal vs time curves of suspected lesions vs normal mucosa, muscle, or vascular structures. This approach requires a dynamic sequence (GE T1), acquiring the same section with a frame rate of 1/s, for 1 min. Signal curves are then calculated by placing regions of interest on the suspect lesion and on adjacent normal tissues (vessels, muscles, mucosa) (Fig. 1.2). Helpful information can be obtained by comparing both the average of maximum signal values and the steepness of the curve, in suspect and presumably normal tissues. The main drawback of this application is represented by its limited coverage: the dynamic sequence acquired allows just a single section to be selected after the acquisition of TSE T2 and plain SE T1 sequence.

Fig. 1.2. Time versus signal curve. Follow-up MR after radical maxillectomy for adenocarcinoma. Dynamic acquisition (single slice, one scan/s, acquisition time 60 s) after bolus injection of Gd-DTPA. By placing regions of interest on the internal carotid artery (red), suspect recurrent tumor (yellow), and presumably normal muscle (green) and mucosa (blue), a time vs signal intensity curve is calculated. Compared to normal tissue, the suspect lesion shows steeper and higher curve. The finding was confirmed at aspiration cytology (true positive)

Sinonasal Adenocarcinoma

Fig. 1.3. Parametric image obtained from the whole stack of 60 frames. Intensity is related to the slope of the time-enhancement curve. Arrows point to the confirmed recurrent tumor

References

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MacLennan AC (1995) Radiation dose to the lens from coronal CT scanning of the sinuses. Clin Radiol 50:265-267 Maroldi R, Battaglia G, Maculotti P et al (1998) Spiral CT vs subsecond conventional CT in head and neck malignancies. In: Krestin GP, Glazer GM (eds) Advances in CT IV. Springer, Berlin Heidelberg New York, pp 70-75 Oliverio PJ, Benson ML, Zinreich SJ (1995) Update on imaging for functional endoscopic sinus surgery. Otolaryngol Clin North Am 28:585-608

Phillips CD (1997) Current status and new developments in techniques for imaging the nose and sinuses. Otolaryngol Clin North Am 30:371-387 Sievers KW, Greess H, Baum U et al (2000) Paranasal sinuses and nasopharynx CT and MRI. Eur J Radiol 33:185-202 Sohaib SA, Peppercorn PD, Horrocks JA et al (2001) The effect of decreasing mAs on image quality and patient dose in sinus CT. Br J Radiol 74:157-161 Zammit-Maempel I (1996) Radiation dose to the lens from coronal CT scanning of the sinuses. Clin Radiol 51:151 Zammit-Maempel I, Chadwick CL, Willis SP (2003) Radiation dose to the lens of eye and thyroid gland in paranasal sinus multislice CT. Br J Radiol 76:418-420 Zinreich SJ (1998) Functional anatomy and computed tomography imaging of the paranasal sinuses. Am J Med Sci 316:2-12

2 CT and MR Anatomy of Paranasal Sinuses: Key Elements

Roberto Maroldi, AnDREA BoRghEsi, Patrizia Maculotti

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