In our typical clinical protocol, US is used as the first imaging assessment of pregnant patients with right lower quadrant pain. MR imaging has typically been restricted to those patients in whom US findings are inconclusive or in whom additional questions must be answered. US was not performed in three of the 51 patients, however, because the clinical staff decided to proceed directly to MR imaging. Two patients underwent CT after MR imaging. One of these patients underwent CT at our institution to help confirm “tip” appendicitis. In the second patient, CT was performed at an outside institution for a repeat episode of right lower quadrant pain.
Informed consent was obtained from all patients before the MR examination.
Patients received an oral contrast material preparation starting 1–1.5 hours before the MR examination. A combination of 300 mL of ferumoxsil (Gastromark; Mallinckrodt Medical, St Louis, Mo) and 300 mL of barium sulfate (Readi-Cat 2; E-Z-Em Canada, Westbury, NY) was used. This solution provides negative contrast on T1- and T2-weighted images within the bowel lumen while eliminating problematic susceptibility artifacts (20). Intravenous contrast material was not used.
MR examinations were performed with 1.5-T units (Vision, Siemens, Iselin, NJ; or Excite TwinSpeed, GE Medical Systems, Waukesha, Wis) and a surface phased-array coil. The patient was imaged in the supine position. Examinations were monitored by a radiologist to ensure adequate coverage of the appendix and area of interest. Delayed repeat imaging was deemed necessary by the monitoring radiologist in two patients to visualize contrast material in the cecum. All sequences were performed during a breath hold of 20–24 seconds, and the total examination time was approximately 30 minutes.
Half-Fourier single-shot fast spin-echo (SE) images were obtained in the transverse, coronal, and sagittal planes through the lower abdomen and pelvis with the following parameters: repetition time msec/echo time msec, 800–1100/60 (in this case, the repetition time is the time between successive single-shot excitations); 4-mm-thick sections; 1-mm gap; 192 × 256 matrix; 130°–155° flip angle; 62-kHz bandwidth; and 35–40-cm field of view (FOV). Transverse single-shot fast SE images were obtained by using the same imaging parameters and frequency-selective fat saturation.
Transverse time-of-flight T2*-weighted gradient-echo images were obtained with the following parameters: repetition time of 30 msec, minimum full echo time, 45° flip angle, 3-mm-thick sections, 1-mm gap, 256 × 128 matrix, 31-kHz bandwidth, and 35-cm FOV. Transverse T1-weighted in-phase and opposed-phase images were obtained with the following parameters: repetition time of 205 msec, echo times of 2.2 and 4.5 msec, 80° flip angle, 5-mm-thick sections, 2-mm gap, 160 × 256 matrix, and 35-cm FOV.
Initial interpretations were provided by one of four attending radiologists who covered the abdominal MR section on a given day, two of whom (I.P., N.M.R.) were authors. The MR experience of the four radiologists at the time of their first interpretation in this study was 1 year (I.P.), 3 years, 9 years (N.M.R.), and 23 years. The appendix was considered normal when its diameter was equal to or less than 6 mm and/or it was filled with oral contrast material, air, or both. Low signal intensity on T2-weighted images and blooming effect caused by magnetic susceptibility on T2*-weighted images within the appendix was used as a sign that there was air or oral contrast material within (Fig 1).
A dilated appendix (>7 mm in diameter) with high-signal-intensity fluid that filled its lumen on T2-weighted images was considered positive for appendicitis. Periappendiceal fat stranding seen as thin linear collections of high-signal-intensity fluid within the periappendiceal fat on single-shot fast SE images was considered indicative of acute appendicitis. An appendix that measured 6–7 mm without evidence of oral contrast material or air in its lumen was considered an indeterminate finding; in these cases, ancillary findings (eg, periappendiceal fat stranding, abscess) were used to make the diagnosis.
Initial diagnoses were recorded as positive, negative, or inconclusive for appendicitis. Inconclusive diagnoses were rendered early in the series in patients in whom the appendix was not visualized but no inflammatory changes were noted. Later in the series, this constellation was interpreted as a negative finding.
Informed consent was obtained from all patients before the MR examination.
Patients received an oral contrast material preparation starting 1–1.5 hours before the MR examination. A combination of 300 mL of ferumoxsil (Gastromark; Mallinckrodt Medical, St Louis, Mo) and 300 mL of barium sulfate (Readi-Cat 2; E-Z-Em Canada, Westbury, NY) was used. This solution provides negative contrast on T1- and T2-weighted images within the bowel lumen while eliminating problematic susceptibility artifacts (20). Intravenous contrast material was not used.
MR examinations were performed with 1.5-T units (Vision, Siemens, Iselin, NJ; or Excite TwinSpeed, GE Medical Systems, Waukesha, Wis) and a surface phased-array coil. The patient was imaged in the supine position. Examinations were monitored by a radiologist to ensure adequate coverage of the appendix and area of interest. Delayed repeat imaging was deemed necessary by the monitoring radiologist in two patients to visualize contrast material in the cecum. All sequences were performed during a breath hold of 20–24 seconds, and the total examination time was approximately 30 minutes.
Half-Fourier single-shot fast spin-echo (SE) images were obtained in the transverse, coronal, and sagittal planes through the lower abdomen and pelvis with the following parameters: repetition time msec/echo time msec, 800–1100/60 (in this case, the repetition time is the time between successive single-shot excitations); 4-mm-thick sections; 1-mm gap; 192 × 256 matrix; 130°–155° flip angle; 62-kHz bandwidth; and 35–40-cm field of view (FOV). Transverse single-shot fast SE images were obtained by using the same imaging parameters and frequency-selective fat saturation.
Transverse time-of-flight T2*-weighted gradient-echo images were obtained with the following parameters: repetition time of 30 msec, minimum full echo time, 45° flip angle, 3-mm-thick sections, 1-mm gap, 256 × 128 matrix, 31-kHz bandwidth, and 35-cm FOV. Transverse T1-weighted in-phase and opposed-phase images were obtained with the following parameters: repetition time of 205 msec, echo times of 2.2 and 4.5 msec, 80° flip angle, 5-mm-thick sections, 2-mm gap, 160 × 256 matrix, and 35-cm FOV.
Initial interpretations were provided by one of four attending radiologists who covered the abdominal MR section on a given day, two of whom (I.P., N.M.R.) were authors. The MR experience of the four radiologists at the time of their first interpretation in this study was 1 year (I.P.), 3 years, 9 years (N.M.R.), and 23 years. The appendix was considered normal when its diameter was equal to or less than 6 mm and/or it was filled with oral contrast material, air, or both. Low signal intensity on T2-weighted images and blooming effect caused by magnetic susceptibility on T2*-weighted images within the appendix was used as a sign that there was air or oral contrast material within (Fig 1).
A dilated appendix (>7 mm in diameter) with high-signal-intensity fluid that filled its lumen on T2-weighted images was considered positive for appendicitis. Periappendiceal fat stranding seen as thin linear collections of high-signal-intensity fluid within the periappendiceal fat on single-shot fast SE images was considered indicative of acute appendicitis. An appendix that measured 6–7 mm without evidence of oral contrast material or air in its lumen was considered an indeterminate finding; in these cases, ancillary findings (eg, periappendiceal fat stranding, abscess) were used to make the diagnosis.
Initial diagnoses were recorded as positive, negative, or inconclusive for appendicitis. Inconclusive diagnoses were rendered early in the series in patients in whom the appendix was not visualized but no inflammatory changes were noted. Later in the series, this constellation was interpreted as a negative finding.
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