Abstract - A Mobile CT with Intraoperative and ICU Applications

Introduction:

A mobile computed tomography (CT) scanner has been developed in which the scan plane is selected by means of gantry translation rather than by translation of the patient table. This permits CT scanning in situ patient who is positioned on a radiolucent surface that fits within the inner diameter of the gantry. We report the design of and initial experience with this scanner as used with adaptors for intraoperative and bedside CT.

Methods:

The scanner is equipped with wheels, runs on wall outlets (120V, 20A) in combination with batteries, and has a translating gantry. Preclinical studies of image quality were performed with phantoms. An operating table adaptor was built for use with a radiolucent cranial fixation device. A bedside adaptor was built that holds the head and shoulders of an intensive care unit (ICU) patient.

Results:

The preclinical phantom studies showed satisfactory image spatial resolution (0.8mm) and low-contrast resolution signal to noise SD (0.37%). Experience to date with 12 operative patients confirmed the feasibility of intraoperative CT on demand. Experience to date has confirmed the feasibility of routine bedside CT in the ICU.

Discussion and Conclusions:

With these adaptations, mobile CT may increase the efficiency of intraoperative scanning by making it available to multiple operating rooms without committing it to any room for an entire operation, and increase the efficiency and safety of CT of critically ill patients who currently need to leave the ICU to travel to a fixed CT installation and back.

Bedside ICU CT scan of 70 F with intracerebral hematoma.

MGH ICU Mobile CT Program

• An ICU patient must be positioned on a radiolucent surface that fits within the inner diameter of the CT gantry. To accomplish this, the patient is turned 90 degrees so that the head and torso are supported by a bedside adaptor. The gantry is positioned about the head, and the CT scan is obtained.

Mobile CT Key Features

Radiation Considerations

These radiation measurements indicate that mobile CT is safe for ICU and OR use with precautions similar to those used for other portable x-ray devices.

Scatter Radiation from the Mobile CT Scanner

Outside of ICU room with no lead shield: 2 mR/exam (20 slices/scan) A lead shield reduces radiation by a factor of approximately 50 Measurements taken using body phantom, 120 KV, 50 mA, 4 seconds, 10 mm slice thickness A at 1 meter from phantom, at 45o angle; B at 1 meter from phantom along table axis; C at door with door closed, standing in corridor; D at door with door open (2.5-2.6 meters); E at window outside room (2.5-2.6 meters); F at window inside room (2.3 meter); G at 1 meter 45o to left, protected by lead shield; H at 1 meter, 45o to left, before lead shield; I at 1 meter from phantom at scanner side.

MGH Intraoperative Mobile CT Program

Patient is positioned in a radiolucent headframe, on a narrow radiolucent shoulder holder.

If intraoperative CT is ordered, the gantry is positioned about the head, and the CT scan is obtained.

Photo of intraoperative CT. A clear sterile bag is placed over the sterile field

Prior to draping, the fit of the head into the gantry is confirmed with a metal loop with same inner diameter as the CT gantry.

Intraoperative CT to Query Residual Tumor 29 F Recurrent Right Thalamic Astrocytoma Preoperative MRI

Intraoperative CT. A barium-impregnated cottonoid is placed at the bottom of the resection margin. This margin is then evaluated with intraoperative CT.

Stereotactic Biopsy. 43M R temporal abscess The stereotactic CT scan is obtained in the OR with the patient on the OR table.

Immediate Postoperative CT

69 M Craniotomy for L frontal parasagital meningioma. Upon emergence from anesthesia and extubation in the OR, the patient was noted to have a dense right hemiparesis. To exclude hematoma at the operative site, the mobile CT was brought into the OR and a head CT obtained. It demonstrated the expected edema. The patient was then released to the recovery room. Preoperative axial MRI Preoperative coronal MRI Post-extubation CT

Links

Representative Publications

A mobile computed tomographic scanner with intraoperative and intensive care unit applications.
Neurosurgery. 1998 Jun;42(6):1304-10; discussion 1310-1.

Stereotactic transcranial magnetic stimulation: correlation with direct electrical cortical stimulation.
Neurosurgery. 1997 Dec;41(6):1319-25; discussion 1325-6.

Functional magnetic resonance imaging and transcranial magnetic stimulation: complementary approaches in the evaluation of cortical motor function.
Neurology. 1997 May;48(5):1406-16.

Initial characterization of the dosimetry and radiology of a device for administering interstitial stereotactic radiosurgery.
Neurosurgery. 1997 Mar;40(3):510-6; discussion 516-7.

Patients with polycystic kidney disease would benefit from routine magnetic resonance angiographic screening for intracerebral aneurysms: a decision analysis.
Neurosurgery. 1996 Mar;38(3):506-15; discussion 515-6.