This a single-center prospective spread-evaluation study where the primary objective is to assess the spread of local anesthesia in an ESPB using magnetic resonance imaging (MRI).

The investigators will include 10 healthy volunteers from the hospitals internal website. All volunteers will receive a one-sided Erector Spinae Plane (ESP) block. 30 min after the block sensitivity to cold and pinprick will be assessed before an MRI is performed after 60 min postblock. An radiology specialist will evaluate the MR images pertaining to the spread of the local anesthesia.

Healthy volunteers working at Ostfold Hospital will be recruited by a message put up on the hospitals intranet front page. As participants makes contact, they will receive a mail sent by a study nurse. The mail will include the patient information sheet and a consent form. There will be offered compensation in the form of a gift card of 1000 NOK to cover any travel expenses. Any travel expenses exceeding 1000 NOK will not be covered. If the volunteer fulfills the eligibility criteria and consent is obtained, the study nurse will contact the volunteer per phone or mail to set up an intervention date.

The investigators aim to enroll 10 healthy volunteers and perform the intervention within six months. The planned project end is during December 2022.

All volunteers will be given the choice of procedural pain relief in the form of rapifen 0,5-1 mg. All volunteers included will receive an unilateral ESPB at the T7 level with 30 ml of 2,5 mg/ml ropivacaine and a total of 0,3 mmol gadolinium. The intervention will be performed by the PhD candidate connected to the study. The ESPB will be performed under ultrasound guidance, where the needle target is the transverse process of the Th7 vertebra, under the musculus (m.) erector spinae. All volunteers will be tested for cold and pinprick sensation 30 minutes after block completion, and the results plotted on a dermatome map before they undergo an MRI.

Magnetic resonance imaging study A 3T MRI examination (Magnetom Skyra, Siemens) will be performed 60 minutes after the injection, covering spine levels Th3 to Th12. 3D T1-weighted sequences with fat suppression as well as a T2-weighted sequence will be performed. The distribution pattern of the ropivacaine-gadolinium solution will be evaluated in the following structures: superficial, paravertebral and intercostal musculature, neural foramina and epidural space. All images will be reviewed and analyzed by the same radiologist.

Inclusion Criteria:

• Age > 18 years
• No comorbidity

Exclusion Criteria:

• Allergy to latex, gadolinium and local anesthesia
• BMI >40
• Severe renal and/or hepatic disease
• Local infection at the site of injection
• Systemic infection
• AV block 2-3
• Inability to understand written or spoken Norwegian
• Inability to cooperate
• Claustrophobia
• Pregnancy - All fertile women will be asked to perform a pregnancy test to ensure that they aren't pregnant before inclusion.
• Metal implants not MRI-compatible

IPD will be available upon request.

At publication date and for three months.