How to recover an iSCSI disk

I run an iSCSI disk on a Linux server (RHEL7). The disk has a normal ext4 partition containing a loop device called disk01.img, which is mapped to a virtual disk with a Windows NTFS file system. All was well untill the Ethernet connection between the Windows and Linux systems was interrupted. Windows decided it should examine the NTFS volume, ultimately advising to re-format it. Before accepting that, I saved the file disk01.img into /savedir on the Linux server. I am now trying to restore disk01.img but I am running into problems.

[root@server ~]# losetup -P /dev/loop1 /savedir/disk01.img
[root@server ~]# mount -t ntfs /dev/loop1 /mount/point
Failed to read bootsector (size=0)
Failed to sync device /dev/loop1: Input/output error
Failed to mount '/dev/loop1': Ongeldig argument
The device '/dev/loop1' doesn't seem to have a valid NTFS.
Maybe the wrong device is used? Or the whole disk instead of a
partition (e.g. /dev/sda, not /dev/sda1)? Or the other way around?

I imagine the NTFS volume might be damaged and I will need to dd the file disk01.img onto a USB disk with an empty NTFS partition, then porting the USB disk to Windows, run chkdsk and if that fails, try recovering the files using something like PhotoRec. Or am I just using the wrong code? Edit: Result of fdisk (in Dutch)

[root@server ~]# fdisk -l /savedir/disk01.img

Schijf /savedir/disk01.img: 750.2 GB, 750155323392 bytes, 1465147116 sectoren
Eenheid = sectoren van 1 * 512 = 512 bytes

Sectorgrootte (logischl/fysiek): 512 bytes / 512 bytes
in-/uitvoergrootte (minimaal/optimaal): 512 bytes / 512 bytes

[root@server ~]#

Edit 2: The NTFS volume is damaged, so losetup -P was working but produced an empty partition. I will probably need to mount /savedir/disk01.img with an offset for the iSCSI sector, like

mount -o loop,offset=512 /savedir/disk01.img /mount/point

but I have difficulty finding the correct offset (looking for NTFS signatures, comparing the hexdump of the *.img file to the hexdump of the newly made virtual disk). BTW: I have also ported a dd copy of disk01.img back to Windows, trying to resolve the files. Still working on that cumbersome action. Finding the start of the NTFS filesystem on disk01.img seems a much better option. Edit 3. Having run TestDisk 4 times there seem to be geometry problems I cannot yet resolve. Output:

losetup -P /dev/loop1 /savedir/disk01.img
testdisk /dev/loop1

Disk /dev/loop1 - 750 GB / 698 GiB - 1465147116 sectors
... ... ...
  Linux filesys. data            0 1465147111 1465147112
  Linux filesys. data            0 1465147111 1465147112
Warning: number of heads/cylinder mismatches 255 (NTFS) != 1 (HD)
Warning: number of sectors per track mismatches 63 (NTFS) != 1 (HD)
Warning: number of heads/cylinder mismatches 255 (NTFS) != 1 (HD)
Warning: number of sectors per track mismatches 63 (NTFS) != 1 (HD)
  MS Data                100452352 1526511615 1426059264
  Linux filesys. data            0 1465147111 1465147112
... ... ...
  Linux filesys. data    730080712 2195227823 1465147112
  Linux filesys. data    730090720 2195237831 1465147112
... ... ...
  Linux filesys. data    730093536 2195240647 1465147112
  Linux filesys. data            0 1465147111 1465147112
Warning: number of heads/cylinder mismatches 255 (NTFS) != 1 (HD)
Warning: number of sectors per track mismatches 63 (NTFS) != 1 (HD)
Warning: number of heads/cylinder mismatches 255 (NTFS) != 1 (HD)
Warning: number of sectors per track mismatches 63 (NTFS) != 1 (HD)
  MS Data               1346517247 2772576510 1426059264

------------------------------------------------------

-- After Reboot --

  Linux                          0 1465147111 1465147112
  Linux                          0 1465147111 1465147112
check_FAT: can't read FAT boot sector
Invalid FAT boot sector
 0 D FAT16 LBA             3179978961 3795078107  615099147
  FAT16 LBA             3179978961 3795078107  615099147
  Linux                          0 1465147111 1465147112
Invalid FAT boot sector
 0 D FAT12                  202831329 1489073369 1286242041
  FAT12                  202831329 1489073369 1286242041
  Linux                          0 1465147111 1465147112
Invalid NTFS or exFAT boot
 0 D HPFS - NTFS           2833862451 3582746086  748883636
  HPFS - NTFS           2833862451 3582746086  748883636
Warning: number of heads/cylinder mismatches 255 (NTFS) != 1 (HD)
Warning: number of sectors per track mismatches 63 (NTFS) != 1 (HD)
Warning: number of heads/cylinder mismatches 255 (NTFS) != 1 (HD)
Warning: number of sectors per track mismatches 63 (NTFS) != 1 (HD)
  HPFS - NTFS            100452352 1526511615 1426059264


Disk /dev/loop1 - 750 GB / 698 GiB - 1465147116 sectors

The harddisk (750 GB / 698 GiB) seems too small! (  HPFS - NTFS            100452352 1526511615 1426059264
   FAT12                  202831329 1489073369 1286242041
   Linux                  730069008 2195218167 1465149160
   Linux                  730071112 2195218223 1465147112
   Linux                  730079744 2195226855 1465147112
   Linux                  730080712 2195227823 1465147112
   Linux                  730090720 2195237831 1465147112
   Linux                  730093536 2195240647 1465147112
   HPFS - NTFS           1346517247 2772576510 1426059264
   HPFS - NTFS           1465145007 2930290014 1465145008


NTFS, blocksize=4096, 730 GB / 679 GiB

--------------------------------------

-- After adding TestDisk MBR, Reboot

  Linux                          0 1465147111 1465147112
  Linux                          0 1465147111 1465147112
  Linux                          0 1465147111 1465147112
  Linux                          0 1465147111 1465147112
check_FAT: can't read FAT boot sector
Invalid FAT boot sector
 0 D FAT16 LBA             3179978961 3795078107  615099147
  FAT16 LBA             3179978961 3795078107  615099147
  Linux                          0 1465147111 1465147112
  Linux                          0 1465147111 1465147112
Invalid FAT boot sector
 0 D FAT12                  202831329 1489073369 1286242041
  FAT12                  202831329 1489073369 1286242041
  Linux                          0 1465147111 1465147112
Invalid NTFS or exFAT boot
 0 D HPFS - NTFS           2833862451 3582746086  748883636
  HPFS - NTFS           2833862451 3582746086  748883636
Warning: number of heads/cylinder mismatches 255 (NTFS) != 1 (HD)
Warning: number of sectors per track mismatches 63 (NTFS) != 1 (HD)
Warning: number of heads/cylinder mismatches 255 (NTFS) != 1 (HD)
Warning: number of sectors per track mismatches 63 (NTFS) != 1 (HD)
  HPFS - NTFS            100452352 1526511615 1426059264

-------------------------------------

-- After Reboot, running Deeper Analysis ---

Disk /dev/loop1 - 750 GB / 698 GiB - 1465147116 sectors


  No partition          36028797018963967 1465147115 1465147117

Enter the ending sector 

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